Biology
Revision
B1
BIOLOGY UNIT B1 Topic 1 Classification, variation and inheritance
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1.1 You must be able to demonstrate an understanding of how biologists classify
organisms according to how closely they are related to one another including:
o The Five Kingdoms of Life are sub-divided into ...
o a) Species – groups of organisms that have many features in common
o b) Genus – contains several species with similar characteristics
o c) Family – comprising of several genera
o d) Order – comprising of several families
o e) Class – comprising of several orders
o f) Phylum – comprising of several classes
o g) The Five Kingdoms of life are ...
 animalia - all animals
 plantae - all plants
 fungi  protoctista  prokaryotes 1.2 Be able to describe the main characteristics of the five kingdoms including:
o a) Animalia – animals are multicellular, do not have cell walls, do not have
chlorophyll, feed heterotrophically (heterotrophs can't make their own food)
o b) Plantae – are multicellular, have cell walls, have chlorophyll, feed autotroprically
(autotrophs can make their own food)
o c) Fungi – multicellular, have cell walls, do not have chlorophyll, feed saprophytically
(saprophytes feed off dead organisms and decaying material)
o d) Protoctista – unicellular (single celled), have a nucleus, protoctista include algae
o e) Prokaryotes – unicellular (single celled), have no nucleus e.g. bacteria
1.3 Be able to explain why scientists do not classify viruses in any of the five kingdoms and
regard them as non-living.
o Viruses, which are smaller than bacteria, cannot reproduce themselves, have
protein coat containing a few genes, they invade cells and make them reproduce the
invading virus.
1.4 Be able to describe the main characteristics of the phylum Chordata as animals with a
supporting rod running the length of the body, an example of this being the backbone in
vertebrates.
o Vertebrates are divided into five classes, groups of amphibians, birds, fish, mammals
and reptiles
o
1.5 Be able to explain how scientists place vertebrates into the five groups based on:
o a) Oxygen absorption methods – lungs, gills and skin
o b) Reproduction – internal or external fertilisation, oviparous (lay eggs) or viviparous
(give birth to live young)
o c) Thermoregulation – homeotherms ('warm blooded' - kept at a constant
temperature) and poikilotherms ('cold blooded' - body temperature varies with
external temperature).
1.6 Be able to demonstrate an understanding of the problems associated with assigning
vertebrates to a specific group based on their anatomy and reproduction methods and why
many vertebrates are difficult to classify.
o The duck-billed platypus has a bill like a duck, tail like a beaver, its homeothermic,
lays eggs but suckles its young. Not an easy one to classify! but its closer to a
mammal than any of the other four vertebrate groups.
1.7 Be able to discuss why the definition of a species as organisms that produce fertile
offspring may have limitations:
o Some organisms do not always reproduce sexually and some hybrids are fertile.
o Some organisms can reproduce asexually but are still classed as the same species.
o Many closely related species can interbreed producing viable offspring and
technically classed as a different species.
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1.8 HT only: Be able to explain why binomial classification is needed to identify, study and
conserve species, and can be used to target conservation efforts.
o The binomial name of species consists of a two part Latin name (handy for use any
country with its own language!).
 The Latin name cannot be confused linguistically with 'local' or country
names.
 Study and identification produces a common data base of information on
species-organisms with a universal name.
 From the database, species at threat can be identified and preservation
strategies put in place.
1.9 Be able to explain how accurate classification may be complicated by:
o a) variation within a species
o b) HT only: hybridisation in ducks produces viable new species
o c) HT only: ring species - a group of related populations that live near each other,
neighbouring populations may interbreed but those well separated geographically
may not. Sorting out which are genuinely different species is not easy.
1.10 Be able to construct and use keys to show how species can be identified.
o Does the organism do this or that? Structural features? etc. etc. working your way
through an identification key.
1.11 Be able to explain how organisms are adapted to their environment and how some
organisms have characteristics that enable them to survive in extreme environments,
including deep-sea hydrothermal vents and polar regions
o In studying these examples know and understand that organisms, including
microorganisms have features (adaptations) that enable them to survive in the
conditions in which they normally live and some cases understand that some
organisms have adapted to live in environments that are very extreme.
 Know that so-called extremophiles may be tolerant to high levels of salt,
high temperatures or high pressures.
 Flamingos filter-feed on brine shrimp and blue-green algae and their pink or
reddish color comes from carotenoid proteins in their diet of animal and plant
plankton which can survive in the very salty lakes the flamingos fly to for
feeding.
 There are certain microorganisms, eg bacteria colonies, that live by hot
volcanic vents of water on land (eg geysers) or on the seabed (where the
vents are called 'black smokers'). The bacteria cannot rely on photosynthesis
so they make there own food by using chemical energy derived from the
minerals on and around the vent. These bacteria then become the producers
for a food chain that can support several animal species - so we still have
food chains and food webs in these extreme conditions.
 There are creatures that happily live on the deep ocean beds where the
pressure from the water above is enormous. Deep sea fish often have large
mouths to collect scraps of food and/or large eyes to cope with dim light
conditions.
o Know and understand animals and plants may be adapted for
survival in the conditions where they normally live, eg deserts,
the Arctic.
 Know and understand that animals may be adapted for
survival in dry and arctic environments by means of:
 Changes to surface area - heat/water
transfer factor
 Desert animals eg in Africa, tend to have a large surface
area/volume ratio to allow excess body heat to be readily
lost. This helps overheating, particularly as they do not sweat
much and produce smaller volumes of concentrated urine,
both helping to reduce water loss.
 Animals living in very cold climates eg
the arctic regions and northern Europe
and Russia, tend to have a smaller
surface area/volume ratio to minimise
heat loss. Their bodies need to compact
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with a minimum volume - 'roundish' to minimise the surface
area through which heat is lost. The arctic fox and wolves
have short ears and a short snout to minimise surface area,
hence minimise heat loss.
 Thickness of insulating coat
 Desert animals have thinner coats than animals in colder
climates, which aids heat loss.
 Animals living very cold climates have thick
hairy coats to minimise heat loss, but the fur
must be in good condition to trap insulating air
and keep cold water away from the skin. The
fur of animals like the arctic fox is an extremely
good insulator and can survive at temperatures
as low as -50oC. It has a long winter coat with thick dense
underfur. Bears, similarly, have thick fur coats.
 Amount of body fat
 Desert animals have thin layers of body fat compared
to animals in colder climates, which aids heat loss.
 Animals in arctic regions have
thick layers of insulating fat or
blubber AND these also act as
an
important energy store fat/blubber has a very high
calorific value, useful in lean
times
and scarcity of food. eg seals,
penguins, polar bears, whales
 Camouflage
 Desert animals have sand coloured coats which give good
camouflage to minimise being seen and attacked by
predators, it also the enables animal to a predator itself, prey
becomes the hunter!
 Arctic animals like polar bears have
white fair to blend in with the icy/snowy
background to increase the chances of
a kill. Smaller white coated animals are
less likely to seen and caught. The
white arctic fox is a mean hunter! Birds
like the ptarmigan stand a better chance of survival from
predators turning white in colour in winter, and brown in the
summer, thereby blending into the landscape with the
change in seasons
Know and understand that plants may be adapted to survive in dry
environments by means of:
 changes to surface area, particularly of the leaves - through which
water is naturally lost by transpiration
 To reduce the surface area, to reduce water loss, plants like
cacti have thin spines instead of broader leaves.
 water-storage tissues
 Plants like cacti have relatively thick fleshy stems which
contain groups of specialised cells that store water. Some
giant cacti like the saguaro cactus in the deserts of Arizona
(USA) can be 20m high and hold in storage several tonnes of
water - more than enough to see it through the driest of dry
seasons.
 extensive root systems
 Cacti generally have one of two kinds of root system. (i)
Some have relatively few roots, but roots that can burrow
deep into the ground to seek out underground water. (ii)
Other cacti have many shallow spread out roots that can
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rapidly absorb water eg if it rains, which may be very
infrequent in desert regions.
1.12 Be able to demonstrate an understanding of Darwin’s theory of evolution by natural
selection including:
o a) variation – most populations of organisms contain individuals which vary slightly
from one to another, those with superior characteristics are more likely to survive,
o b) over-production – most organisms produce more young than will survive to
adulthood ensuring some will survive,
o c) struggle for existence – because populations do not generally increase rapidly in
size there must therefore be considerable competition for survival between the
organisms,
o d) survival - those with advantageous characteristics are more likely to survive this
struggle,
o e) advantageous characteristics inherited – better adapted organisms are more
likely to reproduce successfully passing on the advantageous characteristics to their
offspring
o f) gradual change – over a period of time the proportion of individuals with the
advantageous characteristics in the population will increase compared with the
proportion of individuals with poorly adapted characteristics, and the poorly adapted
characteristics may eventually be lost.
1.13 Be able to describe and understand that variation within a species can be continuous or
discontinuous.
o The differences between species are usually pretty obvious and expected, but there
is also variation within the same species eg different sizes, different shades of
skin/hair/eye colour.
o The causes of variation within a species are twofold - genetic and environmental.
o Continuous variation is when a particular characteristic of an individual lies within a
range with no distinct category.
o Discontinuous variation occurs when a particular characteristic of the species fits
into a few particular and specific categories with no range of variation.
1.14 Appreciate the variations within a species to illustrate continuous variation and
discontinuous variation.
o Examples of continuous variations in humans include height, weight, length of hand
 When data from a large sample are plotted in the form of a distribution graph
of number of individuals (y axis) versus the value or short value range of the
characteristic on (x axis), the graph is usually a 'bell shape' which statistically
is described as a 'normal distribution' graph curve.
 The peak of the graph occurs at the mean value for a given statistical
population.
 The most common values will occur around the average , with a low
probability of a value of being very low or high in the character data
range.
o Examples of discontinuous variation in humans include eye colour, blood grouping,
 Any graph of the number of individuals versus the characteristic will not show
any systematic curve that you see with continuous variation graphs.
1.15 Be able to interpret information on variation using normal distribution curves
1.16 Be able to demonstrate an understanding of the causes of variation, including:
o a) genetic variation – different characteristics as a result of ...
 (i) mutation - mutations that are inherited may change the characteristics of
the species
 (ii) reproduction - the 'controlled randomness' of the possible gene
combinations of the offspring inherited from their parents ensures that no
offspring can be identical to either parent.
o b) environmental variation – different characteristics caused by an organism’s
environment (acquired characteristics) eg
 sun tan caused by extra melanin pigment on exposure to lots of sunlight,
 withering unhealthy plants drying to grow in dry soil, or too shaded light
conditions
1.17 HT only: Demonstrate an understanding of how speciation occurs as a result of
geographic isolation.
o
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A species is group of similar organisms that can interbreed to give fertile offspring.
Speciation is the development of a new species and can happen when populations of
the same original species becomes so different (genetically) that they can no longer
interbreed to give fertile offspring.
o Speciation can occur via isolation – two populations of a species become separated,
eg geographically,
o In the two geographical regions, the climate might be different, the other plants and
animals may be different.
o However, if each population can survive, by the process of natural selection, two
distinct species can evolve (or perhaps one population remains the same, but the
other has to adapt to a different environment).
1.18 Be able to explain how new evidence from DNA research and the emergence of
resistant organisms supports Darwin’s theory.
o DNA research suggests that all life has common origins, we all have a line of
ancestors going back hundreds of thousands or millions of years.
o DNA analysis shows a close relationship between species that have relatively
recently diverged from a common ancestor (a high percentage of our DNA is the
same as the DNA of apes!).
o Evolution has been driven by small changes in DNA over many generations and this
gradually changes the nature of the species and due to speciation, can lead to new
species.
o Today we can see evolution in action and the survival of the 'fittest genes' eg
 The deadly bacteria MSRA is a strain of microorganism that has survived and
prospered by having genetic characteristics making it resistant to most
antibiotics.
 Bacteria (and viruses) can mutate quite quickly and those most resistant (and
carried by us!) will tend to multiply at the expense of bacteria killed by
antibiotics (less carried by us!).
 Certain strains of rats have become resistant to the poison warfarin.
1.19 Be able to explain the role of the scientific community in validating new evidence,
including the use of:
o a) scientific journals - enable new findings to be communicated to other scientists
working in the same areas of science, so ideas and knowledge are widely spread
AND other scientists can check whether the research is valid eg do other scientists
get the same results? do other scientists draw the same conclusions? do other
scientists agree with, and find the theory valid?
o b) the peer review process - a sort of refereeing system, research papers are read
and checked by people competent to understand the contents of research papers
(their peers) - this ensures standards are high in terms of 'good scientific practice'.
o c) scientific conferences enable scientists to meet and present and discuss their
findings, compare their work, listen to new ideas, get ideas to take back to their own
research project. Its also a forum for other scientists to hear about research which
isn't necessarily exactly their own specialist field, but broadens their own knowledge
of related fields of science.
1.20 Be able to describe the structure of the nucleus of the cell as containing chromosomes,
on which genes are located.
o Human cell nuclei contain 23 pairs of chromosomes.
o Chromosomes carry the genes which control the development and subsequent
characteristics of an organism.
1.21 You must understand that genes exist in alternative forms called alleles which give rise
to differences in inherited characteristics.
o A gene is a shorter section of the huge DNA coiled up molecules that make up
chromosomes.
o Alleles are essentially different versions of the same gene.
 Therefore eg in humans, between the two copies of the chromosomes you
can have two alleles the same (homozygous) or different (heterozygous) for a
particular gene.
o Individual alleles can be 'dominant' or 'recessive' in character - see section 1.22.
o In section 1.21 remember alleles are different versions of the same gene.
1.22 Know the meaning of, and use appropriately, the terms:
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genotype - a 'bit of genetic code' pairs of or individual alleles eg XX, XY, X, Y (and it
is the genotype pairs that give rise to the phenotype you observe in the organism).
o dominant - if two alleles for a characteristic are different (heterozygous) then only
one of the alleles can determine the nature of the characteristic - know as the
dominant allele (usually shown as a capital/upper case letter) eg a gene for height
might be H, so HH or Hh genotypes will give a tall organism. A dominant allele will
override a recessive allele.
o recessive - if an allele is not dominant, it is described as recessive (small/lower case
letter), and, in order for the recessive allele to be expressed in the phenotype
observed, you must have a double recessive allele eg homozygous genotype hh will
give rise to phenotype short.
o homozygous - if a pair alleles for a characteristic are the same on a gene eg
genotype XX (phenotype female)
o heterozygous - if a pair of alleles for a characteristic are different on a gene eg
genotype XY (phenotype female)
o phenotype - the result of 'gene expression' - the nature of the characteristic you see
eg tall, blue eyes, male etc.
1.23 Be able to analyse and interpret patterns of monohybrid inheritance using a genetic
diagram, Punnett squares and family pedigrees.
o Just an example, consider some of the results of Mendel’s work which preceded the
work by other scientists which links Mendel’s ‘inherited factors’ with the chromosomes
of the humble pea.
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Punnett square genetic table for crossing tall pea plants
with dwarf pea plants
Parent genotypes: TT x tt
Gametes: T and T
o
o
Genotypes of
children
T
T
t
Tt
Tt
t
Tt
Tt
This gives 100% tall plants (genotype Tt), but they all carry the allele t for dwarf pea
plants
The diagrams above and below give a modern genetic interpretation of Mendel's
results from initially crossing a pure line of tall pea plants with a pure line of dwarf pea
plants (F1) and then cross-breeding their offspring to give F2.
o
o
Punnett square genetic table for crossing tall pea plants
Parent genotypes: Tt x Tt
Gametes: T and T
o
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Genotypes of
children
T
t
T
TT
Tt
t
Tt
tt
The first resulting offspring (F1) were all tall pea plants, and these were then crossed
with each other, to give the second set of offspring (F2) shown above.
o This gave approximately 75% tall plants (genotype TT or Tt) and 25% dwarf pea
plants (genotype tt)
o Mendel found that the second cross produced tall : dwarf pea plants in the
approximate ratio of 3 : 1.
1.24 Be able to calculate and analyse outcomes (using probabilities, ratios and percentages)
from monohybrid crosses.
1.25 Be able to describe the symptoms of the genetic disorders:
o a) sickle cell disease
 Sickle cell anaemia is a genetic (inherited) blood disorder in which red blood
cells (the carriers of oxygen around the body), develop abnormally. Instead of
being round and flexible, the sickle red blood cells become shaped like a
crescent (hence the name 'sickle'). These abnormal red blood cells can then
clog sections of blood vessels (especially the narrow capillaries) leading to
pain. These painful effects can last from a few minutes to several months.
The abnormal blood cells have a shorter life-span and are not replaced as
quickly as normal healthy red blood cells leading to a shortage of red blood
cells, called anaemia. Symptoms of sickle cell anaemia include tiredness,
painful joints and muscles and breathlessness, especially after exercise ie
any extra physical exertion.
o b) cystic fibrosis
 Cystic fibrosis is a genetic disorder disease passed down through families.
Cystic fibrosis causes thick, sticky mucus to build up in the lungs, digestive
tract, and other areas of the body and is one of the most common chronic
lung diseases in children and young adults. Sadly, it is a life-threatening
disorder caused by a defective gene which causes the body to produce
abnormally thick and sticky fluid, called mucus. The thick mucus builds up in
the breathing passages of the lungs (causing lung infections) and in the
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pancreas, the organ that helps to break down and absorb food (causing
digestion problems).
1.26 HT only: Be able to evaluate the outcomes of pedigree analysis when screening for
genetic disorders:
o a) sickle cell disease
o For sickle cell anaemia to occur in a child, both parents must carry the recessive
allele for sickle cell disease, but neither is affected by it.
o However, there is a 1 in 4 chance that one of their children will be affected by this
genetic disorder - refer to table and diagram below, which shows a double recessive
allele is needed for the offspring to be affected (genotype aa).
o
Punnett square genetic table for sickle cell anaemia
Genotypes of parents: Aa x Aa
normal but both carriers
Gametes: F,f plus F,f
o
o
o
o
Genotypes of
children
A
a
A
AA
Aa
a
Aa
aa
b) cystic fibrosis
The parents may be carriers of the cystic fibrosis disorder without actually having the
disorder themselves.
It is caused by a recessive allele of a gene and can therefore be passed on by
parents, neither of whom has the disorder.
o
Punnett square genetic table for cystic fibrosis
Genotypes of parents: Ff x Ff
normal but both carriers
Gametes: F,f plus F,f
Genotypes of
children
F
f
o
o
o
F
FF
Ff
f
Ff
ff
Cystic fibrosis is caused by a recessive allele f (so it needs genotype ff, a double
recessive allele).
The genetic diagram shows that both parents must be carriers of the recessive allele
and there is a 3/4 chance of having a normal child (FF non-carrier or Ff carrier) and a
1/4 chance of having a child with cystic fibrosis (ff sufferer and carrier).
BIOLOGY UNIT B1 Topic 2 Responses to a changing environment
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2.1 Be able to define homeostasis as the maintenance of a stable internal environment in an
organism.
o The body controls itself by means of negative feedback systems which constantly
help keep conditions right for healthy sustainable life - what you might call 'normal
conditions'.
o Basically if something in the changes beyond a certain limit, then the change is
detected and the body automatically responds to balance things up again eg
 If you blood sugar falls too low (levels controlled by insulin), more glucose is
produced from glycogen,
 if your temperature gets too high, heat-temperature receptors send a
message to the central nervous system-brain which automatically triggers the
bodies cooling mechanism.
2.2 You must have an understanding of the homeostatic mechanisms of:
o a) thermoregulation and the effect of temperature on enzymes
 Thermoregulation is the maintaining of a steady body temperature (eg for us
~37.5oC)
 If you get too hot, you need to remove excess heat energy.
 If you get too cold you need to retain heat and reduce heat loss.
 The temperature is particularly important for enzyme action - most enzymes
in the body have an optimum operating temperature of ~37oC, normal body
temperature, so that's what your biochemistry wants, ~37oC!
o b) osmoregulation
 Osmoregulation is the process of regulating water content.
 You do want to be dehydrated if at all possible.
o c) blood glucose regulation
 This regulates the concentration of glucose (needed constantly for energy
from respiration) in the blood stream.
2.3 Be able to explain how thermoregulation takes place, with reference to the function of the
skin, including:
a) the role of the dermis – sweat glands, blood vessels and nerve endings, hair,
erector muscles and sebaceous glands
o b) the role of the hypothalamus – regulating body temperature
2.4 HT only: Be able to explain how thermoregulation takes place, with reference to:
o a) vasoconstriction
o b) vasodilation
o c) negative feedback
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Homeostasis - Extra Notes for sections 2.1 to 2.4
The internal conditions that are controlled in the body include:
The water content of the body – water leaves the body via the lungs when we breathe out
and via the skin when we sweat to cool us down, and excess water is lost via the kidneys in
the urine.
o We need to, and are continually taking in water via drinks and food.
o Any loss needs to be replaced, more so in the summer when we sweat more than in
the winter.
The ion content of the body – ions are lost via the skin when we sweat and excess ions are
lost via the kidneys in the urine.
o For example, the kidney controls the sodium ion (Na+) concentration from digested
food containing salt.
o Any excess of any ion needs to be removed eg by the kidneys and subsequent
excretion of urine.
The body temperature is controlled by the brain to maintain the temperature at which
enzymes work best (~37oC).
o Somewhere in the complexity of the brain (the hypothalamus) some kind of
'biochemical thermostat' is at work.
o This 'thermostat' is sensitive to the blood temperature of the brain and via nerve
impulse signals from temperature receptors in the skin.
o When the hypothalamus receives nerve signals from the skin about its temperature,
either its too cold or its too hot, response mechanisms are automatically triggered in
the dermis - the deeper layer of the skin, this is an example of a 'negative feedback'
mechanism.
 This automatic temperature change response is an example of negative
feedback.
 If you are too cold, hair erector muscles contract, and your hairs stand upright
trapping a layer of insulating air. Your sweating is reduced to a minimum
since heat is absorbed and therefore lost in the process of evaporation. In
vasoconstriction, the blood vessels near the skin surface constrict so less
blood flows and therefore less heat energy is transferred to the cold
surroundings.
 If you are too hot the erector muscles relax allowing the hairs to lie flat on the
skin, no longer trapping insulating air. You also begin to sweat which
removes heat energy in the process of evaporation. The blood vessels near
the skin surface widen (to dilate - process of dilation, vasodilation) which
allows more blood to flow and hence transfer more heat to the surroundings.
 I'm afraid there are limits to your bodies response ...
 A very high temperatures make you feel extremely uncomfortable as
your body struggles to cope with the situation and you suffer from
'heat exhaustion' and then heatstroke - which can be fatal.
 At the other extreme, particularly without adequate clothing, very low
temperatures resulting in great heat loss the body can lead to
hyperthermia and finally death. If body respiration can't replace the
heat loss, then your body gradually cools, it begins to malfunction
and eventually ceases to function at all.
The blood sugar levels – to provide the cells with a constant supply of energy.
o When sugary or carbohydrate foods are digested the blood sugar levels rise as the
sugar is absorbed from the gut into the bloodstream.
o Your cell metabolism uses and hence removes the sugar in your normal energy
releasing chemistry.
o If you are not doing much physical work your blood sugar level will tend to rise.
o
o
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If you are doing some demanding physical exercise your blood sugar level tend to
fall.
It can be dangerous if your blood sugar levels become too high or too low, so your
blood sugar level is regulated by the hormone insulin, which enables your body to
have a regular supply of sugar for a secure supply of energy.
2.5 Know that hormones are produced in endocrine glands and are transported by the blood
to their target organs
o Know and understand that many process within the body are coordinated and
controlled by chemical substances called hormones.
o Know that hormones are secreted by glands eg the endocrine gland, and are usually
transported to their target organs by the bloodstream which determines their speed of
distribution.
o Hormones, being directly released into the blood, are quite rapidly carried to all parts
of the body BUT only affect the function of particular cells.
o The activated cells are called 'target cells' and have a chemical receptor that
responds to the hormone.
o Note on comparing nerve and hormone functions
 Hormones effectively act as 'chemical messages' to trigger particular
biochemical reactions and their effect is more general and relatively longlasting compared to eg the nervous impulses and responses of reflex arc.
 Compared to the hormone system of response and control in the body, nerve
signals are electrical (not chemical), the nerves act very fast - a short burst of
a nervous impulse for a short time, acting from one precise area to another in
the body.
2.6 Be able to explain how blood glucose levels are regulated by insulin and excess blood
glucose is converted to glycogen in the liver
o The blood sugar levels – to provide the cells with a constant supply of energy.
o When sugary or carbohydrate foods are digested the blood sugar levels rise as the
sugar is absorbed from the gut into the bloodstream.
o Your normal cell metabolism uses, and hence removes, the sugar in your normal
energy releasing chemistry.
o If you are not doing much physical work your blood sugar level will tend to rise.
o If you are doing some demanding physical exercise your blood sugar level tend to fall
as the sugar is consumed.
o It can be dangerous if your blood sugar levels become too high or too low, so your
blood sugar level is regulated by the hormone insulin, which enables your body to
have a regular supply of sugar for a secure supply of energy.
o During exercise a number of changes take place eg the heart rate increases and the
rate and depth of breathing increases.
o These changes increase the blood flow to the muscles and so increase the supply of
sugar and oxygen for energy from respiration and also increase the rate of removal of
carbon dioxide - the waste product.
o The muscles store glucose as glycogen, which can then be converted back to
glucose for use during exercise.
o Glycogen is produced and stored and released for conversion to glucose on a supply
and demand basis.
o If there is surplus glucose and physical activity is low, more glycogen is produced.
o The more you physically exercise, the greater the glucose demand, if this exceeds
what is available in the blood stream, then the glycogen reserves are called upon to
fill the energy gap.
2.7 HT only: Be able to explain how blood glucose levels are regulated by glucagon causing
the conversion of glycogen to glucose
o If your glucose level in the blood is too high the 1st hormone insulin is secreted by
the pancreas.
 Insulin makes the liver turn glucose into glycogen.
 Therefore, the conversion of glucose to glycogen, reduces the glucose
concentration in the blood.
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When the glucose level reduces, insulin is no longer secreted by the
pancreas and the conversion of glucose to glycogen stops and the blood
glucose level is stabilised.
 Insulin was once extracted from the pancreas of a pig or cow, but
human insulin is now made genetic engineering and doesn't give the
side effects experienced from patients using animal insulin.
o If your glucose level is too low the 2nd hormone glucagon is secreted by the
pancreas.
 Glucagon makes the liver convert glycogen into glucose.
 So the blood level of glucose increases.
 When the glucose concentration reaches an appropriate level, secretion of
glucagon stops and so does the conversion of glycogen to glucose stabilising
the glucose level.
2.8 Know that Type 1 diabetes is caused by a lack of insulin, the hormone which controls the
level of glucose in the blood.
o Type 1 diabetes occurs when the pancreas produces much too little of the hormone
insulin and in some cases, no insulin at all.
o This causes the blood glucose level to rise to potentially lethal levels.
2.9 Be able to explain how Type 1 diabetes can be controlled, including the roles of diet and
injection of insulin usually into the subcutaneous fat.
o Type 1 diabetes can be controlled by two strategies, and both may be required ..
 (i) Avoid too much sugary foods and carbohydrates in the diet, sugars in
particular, will cause a rapid rise in glucose levels which is difficult to remove
without the presence of sufficient insulin.
 (ii) Injecting insulin which will make the liver remove excess glucose from the
digested food.
 This is an inconvenient, but very effective way, of keeping the blood
sugar level in check.
 Insulin injections can greatly help diabetics in providing the
necessary insulin but it can never be as successful as a properly
functioning normal pancreas and diabetics can suffer from long-term
health problems.
 Diabetics can have a pancreas transplant which, if successful, can
theoretically avoid the need for insulin, but there is always the danger
tissue rejection and costly immunosuppressive drugs must be taken
(with the added complication of serious side-effects).
2.10 Be able to explain how, in Type 1 diabetes, the level of physical activity and diet affect
the amount of insulin required.
o The amount of insulin injected depends on the person's diet and level of activity.
o A healthy balanced diet, regular eating and regular exercise will both help to keep a
diabetic in good health and minimise the amount of insulin needed.
2.11 Know that Type 2 diabetes is caused by a person becoming resistant to insulin.
o The type 2 diabetes condition is when the pancreas doesn't make enough insulin or
the person has become resistant to insulin so the body doesn't even respond
appropriately to any insulin present, and both will cause the blood sugar level to rise.
2.12 Be able to explain how Type 2 diabetes can be controlled by diet and physical activity.
o Type 2 diabetes can be controlled by eating a healthy balanced diet, regular eating,
regular exercise and losing weight if necessary.
o Some Type 2 diabetics take insulin to help control this diabetic condition.
2.13 Be able to evaluate the correlation between obesity (including calculations of BMI) and
Type 2 diabetes.
o Obese people (BMI > 30) do run the risk of developing type 2 diabetes and if their
BMI is over 30, then action should be taken.
o Body Mass Index (BMI) = (body mass in kg) / (height in m)2
2.14 Be able to explain how plant growth substances (hormones) bring about:
o a) positive phototropism in shoots
o b) positive gravitropism (geotropism) in roots
2.15 Be able to explain how auxins bring about shoot curvature using cell elongation
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2.16 You are expected to have investigated, and therefore have some knowledge of tropic
responses e.g growing small plants from seeds under different light conditions and plant
hormone experiments e.g. with auxin and shoot tips.
2.17 Be able to analyse, interpret and evaluate data from plant hormone experiments,
including the action of auxins and gibberellins
2.18 HT only: You should have an understanding of the uses of plant hormones, including:
o a) selective weedkillers
o b) rooting powder
o c) seedless fruit
o d) fruit ripening
Notes for sections 2.14 to 2.18 about plant growth hormones eg auxins
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a) Know and understand that plants are sensitive to, and respond to, light, moisture and
gravity:
o their shoots grow towards light and against the force of gravity,
o their roots grow towards moisture and in the direction of the force of gravity.
b) Know that plants produce hormones to coordinate and control growth.
o Auxin is a plant hormone that controls the growth of the tips of shoots and roots
o Auxin acts by enabling the plant to respond to, and ...
 ... the tips of shoots to grow towards light, the effect is called phototropism,
 ... the tips of shoots to grow upwards (against gravity) and the tips of roots
downwards (with gravity), the effects are called gravitropism,
 ... the tips of roots to seek moisture in the soil.
o Know that auxins controls phototropism and gravitropism (geotropism).
 Auxin is produced in the tips and moves back by diffusion to stimulate cell
growth - cell enlargement-elongation.
 If the tip of shoot is cut off, the shoot may stop growing because the auxin
hormone is no longer available.
 Auxin can promote growth in shoots but a high concentration of auxin can
inhibit growth in the root to ensure it grows in the right direction.
o You should understand the role of auxins in phototropism and gravitropism.
c) The responses of plant roots and shoots to light, gravity and moisture are the result of
unequal distribution of hormones like auxin, causing unequal growth rates and changes in
growth direction.
o How the plant growth hormone auxin works!
 Shoot tips growing towards light - positive phototropism (positively
phototropic)
 When light shines on a shoot, more auxin concentrates on the side
that is in the shade (less light side).
 This stimulates growth to elongate the cells on the shaded side so
the shoot bends towards the light.
 Shoots growing up against gravity - negative gravitropism/geotropism
(negatively gravitropic/geotropic)
 If a shoot starts to grow sideways-horizontally, gravity causes more
auxin to concentrate on the lower side.
 Therefore the lower side cells are stimulated to grow faster causing
the shoot to grow upwards.
 Roots growing down with gravity - positive gravitropism/geotropism
(positively gravitropic/geotropic)
 If a root is tending to grow horizontally, then, due to gravity it tends to
have more auxin on its lower side, BUT excess auxin can inhibit
growth and so the upper cells tend to elongate faster the lower side
cells, causing the root to bend round downwards and become more
firmly embedded in the soil.
 Roots growing towards moisture - positive hydrotropism (positively
hydrotropic)
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If a root is exposed to an uneven distribution of moisture ie one side
of the root is more moist than the other, more auxin concentrates on
the side with the most moisture.
 Consequently the increased auxin level inhibits growth on the moist
side and causes the greater growth rate on the least moist side to
make the root bend towards the moisture.
d) Plant growth hormones are used in agriculture and horticulture as weed killers and as
rooting hormones and is a very important use of plant hormones like auxin.
o Some plant growth hormones can be used as selective weed killers to disrupt the
growth of weeds but leave the crops unaffected.
 Desired crops of grasses and cereals are narrow leafed plants but many
weeds have broad leaves.
 Selective plant growth hormone based weed-killers have been developed
that affect the growth development of broad-leafed weeds and eventually kill
them, BUT, do not affect the grasses and cereals with narrow leaves.
o Some plant cuttings won't always readily grow in soil or compost, but by adding a
rooting powder to the compost containing a plant hormone like auxin, the growth of
roots and subsequent shoots are greatly encouraged.
 It then enables a flower grower or market gardener to rapidly produce lots of
clones of a particular plant - ideally, of the best quality plants.
o Plant hormones can be used to control the ripening of fruit or produce seedless fruit.
 The ripening can be controlled while the fruit are still on the tree/bush or
during transport to the warehouses/shops.
 You can therefore pick fruit before it is ripe and still quite firm - which
means its less easily damaged in transport.
 You can then choose the time when the ripening hormone is added
so the fruit is as fresh as it can be for you the consumer via the
wholesaler, market vendor, small shop or giant supermarket!
 Most fruit plants with seeds in the core, require pollination by insects,
otherwise the fruits and seeds will not grow.
 By applying growth hormones to the unpollinated flowers of some
fruit plants, the fruits grow BUT not the seeds! Sometimes the plant
hormones are applied after pollination, but still prevent the seeds
developing.
 A very handy way of producing common varieties of seedless fruits
like watermelons, grapes, bananas and many seedless citrus fruits,
such as oranges, lemons and limes.
o Gibberellin is another plant growth hormone used to stimulate seed germination, stem
growth (taller) and flowering.
 If a variety of a dwarf plant is treated with Gibberellin, it can grow as high as a
tall variety!
o Sometimes combinations of hormones eg auxins plus gibberellins can be used in
conjunction with each other to have greatly enhanced effect eg producing very tall
plants.
2.19 Know that the central nervous system consists of the brain and spinal cord and is linked
to sense organs by nerves.
2.20 Be able to explain the structure and function of dendrons and axons in the nervous
system.
2.21 Be able to describe how stimulation of receptors in the sense organs sends electrical
impulses along neurones.
2.22 You are expected to have investigated human responses to external stimuli and
therefore have some knowledge of these phenomena.
2.23 You need to be able to describe the structure and function of sensory, relay and motor
neurones and synapses including:
o a) the role of the myelin sheath
o b) the role of neurotransmitters
o c) the reflex arc
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The Central Nervous System: Extra notes for sections 2.19 to 2.23
a) The nervous system enables humans to react to their surroundings and coordinate their
behaviour.
o Any change in your surroundings eg temperature, visual, sound etc. is potentially a
detectable stimulus to one of you sensory organs eg skin, eyes, ears etc. The
stimulus might be chemical, light, pain, position, pressure, sound, temperature, touch
etc.
o You have five different sense organs ears, eyes, nose, skin and tongue which contain
receptors (groups of cells) that are sensitive to particular stimuli.
o In the receptor cells the stimulus input is converted into an electrical signal - an
electrical impulse which is sent to the brain.
o The reflex actions that can happen by virtue of our central nervous system help
prevent injury from various sources in potentially dangerous situations.
b) Cells called receptors can detect stimuli (changes in the environment outside the
organism).
o Receptors and the stimuli they detect include:
 Light receptor cells in the eyes that are sensitive to light, the light energy
creates electrical signals that are sent to the brain for 'processing'.
 Sound receptors in the ears that are sensitive to sound vibrations in the air
 There are also balance receptors in the ears that are sensitive to
changes in position and enable us to keep our balance.
 The receptors on the tongue are sensitive to chemicals and enable us to
taste, and therefore detect, a wide variety of different foods (bitter, salty,
sour, sweet chemical stimuli etc.) or anything else in contact with the tongue good or bad!
 The receptors in the nose are also sensitive to chemicals and enable us to
smell all sorts of different things which may be a pleasant or unpleasant
experience.
 The receptors in the skin that are sensitive to touch, pressure,
pain and to temperature changes.
c) Light receptor cells, like most animal cells, have a nucleus, cytoplasm and cell
membrane.
d) Know and understand that information in the form of an electrical signal, from
receptors, passes along cells in nerves (neurones) to the brain through the central nervous
system (spinal cord ==> brain) and ...
o ... the brain then coordinates the response,
o ... reflex actions are automatic and rapid,
o ... and often involve sensory, relay and motor neurones.
e) You should know and understand the role of receptors, sensory neurones, motor neurones,
relay neurones, synapses, myelin sheath, neurotransmitters and effectors in simple reflex
actions.
o Receptors - groups of cells that respond to a particular stimulus
o Nerve cells are called neurons, elongated cells that carry electrical signals or
impulses all around the body.
 Neurone cells have lots of branched endings called dendrons which connect
with lots of other neurones.
 The electrical impulses of the nervous system are carried by thin 'fibres'
called axons which are surrounded by an insulating myelin sheath.
o Sensory neurones - the nerve cells that transmit the electrical impulse signal from
the receptors in the sense organs to the spinal chord and brain (central nervous
system).
o Relay neurones - the nerve cells that transmit the electrical signals from sensory
neurones to the motor neurones.
o Synapse - a connection between two neurones eg the junction between a sensory
neurone and a relay neurone, it enables the electrical impulse signal to reach the
spinal cord and brain (ie the central nervous system). Between the end of one
neurone, and the start of another, chemicals (neurotransmitters) are released in the
gap that rapidly diffuse across the gap in the synapse, transferring the electrical
signal from one neurone to another.
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Neurotransmitter - chemicals produced that transmit the electrical signal across a
synapse gap between one neurone cell and another.
Myelin sheath - is a fatty electrically insulating tissue layer around the axon
connections between neurones - the axon in the neurone cells carries the electrical
signal - if there was no myelin insulation, the signal will be lost.
Motor neurones - the nerve cells that transmit the electrical signals through the
central nervous system from the brain via the spinal cord to the effector cells of the
muscles or glands.
Effectors - the muscles or glands that respond in a variety of ways to the electrical
signal from the brain.
Reflex actions are automatic responses to stimuli detected by the receptors in the
organs of the body.
 They are an important defence mechanism of our body eg
 If in danger your body releases the hormone adrenaline to heighten your
mental and physical response.
 If the intensity of light impacting on your eye is too great, your pupil
automatically gets smaller to allow less light. In a dimly lit room, the opposite
response occurs and your pupil widens to let more light in.
 If something hot touches your skin, on feeling pain you immediately try to
recoil from the heat source eg on burning your hand, the muscles rapidly
contract to take your hand away.
Know that in a simple reflex arc action from a receptor to an effector (via spinal
cord and an unconscious part of the brain):
 A stimulus detected by receptors (receptor cells) causes impulses from a
receptor to pass along a sensory neurone (nerve cell) to the central
nervous system.
 At a nerve junction (synapse) between a sensory neurone and a relay
neurone in the central nervous system, a chemical is released that causes
an impulse to be transmitted by a relay neurone.
 A chemical is then released at the synapse between a relay neurone and
motor neurone in the central nervous system, causing impulses to be sent
along by a motor neurone to the organ (the effector) that brings about the
response (of the effector cells).
 The effector is either a muscle or a gland, a muscle responds by contracting
or a gland responds by releasing (secreting) chemical substances eg the
central nervous systems decides what is to be done depending on what
stimulus is received, so ...
 Muscles in your arm may contract to withdraw your hand from a heat
source or sharp point.
 Glands may secrete a particular hormone in response to a particular
stimulus eg adrenalin in a 'flight response' from a dangerous
situation.
 The pupils in your eyes respond by decreasing/increasing in size if
the light level is too high/low.
 Summary of the reflex arc sequence via the central nervous system:
 stimulus ==> receptor cell ==> sensory neurone ==synapse==>
relay neurone in central nervous system =synapse==> motor
neurone ==> effector ==> response
 The reflex arc action is fast, no thinking involved, just a rapid
automatic response on the part of your body!
BIOLOGY UNIT B1 Topic 3 Problems of, and solutions to a changing environment
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3.1 Be able to define a drug as a chemical substance, such as a narcotic or hallucinogen, that
affects the central nervous system, causing changes in psychological behaviour and possible
addiction, despite their usefulness.
o Drugs are dangerous if misused, which is why some drugs cannot be bought of the
counter of a shop (e.g. local chemist) without a medical prescription from you doctor,
but other drugs, like the painkiller paracetamol, can readily bought without
prescription from your GP.
o
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It can sometimes be difficult to state whether the addiction is a physical or mental
dependence.
o If some drugs are over used, you may become addicted to them, which means you
have a physical craving for more of it, without which you can suffer withdrawal
symptoms - extreme craving is symptomatic in itself of addition, and sometimes the
body reacts physically in a negative way e.g. becoming very irritable, shaky hands.
o Tolerance is another problem that arises when the body becomes used to a drug and
progressively needs larger quantities of the drug to give the same effect. The
increasingly higher dose rate can lead directly to addiction and examples range from
legal drugs like alcohol and nicotine in tobacco and illegal use of cocaine and heroin.
o Addiction can be cured by slowly decreasing the amounts of the drug administered,
but most drug addicts required lots of support from e.g. the NHS in the UK, help
groups and rehabilitation centres (politely referred to in pop songs as 'rehab').
3.2 Be able to describe the general effects of:
o a) Painkillers that block pain nerve impulses, including morphine - yes it is a narcotic,
but widely prescribed safely and legally!
 If the nerve impulses to the brain are blocked, we do not experience a pain
sensation and morphine molecules are very effective at doing this.
 Morphine type drugs are amongst the strongest painkillers we use.
 Different painkillers are more effective in particular situations and there
maybe safer alternatives that are not as dangerous or addictive e.g.
 paracetamol, an analgesic, is a good relatively safe painkiller for
headaches.
 Ibuprofen is a good anti-inflammatory drug for muscle pain and
rheumatoid arthritis.
o b) Hallucinogens that distort sense perception, including LSD.
 When taken, hallucinogens create hallucinations in your mind so you
experience distorted sounds and images because the normal processing of
nerve impulse is interfered with.
o c) Stimulants that increase the speed of reactions and neurotransmission at the
synapse, including caffeine.
 Stimulants increase the activity of the brain by increasing the amount of
neurotransmitters at certain neurone synapses in the central nervous system
i.e. they speed up your brain functions.
 Stimulants increase your speed of reaction i.e. decrease your response time
to a given physical or mental stimulus.
 Many people take coffee to make them more alert and 'fully awake' in the
morning because coffee is a rich source of the stimulant caffeine.
o d) Depressants that slow down the activity of the brain (opposite of stimulants),
including alcohol.
 Depressants slow down your responses and increasing your reaction times to
a physical or mental situation i.e. they slow down your brain functions.
 'Drink driving' is considered a dangerous activity and a serious criminal
offence because a drunk (or not so drunk) driver is a danger to others and
the driver himself/herself on the road.
 There is a legal limit of alcohol in your blood which you must be below to
'legally drive' a car, and its pretty low!
3.3 Revise any experiments-investigations you did on reaction times e.g. the falling ruler
experiment.
3.4 Be able to explain the effects of some chemicals in inhaled cigarette smoke, including:
o a) Nicotine as an addictive drug which smokers can become dependant on and the
more you smoke, the more you may become dependent on it - like it or not, smoking
can become a drug addiction.
o b) Tar as a carcinogen - several molecules (known collectively as carcinogens) in
tobacco tar can cause mutations in the cells of the throat and lungs.
 Such mutations can eventually lead to throat cancer, and, in particular, lung
cancer - whose incidence correlates very highly with smokers.
o c) Carbon monoxide reducing the oxygen-carrying ability of the blood - carbon
monoxide combines more strongly with haemoglobin than does oxygen and is slower
to be exhaled in the gaseous exchange in the lungs.
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Consequently, smokers will have less oxygen in their circulatory system.
The effect can be damaging in pregnant women, where the foetus in the
womb may receive less oxygen through the placenta causing babies to be
underweight at birth.
3.5 Be able to evaluate data relating to the correlation between smoking and its negative
effects on health.
3.6 Be able to evaluate evidence of some harmful effects of alcohol abuse:
o a) in the short term  blurred vision - at high intoxication levels you don't see things clearly as
normal and your sense of balance is affected - difficulty walking, impaired
memory, slurred speech, in fact most mental and physical activity is
interfered with.
 lowering of inhibitions - antisocial behaviour, from amusing to offensive
actions you wouldn't normally do!
 slowing of reactions - alcohol is a depressant and slows down brain activity
- particularly dangerous for 'drink drivers'
o b) in the long term  liver cirrhosis - many people do not appreciate the poisonous nature of
alcohol which can be toxic with a large intake of high % alcoholic drinks. In
small quantities, the liver can metabolise the alcohol into harmless byproducts. However, high 'doses' of alcohol can cause the death of liver cells
and scarring the liver tissue, eventually restricting the blood flow to the liver.
This inhibits the liver from doing its normal cleaning-filtering job of processing
waste products from the body like urea. A build up of waste products like
urea may harm the rest of your body.
 brain damage - alcohol abuse is associated with widespread and significant
brain lesions - permanent brain damage with potentially fatal consequences.
3.7 Be able to discuss the ethics of organ transplants when the organ is so damaged that a
transplant is required to prolong life, including:
o a) liver transplants for alcoholics  Bearing in mind the acute shortage of organ donors (living or dead), should
alcoholics with serious cirrhosis of the liver be given priority over someone
who develops liver disease through no fault of their own?
 A liver transplant patient should be expected to stop drinking before and after
the liver transplant operation, otherwise why waste a valuable organ to be
damaged by a transplant patient who will not stop drinking?
o b) heart transplants for the clinically obese  Obese people have a greater chance of dying during and after heart surgery
and doctors can insist that the heart patient loses weight before major
surgery is considered.
o c) the supply of organs e.g.
 Organs can be donated in advance by your own consent at your own death
eg kidney donor card, though your family must be consulted too.
 Organs can come from people killed in accidents or even from somebody
declared brain dead, BUT without prior consent of the deceased, organ
transplant consent must come from relatives.
 Organs can be donated by living people e.g. we have two kidneys and we
can donate one and live (with dietary care) very well on one kidney.
 Unfortunately there is a great shortage of organ donors in the UK and so the
medical profession is encouraging people to become organ donors in the
event of their death.
 The ethical issues are complex and whatever you think about whether a
patient deserves an organ transplant, the medical profession basically
decides on the basis of which patients are most likely to benefit from a
transplant operation - sounds simpler than it sounds, it might not be just a
medical opinion (the main factor), the likely patient's attitude post-operation
might be taken into account too? (not sure on the last point? but alcoholics
may be short on sympathy from the public? but the public doesn't decide!)
3.8 Know that infectious diseases are caused by pathogens.
o An infectious disease is one that spreads from one person to another.
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Microorganisms that cause infectious disease are called pathogens.
Bacteria and viruses may reproduce rapidly inside the body and may
produce poisons (toxins) that make us feel ill.
 Bacteria and certain protozoa are very small cells which can
rapidly reproduce by cell division in your body making you feel ill
by damaging your body's cells and producing toxins (poisons produced as a
by-product of the bacteria's cell chemistry).
 Viruses are NOT cells and much smaller than bacteria and damage the cells
in which they reproduce.
 Viruses replicate by invading a cell and using the cell's genetic
machinery to reproduce themselves ie copies of the original virus.
 The virus 'invaded' cell then bursts releasing lots of new viruses.
 Fungi are also pathogens and includes microorganisms like yeasts
and moulds (so don't eat mouldy food!).
 (Knowledge of the structure of bacteria and viruses is not required here.)
 Fungi are also pathogens and includes microorganisms like yeasts and
moulds.
3.9 Be able to describe how pathogens are spread, including:
o a) in water, including cholera bacterium
 You can be infected with a pathogen by coming
into contact with contaminated water - which is
why swimming bath waters are treated to kill bacteria with chlorine or ozone.
In poor third world countries the bacterial infection cholera, which causes
diarrhoea and dehydration, is readily spread in water contaminated with the
faeces of cholera sufferers. It is potentially very serious, particularly for the
very young and the very old and undernourished adults and children in poor
third world countries with poor sanitation.
o b) by food, including Salmonella bacterium infection
 If you eat food contaminated with pathogens the resulting food poisoning
effects can be very unpleasant and potentially very serious, particularly for
the very young and the very old and the poor of the third world. If food is kept
too long at the wrong temperature, left out in the open, or food like meat
undercooked, you may be poisoned by the bacterium salmonella.
o c) airborne (eg coughing, sneezing), including influenza virus (causes flue)
 If you are suffering from a cough, chest infection or flue etc. and you don't
take precautions with a large handkerchief or tissue, when you cough or
sneeze you blast out into the air a fine mist of water droplets containing
millions of bacteria or viruses. People around you breathe in you exhaled
pathogens and potentially become infected. Lots of people in a crowded
room are great breeding places for pathogens!
o d) by contact, including athlete’s foot fungus infection
 You can be infected with a pathogen just by touching a contaminated surface
with e.g. your hand or foot. A common example is the spread of athlete's foot,
a fungal infection easily spread in swimming bath surfaces, shower floors,
towels i.e. anything an athlete's foot carrier has been in contact with.
o e) by body fluids, including HIV infection
 The HIV virus causes AIDS, a disease that stops our immune system from
functioning properly - you become more susceptible to infectious diseases
than a normal healthy person and the condition is often fatal in the end,
despite the best efforts of anti-viral drugs. These kinds of pathogens can only
be passed on by direct contact with body fluids from another person e.g. from
a HIV carrier's sperm during sexual intercourse, or some body penetrating
situation e.g. using the same drug needle as a HIV carrier.
o f) by animal vectors (animals that spread diseases), including:
 (i) housefly: dysentery bacterium
 The common housefly is a carrier of a nasty protozoan bacterium.
This pathogen causes dysentery, a disease that expresses itself with
severe diarrhoea and dehydration. Again this can have serious
consequences for the very young, the very old and the poor of the
third world.
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(ii) Anopheles mosquito: malarial protozoan
 The mosquito is a carrier of protozoan pathogen that causes the
disease called malaria, a disease that causes potentially fatal kidney
and brain damage. This serious infectious disease is passed onto
another animal which is bitten by a mosquito - a mosquito bite is a bit
more serious than a bee or wasp sting!
3.10 Be able to explain how the human body can be effective against attack from pathogens,
including:
o The body has different physical and chemical ways of protecting itself against
pathogens.
o a) Physical barriers – skin, cilia, mucus
 Physical protection from pathogens
 Your skin and hairs and mucous in the respiratory tract can stop a lot of the
pathogen cells from entering your body. The whole of the respiratory tract
from the nasal passage, down the trachea and into the lungs is covered with
mucous and lined cilia (fine hairs that can move freely at their ends). The
mucous traps dust and bacteria before they can get down into the lungs and
the cilia move the mucous along from the lungs up to the nasal passage -and
then you can blow your nose!
 Skin in good condition acts as a very effective barrier against pathogens.
When a cut in the skin occurs, small sections of cells called platelets help the
blood to clot quickly to seal the wound (seal = scab when dry) and prevent
microorganisms entering the skin tissue or blood stream. The greater the
concentration of platelets in the blood the faster the clotting process
('sealing') can occur.
o b) Chemical defence – hydrochloric acid in the stomach, lysozymes in tears
 Chemical protection by killing pathogens
 In tears our eyes produce chemicals called lysozymes that kill bacterial
microorganisms on the surface of the eye.
 Your stomach contains quite concentrated hydrochloric acid which kills the
majority of pathogenic bacteria - sadly not all of them at times!
3.11 Be able to demonstrate an understanding that plants produce chemicals that have
antibacterial effects in order to defend themselves, some of which are used by humans.
o Plants attacked by pathogens can defend themselves by producing chemicals, often
in oil secretions, that have antibacterial properties.
o Some of these oils have medicinal properties that humans have used in traditional
medicine recipes.
o Other oils have been used as additives in products of the cosmetics industry.
3.12 Be able to describe how antiseptics can be used to prevent the spread of infection.
o Antiseptic chemicals are designed to prevent infection rather than treat and cure an
existing infection - prevention is always better than a cure!
o Antiseptics are chemicals that are applied to the outside of your body to kill
pathogens like bacteria or prevent their growth.
o Antiseptics help to prevent infection of cleaned skin wounds and the surface of the
skin e.g. a larger area where a surgical operation might be done and they are also
applied to surfaces where hygiene is important e.g. in the bathroom.
o Antiseptics range from those used in the home e.g. for cuts and bruises, toilet
cleaners, treating food preparation surfaces, and in GP surgeries, and in hospitals to
prevent infection during operations and on hospital wards to prevent the spread of
dangerous pathogens like MRSA - you should always clean your hands with the
antiseptic facilities provided when visiting friends or relatives in hospital.
3.13 Be able to explain the use of antibiotics to control infection, including:
o Antibiotics are taken internally e.g. intravenous syringe injection, or orally taken tablet
or liquid suspension.
 In other words they are treating you from the inside and treat an existing
pathogen infection you have (bacterial or fungal microorganism)
 Compare these two point with the external use of antiseptics in
preventing infection.
o a) antibacterials to treat bacterial infections


Probably the most well known antibacterial is the antibiotic penicillin which is
effective against many bacterial infections BUT NOT viruses like the common
cold or flue.
 An antibiotic can kill bacteria or prevent them growing and reproducing.
o b) antifungals to treat fungal infections
 Antifungal chemicals kill or prevent the growth of fungi microorganisms e.g
creams for the treatment of the fungal infection athlete's foot.
3.14 HT only: Be able to evaluate evidence that resistant strains of bacteria, including MRSA,
can arise from the misuse of antibiotics.
o Antibiotics, including penicillin, are medicines that help to cure bacterial disease by
killing infectious bacteria inside the body.
 What is an antibiotic?
 Antibiotics cannot be used to kill viral pathogens, which live and
reproduce inside cells.
 Antibiotics do not destroy viruses, typified by the cold and flue
viruses we all suffer from. Viruses make your own body cells
reproduce the invasive virus and unfortunately anti-viral drugs may
attack good cells too!
 Antibiotics like penicillin kill or prevent the growth of harmful pathogens,
they kill the bacteria but not your own body cells.
 Different antibiotics attack different bacteria, so it is important that specific
bacteria should be treated by specific antibiotics.
 The use of antibiotics has greatly reduced deaths from infectious bacterial
diseases.
 However, overuse and inappropriate use of antibiotics has increased the
rate of development of antibiotic resistant strains of bacteria.
 You need to be aware that it is difficult to develop drugs that kill viruses
without also damaging the body’s tissues.
o Many strains of bacteria, including MRSA, have developed resistance to antibiotics
due to mutations, which cause stronger more resilient strains of bacteria to survive as
a result of natural selection.
 To prevent further resistance arising it is important to avoid over-use of
antibiotics.
 Knowledge of the development of resistance in bacteria is limited to the fact
that pathogens mutate, producing resistant strains.
o Mutations of pathogens produce new strains.
 Antibiotics and vaccinations may no longer be effective against a new
resistant strain of the pathogen.
 The new strain will then spread rapidly because people are not immune to it
and there is no effective treatment.
 Can bacteria become resistant to antibiotics?
 Unfortunately the answer is yes! Bacteria will sometimes quite
naturally mutate into forms that are resistant to current antibiotics, so
if your infected with a new strain of bacteria, your resistance is not as
effective.
 If an infection is treated with an antibiotic, any resistant bacteria will
survive and this means resistant bacteria can survive and reproduce
to infect other people, while the non-resistant strains will tend to be
reduced.
 This is an example of natural selection at the individual cell level and
drug companies are constantly trying to develop new antibiotics to
combat the new evolving strains of harmful bacteria - but new
harmful 'superbugs' are becoming more common the more we use
antibiotics and new epidemics can break out!
 MRSA, methicillin-resistant staphylococcus aureus, can't be treated
with many current antibiotics and causes serious wound infections
that can be fatal to young babies or elderly people in particular.
 Misuse by over-prescribing antibiotics is believed to be causing the
rise of mutant resistant strains of bacteria, so doctors are being




advised to avoid over-prescribing antibiotics to reduce the mutation
rate and not treating mild infections with antibiotics.
 It isn't just bacteria that can mutate, viruses can also evolve via
new mutations. Viruses are notable for the rapidity with which they
can mutate which makes it difficult to develop new vaccines. The
reason being that changes in the virus (or bacteria) DNA leads to
different gene expression in the form of different antigens, so
different antibodies are needed. The flue virus is a never ending
problem and in the past pandemics (epidemics across many
countries at the same time) have killed millions of people, mercifully
this rarely happens these days thanks to antibiotics.
 Individual resistant pathogens survive and reproduce, so the
population of the resistant strain increases.
 Now, antibiotics are not used to treat non-serious infections, such as
mild throat infections, so that the rate of development of resistant
strains is slowed down.
3.15 Revise any investigation into the effects of antiseptics or antibiotics on microbial cultures.
3.16 Know that interdependence is the dynamic relationship between all living things.
o It is important to understand that all living things are interdependent on each other,
especially through the pathways of food chains, which are effectively energy chains
too.
o Apart from the obvious need for food and energy to survive and reproduce, there are
many other factors too for particular organisms e.g. most flowering plants rely on
insect pollination,
3.17 Be able to demonstrate an understanding of how some energy is transferred to less
useful forms at each trophic level and this limits the length of a food chain.
o Radiation from the Sun is the initial source of energy for
most communities of living organisms - just a bit of revision
of what the main 'producer' is all about.
 Green plants and algae absorb a small amount of the
light that reaches them.
 The transfer from light energy to chemical energy
occurs during photosynthesis.
 Photosynthesis uses sunlight energy to convert
water and carbon dioxide into sugars like
glucose, the 'waste product' being oxygen - though plants need
oxygen for their respiration at night!
 the simple equation to illustrate photosynthesis is
 water + carbon dioxide (+ sunlight) == chlorophyll ==> glucose +
oxygen
 This energy is stored in the substances that make up the cells of
the plants.
 Green plants and algae are the initial producers of food,
after that its all consumers, including us!
 Most food chains, and therefore most life-forms, are
therefore dependent on the initial input of sunlight energy.
 The energy from photosynthesis produces sugars and other
carbohydrates, which in turn a source of energy to make fats and
amino acids and proteins.
 The carbohydrates and fats in the cells of plants and algae form part
of the cell structure.
 Plants are consumed by animals which in turn use the
energy in respiration to build their fat and protein
structures etc.
3.18 Be able to show an understanding that the shape of a pyramid of biomass is
determined by energy transferred at each trophic level.
o Know and understand that the mass of living material (the biomass) at each stage in
a food chain is less than it was at the previous stage.
 Appreciate that the biomass at each stage can be drawn to scale and shown
as a pyramid of biomass.







Food chain and biomass pyramid introduction

Up the food chain: producer ==> primary consumer ==> secondary
consumer ==> tertiary consumer etc.
 The producer is usually a photosynthesising plant or
algae.
 In a biomass pyramid, each horizontal bar (drawn to scale) is
proportional to the mass of the living material at that producing level
and feeding levels (trophic levels).
 How to construct a biomass pyramid: To draw to scale, you can
keep the vertical height the same for each level and make the
horizontal length of the bar proportional to the biomass of that level in
the pyramid.
 Obviously, the bigger the bar, the greater the biomass at the
producer/feeding-trophic level.
 Up the food chain and 'up the pyramid' the biomass gets less
because of loss of organic material, waste energy and even the
energy from respiration, required to sustain life, eventually becomes
waste energy too eg heat energy to the surroundings. More in
section (c).
 Food chain and biomass pyramid example 1


Butterflies/caterpillars feed off cabbage ==> butterflies eaten by
blue/great tit birds ==> bird of prey eg kestrel, catches smaller birds
eg blue/great tits
It takes plenty of vegetables to feed the local population of cabbage
white butterflies.
 Food chain and biomass pyramid example 2


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
o
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Pondweed eat by tadpoles ==> eaten by water beetle ==> perch fish
eat water beetle ==> otter eats perch
It takes al lot of pondweed to feed a batch of tadpoles.
-
Know and understand that the amounts of material and energy contained in
the biomass of organisms is reduced at each successive stage in a food
chain because:
 (i) some materials and energy are always lost in the organisms’ waste
materials by eg excretion (urine, droppings), fallen leaves from trees etc.
 (ii) respiration supplies all the energy needs for living processes, including
movement and much of this energy is eventually transferred to the
surroundings, particularly with warm blooded mammals where much energy
is spent in maintaining their raised body temperature.
 the overall simplistic equation for respiration is the opposite of
photosynthesis
 glucose + oxygen ==> water + carbon dioxide (+ energy)
 This energy is needed for all life processes, energy to do things like
movement of any organism, heat to keep mammals warm,
 The fact of the matter is, that up a food chain/biomass pyramid, only
a small percentage of the mass is passed on eg
 plants producers (100%) ==> primary consumers
(caterpillars, 40%) ==> secondary consumers (small birds
5%) ==> bird of prey (owl, 0.5%)
 This means in this particular food chain, that of all the mass
/energy you start with, only 0.5% (1/200th) eventually ends up
as the owl.
 In the food chain: plants ==> rabbits ==> foxes, all these
fields of plants of large areas of grass support a relatively
smaller population of rabbits, which in turn support a very
small number of foxes - you only get a relatively small
numbers of a top predator!
 This is the reason why you rarely get food chains of more
than five stages (feeding/trophic levels) because there is so
little mass/energy left in the end.
 Once the energy is lost, it can't be used by the animal in the
next stage of the food chain i.e. the next trophic level.
3.19 Be able to explain how the survival of some organisms may depend on the presence of
another species:
o

a) parasitism - where one organism, to survive, feeds off another that acts as the
host - parasites 'take with no give', live in or on the host which they may harm in the
process!, including:
 (i) fleas - insects that live in the fur of live animals and in the bedding of us
humans. They feed by sucking the blood of their host provides all their
feeding needs and helps them to reproduce rather too efficiently for our liking!
 (ii) head lice - insects that live on the upper skin layer of the human scalp.
Like fleas, they suck human blood for all their feeding needs and make your
head feel itchy!
 (iii) tapeworms - a parasite that can live in a person's intestines (bowel) and
they tend to be flat, segmented and ribbon-like. Humans can catch them by
touching contaminated faeces (stools) and then placing their hands near their
mouth, swallowing food or water containing traces of contaminated faeces or
eating raw contaminated pork, beef or fish. Tapeworms are common in many
animals and feed by attaching themselves to the walls of an animal's intestine
and absorb food through their outer body covering. In extreme cases you can
suffer from malnutrition - all take and no give!
 (iv) mistletoe - is a parasitic plant that attaches itself to trees and shrubs and
grows by penetrating between the branches and absorbs nutrients and water
from the host plant. Like the tapeworm producing malnutrition in animals,
mistletoe can affect and reduce the host plant's growth.
o b) mutualism - where two organisms mutually benefit from a relationship - 'give and
take' in a good evolutionary Darwinian deal! - known as a mutualistic relationship!,
including:
 (i) oxpeckers that clean other species - these are birds that live on the backs
of grazing animals (e.g. large mammals like buffalo, oxen, rhinos etc.) and
eat large quantities of ticks, flies and maggots to feed themselves. In doing
so they remove unwanted parasites from the animal, hence they are classed
as a 'cleaner species'.
 (ii) cleaner fish - these small fish feed off dead skin and parasites on the skin
of larger fishes. In doing so they feed well, remove unwanted parasites from
the big host fish and don't get eaten by the host fish!
 HT only (iii) nitrogen-fixing bacteria in legumes - most plants cannot absorb
and chemically process the nitrogen in air to help synthesise amino acids to
convert into proteins. However, leguminous plants (e.g. beans, clover, peas
etc.), have in their root nodules, bacteria with the right enzymes to convert
the nitrogen in air into nitrates, which the plant needs and can use to make
proteins. In return the bacteria get a regular supply of water and sugar for
energy, to everyone's mutual satisfaction!
 HT only (iv) chemosynthetic bacteria in tube worms in deep-sea vents these extremophiles mutually depend on each other to survive. The bacteria
get their necessary 'life chemicals' from the tube worms and in reproducing
themselves they become food for the tube worms which act as the host.
3.20 Be able to analyse, interpret and evaluate data on global population change.
o
o
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


Know and understand that rapid growth in the human population and an increase in
the standard of living means that increasingly more waste is produced and has an
increasing impact on our environment, and on a global scale!
o The world population graph above shows the dramatic exponential growth of the
global population of 'planet Earth' over the past 2000 years.
 In 2013 it is estimated that the world population is now 7 billion! and rising
fast!
 Over the past few hundred years, with increasingly more modern medicine
reducing disease and more efficient agriculture (eg artificial fertilisers
increasing food production with modern farming methods) have enabled
more people to survive and themselves reproduce!
 Therefore there is a greater demand for the Earth's resources from extracting
oil for petrol and plastics to mining/quarrying mineral/metal ores to extract
metals such as iron or copper and these resources are finite - they will run
out eventually - not sustainable for ever!
 The bigger the world's population, the bigger the environmental impact and
the more waste we create and have to deal with by 'safely dumping' in landfill
sites (which may include toxic materials), recycling selected waste materials
or burning to make useful heat etc.
 Recycling reduces polluting waste, and uses less energy than if you were
e.g. producing a metal from its naturally occurring ore.
3.21 Be able to explain how the increase in human population contributes to an increase in
the production of pollutants, including ....
o ... an increasing world population needs an increasing amount of food and an
increasing amount of energy to meet peoples expectations and demands. This puts
pressure on agriculture to produce more food, often by using artificial fertilisers (nonorganic fertiliser) and burning more coal, gas and oil in power stations to make
electrical energy for industrial and domestic consumption.
o Phosphates - pollution from overuse of artificial fertilisers
o Nitrates - pollution from overuse of artificial fertilisers
 both phosphate and nitrate pollution contribute to the problem of
eutrophication (see below).
o Sulfur dioxide - from burning fossil fuels, causes air pollution (affects plants, lichen)
and acid rain (corrodes stonework and metal structures).
3.22 Be able to explain how eutrophication occurs and the problems associated with
eutrophication in an aquatic environment.
o Eutrophication is a rather deadly situation for aquatic ecosystems in lakes and
rivers.
 Fertilisers have improved agricultural crop yields enormously over the past
hundred years, but overuse of nitrogen based artificial fertilisers (e.g. NPK
varieties) has caused some major pollution problems. Rainwater will dissolve
some of the fertilisers salts (e.g. nitrates and phosphates) and the resulting
run-off will concentrate in streams, rivers and lakes. This increases the
nutrient concentrations well above the normal background levels associated
with a stable ecosystem. The richer source of nutrients, like nitrates, causes
a rapid growth in algae, but, so much algae forms, that plants beneath the
surface are starved of light and begin to die. The dead plant material is fed on
by microorganisms and in doing so, use up the oxygen in the water. The lack
of oxygen then begins to kill fish and other animals, which effectively
suffocate due to the lack of oxygen for respiration. Sections of streams, rivers
and lakes can be devoid of most organisms except the algae!
3.23 Revise any investigation you did on the effect of pollutants on plant germination and
plant growth.
3.24 Be able to demonstrate an understanding of how scientists can use the presence or
absence of indicator species as evidence to assess the level of pollution - living indicators:
o Certain organisms are very sensitive to changes in their environment, particularly with
respect to the presence of pollution.
o Some organisms can only live in unpolluted water, air or land, but other organisms
might actually thrive under polluted conditions.
o
o
o
o
o
o
o
o
o
Therefore, by monitoring the populations of both types of these organisms you can
get some idea of whether the environment is polluted or not.
a) polluted water indicator – bloodworm, sludgeworm
b) clean water indicator – stonefly, freshwater shrimps
c) air quality indicator – lichen species, blackspot fungus on roses
Notes for section 3.24 on Indicator Species
You should know and understand that living organisms can be used as indicators
of environmental changes such as pollution.
Despite the presence of pollutants, some species of plants/animals can live in
polluted air or water, but other organisms need clean air or clean water to survive and
prosper.
 The absence or presence of these indicator species e.g. from monitored
population counts, can say much about whether a particular atmospheric or
aquatic environment is relatively polluted or unpolluted.
 These indicator species can be quite sensitive to their environment and we
can put their sensitivity to their surroundings to good use in environmental
monitoring and hopefully control things to improve matters.
 These pollution indicators may live ...
 ... on surface exposed to air e.g. lichen on rocks/stone walls,
blackspot fungus on roses,
 ... live in water e.g. mayfly larvae, stonefly larvae, freshwater
shrimps, bloodworms, sludgeworms
Lichens can be used as air pollution indicators, particularly of the concentration of
sulfur dioxide in the atmosphere.
o
 The cleaner the air in the environment, the more varied species, and the
greater numbers of an individual species of lichen colonies are seen on rocks
and stone walls. You would observe the 'cleaner air' effect if you surveyed
walls all the way from a polluted town or city centre to some rural location
away from roads well beyond the town or city boundary, and no doubt note
the greater the numbers and variety of lichen growing on the walls the further
you where from the town/city centre.
 Therefore, lichen species can be used as quite a sensitive air pollution
indicator i.e. low populations of a limited number of lichen species indicates
polluted air, usually from sulphur dioxide (SO2).
 Particular lichens are sensitive to poisonous sulfur dioxide (even in very low
concentrations of SO2) from fossil fuel burning - road vehicle exhausts,
power station chimneys etc.
 Blackspot fungus readily grows on roses in relatively clean unpolluted air, but
does not grow as readily in polluted air - the fungus is killed by the polluting
sulfur dioxide. One advantage an urban gardener has over a country
gardener!
Invertebrate animals can be used as water pollution indicators and are used as
indicators of the concentration of dissolved oxygen in water.
o
 Lakes that are stagnant from overgrowth of algae (eutrophication) become
devoid of oxygen at lower levels because the decay bacteria use up the
oxygen. This decreases invertebrate populations and animals that feed on
them, like fish, also decline - so whole food-chains and complex ecosystems
are disrupted.
 If rivers become polluted from raw sewage spills or silage spills, the
concentration of pathogens rise (extra food for them e.g. nitrate nutrients)
and these microorganisms use up the oxygen, so all species needing oxygen
decline - which is nearly everything!
 Certain bacteria will thrive in these conditions and consume oxygen
in the process.
 Some species actually thrive in low oxygen polluted water e.g. a high
population of blood worms and sludge worms indicates very polluted
water.


Particular invertebrate animals like the mayfly larvae and stonefly nymphs are
particularly sensitive to pollution, so their population size is a very good
indicator of the purity of the water. The less pollution in the lake or river
water, the less the growth of algae/bacteria etc. and the more oxygen
dissolve in the water (less used up), therefore the more mayflies and
stoneflies hatched out for the trout! and more trout for the fisherman! BUT
only in clean unpolluted water!
o Environmental changes can be measured using non-living indicators (usually
sensors) to monitor factors such as oxygen levels in water, temperature and rainfall.
 You should understand the use of equipment to measure oxygen levels,
temperature and rainfall, all of which are important indicators of environment
change on land or in water and the bigger picture of global climate change.
 Special meter probes can be dipped into water to measure oxygen
levels, a bit like pH meter probes that measure pH (which is also an
important indicator of relative acidity-alkalinity). A decline in aquatic
oxygen levels as measured by an oxygen probe gives an immediate
warning of pollution.
 Temperature can be measured directly and very accurately with a
mercury thermometer (being replaces on health and safety grounds),
or, electronically using a thermocouple system. Average
temperatures for the year, or seasonal averages, are important
indicators of climate change. Both air and sea temperatures are
monitored.
 Specialised electronic instruments can automatically and
continuously monitor air pollution levels of carbon monoxide, sulphur
dioxide and ozone levels in the atmosphere.
 The data can be continuously fed, stored and analysed in
computer systems for detailed analysis of air pollution
patterns on a long-term basis, so a decline or an
improvement in environmental conditions can be seen and its
progress monitored.
 You can do the same with pH, oxygen level and temperature
probes continually monitoring water systems like rivers.
3.25 Be able to demonstrate an understanding of how recycling can reduce the demand for
resources and the problem of waste disposal, including ....
o Paper from wood - recycling paper reduces the number of trees to be cut down (e.g.
deforestation) and both transport and energy costs are reduced. Recycled paper has
become quite acceptable for many paper based products.
o Plastics from limited oil reserves - oil is becoming increasingly expensive and the
reserves will not last forever, so recycling plastics makes the oil go a bit further and
reduces waste that is often not biodegradable or take a very long time to degrade and
decompose.
o Metals from limited mineral ore deposits - high grade ores are being used up and less
economic lower grade ores are increasingly exploited using even more energy, often
from burning fossil fuels.
 We are using up lots of non-renewable resources e.g. like fossil fuels and
metal ores.
 However, in the case of metal ores, we can recycle metals to reduce costs,
including energy bills, and make the original ore source go further.
 BUT note that recycling isn't without its costs and inconveniences. Recycling
involves collection of waste, sorting into different material categories,
purifying each material and then dealing with the residual waste.
 Sorting can take time and some materials are difficult to separate
efficiently e.g. plastics, whereas iron objects can be readily separated
with a magnet.
 Sorting equipment can be expensive and some sorting is done by
hand.
 Recycled material is often not as good as the original material and
cannot be recycled forever. Its easy to recycle metals like iron, steel,


aluminium and copper many times, though each time useful metal is
lost, but plastics and paper can only be recycled a few times.
3.25 and 3.26 Nature's great natural recycling systems!
o All living things are made of elements like carbon, nitrogen, hydrogen and oxygen
which are all obtained from the environment they live in e.g. from the air, soil or water.
o By one means or other these elements are returned to the environment as e.g.
carbon dioxide in air, water or nitrogen in air or nitrogen compounds in soil.
o If this did not happen, new life could not be formed from the living feeding on preexisting food (alive or dead).
o Food chains and decomposers play important roles in this recycling as exemplified by
the carbon cycle and nitrogen cycle, both of which are illustrated and described
below.
o The function of bacteria, decomposers, food chains etc. is all explained.
3.26 Be able to show an understanding of how carbon is recycled (CARBON CYCLE diagram
above):
o a) during photosynthesis plants remove carbon dioxide from the atmosphere
 carbon dioxide + water == light energy/chlorophyll ==> glucose + oxygen
 This is the process by which plants make food, for
themselves, and for most animal life, including us too!
 Note that the only way carbon dioxide is removed from the
air is photosynthesis in green land based plants or marine
organisms like phytoplankton (this point ignores long term
formation of carbonate rocks like limestone).
o b) carbon compounds pass along a food chain
 All food chains involve the passing of carbon compounds e.g. sugars,
carbohydrates, fats and proteins up to the next trophic level i.e. the
consecutive eating along a food chain (and waste produced on the way).
 e.g. grass ==> cow ==> human
o
o
o

c) during plant or animal aerobic respiration organisms release carbon dioxide into
the atmosphere
 sugars e.g. glucose + oxygen ==> carbon dioxide + water (+ energy)
 this is the main aerobic energy releasing process in most living organisms.
d) decomposers release carbon dioxide into the atmosphere - slow aerobic
respiration
 Microorganisms like bacteria and fungi in the soil feed off decaying plant
material and animal droppings or remains.
 Most dead plant matter consists of cellulose which most animals can't digest,
but bacteria and fungi, do have the enzymes to break it down and without
their help there would be no carbon cycle.
 Most of these bacteria and fungi respire aerobically so they need a good
supply of oxygen to produce the carbon dioxide essential to keeping the
carbon cycle going.
e) combustion of fossil fuels releases carbon dioxide into the atmosphere
 Coal, formed millions of years from the remains of tropical plant material,
mainly consists of carbon, Burning coal produces a lot of pollution as the
greenhouse gas carbon dioxide.
 The main reaction on burning is ...
 carbon + oxygen ==> carbon dioxide
 C(s) + O2(g) ==> CO2(g)
 Natural gas (mainly methane) and petrol molecules like octane (and lots
of other molecules) from oil and gas reserves.
 methane + oxygen ===> water + carbon dioxide
 octane + oxygen ===> water + carbon dioxide
3.27 HT only: Be able to show an understanding of how nitrogen is recycled (NITROGEN
CYCLE diagram above):
o a) Nitrogen gas in the air (78%, ~4/5th) cannot be used directly by most plants and
all animals.
 No animals and only a few specialised plants can directly use the very
unreactive nitrogen from air, but all plants nitrogen in some form to
synthesise amino acids and proteins for growth and maintenance and for
DNA in cell reproduction.
 However, nitrogen can be changed into nitrogen compounds like nitrates
which the plants can use.

o
o
o
o
o
o
o
o
o
Animals rely on plants or other animals in the food chain for their source of
nitrogen compounds e.g. protein in grass, crops or other animals.
b) Nitrogen-fixing bacteria living in root nodules of plants or in the soil can fix
nitrogen gas.
 Leguminous plants like peas, lentils, clover and beans can absorb nitrogen
from the air via their root nodules (swellings on the root surface) which
contain enzymes capable of converting ('fixing') atmospheric nitrogen into
soluble nitrate - a nutrient essential for amino acids, proteins and therefore
plant growth.
 Legumes and their root nodule bacteria are an example of mutualism
(see section 3.19 b) because the plant root supplies the bacteria with
carbohydrate food and minerals and the bacteria supplies the plant in
the form of the nitrate ion.
 The process of converting nitrogen in air into nitrogen compounds is
sometimes called 'nitrogen fixation'.
c) The action of lightning can convert nitrogen gas into nitrates.
 The very high electrical energy discharges from lightning activates nitrogen
and oxygen molecules to react and form nitrogen oxides. These dissolve in
rain to form nitrates which end up in the soil when rainwater trickles into the
soil.
d) Decomposers break down dead animals and plants
 Decomposers, e.g. various organisms like bacteria, fungi or worms can break
down dead animals or plants. They break down proteins to amino acids.
e) Soil bacteria convert proteins and urea into ammonia or ammonium ions.
 Decomposer bacteria in the soil can change proteins from dead
plants/animals and urea in animal urine/droppings into ammonia/ammonium
ion compounds.
 d) plus e) is sometimes called putrefaction by putrefying bacteria.
f) Nitrifying bacteria convert this ammonia to nitrates - the process of nitrification
 Nitrifying bacteria oxidise ammonia/ammonium ions from the decayed
material to form nitrates, the nitrate ion can be absorbed by plants through
their root systems.
g) Plants absorb nitrates from the soil.
 Plants absorb nitrates (soluble in water) in the moisture that the roots absorb
from the surrounding soil.
 Plants can use the nitrate ion in forming amino acids from which the plant can
make its proteins.
h) Nitrates are needed by plants to make proteins for growth.
 Nitrates are an essential nutrient for plants to synthesis amino acids and
hence proteins.
i) Nitrogen compounds pass along a food chain or web of food chains.
 All food chains involve the passing of carbon compounds e.g. sugars,
carbohydrates, fats and proteins up to the next trophic level i.e. the
consecutive eating along a food chain (and waste produced on the way).
 e.g. grass ==> cow ==> human
 Plants make their own protein from nitrates, but animals must obtain
it from plants or other animals. In fact the protein is broken down in
digestion to amino acids and each animal makes its own proteins
from these amino acid residues.
j) Denitrifying bacteria convert nitrates to nitrogen gas.
 Particular bacterial organisms can remove the oxygen from nitrate
compounds to form the element nitrogen gas.
 These denitrifying bacteria live in anaerobic conditions like waterlogged soils
and use the nitrate ion to respire.
 This is the opposite function of the nitrogen-fixing bacteria (b).