Unit 2
Learning outcomes
Ecosystems and Energy Flow
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3 components of an Ecosystem are habitat, community & population
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A habitat is the place where an organism lives
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Examples of food chains:-
A population is all the organisms of one type living in a particular area
A community is all the different types of organisms living in a particular
area
Grass
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Rabbit
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Fox
The arrows in food chains and food webs represent the direction of energy
flow
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Producers are organisms that make their own food
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Examples of producers are green plants
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Primary consumers are organisms that eat producers
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Examples of primary consumers are rabbits
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Secondary consumers are organisms that eat primary consumers
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Examples of secondary consumers are foxes
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A herbivore eats only plants
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A carnivores eat only other animals (meat)
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Omnivores eat both plants and animals
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A strong relationship exists between predators and prey. Prey are the
organisms being eaten and the predators are the organisms that eat them.
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If prey numbers increase, predator numbers will increase
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A decomposer is an organism that breaks down dead organisms
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Examples of decomposers are – bacteria and fungi
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Energy is lost from a food chain by heat, movement,
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The niche of an organism is the role it plats within an ecosystem
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Pyramids of energy represent the energy levels at each stage in a food chain
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Pyramids of numbers represent the numbers of organisms at each stage in a
food chain
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Pyramid of biomass represents the mass of organisms at each stage in a
food chain
Factors affecting the variety of species in an ecosystem
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“Biodiversity” is the range of species in an ecosystem
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A “species” is a group of organisms that can interbreed and produce fertile
offspring
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A stable ecosystem is one that has a wide range of species and food webs
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The removal of one or more species has a dramatic effect on other
organisms/populations in a food web.
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“Adaptation” is when organisms have adapted to suit a particular habitat and
niche
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An example of a physical adaptation in an animal would be Darwin’s finches –
adaptations of beak shape and size in order to eat different foodstuffs
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An example of a physical adaptation in a plant would be reduced leaves like
spines in cacti in order to reduce water loss in deserts
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Examples of Environmental stimuli that organisms may respond to include
light and humidity
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An example of a behavioural adaptation to an environmental stimuli in
animals and its survival value would be woodlice moving from a light area to a
dark area. This increase their survival chances as birds can’t see them in the
dark
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Examples of things that plants compete for include light, root space, water,
soil nutrients
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Examples of things that animals compete for include food, water, shelter
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Pollution and habitat destruction to decrease species biodiversity.
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Human activities can decrease biodiversity e.g. overfishing, deforestation,
increased fuel usage leading to pollution
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High intensity grazing will maintain species diversity because strong
competitors are kept at bay allowing weaker competitors to survive
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Very high or low intensity or grazing will decrease diversity because:Low intensity of grazing will allow stronger competitors to succeed and
other species will not survive thus reducing diversity
Very high intensity grazing causes no species to succeed in a given are
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Examples of continuous variation in plants are stem length, root length,
petal size
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Examples of continuous variation in animals are height, mass, ear length
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Examples of discontinuous variation in animals is skin colour, coat colour, eye
colour, wing type,
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Continuous variation is a factor that can be measured
Examples of discontinuous variation in plants include flower colour, petal
colour,
Discontinuous variation is a factor that can be grouped or categorised
Variation and Genetics
Reproduction
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Sexual reproduction affects variety in a species
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In flowering plants the site of fertilisation is in the ovary
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In mammals, the site of fertilisation is in the egg tube (oviduct)
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The cell that is produced after fertilisation is called a Zygote
In flowering plants the:Male sex cell is called Pollen, and is produced in the anthers
Female sex cell is called an Ovule, and is produced in the ovary
Gametes are another word for sex cells
In mammals the: Male sex cell is called Sperm, and is produced in the testes
Female sex cell is egg an Egg, and is produced in the ovary
Fertilisation in when the nucleus of a male sex cell fuses with the nucleus of
a female sex cell
Variation occurs due to the random combination of parental gametes.
Genetics
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Chromosomes are found in the nucleus of a cell
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Chromosomes are made from DNA
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Chromosomes are important as they contain genetic information that
determines an organism’s characteristics.
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The chromosome complement (number of chromosomes) in
(i)
human body cells
= 46 (2 sets of chromosomes)
(ii)
human gametes (sperm/eggs)
= 23 (1 set of chromosomes)
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The basic structure of DNA in is made up of DNA bases & a backbone
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A gene is a small section of a chromosome
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The sequence of DNA bases codes for the sequence of amino acids
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The sequence of Amino Acids determines the structure and function of the
protein produced
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The structure of a protein is important for its function as proteins have a
specific shape e.g. enzymes fit specifically to one substrate
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Examples of other protein molecules and their importance:Haemoglobin – carries oxygen
Catalase breaks down hydrogen peroxide
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Mitosis is the process of cell division and it produces cells identical to the
parent cell.
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Stages of Mitosis
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Mitosis is important because it makes sure that the new cells do exactly the
same job as the original mother cell
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Meiosis is the production of sex cells (also called gametes) e.g. sperm and
egg cells
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Meiosis is important because it ensures that a single set of chromosomes
are produced in gametes. Two sets of chromosomes are made during
fertilisation
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Random assortment of chromosomes during meiosis leads to variation in
offspring.
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The sex of a human is determined in terms of X and Y chromosomes.
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XX = Female, XY = Male
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Sperm can have an X or a Y chromosome, but eggs only have an X
1 – Mother Cell
2- chromosomes become visible
3- chromosomes line up at equator
4- chromatids are pulled to opposite poles by fibres
5- chromatids are divided at each pole by a membrane
6- 2 cells identical to the mother cell are produced
Genotype and phenotype
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Genes are small sections of a chromosome
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Different forms of a gene are called alleles
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Each gamete carries one allele of the gene
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Characteristics are inherited from both parents – one set of chromosomes
are received from the mother and one set of chromosomes are received
from the father
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A Homozygous individual has 2 identical alleles
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Recessive alleles are always represented by a small letter and they are the
alleles that are hidden
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Genotype is the genetic make-up of an organisms (e.g.BB or Ff)
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The genotype (genetic make up) determines the phenotype (appearance)
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A monohybrid cross is cross involving parents differing in one factor
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A true breeding organism is one which has parents with homozygous alleles
A Heterozygous individual has 2 different alleles
Dominant alleles are always represented by a capital letter and they hide
the recessive alleles
Phenotype is the appearance of an organism (e.g. Brown or Black coat)
Examples of the same phenotype with different genotypes
e.g. Brown (BB) Brown (Bb)
and it has homozygous alleles
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In genetics crosses the term P = parents, F1 = 1st generation and F2 = 2nd
generation
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Make sure you can solve problems related to monohybrid crosses in plants
and animals following crosses from the P generation to the F2 generation,
using dominant and recessive alleles
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Examples of ratios of phenotypes of the F1 and F2 offspring e.g. 3:1
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Sometimes the predicted ratios in monohybrid crosses are different to the
actual observed ratios and this is due to the fact that “Fertilisation is a
random process involving an element of chance”
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Co-dominance is when the alleles of a gene are neither dominant nor
recessive.
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Co-dominance example – Brown Cow crossed with a Black Cow neither one is
dominant so the offspring are Red Cows
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Polygenic inheritance is when several genes interact with one another and
causes a range of phenotypes
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Examples of phenotypes produced due to polygenic inheritance are skin
colour in humans and seed mass in plants
Evolution and Uses of Genetics
Environmental impact on phenotype
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The 2 factors that affect the phenotype (final appearance) of an organism
are due to genotype and the effects of the environment
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Example of the effects of different environments on the phenotypes of
organisms with identical genotypes e.g. twins – one brought up in USA, one
brought up in UK. Look different due to different skin colours (environment)
and one has had a healthy diet so is thin and the other had an unhealthy diet
so is overweight (environment)
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The effects of environment on phenotype have no evolutionary significance
as they are not traits that can be passed on
Natural selection
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Natural selection is when organisms that are better suited to the
environment survive and breed and those less well suited die off.
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Better adapted organisms are more likely to pass their characteristics to
the next generations and they have survived long enough to mate and
reproduce
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Natural selection using the Peppered Moth example
1. 2 forms of moth exist (light and dark forms)
2. Light form had a selective advantage as it was camouflaged against white
lichens growing on trees so birds could not see them.
3. Before the Industrial Revolution there were lots of white moths but few
dark moths (as dark moths were easily spotted by birds)
4. After the Industrial Revolution, lichens on trees died and tree trunks
turned black. Then the dark moths had a selective advantage and survived,
mated and reproduced
5. Now there are more dark moths than light moths
Selective Breeding
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Selective breeding is when humans are involved in choosing which plants and
animals they should breed for human benefits.
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The benefits of selective breeding are that after a few generations you will
gain plants or animals with desirable traits
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Disadvantages of selective breeding are – it’s takes a long time and good
results are not always guaranteed
Genetic Engineering
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Stages in Genetic Engineering
1 – Identify the required gene from a chromosome
2 – Remove the required gene from chromosome
3 – Insert the gene into a bacterial plasmid
4 – Insert plasmid into bacteria
5 – Bacteria reproduce and make the desired product (e.g.insulin)
6 – Product purified and ready to use
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Advantage of genetic engineering is it is fast (faster than Selective
Breeding)
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Disadvantages of genetic engineering is it is expensive and there may be the
possible release of genetically engineered bacteria into the environment