Control and Regulation
Higher Biology Unit 3
Growth and development
Growth patterns in plants and animals
Growth is the irreversible increase in the
dry mass of an organism.
To avoid killing the organism other
factors, such as height or fresh weight,
may be used to measure.
(a) Growth patterns
A graph of growth measurements taken
during the life of an organism often
shows an “s-shaped” curve.
Some different organisms show slightly
different growth curves.
Human
Insect
Annual plant growth curve:
Perennial plant growth curve (Tree):
(b) Meristems
A meristem is a group of undifferentiated
plant cells which are capable of dividing
repeatedly.
Animals do not have meristems, growth
takes place all over the organisms.
Apical meristems
These increase the length of stems and
roots.
They are found at the tips of stems and
roots.
Cell division here produces primary
tissues.
ROOT TIP
Cell
division
zone
ROOT HAIRS
Elongation
+
Vacuolation
zone
Differentiation
zone
Cell division zone: Following
mitosis the resulting cells are small
cubes with a dense cytoplasm.
Elongation and vacuolation zone:
The cells absorb water by osmosis
causing them to elongate. Many
small vacuoles appear in the
cytoplasm.
They eventually merge to form a
large sap vacuole.
Differentiation zone: Here,
unspecialised cells become altered
to perform a special function in a
permanent tissue. e.g. Xylem
vessels or phloem tubes.
2. Lateral meristems
These produce an increase in the
thickness of stems and roots.
The tissues produced by lateral
meristems are called secondary tissues
and they cause secondary thickening.
Development of tissues in the
stem
When primary
tissues are fully
formed, the
stem (in cross
section) looks
like this:
Inside each vascular bundle a narrow
meristem called cambium arises.
Cambium is a lateral meristem which
produces secondary xylem and
secondary phloem.
In time, the cambium extends between
the vascular bundles where it continues
to divide and produce a complete ring of
secondary xylem and phloem.
Each year a new ring of secondary xylem
is formed. After 4 years the stem will
look like this:
The xylem vessels (cells) produced in the
cambium in the spring are larger then
those produced in late summer and
autumn.
This difference shows up as an annual
ring.
The inner core of xylem is called wood.
Regeneration
Regeneration is the process by which an
organism replaces lost or damaged
parts.
The ability to regenerate depends on the
presence of relatively undifferentiated
cells.
1. Angiosperms (flowering
plants)
These have extensive powers of
regeneration.
• Cuttings
Sections of plant are cut off and then
planted in the soil.
The cutting is able to produce shoots and
roots by regeneration.
(b) Tissue culture
Growers can mass
produce
identical clones
of plants which
show desirable
features.
2. Mammals
Mammals have only limited regenerative
powers.
– Regeneration is restricted to the healing of
wounds
– Mending broken bones
– The replacement of blood
– The regeneration of damaged liver
Genetic control of growth and
development
1. Jacob-Monod hypothesis of gene action
in bacteria
e.g. Lactose digestion by the bacterium E.
coli.
Lactose sugar is digested by E. coli into
glucose and galactose.
The reaction is controlled by the enzyme
ß-galactosidase.
ß-galactosidase
lactose
glucose + galactose
The enzyme is only produced by the
bacteria when the substrate (lactose) is
present.
The substrate therefore acts as an
inducer in the following way:
On the bacterial chromosome, three
genes control the production of the ßgalactosidase enzyme.
(a)Structural gene – codes for the
manufacture of ß-galactosidase.
(a) Operator gene – switches on the
structural gene.
(a) Regulator gene – produces repressor
molecules which stop the operator
switching on the structural gene.
Operon = structural gene + operator gene
If lactose is absent:
Repressor molecules prevent the operator
gene from switching on the structural
gene.
No ß-galactosidase enzyme is produced.
If lactose is present:
Repressor molecules are “mopped up” by
some of the lactose.
The operator gene is now free to switch
on the structural gene.
ß-galactosidase is produced.
2. Genetic control of metabolic pathways
A metabolic pathway consists of several
stages, each of which involves the
conversion of one molecule to another
during a break-down or synthesis
process.
Each stage in a metabolic pathway is
controlled by an enzyme, as shown in the
imaginary example below.
Metabolite A
GENE 1
GENE 2
GENE 3
ENZYME 1
ENZYME 2
ENZYME 3
Metabolite B
Metabolite C
Metabolite D
If any one of the 3 genes is faulty then
the enzyme is not made and the pathway
is blocked.
This happens with the illness
phenylketonuria (PKU).
In an unaffected person, surplus amounts
of an amino acid phenylalanine are
converted to harmless substances by a
the following pathway:
ENZYME 1
ENZYME 2
Phenylalanine
Tyrosine
Melanin
In a PKU sufferer, a gene mutation means
that ENZYME 1 cannot be made.
Phenylalanine is then broken down into
toxic wastes which can cause brain
damage.
Essay practice
Write an essay on:
(i) The control of lactose metabolim in E.
coli.
(6 marks)
(ii) Phenylketonuria in humans.
(4 marks)
3. Genetic control of cell
differentiation
Gene Activation
Every cell contains every gene but some
genes are switched on (activated) in all
cells while other genes are switched off
in cells where they are not required (e.g
insulin formation genes only remain
switched on in pancreas cells).
Genetic control of blood cell formation
Differentiated red blood cells,
phagocytes and lymphocytes are formed
from undifferentiated cells by
switching on of relevant genes (to make
haemoglobin, antibodies etc) and the
switching off of irrelevant genes.
Hormonal influences on growth
Hormones are chemical “messengers”
secreted into the blood by endocrine
glands.
They travel in the blood to target sites
where they have their effect.
(a) Pituitary hormones
The pituitary gland produces 2 hormones
which affect growth and development:
1) Growth hormone
Promotes growth by increasing amino acid
transport into growing tissues, which
stimulates protein production.
2) Thyroid-stimulating hormone
Stimulates the thyroid gland to produce
thyroxin.
Thyroxin controls the rate of ATP
synthesis in the cytochrome system
and therefore the rate of metabolism
and growth
Too much HGH
Too much TSH
(b) Plant growth substances
(Plant hormones)
Plant growth substances (hormones) which
affect the growth and development of
plants.
Two important growth substances are
• Indole acetic acid (IAA)
• Gibberellic acid (GA)
(a) Auxins
The commonest auxin is indole acetic acid
(IAA).
IAA is produced in apical meristems.
It moves back from the meristems in two
ways:
(i) Diffusion, over short distances, from
cell to cell.
(ii) Translocation, over longer distances, in
the phloem.
IAA affects plant growth in the following
ways:
At cell level (in meristems)
• Increases cell division
• Causes cell elongation by making cell
walls more “stretchy”
• Causes phototropism (shoots growing
towards the light) by stimulating growth
on the shaded side.
At organ level
Elongation of roots and shoots is
affected by IAA in the following way:
Concentration
of IAA (ppm)
Effect on root
Effect on shoot
Low (10-4)
Stimulates
elongation
No effect
Medium (1)
Inhibits
elongation
Stimulates
elongation
High (500)
Inhibits
elongation
Inhibits
elongation
At the organ level: IAA has these
effects
(1)Apical dominance
• IAA from the apical bud at the shoot
tip inhibits development of side
branches further down the stem.
(2) Fruit formation
• Following fertilisation, IAA stimulates
the formation of the fruit around the
seeds
(3) Leaf abscission
• In autumn, IAA concentration drops and
an abcission layer of cells forms at the
base of the leaf or fruit stalk.
The stalk snaps at this point and the leaf
or fruit falls.
Commercial applications of
auxins
Make notes on the following (pg 255 –
256)
• Delaying fruit abscission
• Rooting powder
• Herbicides
(b) Gibberellins
The commonest gibberellin is gibberellic
acid (GA).
GA plays a role in 3 aspects of plant life:
• Dwarf plant varieties
• GA affects the height of a plant be
elongating the internodes (sections of
stem between the leaves).
• GA is deficient (for genetic reasons) in
some dwarf varieties:
(2) Effect on bud dormancy
Buds of deciduous (leaf-dropping) trees
remain dormant during winter to
protect delicate tissues from frost.
In spring, GA is produced by the plant
which breaks the dormancy and the
buds open.
(3) Role in germination of barley grains
This is the sequence of events:
• Embryo absorbs water
• Gibberellin is produced by the embryo.
• Gibberellin diffuses out to the aleurone
layer.
• Aleurone layer produces α- amylase
• α- amylase converts starch in
endosperm to maltose sugar.
• Sugar used in respiration to release
energy, which is used for growth.
Environmental influences on
growth
(1)Importance on macro-elements
(a)Plants
All plants need carbon, hydrogen and
oxygen. They also need a variety of
other elements of which the most
important are called macro-elements.
The macro-element requirements of
plants can be investigated by means of
water-culture experiments:
Need for:
1. Air supply – gives roots oxygen for
respiration
2.Blackened glass – excludes light. This
stops algae from growing and using up all
the nutrients.
ELEMENT
NITROGEN
PHOSPHOROUS
MAGNESIUM
POTASSIUM
WHY IT IS
NEEDED
To make amino
acids and
proteins
DEFICIENCY
SYMPTOMS
Reduced growth
and yellowish
(chlorotic) leaves
Reduced growth,
To make ATP and
leaf bases turn
DNA
reddish
Reduced growth
To make
and leaves
chlorophyll
chlorotic between
veins
For transport of Reduced growth,
molecules across leaves die and fall
membranes
off prematurely
PHOSPHORUS
NITROGEN
POTASSIUM
MAGNESIUM
(b) Animals
Element
Iron
Calcium
Why it is needed
1. To make cytochrome
2. Constituent of many
enzymes
3. Forms part of
haemoglobin
1. Form bones and
teeth
2. Clotting of blood
3. Contraction of
muscle
(c) Inhibiting effect of lead
on enzyme activity
Lead can inhibit the activity of many of
the enzymes which control metabolic
pathways in the human body.
This disrupts respiration and growth. It
may also cause learning difficulties.
2. Effect of vitamin D
deficiency in humans
Role of vitamin D
• Essential to promote the absorption of
calcium and phosphate from the
intestine and their uptake by bones.
Symptoms of deficiency
• Causes formation of soft abnormal bone.
This is called Rickets.
3. Effects of drugs on foetal
development
Thalidomide:
Thalidomide
• Taken during pregnancy to reduce
morning sickness.
• Caused foetal limb deformity such as
hands attached to shoulders, and feet
to hips.
Alcohol and nicotine
Drinking alcohol and smoking cigarettes
containing nicotine during pregnancy can
affect the foetus in these ways:
• Retarded growth
• Reduced birth weight
• Slower mental development
Foetal alcohol syndrome:
4. Light
(a)Effects of light on vegetative shoot
growth
(i) Etiolation:
Etiolation (a tall, yellow stem) results
from increased cell elongation
produced by high auxin levels.
The advantage of
etiolation is to raise
some of the plants
leaves quickly above
the soil or competing
plants, so that
photosynthesis can
begin.
(ii) Phototropism:
This is the directional growth by part of a
plant in response to light from one
direction.
Positive phototropism
(growth towards light)
This is caused by greater elongation of
cells on the shaded side of the plant.
This is due to higher IAA levels on the
shaded side.
Positive phototropism exposes the shoot
to maximum light energy needed for
photosynthesis.
(b) Effect of light on flowering
For many plants this depends on the
photoperiod.
The photoperiod is the number of hours
of daylight in a 24 hour period.
(i) Long day plants flower when the
photoperiod is above a certain length
(e.g. Clover needs 12 hours or more of
light).
(ii) Short day plants flower when the
photoperiod is below a certain length
(e.g. Chrysanthemum needs 4 hours or
more of light).
(iii) Day neutral plants flower at any time
of the year, regardless of photoperiod.
Note:
• Other factors (temperature, nutrient
availability) also affect flowering.
• Photoperiod “works” by triggering
production of plant hormones.
• Synchronised flowering (controlled by
photoperiod) increases pollination
chances.
(c) Effect of light on timing of breeding
seasons
(i) Birds
Birds are long day breeders. Increasing
daylength (light reaches the brain
through the skull) stimulates sex
hormone production.
Territorial behaviour and sexual activity
follow.
(ii) Mammals
Mammals have varying gestation period
(pregnancy) and show two main breeding
strategies:
Gestation
Strategy
Stimulus
Mating
season
Young
born
Example
Short
(few
weeks)
Long day
breeder
Increasing
photoperiod
Spring
Early
summer
Hare
Long
(several
months)
Short day
breeder
Decreasing
photoperiod
Autumn
Early
summer
Red Deer
Each strategy results in the birth of
young at a time when weather and food
supply are likely to be favourable.
Physiological homeostasis
This is the ability of an animal to keep the
internal conditions of its body within
tolerable limits.
Some factors (e.g. water and glucose
concentration of the blood) are
controlled by negative feedback.
Negative feedback means that the action
of an effector organ brings about the
opposite action a short while later.
1. Water content of the blood
This needs to be keep constant to avoid:
(a) Osmotic problems – any increase in
water content causes blood cells to
swell and block capillaries.
(b) Changes in concentration of salts
dissolved in blood.
The blood water control is monitored by
the hypothalamus in the brain.
This causes the nearby pituitary gland to
vary the level of ADH it produces.
Negative
feedback control
of water content
of the blood
ADH (anti-diuretic hormone) travels in
the blood to the kidney nephrons, where
it affects the rate of water
reabsorption from the glomerular
filtrate into the blood capillaries.
Revision Sheet
On one side of A4 – make small revision poster –
explaining homeostasis and control of water
content of the blood.
• Why controlling water content is important?
• What is the receptor?
• What message is sent to the kidneys?
• What happens at the effector (the nephron)?
Try to think of a mnemonic or a rhyme to help you
remember it!
Make it colourful – as colour helps you remember
things.
2. Control of blood sugar level
Glucose is continuously consumed from
the blood during respiration by the
body’s cells.
Fresh glucose is only obtained when we
eat, but a homeostatic mechanism
ensures an adequate level in the blood
at all times.
A raised blood sugar level is detected by
the pancreas which increases insulin
production.
Insulin (a hormone) travels in the blood to
the liver where it causes the conversion
of glucose to glycogen.
When blood glucose falls the pancreas
increases production of another
hormone, glucagon.
This travels to the liver and causes
glycogen to turn back to glucose.
Negative
feedback control
of blood glucose
level
Diabetes mellitus
Make own notes from Higher Biology
textbook.
Adrenaline
Adrenaline is a hormone released by the
adrenal glands in cases of stress and
danger.
Adrenaline promotes the rapid breakdown
of glycogen to glucose so that more
energy can be provided quickly.
3. Control of body
temperature
This is controlled to provide optimum
conditions for our enzyme-controlled
metabolism.
Endotherm: An animal which produces its
body heat internally. It possesses
homeostatic mechanisms to maintain a
constant body temperature. e.g.
Mammals and birds
Ectotherm: An animal which receives most
of its heat from the environment. e.g.
Snakes or lizards.
The temperature monitoring centre is in
the hypothalamus in the brain.
This controls homeostatic mechanisms to
regulate the body’s core temperature at
37 ºC.
The hypothalamus receives information
about body temperature from two
sources:
(i)Skin thermoreceptors
–
–
Communicate with hypothalamus by nerve
impulses
Give information to on body surface
temperatures.
(ii) Central thermoreceptors
– In hypothalamus itself
– Detect body temperature (body core)
changes
Necessary action to adjust body
temperature is sent by nerve impulses
to effector organs.
Role of the skin
1. Correction of overheating
(a) Vasodilation
Skin surface
Nerve from
hypothalamus
Shunt Vessel
Direction of
blood flow
Arteriole
Venule
(b) Increase in rate of sweating
As sweat evaporates from the skin
surface, heat energy is taken away from
the body, cooling the skin.
2. Correction of overcooling
(a) Vasoconstriction
Skin surface
Nerve from
hypothalamus
Shunt Vessel
Direction of
blood flow
Arteriole
Venule
(b) Decreased rate of sweating
Sweating is reduced to a minimum to
conserve heat.
(c) Contraction of hair erector muscles
Body response to heat loss
The subject’s arm was stuck in a basin of
ice cold water. One temperature sensor
was placed between the thumb and
forefinger, the other was placed under
the arm to monitor core temperature.
Core temperature v. Skin temperature
37
Temperature (C)
35
33
Skin Temp
31
Core Temp
29
27
25
0
50
100
Time (seconds)
150
200
The finger temperature reading
decreased as the body redirects the
blood to the more vital organs.
The core temperature increases as the
metabolic rate of the body increases
hence producing more heat.
Regulations of populations
Population is a group of individuals of the
same species which makes up part of an
ecosystem.
Population density is the number of
individuals of the same type present per
unit area of a habitat.
Population dynamics is the study of
population changes (growth,
maintenance and decline) and the
factors which cause these.
Birth rate of a population is a measure of
the number of new individuals produced
by a population over a certain time
period.
Death rate is a measure of the number of
individuals that died during the same
time interval.
At points “A” and “B” the birth rate is
higher than the death rate and the
population grows.
At point “C” the birth and death rates are
equal. At this time the population size
will remain relatively stable – this is the
carrying capacity of the ecosystem.
Population stability
Animal populations usually fluctuate
around a certain level which the
available environmental resources can
maintain.
This is the carrying capacity of the
environment.
Despite short-term fluctuations the birth
rate equals the death rate and, in the
longer term, number remain fairly
stable.
Very stable populations can be maintained
in the laboratory where the conditions
can be carefully maintained:
Wild populations fluctuate more than this
due to environmental factors:
Factors affecting population
change
Density-independent factors
These factors affect the death rate of a
population equally, regardless of the
size of a population.
Abiotic factors
operate in this
way.
The % loss is the same, regardless of the
size of the original population.
Density-dependent factors:
These factors have a greater or lesser
effect, depending on the population
density.
A higher proportion of the population will
die when the population density is high.
Density dependent factors include food
supply, disease, predators and
competition.
(a)Food supply
When there is not enough food for a
population some individuals (probably
the weakest) will starve. The denser
the population the more individuals will
suffer.
(b) Disease
If a population of animal is living at high
density then disease transmission is
more likely and the death rate will
increase.
e.g. Myxomatosis rabbits
(c) Competition
This may involve competition for food,
living space etc.
When the number of animals present
outstrips the available food supply,
competition occurs between individuals.
(d) Predation
A dense prey population is more likely to
attract predators than a small
population.
Predator-prey interactions
A balance exists between populations of
predators and their prey.
• An increase in prey leads to an increase
in predators.
• The increased predator population
reduces the prey numbers
• The predators have less prey and their
numbers fall.
A classic example of this is the
interaction between snowshoe hares and
lynxes in Canada.
Monitoring populations
Monitoring populations of certain species
is important for the following reasons:
1. Food species
(a)Fish
Stocks of edible species need to be
monitored to ensure catches do not
exceed the rate of reproduction.
(b) Red deer
Deer populations have grown in Scotland
as a result of lack of predators. To
prevent environmental damage many
deer are culled and the meat sold as
venison.
2. Control of pest species
Monitoring populations of pest species
provides information needed for their
control.
(a)Greenfly
• Greenfly reproduce when environmental
conditions are favourable and wingless
individuals are produced.
• When conditions deteriorate, winged
greenfly are produced allowing them to
be dispersed.
• Gardeners can spray plants with
pesticide or introduce ladybirds when
it will have the maximum effect.
(b) Mosquitoes
• Blood sucking female mosquitoes are
vectors for several diseases such as
malaria that affects humans.
Monitoring populations of mosquitoes
enables scientists to find out:
• Where the eggs are laid
• What time of day the females feed on
blood
• How often the females feed
• Where the insect rests when its not
feeding
Such information is vital when planning a
programme of control measures.
3. Endangered species
Any successful conservation programme
depends on accurate knowledge of
population changes of the organism
concerned.
e.g. Black rhino, dolphin, albatross, panda
4. Indicator species
Some wildlife species act as an indicator
of the “health” of the environment by
their presence or absence.
(a)Freshwater invertebrates
Presence of mayfly or stonefly nymphs
shows high oxygen levels in the water.
Many sludgeworms or rat-tailed maggots
shows low oxygen levels in the water.
(b) Lichens
The presence or absence of lichens on
tree trunks and walls indicates a low
level of sulphur dioxide air pollution.
Plant succession
Plant succession is the natural change in a
habitat from an initial simple pioneer
community to a final, relatively stable,
climax community.
The change at each stage may modify the
habitat in one or more ways:
• Addition of humus (dead organic
matter)
• Increase in fertility (e.g. Clover family)
• Change in soil moisture
Each change makes the habitat less
suitable for the current community and
more favourable for a different
community which succeeds it.
(e.g. Reeds lower the water level of a
marsh, drying it enough for willow trees
to grow).
Primary succession
Takes place during colonisation of a
barren area which has not been
previously inhabited (e.g. Bare rock).
Secondary succession
Occurs during the colonisation of an area
which has previously been occupied by a
well-developed community but has
become barren (e.g. A felled forest).
During succession the following changes
take place:
1. Increase in biomass of the community
2. Increase in the species diversity
(especially plants and invertebrates)
3. Increase in the food web complexity.
Effect of environment on climax
plant communities
A climax community is:
• The final product of long-term
unidirectional change with in a community.
• Self-perpetuating and, under natural
conditions, not replaced by another
community.
• A mature community is in dynamic
equilibrium with its environment.
1. Climate
Temperature and rainfall vary widely
round the world, resulting in different
climax communities, e.g.:
• very hot, very dry = desert
• Very hot, always wet = rainforest
• Very hot, seasonal rain = savannah
• Warm, regular rain = broadleaf forest
• Very cold, dry = Tundra
2. Soil type
The chemical composition of the
underlying rock affects the pH and the
mineral content of the soil.
In North East Scotland:
Acid soils (common): Heather is dominant
Basic soils (alkali, over limestone):
Support a rich variety of flowering
plants.
THE END!!!