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.

Cell division

zone

Elongation +

Vacuolation zone

Differentiation zone

ROOT TIP ROOT HAIRS

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.

• CuttingsSections 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-galactosidaselactose 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 ß-galactosidase 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 Metabolite B Metabolite C Metabolite D

ENZYME 1 ENZYME 2 ENZYME 3

GENE 1 GENE 2 GENE 3

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:

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.

Phenylalanine Tyrosine Melanin

ENZYME 1 ENZYME 2

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 ActivationEvery 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 hormonePromotes growth by increasing amino

acid transport into growing tissues, which stimulates protein production.

2) Thyroid-stimulating hormoneStimulates 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 levelElongation of roots and shoots is

affected by IAA in the following way:

Concentration of IAA (ppm)

Effect on rootEffect on

shoot

Low (10-4)Stimulates elongation

No effect

Medium (1)Inhibits

elongationStimulates elongation

High (500)Inhibits

elongationInhibits

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 dormancyBuds 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)PlantsAll 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

respiration2.Blackened glass – excludes light.

This stops algae from growing and using up all the nutrients.

ELEMENTWHY IT IS NEEDED

DEFICIENCY SYMPTOMS

NITROGENTo make amino

acids and proteins

Reduced growth and yellowish

(chlorotic) leaves

PHOSPHOROUSTo make ATP

and DNA

Reduced growth, leaf bases turn

reddish

MAGNESIUMTo make

chlorophyll

Reduced growth and leaves chlorotic

between veins

POTASSIUM

For transport of molecules

across membranes

Reduced growth, leaves die and fall off prematurely

NITROGEN

PHOSPHORUS

MAGNESIUM

POTASSIUM

(b) Animals

Element Why it is needed

Iron

1.To make cytochrome

2.Constituent of many enzymes

3.Forms part of haemoglobin

Calcium

1.Form bones and teeth

2.Clotting of blood3.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)BirdsBirds 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:

Gestat-ion

StrategyStimulu

sMating season

Young born

Example

Short (few

weeks)

Long day breeder

Increasing photo-period

SpringEarly

summerHare

Long (several months)

Short day breeder

Decreasing photo-period

AutumnEarly

summerRed 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 SheetOn 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

Nerve from

hypothalamus

Arteriole Venule

Shunt Vessel

Skin surface

Direction of blood flow

(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

Nerve from

hypothalamus

Arteriole Venule

Shunt Vessel

Skin surface

Direction of blood flow

(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

25

27

29

31

33

35

37

0 50 100 150 200

Time (seconds)

Tem

per

atu

re (

C)

Skin Temp

Core Temp

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 factorsThese factors affect the death rate of a

population equally, regardless of the size of a population.

Abiotic factorsoperate in thisway.

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 supplyWhen 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) DiseaseIf 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) CompetitionThis may involve competition for food,

living space etc.When the number of animals present

outstrips the available food supply, competition occurs between individuals.

(d) PredationA 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)FishStocks of edible species need to be

monitored to ensure catches do not exceed the rate of reproduction.

(b) Red deerDeer 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 speciesMonitoring 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

feedingSuch information is vital when

planning a programme of control measures.

3. Endangered speciesAny successful conservation programme

depends on accurate knowledge of population changes of the organism concerned.

e.g. Black rhino, dolphin, albatross, panda

4. Indicator speciesSome wildlife species act as an

indicator of the “health” of the environment by their presence or absence.

(a)Freshwater invertebratesPresence 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) LichensThe 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 successionTakes place during colonisation of a

barren area which has not been previously inhabited (e.g. Bare rock).

Secondary successionOccurs 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. ClimateTemperature 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 typeThe 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

dominantBasic soils (alkali, over limestone):

Support a rich variety of flowering plants.

THE END!!!