Presentation on theme: "Control and Regulation Higher Biology Unit 3. Growth and development Growth patterns in plants and animals Growth is the irreversible increase in the."— Presentation transcript:
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.
(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 TIPROOT 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. 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 lactoseglucose + 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.
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 AMetabolite BMetabolite C Metabolite D ENZYME 1ENZYME 2ENZYME 3 GENE 1GENE 2GENE 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. PhenylalanineTyrosineMelanin ENZYME 1ENZYME 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 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
(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 rootEffect on shoot Low (10 -4 ) Stimulates elongation No effect Medium (1) Inhibits elongation Stimulates elongation High (500) 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.
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 WHY IT IS NEEDED DEFICIENCY SYMPTOMS NITROGEN To make amino acids and proteins Reduced growth and yellowish (chlorotic) leaves PHOSPHOROUS To make ATP and DNA Reduced growth, leaf bases turn reddish MAGNESIUM To make chlorophyll Reduced growth and leaves chlorotic between veins POTASSIUM For transport of molecules across membranes Reduced growth, leaves die and fall off prematurely
(b) Animals ElementWhy 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 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.
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:
Gestat- ion StrategyStimulus Mating season Young born Example Short (few weeks) Long day breeder Increasing photo- period Spring Early summer Hare Long (several months) Short day breeder Decreasing photo- period 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.
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.
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.
(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.
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.