CHEMICAL CONTROL OF PLANT GROWTH
plant hormones / plant growth regulators/substances = chemical subs. produced in plants; acc., inhibit, modify growth
five groups: auxins, gibberellins, cytokinis, abscissic acid + ethene (ethylene)

Auxins (universally occurring) (diffusiable through water-soluble subs.)
-most common: IAA = indoleacetic acid (organic), from amino acid tryptophane
-very powerful subs., causes cell elongation [0.01mg/dm³ causes growth]
-transport: polar-one direction, i.e. away from tip. for short dist.-diffusion, long dist.-phloem
-causes phototropic response, unilateral illumination > auxin redistribution, more on dark side > more elongation > grow towards light
-stimulates cell division, helps maintain cell wall structure + in high conc. inhibit growth
-stimulates growth of adventitious roots
-stimulates pathenocarpy: fruit development, w/o fertilization
-used as an effective herbicides; synthetic auxin 2,4-D = 2, 4 dichlorophenoxyacetic acid, low conc. > distorted plant
growth + excessive resp. > plant dies (more effective on broad-leafed plants > selective weedkiller) high conc.>no long term growth

Tropism
Tropism = growth movement by parts of plant (shoot + root) with reference to direction of stimulus
+tive- move towards-tive-move away

Phototropism =growth movement of plant part in response to unilateral stimulation by light
-unilateral illumination > auxin redistribution, more on dark side > more elongation > grow towards light
-shoots + phototropismroots - phototropism

Geotropism =growth movement of plant part in response to gravity
-shoots + roots respond differently to conc. of auxins: shoot- high conc. >growth promoted
root- high conc.> growth inhibited, low conc.> growth promoted
-shoot placed horizontally > more auxins on lower side > stimulate elongation > grow upwards
root placed horizontally > more auxins on lower side > inhibit growth > grow downwards
-shoots - geotropismroots + geotropism

Clinostat/Klinostat
-an instrument that can negate effect of gravity on plants
-consist of a turntable that moves slowly
-very slow > shoot + root = corkscrew shape
-slow > no effect (each side of shoot + root exposed to gravitational stimulus for a short time > no time to respond)

Advantages of tropisms
+ phototropism : max. sunlight for photosynthesis + expose to pollination agents (insects) for better cross-pollination
- geotropism : shoots: grow away from earth > sunlight for chlorophyll formation & photosynthesis
+ geotropism : roots: grow into earth > anchor plant + absorb H₂O + mineral salts
- geotropism : roots (plants in swampy areas, mangrove) > get O₂

Coordinating & response
2 coordinating systems; nervous system + endocrine system for homeostasis
nervous system-rapid, short-lived response
endocrine system-slow, long-term/permanent response

glands-collection of tissues > structure which secretes a specific chemical substance which has a function
endocrine + exocrine glands
exocrine glands-glands that secrete secretions in large quantities that are carried through ducts to target organ
endocrine (ductless) glands-glands that secrete hormones in small quantities that are carried by blood plasma to target organ [hormones have no effect on place produced, but major effect on target organ] (controls growth, metabolism, etc)
most endocrine glands work under the master gland = pituitary gland. hormones are after destroyed in liver
Adrenal glands
~ 5g each, situated anterior to kidneys
-adrenal cortex (outer)+ medulla (inner). adrenaline- secreted by adrenal medulla in stressful conditions, "flight-fight" hormone > prepares organism to flee / face foe / face stressful condition

Effects of adrenaline
1 bronchioles dilate-breathing faster & easier > more O₂ for resp.
2 glycogen (in liver + muscles)> glucose-more glucose for resp.
3 cardiac muscles beat faster-blood pressure increase > more blood pump > more O₂ + glucose, more CO₂ removed
4 blood diverted (digestive+reproductive systems>muscles,lungs+ liver)-more blood to organs which need more energy
5 peristalsis + digestion inhibited-allows blood to be diverted
6 sensory perception increased-more rapid reaction to stimuli
7 mental awareness increased-more rapid reaction to stimuli
8 pupils dilate-increase range of vision > increase perception
9 hair erector muscles contract-hair stands upright > scares foes

Pancreas
-mixed gland, exocrine; cells in pancreas secretes pancreatic juice, passed to duodenum by pancreatic duct, endocrine; cells in islets of Langerhans secrete hormones: a cells = glucagon, b cells = insulin (target-liver cells)
Insulin-protein (51 amino acids), released when blood glucose level >1mg/cm3 or a rise in glucagon level. cell membrane (receptors sites) bind insulin > change cell permeability to allow glucose to enter to be converted to glycogen+ change enzyme activity systems

Insulin increase-rate of conversion of glucose to glycogen
-rate of uptake of glucose by muscles and fats by cell membranes
-protein + fat synthesis
-formation of RNA, DNA, ATP
insulin-only hormone that lowers blood sugar level, deficiency-diabetes mellitus-excess blood glucose level, kidneys can not reabsorb glucose > glucose in urine, may cause blindness + kidney failure

Defiency-high blood glucose level
-breakdown of muscle tissue, loss of weight, tiredness
-body fat(+protein) oxidised as glucose is excreted > poisonous ketones produced
-coma + death
Excess-low blood glucose level
-hunger, sweating, irritability, double vision
-coma + death
Treatment-insulin injections (used to be taken from animal's pancreases , now by using bacteria: gen. eng.)

Tactic movement
-movement by unicellular animals + some invertebrates whereby the whole organism moves in reference to the direction of the stimuli +tive = move towards -tive = move away

The Use and Abuse of Drugs
Diversity of Organisms
Nutrient cycles and Ecology
Parasitism
The Human Impact on the Environment
Reproduction in plants
Sexual reproduction in animals
Genetics
Cell Structure and Organisation
Enzymes
Nutrition
Transport in Plants
Support, Movement and Locomotion
Transport system in man-circulatory system
Respiration
Excretion
Homeostasis
The Eye
Nervous System

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