Define abiotic components
Components of an ecosystem that are non-living
Define biotic components
Components of an ecosystem that are living
Define tropism
A directional growth response in which the direction of the response is determined by the direction of the external stimulus
What are tannins?
Phenolic compounds, located in cell vacuoles or in surface wax on plants.
- prevent infiltration of pathogenic microorganisms
What are alkaloids?
Organic nitrogen-containing bases that have important physiological effects on animals, they may taste bitter for example
Examples of alkaloids
- nicotine
- quinine
- strychnine
- morphine
What are pheromones?
Chemical substances released by one living thing, which influences the behaviour or physiology of another living thing
Example of chemotropism
pollen tubes growing down the style, attracted by chemicals, towards the ovary where fertilisation takes place
Whats a non-directional response to an external stimulus called?
Nastic response
Example of nastic response?
Folding leaves in response to touch
Which plant is folds its leaves as a form of thigmonasty?
Mimosa pudica
What do cytokinins do?
- promote cell division
- delay leaf senescence (ageing)
- overcome apical dominance
- promote cell expansion
What does abscisic acid do?
- inhibits seed germination and growth
- causes stomatal closure when the plant is stressed by low water availability
What do auxins do?
- promote cell elongation
- inhibit growth of side shoots
- inhibit leaf abscission (leaf fall)
What do gibberellins do?
- promote seed germination
- promote stem elongation
What does ethene do in plants?
-promotes fruit ripening
How can hormones move around the plant?
- active transport
- diffusion
- mass flow in the phloem sap or in xylem vessels
What is apical dominance?
inhibition of lateral buds further down the shoot by chemicals produces by the apical bud at the tip of a plant shoot
What actually happens to a plant when the tip is cut off in terms of abscisic acid?
Apex gone, auxins cant regulate the concentrations of abscisic acid in lateral buds and so conc. drops
lateral buds grow
What happens to a plant when the apex is cut off in terms of cytokinins?
Usually auxin is a sink for cytokinins and concentrates the in the apex
No auxin, cytokinins arn’t targeted to the shoot and is spread throughout the plant
Promotes bud growth elsewhere
What happens when you apply a lot of cytokinins to normal plants?
Apical dominance is overwritten
Whats an important auxin example?
IAA
How does gibberellin cause seed germination?
water absorption by the embryo causes GA release
- causes alpha amylase to be released
- amylase breaks down starch so the embryo can use the energy for germination
Where are there meristems?
- apical meristem
- roots
- lateral bud meristem
- intercalary meristems
- lateral meristems (makes stem thicker)
What piece of equipment is used to measure the effects of gravity on a plant?
Klinostat spins it round and round
How does auxin work?
- light causes auxin to go to shaded side
- auxin causes active transport of H+ ions into cell wall
- this decreases pH of cell wall
- disrupts H bonding in wall and makes optimum pH for expansins to loosen walls
- wall less rigid and can elongate as they take up water
How do auxins affect roots and shoots?
Different levels of auxins affect them different
How is auxin transported to the shaded side of plants?
By PIN proteins
How is leaf loss in deciduous plants controlled?
- Auxins inhibit leaf loss (auxins are produced by younger leaves, as the leaf gets older, less auxin is produced, leading to leaf loss)
- Ethene stimulates leaf loss and is produced in ageing leaves (the abscission layer separates the leaf from the rest of the plant and ethene makes the cells in this expand and break the cell walls)
How are hormones involved in stomatal closure?
Abscisic acid triggers stomatal closure
- binds to receptors
- Ca2+ ions enter through newly opened ion channels
- Ca2+ go into the cytosol from the vacuole
- Increased calcium conc. in cytosol causes other ion channels to open, allowing ions to leave the cell, RAISING its water potential
- water leaves the guard cell by osmosis and it becomes flaccid and stomata close
Commercial uses of auxins
- herbicides (make weeds produce long stems instead of lots of leaves and they grow too fast, cant get enough water or nutrients and die)
- rooting hormones (make plants grow roots) and cuttings
- prevent leaf and fruit drop
- promote flowering
- seedless fruit
Commercial uses of cytokinins
- prevent yellowing of leaves
- plant mass production
Commercial uses of gibberellins
-delay senescence of citrus fruits
-elongate apples
-less compact grape stalks so grapes can grow more
-brewing (produces amylase, breaks down starch into maltose)
sugar cane production (stimulate growth between nodes)
-plant breeding (induces seed formation)
Commercial uses of ethene
- stimulates enzymes that break cell walls, break down chlorophyll and starch into sugars - make fruit nice and soft eg banana
- ripening in apples, tomatoes + citrus
- fruit drop in cotton, cherry + walnut
What inhibits the effects of ethene on plants?
silver salts
What is a tropism?
Directional growth response
What do synergic hormones do?
Amplify each others effects
What do antagonistic plant hormones do?
Oppose each others effects
How does growth occur in the meristem tissue?
By two processes:
- cell elongation
- cell division
What is the Le gene responsible for?
producing enzyme that converts GA20 to GA1
Is Le in tall or short?
tall
Is le in tall or short?
short
first experiments on role of auxins
in the control of apical dominance
- suggestion = auxins from apical bud prevent later buds from growing
- auxins applied to cut end and lateral buds do not grow
- UNEXPECTED effect = upon exposure to oxygen, cells at cut end could have produced hormone that promoted lateral bud growth
- new suggestion = normal auxin inhibits and low auxin promotes
the experimental evidence for the role of
gibberellin in the control of stem elongation
- when gibberellic acid on dwarf varieties = grow taller
- compare GA levels in tall (Le) pea plants and dwarf (le) showed higher GA levels = taller
- Le gene responsible for GA20 to GA1
- plants with mutated gene are short
the experimental evidence for the role of
gibberellin in the control of seed germination
when seed absorbs water, gibberellin released
goes to aleurone layer in endosperm region
enables production of amylase which = starch to glucose
=substrate for respiration = growth
Describe mechanism of auxin
promotes active transport of H+ into cell wall
low pH = optimum for wall loosening enzymes (expansins) to work
break bonds between cellulose