Module 5 - Plant and animal responses Flashcards
(24 cards)
Limitations of plant responses
Plants are mobile and do not have a rapidly responding nervous system.
How do plants respond to the environment?
Producing hormones transported throughout the plant and affecting different areas
The role of gibberellins in stem growth
Plant growth regulation, they can elongate plant stems by increasing length of internodes
The role of gibberellins in seed germination
Play a role in ending a seed’s dormant stage by a few key processes
1. water enters seed
2. absorption of water causes embryo to synthesise gibberellins
3. amylase and maltase are synthesised
4. amylase hydrolyses starch stored in endosperm into maltose
5. this can be broken down to glucose which provides embryos with sugars that are essential for energy and growth
This allows the mobilisation of stored starch to begin germination process
Plant hormone interactions
Synergistic: different hormones work together to give a greater response than they would on their own
Antagonistic: different hormones have opposing effects, balance between them determiens response of the plant
WHat are auxins, their function and effect on plant tissues?
Plant growth factors synthesised in meristem of shoots and roots.
Functions include:
- cell expansion and differentiation
- apical dominance: suppression of lateral bud growth
-Tropisms: directional growth responses
Effects:
- High IAA conc. inhibits root growth and promotes shoot growth
- Low IAA conc. does the opposite
How does IAA create shoot growth via cell elongation?
- IAA diffuse down shoot away from tip
- They bind to receptors on cell-surafce membrane
- low pH develops in cell walls
- cells absorb water by osmosis forming vacuoles and increasing internal pressure so cell walls expand
- cell elongates and plant grows
Role of IAA in apical dominance
removal of apical bud (source of IAA) releases inhibition on lateral bud growth allowing a bushier plant to develop
Abiotic stresses in plants (non-living factors)
- changes in day length
- excessive cold and heat
- lack of water or excess water
- high winds
- changes in salinity
They can affect growth, productivity and survival of plants so adaptations are required
What is photoperiodism and what is its effect on plants?
Sensitivity of plants to levels of light in the environment
1. Summer: decidious trees are in full leaf, more photosynthesis and growth
2. Autumn: longer dark periods means leaves start to fall off
3. Winter: trees maintain a period of dormancy due to little light
4. Spring: tress come out of dormancy
What is phytocrome and how can it affect plant responses involving photperiodism?
A pigment that senses duration of light and darkness and exists in 2 different forms that absorb different types of light ( Pr and Pfr)
They can affect plant responses by:
- breaking dormancy in buds
- initiating tuber formation
- timing flowering phase
What is abscission and its triggers?
When plants lose their leaves triggered by:
- longer dark periods, less photsynthesis
- energy demands for respiration outweigh glucose availability
- need for dormancy to avoid winter-related damage
Stages of abscission
- decrease in light prompts decrease in auxin
- ethene released my leaves
- helps switch on genes in abscission zone at the base of leaf stalk
- enzymes digest and weaken cell walls
- vascualr tissue sealed off blocking transport to the leaf
- fatty material deposited in inner layer od abscission zone
- cells in separation layer swell and weaken
- wind spearates leaf from plant
9 a scar is created to prevent entry of pathogens
How do plants prevent cellular freezing?
- Synthesise compounds like sugars, amino acids, proteins which act as antifreese and prevent cytoplasm freezing
- Modulate gene expresssion to bolster cold resistance
- Adjusting sap solute conc. to lower freezing point
Role of Abscisic Acid (ABA) in stomatal regulation
- low water availability triggers production of ABA
- this moves from roots to leaves and binds to receptors on guard cells
- This activates changes in ionic conc. of guard cells reducing WP and turgor of cells
- results in stomatal closure to minimise water loss
Plant defences against herbivores
-Thorns, barbs, spikes
- Tough fibrous tissues
- Stinging hairs
- Densely hairy leaves
Chemical defences: Alkaloids
Bitter, nitrogen containing compounds
1. Morphine and cocaine act as drugs and affect metabolism of animlas so herbivores are discouraged from eating it
2. Caffeine and nictoine are toxic to animals
Volatile Organic Compounds (VOCs) for pest control
affect social behvaiour of animals
1. attract predators for pests
2. repel herbivores from eating plants
3. signal neighbouring plants to prepare defences
Plant movement in response to touch
Mimosa pudica close when touched to prevent insects eating them because they look smaller and less appetising
Phototropism and its 2 types
Ability of a plant’s shoots to capture light for photosynthesis:
Positive phototropism: shoots grow towards light
Negative phototropism: roots grow away from the light
Geotropism and its 2 types
Helps roots anchor in soil to support growth
Positive: roots grow downwards towards gravitational pull
Negative: shoots grow upwards away from gravitational pull
Control of positive phottropism in shoots
- IAA is produced in cells in the tip of the plant shoot.
- IAA is transported down the plant shoot.
- Light stimulates IAA to move from the light side of the shoot to the shaded side.
- IAA becomes concentrated and stimulates more cell elongation on the shaded side of the shoot.
- The shoot bends towards the light.
Control of negative tropism in plant roots
- IAA is produced in cells in the tip of the plant root.
- IAA is transported along the plant root.
- Any light available stimulates IAA to move from the light side of the root to the shaded side.
- Gravity also pulls IAA from the upper side of the root to the lower side of the root.
- IAA becomes concentrated and inhibits cell elongation in the lower, shaded side of the root.
- The root bends away from any available light and downwards towards the pull of gravity.
