Plant responses

Question 1

What are the 2 limitations of plant responces?

Answer 1

• rooted to spot so aren’t mobile
• don’t have a rapidly responding nervous system

Question 2

How do plants respond to their environment?

Answer 2

produce hormones that are transported through plant and affect different parts of plant

Question 3

What is plant dormancy?

Answer 3

period of inactivity allowing seed to withstand various adverse environmental condition

Question 4

What are the 2 key structures in initiating the germination process?

Answer 4

Embryo = developing plant

Endosperm = an energy store containing starch and surrounds the embryo

Question 5

What is the process of plant germination?

Answer 5

1) water enters seed

2) absorption of water causes embryo to synthesise gibberellins

3) in response amylase and maltase enzymes are synthesised

4) amylase enzymes hydrolyse starch stored in the endosperm into maltose

5) this can be broken down into glucose which provides embryo with sugars essential for energy and growth

Question 6

What are plant growth factors?

Answer 6

chemicals that influence plant development mainly by modulating cell elongation and division

Question 7

What is synergistic plant hormone interaction?

Answer 7

when different hormones work together giving a greater response than on their own

Question 8

What is antagonistic plant hormone interaction?

Answer 8

different hormones have opposing effects like one promoting growth and one inhibiting it

balance between them determines response of plant

Question 9

What are auxins and give an example of one?

Answer 9

Auxins are crucial plant growth factors

e.g indoleacetic acid (IAA) is synthesised in the growing tips of shoots and roots where cell division occurs

Question 10

What aspects of plant growth do auxins regulate?

Answer 10

• cell expansion + differentiation
• suppression of lateral bud growth (apical dominance)
• directional growth responses (tropisms)

Question 11

What are the 2 effects auxin has on plant tissue?

Answer 11

• high concentration inhibit root growth and promote shoot growth
• low concentration promote root growth and inhibit shoot growth

Question 12

What is the role of IAA in shoot elongation?

Answer 12

1) auxins are synthesised by meristem cells in shoot tips

2) auxins diffuse down shoot away from tip

3) auxins bind to receptor sites on cell-surface membranes

4) low pH develops in cell walls

5) cells absorb water by osmosis forming vacuoles increasing the internal pressure causing cell walls to expand

6) cells elongate and plant grows

Question 13

What are abiotic stresses?

Answer 13

non-living factors in environment that can negatively affect organisms survival

Question 14

What are examples of abiotic plant stresses?

Answer 14

• changes in day length
• excessive cold and heat
• lack of water or excess water
• high winds
• changes in salinity

Question 15

What is photoperiodism?

Answer 15

sensitivity of plants to level of light in their environment

Question 16

How does photoperiodism align with the changing seasons?

Answer 16

Summer = daylight hours are maximum and trees are in full leaf maximising photosynthesis and growth

Autumn = lengthening of dark period triggers leaf fall in trees

Winter = daylight hours are at a minimum and trees maintain a period of dormancy

Spring = days lengthen and temp rises causing trees to come out of dormancy

Question 17

What does the phytochrome pigment do and what are it’s 2 forms?

Answer 17

Sense the duration of light and darkness

Pr and Pfr absorbing different light types

Question 18

What response might plants have to phytochrome?

Answer 18

• break dormancy in buds
• initiate tuber formation
• time flowering phase

Question 19

What is abscission?

Answer 19

When plants lose their leaves

Question 20

What is abscission triggered by?

Answer 20

• lengthened dark period during autumn leading to reduced photosynthesis
• energy demands for respiration outweighing glucose availability
• need for dormancy to avoid winter-related damage

Question 21

What are the stages of leaf abscission?

Answer 21

1) decrease in light prompts decrease in auxin levels
2) hormone ethene is released by leaves
3) ethene helps switch on genes in cells in abscission zone at base of leaf stalk
4) enzymes digest and weaken cell walls in separation layer
5) vascular tissues are sealed off blocking transport to leaf
6) fatty material is deposited in cells inner, protective layer of abscission zone
7) cells within separation layer swell with water straining weakened walls
8) environmental factors such as winds separate leaf from plant
9) protective layer remaining forms a scar to prevent entry of pathogens

Question 22

What are some examples of responses of plants to freezing conditions?

Answer 22

• synthesise compounds e.g sugars, AA’s, and proteins acting as antifreeze preventing cytoplasm freezing
• modulating gene expression to bolster cold resistance
• adjusting sap solute concentrations to lower freezing point

Question 23

What hormone is involved in stomatal regulation?

Answer 23

Abscisic acid (ABA) signals for conserving water during heat and drought

Question 24

What is the mechanism of ABA in stomatal regulation?

Answer 24

1) low water availability triggers production of ABA
2) ABA moves from roots to leaves
3) ABA binds to receptors on guard cells
4) ABA activates changes in ionic concentration of guard cells, reducing Ψ and turgor of cells
5) results in stomatal closure minimising water loss

Question 25

Describe and explain plants physical responses to herbivory?

Answer 25

Thorns/barbs/spikes = sharp structures cause physical harm to herbivores deterring them from eating plant Tough fibrous tissue = makes = plant hard to chew and digest Stinging hairs = inject irritating substances into herbivores Densely hairy leaves = create physical barrier difficult for many herbivores to overcome

Question 26

What are the key types of chemical defences a plant uses?

Answer 26

- tannins - alkaloids - terpenoids

Question 27

What are alkaloids?

Answer 27

Bitter nitrogen-containing compounds

Question 28

What are the effect of alkaloids?

Answer 28

Alkaloids e.g morphine and cocaine act as drugs affecting metabolism of animals discouraging some herbivores from consuming plant producing them Alkaloids e.g caffeine and nicotine are toxic or poisonous to animals discouraging herbivores from consuming plant or even killing them

Question 29

what are VOC's?

Answer 29

Volatile organic compounds chemicals made by an organism affecting social behaviour of other members of the same or different species

Question 30

What is the purpose of VOC's?

Answer 30

Attracting predators = e.g VOCs from pest-damaged cabbages can attract wasps that prey on pests Repelling herbivores = can discourage other herbivores from feeding on plant Signalling neighbouring plants = alert nearby plants to prepare defences even before attack themselves

Question 31

What is tropism?

Answer 31

Directional growth responses of organisms like plants to specific stimuli

Question 32

What does tropism allow?

Answer 32

Allows plants to respond to variations in environmental conditions helping make maximum use of environment for survival

Question 33

What are some examples of tropism in plants?

Answer 33

Phototropism = growth towards or away from light Geotropism = growth towards or away from gravity Chemotropism = growth towards or away from certain chemicals Thigmotropism = growth towards or away from touch or physical contact

Question 34

What is the purpose of phototropism?

Answer 34

Maximises ability of plant’s shoots and leaves to capture light for photosynthesis essential for release of energy in plant

Question 35

What are the 2 types of phototropism?

Answer 35

Positive phototropism = occurs when shoots grow towards light Negative phototropism = occurs when roots grow away from light

Question 36

What is the purpose of geotropism?

Answer 36

Helps plant establish its roots and shoots in optimal orientation, helping the roots anchor in soil supporting plant and obtain nutrients and minerals

Question 37

What are the 2 types of geotropism?

Answer 37

Positive geotropism = roots grow downwards towards gravitational pull Negative geotropism = shoots grow upwards away from gravitational pull

Question 38

What is IAA's role in tropism?

Answer 38

Simulates cell elongation in shoots but inhibits cell elongation in roots

Question 39

Describe the control of positive phototropism in plants?

Answer 39

1) IAA is produced in cells in tip of plant shoot 2) IAA is transported down plant shoot 3) light stimulates IAA to move from light side of shoot to shaded side 4) IAA concentrates stimulating more cell elongation on shoots shaded side 5) shoot bends towards light

Question 40

Describe the control of negative phototropism and positive geotropism?

Answer 40

1) IAA is produced in cells in tip of plant root 2) IAA is transported along plant root 3) light available stimulates IAA to move from light side of root to shaded side 4) gravity also pulls IAA from upper side of root to lower side of root 5) IAA becomes concentrated and inhibits cell elongation in lower shaded side of root 5) root bends away from any available light downwards towards pull of gravity

Question 41

What is etiolation?

Answer 41

Rapid upward growth taking place in a plant grown in dark

Question 42

What is the purpose of etiolation and what type of plant does it produce?

Answer 42

Grow rapidly to reach light for photosynthesis plants are thin and pale due to a lack of chlorophyll

Question 43

What causes etiolation?

Answer 43

Gibberellins are responsible for extreme elongation of internodes when a plant is grown in the dark helping seedlings grow out of soil

Question 44

What is ethene?

Answer 44

hormone playing crucial role in ripening of climacteric fruits e.g bananas

Question 45

How is fruit ripening controlled?

Answer 45

1) climacteric fruits are picked when unripe 2) exposed to ethene gas in a controlled environment 3) triggers and synchronises ongoing ripening process

Question 46

What are the benefits of using ethene gas to control ripening?

Answer 46

- ensures fruits ripens uniformly - reduces risk of spoilage and damage during transportation and storage - helps fruits reach market in ideal consumption state

Question 47

What are the commercial roles of auxin for root growth?

Answer 47

Rooting powders contain auxins stimulate root cell development when applied to plant cuttings increasing success rate of plant propagation Auxins essential in micropropagation to mass produce genetically identical plants from small tissue samples ensuring consistency and quality in crops

Question 48

What are synthetic auxins?

Answer 48

Class of herbicides mimicking action of natural auxin hormones with exaggerated effects used to target and eliminate broad-leaf weeds in agricultural fields

Question 49

How do synthetic auxins eliminate broad leaf weeds?

Answer 49

1) weeds absorb synthetic auxins experiencing accelerated and unsustainable growth rate 2) leads to their death 3) selective action is beneficial doesn't harm nearby narrow-leaf crops 4) allows plants to thrive without competition from weeds

Question 50

What are the advantages of using synthetic auxins like weed killers?

Answer 50

- simple and cheap to produce - low toxicity to mammals - selective affecting only broad-leaf plants

Question 51

What are the other commercial users of plant hormones?

Answer 51

Use auxins = simulate fruit development without fertilisation preventing formation of seeds in fruit Use ethene = promote dropping of fruits before harvest easing harvesting Use cytokinins = extend shelf-life of produce slowing down ageing processes Use gibberellins = improve size and shape of fruits enhancing their market appeal and value