Plant Response

Question 1

What are some examples of abiotic stress for plants?

Answer 1

• Freezing
• Drought
• Increased soil water salinity
• Presence of heavy metals (e.g. lead, copper, zinc, mercury)

Abiotic stress refers to non-living environmental factors that can negatively impact plant growth and development.

Question 2

How can plants respond to drought to reduce water loss?

Answer 2

• Shutting stomata
• Dropping leaves

These adaptations help minimize transpiration and conserve water during periods of drought.

Question 3

Some plants can respond to freezing temperatures by producing what type of chemical?

Answer 3

Antifreeze chemical

This chemical decreases the formation of ice crystals in plant cells, which can be damaging.

Question 4

What is the mode of action of alkaloids such as caffeine and nicotine?

Answer 4

• Bitter-tasting or toxic
• Deterring or killing herbivores

Alkaloids serve as a defense mechanism for plants against herbivores.

Question 5

What role do pheromones play in plant defense?

Answer 5

• Signal to nearby plants of the same species that they are under attack
• Triggering other defenses
• this attacks the predators of the herbivorous insect

Question 6

How do some plants respond to touch

Answer 6

When some plants are touched there leaves fold in rapidly

Question 7

What is a Nastic response

Answer 7

Non-directional growth response to a stimulus

Question 8

What is tropism?

Answer 8

A plant’s growth response to environmental stimuli

Tropism involves directional growth towards or away from stimuli.

Question 9

Define phototropism.

Answer 9

Growth response to light

Ensures plant gets access to as much light as possible, maximizing photosynthesis.

Question 10

Define geotropism.

Answer 10

Growth response to gravity

Shoots show negative geotropism (grow away from gravity) and roots show positive geotropism (grow towards gravity).

Question 11

Define hydrotropism.

Answer 11

Growth response to moisture

Root tips normally grow towards damper areas of soil, increasing their access to water.

Question 12

Define thigmotropism.

Answer 12

Growth response to touch

Important in climbing plants, allowing them to detect support and curl around it.

Question 13

Define chemotropism.

Answer 13

Growth response to chemicals

Some plants show a tropic response to certain chemicals, such as pollen tubes growing down the flower’s stigma towards the ovules.

Question 14

What hormones are involved in leaf loss

Answer 14

• ethene
• auxins

Question 15

How is Ethene involved in leaf loss

Answer 15

stimulates the breakdown of cell walls in the abscission layer, causing the leaf to drop off

Question 16

What is the abscission layer

Answer 16

Layer of parenchyma cells with thin cell walls at the base of the leaf stalk
- makes leaf stalk weak & easy to break

Question 17

How are auxins involved in leaf loss

Answer 17

• auxins are produced in young leaves and make the plant insensitive to ethene, inhibiting leaf loss
• as plant ages concentration of auxins decreases so leaf loss occurs in response to ethene

Question 18

What triggers leaf loss in plants and why?

Answer 18

• hot and dry environment = reduce water loss
• during winter = water absorption is difficult, limited photosynthesis

Question 19

What triggers the hormones for leaf loss in temperate climates

Answer 19

Shortening day length

Question 20

What causes stomatal closure in plants

Answer 20

Stimulated during times of water stress as abscisic acid is produced

Question 21

What do guard cells have on their cell surface membranes that are involved in stomatal closure?

Answer 21

ABA receptors

These receptors bind with abscisic acid (ABA) to initiate the stomatal closure process.

Question 22

What happens when ABA binds with its receptors on guard cells during stomatal closure?

Answer 22

Inhibits proton pumps

This stops the active transport of hydrogen (H+) ions out of the guard cells.

Question 23

What ions move into the cytoplasm of guard cells as a result of ABA action during stomatal closure?

Answer 23

Calcium (Ca2+) ions

These ions act as second messengers in the stomatal closure process.

Question 24

What do calcium ions cause to happen in guard cells that leads to stomatal closure?

Answer 24

• Open channel proteins for negatively charged ions to leave
• Stimulate opening of further channel proteins for potassium (K+) ions to leave
• Stimulate closing of channel proteins for potassium (K+) ions to enter

These actions contribute to the loss of ions and subsequent changes in water potential.

Question 25

What effect does the loss of ions have on the **water potential** of guard cells? How does this lead to stomatal closure?

Answer 25

Increases water potential - This increase leads to water leaving the guard cells by osmosis, so they become flaccid

Question 26

What is the role of abscisic acid in seed dormancy? How?

Answer 26

- maintains seed dormancy - it inhibits amylase production

Question 27

What are gibberellins involved in

Answer 27

- seed germination - stem elongation

Question 28

What causes amylase to be synthesised during seed germination

Answer 28

- when conditions are right, seed starts to absorb water - stimulates embryo to produce gibberellins, which diffuse into the aleurone layer - this stimulates the synthesis of amylase

Question 29

What is the affect of amylase being synthesised during seed germination

Answer 29

- amylase hydrolyses starch molecules in the endosperm, producing maltose - maltose converted to glucose & transported to embryo - glucose respired by embryo providing energy for growth

Question 30

What are the 3 sections of a seed

Answer 30

- embryo - endosperm - starch containing energy store around embryo - aleurone layer - protein rich layer on outer edge of the endosperm

Question 31

What is the role of auxins and where are they produced?

Answer 31

Role: - control cell elongation - maintain apical dominance (can inhibit lateral shoots) - involved in phototropism and geotropism They are produced by meristems

Question 32

What are apical and lateral shoots?

Answer 32

Apical = Main vertical stem Lateral = side branches

Question 33

What do auxins inhibit

Answer 33

- Fruit ripening - abscission

Question 34

What is the role of ethene

Answer 34

- promotes fruit ripening - promotes abscission

Question 35

What is the role of gibberellins

Answer 35

- promotes stem elongations by increasing the length of internodes - promotes germination - stimulate pollen tube growth in fertilisation

Question 36

What is the role of ABA

Answer 36

- maintain dormancy of seeds and buds - stimulates protective measures e.g stomatal closure, antifreeze

Question 37

What is synergism

Answer 37

Hormones working together

Question 38

What is antagonism

Answer 38

Hormones opposing each other

Question 39

What happens during seed germination

Answer 39

gibberellins stimulate the production of digestive enzymes to release glucose from food stores - energy is released for seedling growth

Question 40

What is the purpose of apical dominance and stem elongation?

Answer 40

Stem elongation allows for taller plants - combined with apical dominance this helps the plant compete for light

Question 41

Why do farmers try to limit stem elongation

Answer 41

- can reduce waste - prevents crop damage by bad weather

Question 42

Why is abscission beneficial to a plant?

Answer 42

1) reduces energy needed to maintain leaves in winter 2) fallen leaves insulate the roots 3) rotten leaves provide minerals

Question 43

What are the benefits of phototropism

Answer 43

- shoots exhibit + phototropism ensuring maximum rate of photosynthesis - roots exhibit - phototropism to get water and minerals from the soil