5.5 Plant Responses

Question 1

Define abiotic components

Answer 1

Components of an ecosystem that are non-living

Question 2

Define biotic components

Answer 2

Components of an ecosystem that are living

Question 3

Define tropism

Answer 3

A directional growth response in which the direction of the response is determined by the direction of the external stimulus

Question 4

What are tannins?

Answer 4

Phenolic compounds, located in cell vacuoles or in surface wax on plants.
- prevent infiltration of pathogenic microorganisms

Question 5

What are alkaloids?

Answer 5

Organic nitrogen-containing bases that have important physiological effects on animals, they may taste bitter for example

Question 6

Examples of alkaloids

Answer 6

• nicotine
• quinine
• strychnine
• morphine

Question 7

What are pheromones?

Answer 7

Chemical substances released by one living thing, which influences the behaviour or physiology of another living thing

Question 8

Example of chemotropism

Answer 8

pollen tubes growing down the style, attracted by chemicals, towards the ovary where fertilisation takes place

Question 9

Whats a non-directional response to an external stimulus called?

Answer 9

Nastic response

Question 10

Example of nastic response?

Answer 10

Folding leaves in response to touch

Question 11

Which plant is folds its leaves as a form of thigmonasty?

Answer 11

Mimosa pudica

Question 12

What do cytokinins do?

Answer 12

• promote cell division
• delay leaf senescence (ageing)
• overcome apical dominance
• promote cell expansion

Question 13

What does abscisic acid do?

Answer 13

• inhibits seed germination and growth

- causes stomatal closure when the plant is stressed by low water availability

Question 14

What do auxins do?

Answer 14

• promote cell elongation
• inhibit growth of side shoots
• inhibit leaf abscission (leaf fall)

Question 15

What do gibberellins do?

Answer 15

• promote seed germination

- promote stem elongation

Question 16

What does ethene do in plants?

Answer 16

-promotes fruit ripening

Question 17

How can hormones move around the plant?

Answer 17

• active transport
• diffusion
• mass flow in the phloem sap or in xylem vessels

Question 18

What is apical dominance?

Answer 18

inhibition of lateral buds further down the shoot by chemicals produces by the apical bud at the tip of a plant shoot

Question 19

What actually happens to a plant when the tip is cut off in terms of abscisic acid?

Answer 19

Apex gone, auxins cant regulate the concentrations of abscisic acid in lateral buds and so conc. drops
lateral buds grow

Question 20

What happens to a plant when the apex is cut off in terms of cytokinins?

Answer 20

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

Question 21

What happens when you apply a lot of cytokinins to normal plants?

Answer 21

Apical dominance is overwritten

Question 22

Whats an important auxin example?

Answer 22

IAA

Question 23

How does gibberellin cause seed germination?

Answer 23

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

Question 24

Where are there meristems?

Answer 24

• apical meristem
• roots
• lateral bud meristem
• intercalary meristems
• lateral meristems (makes stem thicker)

Question 25

What piece of equipment is used to measure the effects of gravity on a plant?

Answer 25

Klinostat spins it round and round

Question 26

How does auxin work?

Answer 26

- 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

Question 27

How do auxins affect roots and shoots?

Answer 27

Different levels of auxins affect them different

Question 28

How is auxin transported to the shaded side of plants?

Answer 28

By PIN proteins

Question 29

How is leaf loss in deciduous plants controlled?

Answer 29

- 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)

Question 30

How are hormones involved in stomatal closure?

Answer 30

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

Question 31

Commercial uses of auxins

Answer 31

- 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

Question 32

Commercial uses of cytokinins

Answer 32

- prevent yellowing of leaves | - plant mass production

Question 33

Commercial uses of gibberellins

Answer 33

-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)

Question 34

Commercial uses of ethene

Answer 34

- 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

Question 35

What inhibits the effects of ethene on plants?

Answer 35

silver salts

Question 36

What is a tropism?

Answer 36

Directional growth response

Question 37

What do synergic hormones do?

Answer 37

Amplify each others effects

Question 38

What do antagonistic plant hormones do?

Answer 38

Oppose each others effects

Question 39

How does growth occur in the meristem tissue?

Answer 39

By two processes: - cell elongation - cell division

Question 40

What is the Le gene responsible for?

Answer 40

producing enzyme that converts GA20 to GA1

Question 41

Is Le in tall or short?

Answer 41

tall

Question 42

Is le in tall or short?

Answer 42

short

Question 43

first experiments on role of auxins | in the control of apical dominance

Answer 43

- 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

Question 44

the experimental evidence for the role of | gibberellin in the control of stem elongation

Answer 44

- 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

Question 45

the experimental evidence for the role of | gibberellin in the control of seed germination

Answer 45

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

Question 46

Describe mechanism of auxin

Answer 46

promotes active transport of H+ into cell wall low pH = optimum for wall loosening enzymes (expansins) to work break bonds between cellulose