M5Ch16 Plant Responses

Question 1

Hormones found within plants

Answer 1

Hormones found within plants:
-Auxin
-Giberellin
-Ethene
-ABA (abscisic acid)

Question 2

Roles of auxin in plants

Answer 2

Auxin:
-Controls cell elongation
-Prevent leaf fall (abscission)
-Maintain apical dominance
-Involved in tropisms
-Stimulate the release of ethene
-Fruit ripeningq

Question 3

Roles of giberellin

Answer 3

Roles of giberellin:
-Causes stem elongation-Trigger the mobilisation of food stores in a seed at germination
-Stimulate pollen tube growth in fertilisation

Question 4

Roles of ethene

Answer 4

Roles of ethene:
-Causes fruit ripening
-Promotes abscission in deciduous trees

Question 5

Roles of ABA (abscisic acid)

Answer 5

Roles of ABA:
-Maintains dormancy of seeds and buds
-Stimulates cold protective responses for example antifreeze production
-Stimulates stomatal closing

Question 6

Process of seed germination

Answer 6

Process of seed germination:
-Embryo activated and produced gyberellins
-Stimulates enzyme release that break down food stores in the seed
-ATP produced + digestive enzymes released

Question 7

Where is the food store found for plants in order to geminate?

Answer 7

The food store is in the cotyledones in dicot seeds and the endosperm in monocot seeds

Question 8

What is the experimental evidence supporting the role of giberellins in seed germination?

Answer 8

Experimental evidence of giberellin:
-Mutant varies of seeds bred that lacks gene which produce giberellin -> no germination
-Giberellin biosynthesis inhibitors applied to seeds and germination does not occur

Question 9

Effects of auxin on plant growth

Answer 9

Effects of auxin on plant growth:
-Stimulate the growth of the main, apical shoot
-High auxin concentrations supress growth of lateral shoots, leading to apical dominance
-Low concentration of auxin promote root growth

Question 10

How do auxins stimulate the growth of the main, apical shoot

Answer 10

How auxins stimulate growth of main apical shoot:
-Cell walls stretch more easily due to auxin
-Binds to receptor sites in membrane causing pH to fall - optimum for enzymes to maintain the wall plasticity
-Cells mature = auxin destroyed
-pH rises back and wall becomes rigid

Question 11

How do high auxins supress the growth of lateral shoots? (apical dominance)

Answer 11

-Growth in the main shoort is stimulated by auxins but lateral shoot growth inhibited by it
-Lateral shoots grow stronger lower down stem where auxin less strong

Question 12

Why does low concentrations of auxin promote root growth?

Answer 12

-Auxins used stimulate growth of main apical shoot by affecting cell wall plasticity so reduced amounts in roots increases root growth

Question 13

What is synergism?

Answer 13

Synergism is when different hormones work together to produce a greater response

Question 14

What is antagonism?

Answer 14

Antagonism is when opposing hormones have opposing effects and so do not work well together

Question 15

What is Photoperiodism?

Answer 15

Photoperiodism is a plant’s sensitivity to lack of light in their environment
-Responsible for variety of changes in plants such as dormancy of leaf buds. time of flowering and tuber formation for overwintering

Question 16

Abscission in deciduous plants

Answer 16

Abscission in deciduous plants:
-Lose their leaves in the winter as the cost of glucose required to maintain leaves and produce anti freezing chemicals is greater than glucose produced

Question 17

How is freezing in plants reduced?

Answer 17

Freezing in plants are reduced by actively transporting salts into the vacuole and cyotplasm
-Freezing point lowered, water does not expand as freezing causes breakage of H bonds in cell wall

Question 18

Stomatal control in plants

Answer 18

Stomatal control in plants:
Roots detect abiotic stress of lack of water -> hormone ABA produced and travels in vascular system -> ABA binds to receptor on stomata -> activates change in ionic conc of guard cells + reduces water potential and turgour -> closing cells and reducing water potential

Question 19

Plant physical defences

Answer 19

Plant physical defences:
-Thorns, spiny leaves, inedible tissue, hairy leaves, stingers

Question 20

Substances released from the plant as part of the chemical defence of plants

Answer 20

Chemical defences:
-Tannins
-Alkaloids
-Terpenoids
-Pheromones

Question 21

Tannins

Answer 21

Tannins: bitter tasting to deter large animals, toxic to insects

Question 22

Alkaloids

Answer 22

Alkaloids:
-Bitter tasting compounds
-Poisonsinsects
-Eg morphine, caffeine

Question 23

Terpenoids

Answer 23

Terpenoids:
-Essential oils produced by plants
-Toxic to insects and gfungi

Question 24

Pheromones

Answer 24

Pheromones:
-Chemical that affects the social behaviour of the same species

Question 25

Behavioural plant defence

Answer 25

Behavioural plant defence:
-Folding in response to touch, which collapses to frighten large herbivores and dislodge small pests
-Occurs as a result of electrochemical change in cells

Question 26

Plant responses to changes in their environment

Answer 26

Plant responses to changes in their environment:
-Phototropism = growth in response to light
-Geotropism = growth in response to gravitational pull
-Hydrotropism = growth in response to water
-Chemotropism = growth in response to chemicals
-Thigmotropism = growth in response to touch

Question 27

Why is tropism important?

Answer 27

Tropism are important in plants, as if unable to response to their environments plants may become malnourished and dead

Question 28

Why are monocotyledenous seedlings used in research on tropism?

Answer 28

Monocotyledonous seedlings are used most commonly in reseach on tropism as the stem has no lateral growth and change can be seen and manipulated rapidly

Question 29

Phototropism in plants

Answer 29

-Phototropism = growth in response to light
-Result of auxins moving across root/shoot so stem bends towards direction in sunlight
-Shoots are more positively phototropic and roots are negatively phototropic

Question 30

Outline the process of phototropism

Answer 30

Outline the process of phototropism:
-Shoot exposed to unilateral light source, cells are equal length
-Auxin moves to the shaded side of the plant, creating high conc
-Higher conc causes cells to elongate, making stem bind to light source
-Auxin transport stops and plant grows towards light source

Question 31

How can we explore phototropism?

Answer 31

-Growing plants in omnilateral, unilateral or completely withou light then observing rates nad directions of growth
-Growing plants with different filters, to see which wavelength of light trigger phototropism

Question 32

Geotropism in plants

Answer 32

Geotropism = plants sensitive to gravitational pull
-Shoots are negatively geotropic and roots are positively geotropic

Question 33

What is a clinostate?

Answer 33

A clinostat is a contantly rotating horizontal drum which can cause a plant grown horizontally to grow straight out, as regular rotation causes equal force of gravity on all sides

Question 34

Ethene and plants

Answer 34

Ethene is a gaseous plant hormone important in ripening climacteric fruit

Question 35

Hormone rooting powders

Answer 35

-Auxin application to cut roots increase root growth
-Used on a large scale for micropropagation for clones

Question 36

Use of synthetic auxins

Answer 36

Synthetic auxins:
-Fine balance of hormones lost = plants will die
-As metabolism is increased and rapid growth becomes unsustainable and plant dies

Question 37

Commercial use of plant hormones

Answer 37

Commercial use of plant hormones:
-Auxins can be used in production of seedless fruit
-Ethene can be used to cause fruit to fall
-Cytokines prevent ripe fruit from ageing and control tissue development
-Giberellins delay ripening and ageing in fruit