Plant Resposnes

Question 1

Define and give examples of tropism

Answer 1

Tropism is growth responses to a directional stimulus
Phototropism - response to light
Geotropism - response to gravity
Chemotropism - chemical gradient
Thigmotropism - growth response to solid structure

Question 2

What chemicals are released for survival

Answer 2

Survival plants can release
Tannins- toxic to herbivores and microorganisms eating the plant
Alkaloids - give bitter taste,preventing plant being eaten
Pheromones - to elicit behavioural response in other organisms

Question 3

Auxin is a plant hormone produced in the shoot tip. Auxin causes cell elongation and travels down the stem from the tip. Auxin is destroyed by sunlight. Explain how this leads to positive phototropism in the plant

Answer 3

Auxin is broken down on the sunny side of the plant. Cells on the shaded side will elongate due to auxin, causing curvature of the stem so that the plant grows towards the light

Question 4

Ivy plants often use walls or other plants as support when growing. State the type of tropism being used

Answer 4

Thigmotropism

Question 5

Roots grow towards the centre of gravity. State the specific type of tropism being demonstrated

Answer 5

Positive geotropism

Question 6

Define and explain the role of the hormone auxin

Answer 6

Auxin is thought to inhibit lateral bud growth.

Controls cell elongation , prevent leaf fall

Question 7

Define and explain the role of of Gibberllins

Answer 7

Causes stem elongation and seed germination. Trigger the mobilisation of food stores in a seed at germination
The La gene,coding for an enzyme that forms gibberliens is expressed in more taller plants

Question 8

Name a control variable that would be considered in investigating phototropism
Name the independent variable that students change

Answer 8

CO2 concentration

Intensity of light

Question 9

Students used a control plant placed in the dark. Explain why they did this

Answer 9

Allowed the students to compare how light intensity affected the growth direction of a plant in differing levels of sunlight to a plant not in sunlight

Question 10

How can you investigate geotropism

Answer 10

By allowing gravity to work on one side of the experiment plant and observing root growth
Control plant is spun on a kilnostat to apply gravity on all sides. Roots normally follow the centre of gravity to support the plant in the ground

Question 11

Explain why the control plant must be spun

Answer 11

Control plant is spun so that gravity affects the plant root on all sides.,
Means the roots should grow horizontally, compared to the experimental roots, which should grow downwards due to gravity

Question 12

How can you investigate auxins

Answer 12

Auxin moves shaded side of the shoot causing cells to elongate and bend the shoot towards the light
Serial dilutions of auxin solution can be made to test the effects of different auxin concentration

Question 13

How can you investigate gibberellins

Answer 13

1) make up serial dilutions of GA concentrations
2) apply each solution to seeds of the same species
3) seeds with higher concentration will have higher mean stem lengths

Question 14

Explain how gibberellins activate seed germination

Answer 14

When seeds absorb water from environment, embryo of the seed releases gibberellins. This travels to the aleurone layer of the endosperm in the seed. Here gibberellin causes production of enzyme amylase, which breaks starch into glucose. Glucose is used as a substrate for respiration, energy for growth

Question 15

What is the the commercial use of cytokinins and ethene

Answer 15

Cytokines - delays leaf loss and used in tissue culture to mass produce plants
Ethene- speed up fruit ripening, enhances lateral bud growth. Inhibiting ethene prolongs shelf life

Question 16

State 2 commercial use of gibberellins with reference to plants

Answer 16

Enhance seed germination in growing malt for beer and delay senescence of citrus fruits, making them available for longer in shop

Question 17

State 2 commercial use of auxins

Answer 17

Auxins can be used in rotting powder to grow roots in young plant cuttings and can be used as a herbicide to kill weeds

Question 18

Why are chemicals important in coordinating the growth of plants

Answer 18

Plants are multicellular and often large so need coordination, plants don’t appear to have nervous system so no electrical coordination system, chemicals can carried in plant transport systems and move from cell to cell to coordinate responses

Question 19

Why is it so important for plants to be able to response to their surroundings

Answer 19

Rooted to the ground so cannot move their bodies therefore very important that they are sensitive so they can grow in the right direction and make the best circumstances where they have germinated

Question 20

Why do many trees in temperate climates lose all their leaves in winter

Answer 20

Amount of photosynthesis that can take place decreases as day length is reduced and temperature falls- amount of glucose produced by photosynthesis falls.
Amount of glucose needed for respiration to maintain leaves through the winger and produce chemicals to prevent freezing damage increases- more efficient to lose the leaves and became dormant

Question 21

The explain the process of abscisson

Answer 21

Falling light levels - decreased concentration of auxin - leaves produce hormone ethene - ethene initiates gene switching in abscisson zone at base of leaf stalk - gene switching causes production of new enzymes - new enzymes digest and weaken cell walls in outer layer of abscisson zone (separation zone) - cells separation zone respond to hormonal cues by retaining water and swelling putting more strain on outer layer - further abiotic factors finish process- strain is too much and leaf separates from plant leaving nest waterproof scar max

Question 22

How do hormones affect stomatal control

Answer 22

Heat and water availability major abiotic stresses for plants
Opening and closing of the stomata in response is under control of hormone ABA

Question 23

What are tannins

Answer 23

Water soluble carbon compounds in the chemical group known as flavonoids,stored in the vacuoles of plant cells, bitter taste
E.g Gallic acid

Question 24

What are alkaloids

Answer 24

Nitrogenous compounds derived from AA, bitter tasting and can be toxic,
E.g caffeine

Question 25

What are pheromones

Answer 25

Chemicals released by one member of a species that affect physiological or behaviour of another member of that species
Trigger other chemical defences in plants

Question 26

How do abscisic acid trigger stomata closure

Answer 26

ABA binds to receptors on the guard cell membranes - specific ion channels open, allows calcium ions to enter cytosol from vacuole increased concentration of calcium ions in the cytosol causes other ion channels to open. These ion channels allow ions to leave the guard cells, raising the water potential of the cells.

3. Water leaves the guard cells via osmosis
4. The guard cells become flaccid and the stomata close.

Question 27

What happens if you remove the apical bud

Answer 27

Plants will not produce auxins, side shoots will therefore start growing

Question 28

Which hormones inhibit and stimulate leaf loss

Answer 28

Auxins inhibit leaf loss

Ethene stimulate leaf loss

Question 29

Outline the commercial uses of plant hormones

Answer 29

Selective weed killers - high enough concentrations, rapid growth plant tissues become distorted and damaged, effective against weed in field that occurs in fields of grass lawns
Rooting powders - low doses, stimulate cuttings to grow new roots, lower end of the cutting is dipped into the powder before being planted in compost
Ethene - stimulate fruit to ripen, stimulate enzymes that break down cell walls, break down chlorophyll and convert starch into sugars