F215:04:01 Why plants respond to the environment

Question 1

What is a tropism?

Answer 1

a directional growth response in which the direction of the response is determined by the direction of the external stimulus (away or towards the stimuli)

Question 2

What are the 3 things plants respond to?

Answer 2

Biotic components of their environment
Abiotic components of their environment
External stimuli

Question 3

Why do plants need to actively respond to external components?

Answer 3

To avoid stress
To avoid being eaten
To survive long enough to reproduce

Question 4

What are the 4 types of tropism?

Answer 4

• Photortropism
• Geotropism
• Chemotropism
• Thigmotropism

Question 5

What is phototropism?

Answer 5

Where shoots tend to grow towards the light which enables them to photosynthesise
(they are positively phototrophic)

Question 6

What is geotropism?

Answer 6

Where the roots grow towards the pull of gravity
This anchors the plant in the soil and helps to take up water (to remain turgid, as a raw material for photosynthesis and to help cool the plant), and the uptake of minerals e.g. nitrates that are needed for the synthesis of amino acids

Question 7

Why is geotropism vital?

Answer 7

This anchors the plant in the soil and helps to take up water (to remain turgid, as a raw material for photosynthesis and to help cool the plant), and the uptake of minerals e.g. nitrates that are needed for the synthesis of amino acids

Question 8

Why is phototropism vital?

Answer 8

growing towards light enables them to photosynthesise

Question 9

What is chemotropism?

Answer 9

On a flower, the pollen tubes grow down to the style towards the ovary where fertilisation can take place (attracted by chemicals)

Question 10

How do pollen tubes know where to grow towards the ovary?

Answer 10

They are attracted by chemicals

Question 11

Why is chemotropism vital?

Answer 11

It aids reproduction in plants

Question 12

What is thigmotropism?

Answer 12

shoots of climbing plants, such as ivy, wind round other plants or solid structures to gain support

Question 13

Why is thigmotropism vital?

Answer 13

To gain support from other plants/solid structures

Question 14

What co-ordinates a plants response to environmental stimuli?

Answer 14

hormones, but are often known as plant growth regulators because unlike animal hormones, they are not produced in endocrine glands but by cells in a variety of tissues in the plant

Question 15

Whats the difference between tropic and trophic?

Answer 15

tropic: a growth response towards or away from a stimulus
trophic: connected with how living things feed

Question 16

What is the difference between negative and positive tropic responses?

Answer 16

positive is towards the stimulus

negative is away from the stimulus

Question 17

Why are plant hormones often known as plant growth regulators?

Answer 17

because unlike animal hormones, they are not produced in endocrine glands but by cells in a variety of tissues in the plant

Question 18

How do plants ensure hormones only act upon the correct tissues?

Answer 18

• When the hormone reaches the target cells, they bind to receptors on the plasma membrane.
  Specific hormones have specific shapes which can only bind to specific receptors with complimentary shapes of particular cells

Question 19

Name the 3 methods hormones are transported round a plant

Answer 19

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

Question 20

What is synergy?

Answer 20

(The fact that some hormones have different effects on different tissues, and) some can amplify each others’ hormones effects

Question 21

What is antagonism?

Answer 21

(The fact that some hormones have different effects on different tissues, and) some can even cancel out each other’s effecrs

Question 22

What are the 3 things hormones can influence in a plant?

Answer 22

cell division
cell elongation
cell differentiation

Question 23

Name the main 5 plant hormones

Answer 23

Auxins
Cytokinins 
Gibberellins 
Abscisic acid 
Ethene

Question 24

What effect do Auxins have on plants?

Answer 24

They promote cell elongation, inhibit the growth of side shoots and inhibit leaf abscission (leaf fall)

Question 25

What is leaf abscission?

Answer 25

leaf fall

Question 26

What effect do cytokinins have on plants?

Answer 26

they promote cell division

Question 27

What effect do gibberellins have on plants?

Answer 27

They promote seed germination and the growth of stems

Question 28

What effect does abscisic acid have on plants?

Answer 28

It inhibits seed germination and growth

causes stomatal closure when the plant is stressed by low water availablility

Question 29

What effect does Ethene have on plants?

Answer 29

it promotes fruit ripening

Question 30

Apart from tropism, what other responses to plants make to environmental stimuli?

Answer 30

nasties (nastic responses) that are non-directional responses

Question 31

Give an example of thigmonaty

Answer 31

Mimosa pudica (a sensitive plant) responds to touch with a sudden drooping of the leaves

Question 32

What are nasties/nastic responses?

Answer 32

non-directional responses

Question 33

How might thigmonastic responses in plants help them to survive?

Answer 33

The response of sensitive plants may make it more difficult for herbivores to eat its leaves

Question 34

Explain how such a response as thigmonastism might have evolved?

Answer 34

Variation in extent of response between individuals
Those with the most pronounced response are less likely to be eaten as their leaves droop more quickly and hence are more likely to survive longer and reproduce
After many generations, eventually the whole population will respond more dramatically

Question 35

What does it mean to photoperiod?

Answer 35

When plants in temperate zones respond to day length

Question 36

What influence does photoperiod have on plants?

Answer 36

It influences their flowering
Some are short-day plants, which flower in the autumn and spring
Some are long-day plants which flower in the summer

Question 37

What has research shown about photoperiod plants?

Answer 37

that it is the length of darkness that is really crucial as short-day plants need a long period without light each night

Question 38

Suggest how flower growers can make plants flower out of their normal season

Answer 38

Impose an artificial day length using artificial lights

Question 39

Suggest why research into photoperiodism could be beneficial in agriculture to help increase the yield from food crops

Answer 39

Finding out which day length promotes flowering enables growers to manipulate the day length to encourage sustained flowering
Fertilisation of flowers leads to fruit and seed production, hence more flowering gives a higher yield

Question 40

Suggest why plant growth regulators are called hormones, even though they arent produced in endocrine glands

Answer 40

They are chemical messengers that can be transported away from their site of manufacture to act in other parts (target cells or tissues) of the plant
When they reach their target cells, they bind to receptors on the plasma membrane

Question 41

Explain why only certain tissues in a plant will respond to a particular plant hormone/growth regulator substance

Answer 41

Specific hormone molecules have specific shapes which can only bind to specific receptors with complementary shapes on the membranes of particular cells

Question 42

Ethene is a gas, ripe fruit produces it, and bananas produce a lot of it. Why is it not advisable to place a vase of cut flowers next to a fruit bowl containing bananas?

Answer 42

Because the flowers release ethene in gaseous form, which causes the banana to ripen and may cause them to become over ripe

Question 43

Describe Ethene and how it works etc

Answer 43

Its a gas
It is produced by flowers, stems, leaves and ripe fruit
Bananas produce a lot of it