6A - Responses in plants and animals

Question 1

What factors do plants respond to?

Answer 1

Gravity and light.

Question 2

How do plants respond to stimuli?

Answer 2

• Sense the direction of light and grow towards it to maximise light absorption for photosynthesis.
• Sense gravity, so their roots and shoots grow in the right direction.
• Climbing plants have a sense of touch, so they can find things to climb up and reach the sunlight.

Question 3

What is a tropism?

Answer 3

A plant’s growth response to an external (directional) stimulus.

Question 4

What is a positive tropism?

Answer 4

Growth towards the stimulus.

Question 5

What is a negative tropism?

Answer 5

Growth away from the stimulus.

Question 6

What is phototropism?

Answer 6

The growth of a plant in response to light.

Question 7

How do shoots respond to light?

Answer 7

They are positively phototropic and grow towards light.

Question 8

How do roots respond to light?

Answer 8

They are negatively phototropic and grow away from light.

Question 9

Why do shoots grow towards light?

Answer 9

For photosynthesis - light energy for growth.

Question 10

Why do roots grow away from light?

Answer 10

For nutrients/water for photosynthesis.

Question 11

What is it called when shoots grow towards light?

Answer 11

Positive phototropism.

Question 12

What is it called when roots grow away from light?

Answer 12

Negative phototropism.

Question 13

What is gravitropism?

Answer 13

The growth of a plant in response to gravity.

Question 14

How do shoots respond to gravity?

Answer 14

They are negatively gravitropic and grow upwards.

Question 15

How do roots respond to gravity?

Answer 15

They are positively gravitropic and grow downwards.

Question 16

Why do shoots grow away from gravity?

Answer 16

High - get light for photosynthesis.

Question 17

Why do roots grow towards gravity?

Answer 17

Water for photosynthesis.

Question 18

What is it called when shoots grow away from gravity?

Answer 18

Negative gravitropism.

Question 19

What is it called when roots grow towards gravity?

Answer 19

Positive gravitropism.

Question 20

What are plant responses brought about by?

Answer 20

Growth factors.

Question 21

What are growth factors?

Answer 21

Hormone-like chemicals that speed up or slow down plant growth.

Question 22

Where are growth factors produced?

Answer 22

In the growing regions of the plant (e.g. shoot tips, leaves).

Question 23

Where do growth factors move from and too?

Answer 23

Where they are produced in the growing regions of the plant to where they’re needed in other parts of the plant.

Question 24

Give a general name of a growth factor

Answer 24

Auxins

Question 25

What do auxins do?

Answer 25

Stimulate the growth of shoots by cell elongation where the cell walls become loose and stretchy, so the cells get longer.

High concentrations of auxins inhibit growth in roots though.

Question 26

Give an example of an auxin

Answer 26

Indoleacetic acid (IAA)

Question 27

What is IAA?

Answer 27

An important auxin.

Question 28

Where is IAA produced?

Answer 28

In the tips of shoots in flowering plants.

Question 29

Why is IAA moved around the plant?

Answer 29

To control tropisms.

Question 30

How does IAA move around a plant?

Answer 30

By diffusion and active transport over short distances, and via the phloem over long distances.

Question 31

What does the fact that IAA is moved around the plant mean?

Answer 31

Different parts of the plant have different concentrations of IAA.

Question 32

What is the effect of the fact that different parts of the plant have different concentrations of IAA?

Answer 32

The uneven distribution of IAA means there’s uneven growth of the plant.

Question 33

What is the effect of IAA on roots?

Answer 33

Inhibits growth of roots.

Question 34

What is the effect of IAA on shoots?

Answer 34

Promotes growth in shoots.

Question 35

How does IAA promote shoot growth?

Answer 35

Promotes plasticity of cell walls by actively transporting hydrogen ions from the cytoplasm to the spaces in the cell wall allowing the cell walls to expand.

Question 36

What is the effect of IAA on phototropism?

Answer 36

IAA moves to the more shaded parts of the shoots and roots, so there’s uneven growth.

IAA accumulation of the shaded side of the shoot promotes elongation of cells on the shaded side - bending towards the light.

IAA accumulation on the shaded side of the roots inhibits growth of cells on the shaded side - bending away from light.

Question 37

What is the effect of IAA on gravitropism?

Answer 37

IAA moves to the underside of shoots and roots, so there’s uneven growth.

IAA promotes elongation of cells on the lower side of the shoot - bending plant upwards.

IAA on the lower side of roots inhibits elongation on lower side so plant bends downwards.

Question 38

What do simple responses do?

Answer 38

Keep simple organisms in a favourable environment.

Question 39

Give examples of simple organisms

Answer 39

Woodlice and earthworms.

Question 40

Why do simple organisms have simple responses?

Answer 40

To keep them in a favourable environment.

Question 41

What are the simple responses of simple organisms?

Answer 41

Taxis and kineses (tactic/kinetic responses).

Question 42

What are tactic responses (taxis)?

Answer 42

The organism moves towards or away from a directional stimulus.

(Simple response whose direction is determined by the direction of a stimulus).

Motile organism moves whole body either towards (positive taxis) or away (negative taxis) from a favourable environment.

Question 43

What is a tactic response to light called?

Answer 43

Phototaxis.

Question 44

What are kinetic responses (kineses)?

Answer 44

The organisms’ movement is affected by a non-directional stimulus, e.g. humidity.

(Simple response where the speed and rate of change of direction will change in response to a stimulus).

Movement is random and related to intensity of stimulus.

Question 45

Is taxis or kinesis movement random?

Answer 45

Kinesis.

Question 46

How can you investigate animal repsonses?

Answer 46

Choice chambers.

Question 47

What is a choice chamber?

Answer 47

A container with different compartments, in which you can create different environmental conditions.

Question 48

What can a choice chamber be used to investigate?

Answer 48

How animals, such as woodlice, respond to conditions like light intensity or humidity in the laboratory.

Question 49

Explain how you can use a choice chamber to investigate animal responses:

Answer 49

1) Construct a choice chamber (using the equipment; petri dish base divided into two compartments, fine mesh, petri dish lid, woodlice placed onto mesh).
2) To investigate the effect of light intensity on woodlouse movement, cover one half of the lid (including the sides) with black paper. This will make one side of the chamber dark, Put damp filter paper in both sides of the base.
3) Place 10 woodlice on the mesh in the centre of the chamber and cover the chamber with a lid.
4) After 10 mins, take off the lid and record the number of woodlice on each side of the chamber. (Place the lid back on as quickly as possible to reduce the disturbance of the environmental conditions you have created.)
5) Repeat the experiment after gently moving the woodlice back to the centre. You should find that most woodlice end up on the dark side of the choice chamber (a tactic response to light).
6) To investigate humidity, place some damp filter paper in one side of the base and a desiccating (drying agent) in the other side. Don’t cover the lid with paper. Put the lid on and leave the chamber for 10 mins to stabilise before carrying out steps 3-5 above.
7) You can do a similar experiment using a maze instead of a choice chamber.