6A - Responses in plants and animals Flashcards

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1
Q

What factors do plants respond to?

A

Gravity and light.

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2
Q

How do plants respond to stimuli?

A
  • 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.
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3
Q

What is a tropism?

A

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

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4
Q

What is a positive tropism?

A

Growth towards the stimulus.

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5
Q

What is a negative tropism?

A

Growth away from the stimulus.

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6
Q

What is phototropism?

A

The growth of a plant in response to light.

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7
Q

How do shoots respond to light?

A

They are positively phototropic and grow towards light.

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8
Q

How do roots respond to light?

A

They are negatively phototropic and grow away from light.

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9
Q

Why do shoots grow towards light?

A

For photosynthesis - light energy for growth.

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10
Q

Why do roots grow away from light?

A

For nutrients/water for photosynthesis.

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11
Q

What is it called when shoots grow towards light?

A

Positive phototropism.

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12
Q

What is it called when roots grow away from light?

A

Negative phototropism.

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13
Q

What is gravitropism?

A

The growth of a plant in response to gravity.

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14
Q

How do shoots respond to gravity?

A

They are negatively gravitropic and grow upwards.

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15
Q

How do roots respond to gravity?

A

They are positively gravitropic and grow downwards.

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16
Q

Why do shoots grow away from gravity?

A

High - get light for photosynthesis.

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17
Q

Why do roots grow towards gravity?

A

Water for photosynthesis.

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18
Q

What is it called when shoots grow away from gravity?

A

Negative gravitropism.

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19
Q

What is it called when roots grow towards gravity?

A

Positive gravitropism.

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20
Q

What are plant responses brought about by?

A

Growth factors.

21
Q

What are growth factors?

A

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

22
Q

Where are growth factors produced?

A

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

23
Q

Where do growth factors move from and too?

A

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

24
Q

Give a general name of a growth factor

A

Auxins

25
Q

What do auxins do?

A

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.

26
Q

Give an example of an auxin

A

Indoleacetic acid (IAA)

27
Q

What is IAA?

A

An important auxin.

28
Q

Where is IAA produced?

A

In the tips of shoots in flowering plants.

29
Q

Why is IAA moved around the plant?

A

To control tropisms.

30
Q

How does IAA move around a plant?

A

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

31
Q

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

A

Different parts of the plant have different concentrations of IAA.

32
Q

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

A

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

33
Q

What is the effect of IAA on roots?

A

Inhibits growth of roots.

34
Q

What is the effect of IAA on shoots?

A

Promotes growth in shoots.

35
Q

How does IAA promote shoot growth?

A

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.

36
Q

What is the effect of IAA on phototropism?

A

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.

37
Q

What is the effect of IAA on gravitropism?

A

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.

38
Q

What do simple responses do?

A

Keep simple organisms in a favourable environment.

39
Q

Give examples of simple organisms

A

Woodlice and earthworms.

40
Q

Why do simple organisms have simple responses?

A

To keep them in a favourable environment.

41
Q

What are the simple responses of simple organisms?

A

Taxis and kineses (tactic/kinetic responses).

42
Q

What are tactic responses (taxis)?

A

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.

43
Q

What is a tactic response to light called?

A

Phototaxis.

44
Q

What are kinetic responses (kineses)?

A

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.

45
Q

Is taxis or kinesis movement random?

A

Kinesis.

46
Q

How can you investigate animal repsonses?

A

Choice chambers.

47
Q

What is a choice chamber?

A

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

48
Q

What can a choice chamber be used to investigate?

A

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

49
Q

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

A

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.