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Biology > 6.1.1 Survival and response > Flashcards

6.1.1 Survival and response Flashcards

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1
Q

Define stimulus

A

Detectable change in the internal and external environment

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2
Q

Define response:

A

The organism’s response to that change

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3
Q

Give three important directional stimuli that plants respond to:

A
  • Light
  • Gravity
  • Water
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4
Q

What is the advantage to a plant of this type of response?

A
  • Maximising photosynthesis conditions
  • Roots grow towards water in order to absorb it for use of photosynthesis
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5
Q

What are tropisms co-ordinated?

A

Plant growth factors - Indoleacetic Acid (IAA) - type of auxin

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6
Q

What effect does IAA have on cells:
In the shoots?

A

IAA stimulate cell elongation

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7
Q

What effect does IAA have on cells:
In the roots?

A

IAA inhibits cell elongation

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8
Q

What phototropism does shoots show?

A

Positive

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9
Q

What phototropism does roots show?

A

Negative

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10
Q

What is IAA’s effect in even light (non-directional)?

A
  • IAA is made in the shoot tip
  • IAA moves down the shoot by diffusion, where it causes cell elongation
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11
Q

What is IAA’s effect in directional light?

A
  • When light is directional the IAA moves away from the light, towards the shaded side of the shoot
  • This causes uneven cell elongation, and causes the shoot to bend towards the light
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12
Q

Where is IAA produced? How it moves and where it has its effect?

A

ROOT:
- Auxin inhibits cell growth/elongation
- Lower cell layer is shorter
- Turns down/away from light

STEM:
- Auxin stimulates cell growth
- Lower cell layer is longer
- Turns up/towards the light

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13
Q

What is gravitropism?

A

A response to gravity

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14
Q

What gravitropism in the shoots show?

A

Negative gravitropism

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15
Q

What gravitropism in the roots show?

A

Positive gravitropism

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16
Q

Why is gravitropism important?

A

Important during germination - seed is under-ground, there is no light
Therefore gravitropism ensures that root will grow downwards, and shoots up towards the light

17
Q

What is gravitropism also controlled by?

A

By the distribution of IAA within the plant cells
- IAA will accumulate on the lower side of the plant in response to the force of gravity

18
Q

What does positive gravitropism in the roots look like?

A
  • high IAA concentration inhibits cell elongation causing a positive gravitropic response
19
Q

What happens in the roots at high auxin concentration?

A

In roots, high auxin concentrations inhibit cell elongation, meaning that the lower side of the root becomes shorter and the roots turn downwards into the earth

20
Q

What happens in the shoots at high auxin concentration?

A

In shoots, high auxin concentrations promotes cell elongation, meaning that the lower side of the shoot elongates and shoots grow away from the ground

20
Q

How does IAA increase cell elongation in shoots?

A
  • Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall
  • The resultant decrease in pH causes cellulose fibres (H+ disrupts hydrogen ions) within the cell wall to loosen and become more plastic (stretch and stay stretched)
  • This increases the elongation possible, particularly in young cells
21
Q

What are reflex arcs?

A

Simple, fast, involuntary responses, that protect the body from harm

22
Q

What is the sequence when reflex arc happens?

A

Stimulus -> receptor -> sensory neurone -> coordinator - CNS/relay neurone -> motor neurone -> effector -> response

23
Q

Why are reflex arcs important?

A
  • Rapid (short pathway) because only 3 neurones and few synapses (synaptic transmission is slow)
  • Autonomic because doesn’t involve passage to brain - doesn’t have to be learnt
  • Protect from harmful stimuli eg/ escape from predator/prevents damage to body tissues
24
Q

What is taxis?

A

A directional response to a particular stimulus. Can be positive or negative depending if the movement is towards (positive) or away (negative) from the stimulus
- Allows organisms to move towards favourable conditions and away from unfavourable ones

25
Q

Example of taxis response?

A

Euglena (single cells photosynthetic organism) slows positive phototaxis
- Moves towards light therefore better conditions for photosynthesis

26
Q

What is kinesis?

A

An organism changes the speed at which it moves, and the rate at which it changes direction. Kinesis is not a directional response

27
Q

What happens in favourable conditions (kinesis)?

A
  • Slow movement
  • Organism remains in favourable conditions
28
Q

What happens in unfavourable conditions (kinesis)?

A
  • Rapid movement
  • Organism is more likely to leave the conditions

Biology (47 decks)

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