The Nervous System

Question 1

Why do organisms need to respond to changes in their environment?

Answer 1

Increase survival and reproduction by:

• Avoiding harmful environments, competition and predators
• Keep in a favourable environment (correct temps/humidity) - Mobile organisms
• Grow towards/ away from stimuli (flowering plants)
• Dispersing to find new mates

Question 2

Describe what is meant by the term kinesis

Answer 2

• Movement is random/non-directional response
  OR
• Insect is not moving towards a particular stimulus;

Question 3

Describe negative and positive TAXIS

Answer 3

• positive = towards stimulus
• negative= away from stimulus

Question 4

advantages of earthworms moving away from light ( negative taxis )

Answer 4

• more chance of survival as move into soil
• more likely to find food
• more likely to avoid predators

Question 5

Describe what is meant by the term taxis

Answer 5

• Moves towards or away from directional stimulus

Question 6

Compare & Contrast taxis and tropism

Answer 6

• Both are directional responses to stimuli
• Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism

Question 7

Describe the effect of Indoleacetic acid (IAA) on root growth.

Answer 7

• IAA synthesised in root tips.
• IAA diffuses into growing (cell elongating) region.
• IAA moves towards underside/shaded side.
• Inhibits cell elongation.
• Uneven growth (more elongation on side with less IAA).
• Causes directional growth away from light and downwards towards gravity.

Question 8

Describe the effect of Indoleacetic Acid (IAA) on shoot growth

Answer 8

• IAA synthesised in shoots tips.
• IAA diffuses into growing (cell elongating) region.
• Light causes movement of IAA from light side to shaded side.
• Proportionally more IAA on shaded side.
• Causes directional growth as there is greater cell elongation on shaded side.
• Shaded side grows faster and causes shoot to bend towards the light.

Question 9

Explain the advantages of simple reflex arcs

Answer 9

• Rapid;
• Protect against damage to body tissues;
• Do not have to be learnt;
• Help escape from predators;
• Enable homeostatic control;

Question 10

Describe how a resting potential is maintained in a neurone.

Answer 10

• active transport/pumping of sodium (ions across membrane);
• out of neurone/higher concentration outside;
• differential permeability to K+ and Na+;
• Membrane more permeable to K+ ions;

Question 11

Why do plants shoots grow towards light (positive tropism)

Answer 11

• increase chance of light falling on leaves, thus increase rate of photosynthesis

Question 12

Why do plants roots grow away from light (negative tropism)

Answer 12

• roots grow into soil, more likely to absorb water and mineral ions

Question 13

What is IAA

Answer 13

• plant growth factor (NOT HORMONE)

Question 14

define the term neurones

Answer 14

• specialised cells that are adapted to their function carry electrical impulses from one part of body to another