Unit 6-Stimulus and Response

Question 1

Give three ways reflex actions are important for an organism

Answer 1

Reduce risk of damage to tissue; Escape predators; Maintain posture; homeostasis

Question 2

Hydra is a small animal that lives in water. It traps food particles by random movement of its tenticles. The rate of tenticle movement is usually slow but becomes faster as more tenticles touch food. Name the type of behaviour described

Answer 2

Kinesis

Question 3

Name the neurones involved in a reflex

Answer 3

Motor; Sensory and Relay

Question 4

Which type of neurone transmits impulses to effectors?

Answer 4

Motor

Question 5

Why is being able to respond to changes in its environment beneficial to an organism?

Answer 5

Increases an organism’s chance of survival; allows organism to avoid harmful environments; ensure its internal conditions remain optimal.

Question 6

Give an example of a stimulus that would produce a kinetic response in a simple mobile organism

Answer 6

E.g. Humidity-in a kinetic response, am organism’s movement is affected by a non-directional stimulus.

Question 7

Roots are positively gravitropic. Which direction do they grow in, and how do auxins cause this?

Answer 7

Roots grow downwards. This happens because the auxin concentration on the lower side of roots increases in response to gravity. A high concentration of auxin inhibits growth in roots so cell elongation occurs at a greater rate on the upper side of the roots causing them to bend downwards.

Question 8

Identify the structures A, B & E

Answer 8

A-Relay neurone B- sensory neurone E-motor neurone

Question 9

Describe how the diagram demonstrates that the seedlings show positive phototropism and that the stimulus is detected by the tip.

Answer 9

In the control/J the seedling grow towards the light;

Covering tip/K stops the response, covering the base/L doesn’t so tip is responsible for it.

Question 10

Explain how positive phototropism helps a plant to grow.

Answer 10

Grows into an area of higher light intensity;

More photosynthesis/more sugar production (so more growth)

Question 11

Explain the effect of IAA on shoot growth

Answer 11

Increases growth of shoot by increasing elongation of cells when present;

Question 12

Describe how IAA could cause the results shown in the figures

Answer 12

IAA moves away from the light side of the shoot/to shaded side (Fig 13);
More IAA causes more growth /more cell elongation (Fig 13);
IAA evenly spread so grows straight (Fig 14);

Question 13

Give a reason why the students put the seedlings on a rotating turn table in figure 14

Answer 13

So all sides are equally exposed to light;

Question 14

The student concluded that all parts of the plant showed positive phototropism. Give one reason to support then conclusion and one reason against the conclusion

Answer 14

In support:
Plants grow/bend towards light source so positive;
Against:
only one plant/species for 3 days;
don’t know what’s happening to roots or other plant parts;
some plant tissues could be influenced by gravity/water;
no length measurements made (so don’t know if its growing;

Question 15

Define the term chemotaxis

Answer 15

Movement away or towards a chemical (stimulus)

Question 16

Mammals can respond to a stimulus with a reflex. Define reflex.

Answer 16

Rapid involuntary/automatic response to a stimulus

Question 17

Suggest three conclusion you can make from the results shown in the figure.

Answer 17

P & Q roots grow towards source of gravity;

(Q) Mustard roots grow towards water or (S) cucumber roots don’t grow towards water;

Cucumber seeds more sensitive to gravity than direction of water;
or
Mustard seeds more sensitive to direction of water than gravity;
or
Mustard seeds equally sensitive to direction of water or gravity;