Topic 6- Survival & response

Question 1

What is a stimulus?

Answer 1

This is a detectable change within an organisms environment

Question 2

What cells detect stimuluses?

Answer 2

Receptors

Question 3

Explain the relationship between an organisms chances of survival and stimuli’s presented to them

Answer 3

An organisms chance of survival will increase as it responds to stimuli via response mechanisms.

Question 4

Define Taxes and Kinesis on a simple level

Answer 4

These are simple responses which keep organisms within favourable conditions of their environment (light moisture, chemicals)

Question 5

Define Taxes

Answer 5

A simple response in which organisms move its entire body towards a favourable stimulus or away from an unfavourable stimulus.

Question 6

Explain the two types of Taxes

Answer 6

1) Positive Taxes- when an organism moves towards a stimulus

2) Negative Taxes- When an organism moves away from a stimulus

Question 7

Explain what Kinesis is

Answer 7

This is when an organism does 2 things

1) Changes the speed of movement
2) Changes the direction of it

Question 8

What is a tropism?

Answer 8

The term given for when plants respond to a stimuli e.g by growth

Question 9

Explain what the 2 different types of tropisms are?

Answer 9

Tropisms can be-

1) Positive- grow towards the stimulus
2) Negative- grow away from the stimulus

Question 10

What are tropisms controlled by?

Answer 10

They are controlled by specific growth factors E.G: IAA

Question 11

IAA is known as a type of…..

What does IAA do?

Answer 11

Known as a type of auxin

It controls cell elongation in shoots, inhibit growth of cells in roots.

Question 12

Where is IAA made?

Answer 12

It is made in the tip or the roots and shoots but it CAN diffuse

Question 13

Explain positive phototropism in the SHOOT when..

a) light is evenly distributed

Answer 13

• IAA is produced in the tip off the shoot.
• IAA diffuses downwards away from overall distribution of light source.
• Cells elongate throughout shoot
• Therefore plant grows UPWARDS.

Question 14

Explain positive phototropism in the SHOOT when..

b) Light is unilaterally distributed

Answer 14

• IAA diffuses from shoot tip towards most shaded part of shoot.
• Higher conc of IAA on shaded side
• Cell elongation on shaded side
• shaded side= longer
• extra weight= plant BENDS

Question 15

Explain negative phototropism in the ROOTS

Answer 15

Background info- Roots= don’t need to photosynthesise= they don’t need light BUT they need to ANCHOR the plant if they are deep in the soil.

• High conc of IAA= inhibits cell elongation(helps)
• root cells elongate more on lighter side
• Root bends AWAY from the light

Question 16

Explain negative gravitropism in the SHOOTS when…

a) IAA diffuses down the shoot

Answer 16

a) IAA will diffuse from upper side to lower side of shoot.

Question 17

Explain negative gravitropism in the SHOOTS when…

b) Plant is vertical

Answer 17

b) plant= vertical

plant cells elongate & plant grows upwards

Question 18

Explain negative gravitropism in the SHOOTS when…

c) Plant is on its side

Answer 18

c)Plant= on its side

shoots will bend upwards and this is NEGATIVE GRAVITROPISM

Question 19

Explain positive gravitropism in the roots.

Answer 19

IAA diffuses to the lower side of roots- towards gravity
In roots IAA cause inhibition= cell elongation

• roots bend TOWARDS gravity (downwards), helping to anchor the plant and so this is POSITIVE GRAVITROPISM

-