Organisms Respond To Changes In Their Internal And External Environments (3.6)

Question 1

how can receptor cells respond to stimuli?

Answer 1

• some produce electrical activity in nerve cells
• some secrete substances

Question 2

what are 2 examples of a coordinator?

Answer 2

brain
spinal chord

Question 3

what are the 3 stages in the reflex arc?

Answer 3

detection
coordination
action

Question 4

describe the reflex action process

Answer 4

stimulus -> receptor -> coordinators -> effectors -> response

Question 5

how do organisms respond to change?

Answer 5

they detect a stimulus (by a receptor cell)

Question 6

an organism must find ________ conditions to survive

Answer 6

favourable

Question 7

what is taxis and kinesis?

Answer 7

simple responses that enable mobile organisms to stay in a favourable environment

Question 8

what is kinesis?

Answer 8

a non-directional response to a stimuli
e.g when flatworms under a stone are exposed to light they move in random directions which eventually bring them back into the darkness, they will then stop moving

Question 9

the rate of movement of an organism is affected by the ________ of the stimulus

Answer 9

intensity

Question 10

what is taxis?

Answer 10

a directional response to a stimulus (the organism moves directly away or towards the stimulus)
e.g euglena swims directly towards the light in a pond using its flagellum

Question 11

what is phototropism?

Answer 11

a growth response to light

Question 12

what is a tropism?

Answer 12

a growth response towards a stimulus (in plants)

Question 13

what is geotropism?

Answer 13

growth response to gravity

Question 14

a tropism can be __________ or __________ causing the plant to grow towards or away from the stimulus

Answer 14

positive
negative

Question 15

plant growth regulators act in a similar way to _________________ in animals

Answer 15

hormones

Question 16

the growth response in plants relies on plant growth ____________ that are released in response to a _________.

Answer 16

regulators
stimulus

Question 17

what are 2 examples of plant growth regulators?

Answer 17

auxin
IAA’s

Question 18

what does IAA stand for?

Answer 18

indoleactic acid

Question 19

where is IAA found in the plant

Answer 19

just before the tip

Question 20

how does IAA influence the growth of a plant towards a stimulus?

Answer 20

• when IAA moves into the elongating region of the shoot it lowers the PH
• this breaks some of the bonds in the cellulose cell wall
• the cell wall loosens and the cells can be more easily stretched (cell elongation)
  -by effecting the cell elongation, IAA influences the growth of a plant towards the stimulus

Question 21

what is it called when shoots grow towards the light?

Answer 21

positive phototropism

Question 22

describe the process of phototropism?

Answer 22

-in shoots, higher concentrations of IAA results in a greater rate of cell elongation
-IAA moves from the illuminated side of a shoot to the shaded side
- the higher concentration of IAA on the shaded side causes a faster rate of cell elongation
- this causes the shoot to bend towards the light