6: Organisms Response to Changes

Question 1

How do organisms increase their chances of survival?

Answer 1

• living organisms (plants and animals) increase survival chance by responding to changes in their internal/ external environment

Question 2

How will organisms react in different environments?

Answer 2

• either move away from harmful environments or towards favourable environments
• ensure their conditions are always optimal for metabolism

Question 3

What is nervous communication?

Answer 3

Response to a stimulus (change in environment) coordinated by the nervous system
made of: sensory neurones, CNS, motor neurones, effector

Question 4

How does simple reflex work and triggered?

Answer 4

to respond to a stimulus, it must be detected first by receptors (cells/ proteins on surface membrane )
- each receptor is specific to 1 type of stimulus
- when a stimulus is detected by receptor cells an electrical impulse is sent along the sensory neurone
- electrical impulse transmitted to central nervous system
- when the electrical impulse reaches the end of the sensory neurone a chemical (neurotransmitter) is released into the **synapse ** (a gap between 2 neurones)
- this passes on information and the new electrical impulse is generated in the relay neurone in the cns
- cns processes the information and sends impulses along the motor neurone to the effector (muscle/ gland)

Question 5

What is the simple reflex?

Answer 5

rapid involuntary response to a stimulus
- as it doesn’t involve brain, we don’t waste time thinking (fast response)
- simple reflexes produce a protective effect

Question 6

why do species have simple responses?

Answer 6

• simple mobile organisms
• to keep them in a favourable environment

Question 7

What are the 2 types of simple responses?

Answer 7

tactic & kinetic

Question 8

What is a tactic response?

Answer 8

• directional movement in response to a stimulus and involves the organism either moving towards something (positive tatic response) or away from something (negative tactic response)
• eg.phototaxis (light), thermotaxis (temperature) and chemotaxis (chemicals)

Question 9

What is a kinetic response?

Answer 9

• non-directional movement in response to stimulus
• woodlice show kinetic response to humidity
• in high humidity, they’ll move slowly and turn less often so they’ll stay where they are
• when air gets drier, woodlice will move faster and will turn more often do they will move into a new area
• this increses their chances of survival with a high humidity as this will reduce water loss and conceal them from predators