6. Organisms Respond to changes in their internal and external environments

Question 1

how do organisms increase their chance of survival?

Answer 1

by responding to changes in their environment

Question 2

what is a stimulus?

Answer 2

a change in the internal or external environment detected by receptors

Question 3

what is a receptor?

Answer 3

a specialised cell or protein that detects stimuli, and is specific to one type of stimulus

Question 4

what is an effector?

Answer 4

a cell that brings about a response (eg muscles and glands)

Question 5

what is the simple reflex arc made up of?

Answer 5

3 neurones

sensory, relay and motor

Question 6

what does the sensory neurone do? what does it look like?
what does the relay neurone do? what does it look like?
what does the motor neurone do? what does it look like?

Answer 6

• sensory neurone transmits impulses from receptors to the CNS/relay neurone. its cell body is in the middle of the axon terminal
• the relay neurone transmits impulses from the sensory neurone to the motor neurone. it is very branched, has and has no mylein sheath
• the motor neurone transmits impulses from the CNS/relay neurone to the effectors
  it has a long axon terminal and the cell body is at the start, not the middle

Question 7

where can the relay neurone be found? why does it not have a myelin sheath?

Answer 7

• relay neurone is only found in the CNS (the grey matter)
• it does not need a mylein sheath as it only needs to transport impulses short distances, so it doesnt need the extra speed provided by the insulation of the myelin sheath

Question 8

how does the nervous system communicate?

Answer 8

using electrical impulses

Question 9

what is a reflex?
what do reflexes do?

Answer 9

a rapid, automatic response that is involuntary and does not need to be learnt

• reflexes are protected and prevent damage to the tissues

Question 10

describe the process of the reflex arc if someone were to touch a hot plate

Answer 10

• the STIMULUS is the hot object
• the temperature and pain RECEPTORS IN THE SKIN would detect the stimulus
• the SENSORY NEURONE would transmit this impulse to the spinal cord (as it is the closest component of the CNS) and into the relay neurone
• the RELAY NEURONE would transmit this impulse to the motor neurone
• the MOTOR NEURONE would then transmit this impulse to the effector
  the EFFECTOR would be the muscles in the arm which would contract to move the hand away

Question 11

state 7 reasons why the reflex arc is important in organisms

Answer 11

• its automatic and involuntary
• it doesnt have to be learnt
• it helps organisms escape predators
• it prevents damage to body tissues
• it helps maintain posture and balance
• it helps animals find a mate
• it regulates the control of homeostasis

Question 12

-what pathway does the impulse from the sensory neurone take to reach the CNS?
-what is the bump in this pathway called, and why is it there?
-where is the relay neurone positioned in the CNS? why is this made up of? what surrounds this?
-what pathway does the impulse from the motor neurone take on its way to the effector?

Answer 12

• dorsal root
• dorsal ganglia, it is the cell body of the sensory neurone
• in the grey matter/ due to a collection of cell bodies and nuclei/ white matter
• ventral root