Survival and Response

Question 1

What is a stimulus?

Answer 1

• A detectable change in the internal or external environment that leads to a response in an organism

Question 2

How does the ability to respond to a stimulus help organisms?

Answer 2

• The ability to respond to stimuli increases the chances of survival of an organism so they can move away from harmful stimuli and extreme temperatures
• This means organisms can move towards sources of food and also have a greater chance of raising offspring and passing advantageous alleles to the next generation
• There is always a selection pressure favouring organisms with more appropriate responses

Question 3

What detects stimuli?

Answer 3

• Receptors

Question 4

What does a coordinator do?

Answer 4

• A coordinator formulates a response to stimuli
• This can be at a molecular level or involve large organs

Question 5

What produces a response?

Answer 5

• An effector
  -An example of a response are organisms communicating through the release of hormones or the nervous system

Question 6

What is the process of producing a response?

Answer 6

• Stimulus - receptor - coordinator - effector - response

Question 7

What is a taxes?

Answer 7

• A taxis is a simple response whose direction is determined by the direction of the stimulus
• As a result, motile organisms will move/respond to environmental changes by moving its entire body away from an unfavourable stimulus or toward a favourable stimulus

Question 8

What is positive and negative taxis ?

Answer 8

Positive stimulus = movement toward stimulus
negative stimulus = movement away from stimulus

Question 9

Describe how single - celled algae is an example of positive taxis?

Answer 9

• Algae will respond to the stimuli of light (positive phototaxis) to increase their survival and photosynthesise. This means they can use light to manufacture food

Question 10

Describe how earth worms is an example of negative taxis?

Answer 10

• earth worms will respond to light and move away from it (negative phototaxis). This increases their chances of survival by taking them away from light and toward soil where they can find food and avoid predation

Question 11

What is kinesis?

Answer 11

• A form of response in which the organism does not move toward or away from a stimulus
• instead, it changes direction and speed at which it moves at

Question 12

What happens when an organism crosses the line between a favourable and non - favourable environment?

Answer 12

• The rate of turning of an organism increases which will increase its chances of returning back into favourable environment

Question 13

What happens when an organism move considerably into an unfavourable environment?

Answer 13

• Its rate of turning may decrease and its speed increases in straight lines before it turns very sharply to increase its chances of returning into favourable conditions