Survival and response

Question 1

What is a stimlus?

Answer 1

A dectable change in the internal or external environment of an organism that leads a response in the organism

Question 2

Why is the ability to respond to stimuli a desirable characteristic of life?

Answer 2

Increase the chance of survival of an organism

Question 3

What is an example of organism survivng to respond to stimlui?

Answer 3

Being able to detect and move away from harmful stimuli

e.g predator/extreme temperatures

or

detect and move towards a source of food

aid survival

They have greater chance of surviving and rasing offspring and pass on their alleles to next generation

There is always a selection pressure favouring organisms with more appropriate responses

Question 4

What are stimuli detected by?

Answer 4

Receptors

Question 5

What are receptors specific to?

Answer 5

To one type of stimlus

Question 6

What does a coordinator formulate?

Answer 6

A suitable response to a stimulus

Question 7

What does coordination involve?

Answer 7

At a molecular level or involve a large organ like a brain

Question 8

What is a response produced by?

Answer 8

An effector

Question 9

What does this response involve?

Answer 9

At a molecular level or involve the behaviour of a whole organism

Question 10

Why are hormones important?

Answer 10

One means of communication in large multicellular organism

occurs via chemicals - hormones

which is a slow process found in plants and animals

Question 11

What do animals have other mean of communication instead of hormones?

Answer 11

Their nervous system

Usually have different receptors that control effectors

Each receptor linked with a central coordinator of some type

Act as a switchboard connecting information from each receptor with appropriate effector

Question 12

What is the sequence?

Answer 12

stimulus - receptor - coordinator - effector - response

Question 13

What is taxis?

Answer 13

A simple response whose direction is determined by the direction of stimulus

Question 14

What is a result of a taxis?

Answer 14

A motile organism responds directly to an environmental change by moving its whole body either towards a favourable stimulus or away from an unfavourable one

Question 15

What are taxis classified as?

Answer 15

According to whether

Towards a stimlus (positive taxis)

Or

Away from stimulus (negative taxis)

also by nature of stimulus

Question 16

An example of positive phototaxis

Answer 16

Single-celled algae will move towards light (positive phototaxis)

This will increase their chance of survival since, being photosynthetic they require light to manfacture food

Question 17

An example of negative phototaxis

Answer 17

Earthworms will move away from light

This will increase their chance of survival because it takes them into the soil

They are better able to conserve water, find food and avoid some predators

Question 18

An example of positive chemotaxis

Answer 18

Some species of bacteria will move towards a region where glucose is highly concentrated (positive chemotaxis)

This will increase their chance of survival because they use glucose as a source of food

Question 19

What is kinesis?

Answer 19

It is a form of response where the organism does not move towards or away from a stimulus

Instead it changes the speed at which it moves and rate at which it changes direction

e.g humidity and temperature

Question 20

How is an organism increases its chance to get into a favourable envirnoment?

Answer 20

Move slower/less

Turn less

Question 21

How does organism increases its chances to get to new area?

Answer 21

From unfavourable envirnoment

Move more faster

Turn faster

Question 22

An example of kinesis

woodlice

Answer 22

• Woodlice lose water from their bodies in dry condtions
• Move to damp area into dry , move rapidly and change direction more - moving to new area
• This increase their chance of moving back to damp area
• When moving back they slow down and change direction less often - stay in damp area
• Change direction rapidly they still stay in dry area and into a new damp area
• They spend more time in favourable damp conditions and less favourable drier ones
• Prevents from drying out and increase chance of survival

Question 23

What is tropism?

Answer 23

Growth of part of a plant in response to a directional stimulus

Question 24

What are the cases of tropisms?

Answer 24

Plant grows towards(positive response)

orgrow away (negative response)

from a stimulus

Question 25

What is example of postivie phototropism?

Answer 25

Plant shoots grow towards light (positive phototropism)

awat from gravity(negative gravitropism)

so that their leaves are in favourable position to capure light for photosynthesis

Question 26

What is negative phototropism?

Answer 26

Plant roots grow away from the light (negative phototropism)

and towards gravity (positive gravitropism)

In both cases the responses increases probability that the roots will grow into the soil, where they are able to absorb water and mineral ions