6.1 Exchange between organisms and their environment

Question 1

Define tissue fluid

Answer 1

the fluid that surrounds cells of the body.
(Its composition is similar to that of blood plasma except that it lacks proteins. It supplies nutrients to the cells and removes waste products.)

Question 2

List the 4 things that need to be interchanged between an organism and its environment.

Answer 2

1. respiratory gases (oxygen and carbon dioxide)
2. nutrients ( glucose, fatty acid, amino acids, vitamins, minerals)
3. excretory products (urea and carbon dioxide)
4. heat

Question 3

What are the 2 ways exchange can take place and by using what mechanisms?

Answer 3

1. passively by diffusion and osmosis

2. actively by active transport

Question 4

Where does exchange take place on an organism?

Answer 4

On its surface area

Question 5

What must happen in order for exchange to be effective?

Answer 5

The exchange surface(s) of the organism must be large compared with its volume.

Question 6

Why does simple diffusion of substances across the outer surface only meet the needs to relatively inactive organisms?

Answer 6

Because organisms become large which increases their volume at a faster rate than their surface area.

Small organisms have a surface area that is large enough compared to their volume to allow efficient exchange across their body surface.

Question 7

How have organisms developed for more efficient exchange?

Answer 7

1. a flattened shape so that no cell is ever far from the surface
2. specialised exchange surfaces with large areas to increase the surface area to volume ratio

Question 8

What are the 5 features of specialised exchange surfaces?

Answer 8

1. large surface area relative to the volume of the organism which increase the rate of exchange
2. very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly
3. selectively permeable to allow selected materials to cross
4. movement of the environmental medium
5. a transport system to ensure the movement of the internal medium in order to maintain a diffusion gradient

Question 9

Why do multicellular organisms require specialised exchange surfaces?

Answer 9

The distance for exchange is much larger due to a higher surface area to volume ratio hence specialised exchange surfaces are required for efficient gas exchange of carbon dioxide and oxygen.