B1 More on Exchanging Substances (page 22)

Question 1

What do the Structure of Leaves let gasses do?

Answer 1

it lets gasses diffuse in and out of cells.

Question 2

Where do Photosynthesis happen?

Answer 2

Carbon Dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells - this is when photosynthesis happens. (The leaf’s structure is adapted so that this can happen easily).

Question 3

The underneath of the leaf is an exchange surface, explain what it looks like, and what it is for?

Answer 3

it is covered in little holes called stomata, which the carbon dioxide diffuses in through.

Question 4

What else diffuses out through the stomata?

Answer 4

Oxygen (produced in photosynthesis) and water vapour also diffuse out through the stomata. (Water vapour is actually lost from all over the leaf surface, but most of it is lost through the stomata).

Question 5

The size of the Stomata are controlled by what?

Answer 5

by Guard cells (see page 41). These close the stomata if the plant is losing waer faster than it is being replaced by the roots.

Without these guard cells the plant would soon wilt.

Question 6

The flattened shape of the leaf increases the area of this exchange surface, why?

Answer 6

so that it is more effective.

Question 7

The walls of the cells inside the leaf form another exchange surface, what is this?

Answer 7

The air spaces inside the leaf increase the area of this surface so there’s more chance for carbon dioxide to get into the cells.

Question 8

What happens to the water vapour from cells inside the leaf?

Answer 8

the water vapour evaporates from the cells inside the leaf. The it escapes by diffusion because there’s a lot of it inside the leaf and less of it in the air outside.

Look at diagram on page 22

Question 9

What are Gills?

Answer 9

The gills are the gas exchange surface in fish.

Question 10

How do the Gills work?

Answer 10

Water (containing oxygen) enters the fish through its mouth and passes out through the gills. As this happens, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water. (see picture on page 22).

Question 11

What is each Gill made of?

Answer 11

Each Gill is made of lots of thin plates called gill filaments, which give a big surface area for exchange of gasses (look at diagram on page 22, you may need this for your exam).

Question 12

What are the gill filaments covered in?

Answer 12

they are covered in lots of tiny structures called lamellae, which increase the surface area even more.

Question 13

How do Lamellae speed up diffusion?

Answer 13

they have lots of blood capillaries - this speeds up diffusion.

Question 14

They also have a thin surface layer of cells, what for?

Answer 14

to minimise the distance that the gasses have to diffuse.

Question 15

Explain how blood/water flows through the lamellae?

Answer 15

Blood flows through the lamellae in one direction and water flows over in the opposite direction. This maintains a large concentration gradient between the water and the blood.

Question 16

Why is the concentration of oxygen in the water always higher than that in the blood?

Answer 16

so as much oxygen as possible diffuses from the water into the blood.

Question 17

If Multicellular organisms weren’t really well adapted for getting the substances they need, what could happen?

Answer 17

if they couldnt do this very well, they’d die out.

(if you’re asked in an exam how something’s adapted for exchange, think about whether surface area is important - cos it often is).

Question 18

Give two ways in which the structure of a gill is adapted for effective gas exchange (2 marks)?

Answer 18

Any two from:

it is made up of gill fillaments which give a large surface area.

each gill filament is covered in lamellae, which further increases the surface area.

The lamellae have a thin surface layer of cells.

The lamellae have lots of capillaries.

A large concentration gradient is maintained between the water and the blood. (2 marks)