Gas exchange

Question 1

What is a gas exchange surface?

Answer 1

A boundary between the outside environment and the internal environment of an organism

Question 2

What features do gas exchange surfaces have to increase the rate of diffusion?

Answer 2

Large surface area

Thin

Question 3

Why is it beneficial for the organism to have a thin gas exchange surface?

Answer 3

Creates a short diffusion pathway

Question 4

What does the organism need to maintain in order to increase the rate of diffusion?

Answer 4

Steep concentration gradient

Question 5

Why don’t single celled organisms need a specialised gas exchange system?

Answer 5

They have a short diffusion pathway so the oxygen can take part in biochemical reactions as soon as it diffuses into the cell

Question 6

What are the thin plates on the gills of a fish called?

Answer 6

Gill filaments

Question 7

How do gill filaments benefit the rate of diffusion?

Answer 7

They give a large surface area which increases the rate of diffusion

Question 8

What covers gill filaments?

Answer 8

Lamellae

Question 9

What do lamellae have which increase the rate of diffusion?

Answer 9

They have lots of blood capillaries and a thin surface layer of cells

Question 10

What is the counter-current system?

Answer 10

The blood flows through the lamellae in one direction and water flows over them in the opposite direction

Question 11

How is the counter-current system effective for diffusion?

Answer 11

The water with a high concentration of oxygen always flows next to the blood with a low concentration of oxygen
This creates a steep concentration gradient which is maintained across the whole length of the gill filament

Question 12

What is the main gas exchange surface of a plant?

Answer 12

Mesophyll cells

Question 13

How are mesophyll cells adapted for their role in diffusion?

Answer 13

Large surface area

Question 14

How do gases move in and out of the leaf?

Answer 14

Through the epidermis

Question 15

What controls the opening and closing of the epidermis?

Answer 15

Guard cells

Question 16

What do insects use for gas exchange?

Answer 16

Microscopic air filled pipes called tracheae

Question 17

What does the air move into the insect through?

Answer 17

Pores on their skins surface called spiracles

Question 18

Where does the oxygen flow in an insect?

Answer 18

Down the concentration gradient towards the cell

Question 19

What do the tracheae branch off into?

Answer 19

tracheoles

Question 20

How does oxygen diffuse directly into the respiring cells?

Answer 20

the tracheae splits off into tracheoles which have thin permeable membranes which attach to individual cells

Question 21

What does the insect use to move the air in and out?

Answer 21

Rhythmic abdominal movements

Question 22

What do insects do if they are losing too much water through gas exchange?

Answer 22

Close their spiracles

Question 23

Which features of an insect reduce evaporation?

Answer 23

Tiny hairs around spiracles

Waxy cuticle layer on their skin

Question 24

What happens when a plant becomes dehydrated?

Answer 24

Guard cells close

They become flaccid which closes the pore to reduce evaporation

Question 25

What are xerophytes?

Answer 25

Plants adapted to live in dry, warm or windy habitats

Question 26

What features do xerophytes have to reduce water loss and how do they reduce it?

Answer 26

Sunken stomata - trap water vapour
Hairs on epidermis - trap water vapour
Curled leaves - protect from wind
Fewer stomata - less places for it to escape
Thicker waxy, waterproof cuticles - reduce evaporation

Question 27

Explain how two features of the gills allow efficient gas exchange? (2 marks)

Answer 27

1) Large surface area = larger gas exchange surface
2) Thin = short diffusion pathway
Both increase the rate of diffusion

Question 28

Suggest why the volume of water passing over the gills increases if the temperature of the water increases (1 mark)

Answer 28

The fish has a higher metabolism

Question 29

How would you measure the surface area of a leaf? (3 marks)

Answer 29

1) place the leaf on a grid and draw around
2) count how many squares it takes up, including any that are more than half
3) multiply by two (both sides)

Question 30

Explain why abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of an insect. (2 marks)

Answer 30

1) more air can enter more quickly

2) maintains concentration gradient

Question 31

What is the advantage of insects opening its spiracles at a lower frequency in very dry conditions?

Answer 31

Lose less water vapour by evaporation