Gas Exchange

Question 1

Where does gas exchange occur?

Answer 1

Over a gas exchange surface.

Question 2

What is a gas exchange surface?

Answer 2

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

Question 3

What do organisms need for diffusion across a gas exchange surface?

Answer 3

Oxygen and carbon dioxide (makes diffusion quicker).

Question 4

What increases the rate of diffusion over gas exchange surfaces?

Answer 4

• They have a large surface area

* They are thin (often just one layer of epithelial cells).

Question 5

What does a thin gas exchange surface provide?

Answer 5

A short diffusion pathway across the gas exchange surface.

Question 6

What do single-celled organisms not require for gas exchange?

Answer 6

A specialised gas exchange system.

Question 7

Why do single-celled organisms not require a gas exchange system?

Answer 7

• They have a relatively large surface area

* A thin surface, thus a short diffusion pathway

Question 8

Where does gas exchange occur in single-celled organisms?

Answer 8

They absorb and release gases by diffusion through their cell-surface membranes.

Question 9

Where does gas exchange occur in fish?

Answer 9

In the gills

Question 10

Why does gas exchange occur in the gills of a fish?

Answer 10

Because the gills are specially adapted to get enough oxygen.

Question 11

Why do fish gills need to be adapted to get enough oxygen?

Answer 11

Because there is a lower concentration of oxygen in water than in air.

Question 12

How does gas exchange occur in fish?

Answer 12

Water containing oxygen enters the fish through its mouth and passes out through the gills.

Question 13

What do gills have which are beneficial to gas exchange?

Answer 13

A large surface area for gas exchange.

Question 14

Why do gills have a large surface area for gas exchange?

Answer 14

• Each gill is made of lots of thin plates called gill filaments.
• These gill filaments are covered in lots of tiny structures called lamellae.

Question 15

How do the lamellae in gills increase the rate of diffusion further?

Answer 15

• They increase the surface area even more.
• They have lots of blood capillaries.
• They have a thin surface layer of cells.

Question 16

What do fish gills look like?

Answer 16

image

Question 17

What system do gills have that ensure a high rate of diffusion?

Answer 17

The counter-current system.

Question 18

What is the counter-current system in fish gills?

Answer 18

• The blood flows through the lamellae in one direction.

* The water flows over the lamellae in the opposite direction.

Question 19

What does the counter current system do in gills?

Answer 19

It ensures that the water with a relatively high oxygen concentration always flows next to blood with a lower oxygen concentration.

Question 20

How does the counter-current system ensure a high rate of oxygen diffusion from water to blood in gills?

Answer 20

Because it maintains a steep concentration gradient between the water and the blood.

Question 21

What does the counter-current system in gills look like?

Answer 21

Image

Question 22

How does gas exchange occur in dicotyledonous plants?

Answer 22

Gases move in and out through special pores in the lower epidermis called stomata.

Question 23

Where does gas exchange occur in dicotyledonous plants?

Answer 23

Mesophyll cells in the leaf (well adapted with a large surface area).

Question 24

What do the stomata do during gas exchange in dicotyledonous plants?

Answer 24

Stomata open to allow gas exchange and close if the plant is losing too much water.

Question 25

What does gas exchange in dicotyledonous plants look like?

Answer 25

image

Question 26

Where does gas exchange in insects occur?

Answer 26

They have microscopic air filled pipes called trachea.

Question 27

How does gas exchange occur in the trachea of insects?

Answer 27

• Air moves into the trachea through pores on the surface called spiracles.
• Oxygen travels down he concentration gradient towards the cells.
• The trachea branch off into smaller trachioles.

Question 28

Why do the trachea branch off into trachioles during gas exchange in insects?

Answer 28

Because they go to individual cells and they have thin, permeable walls, so oxygen diffuses directly into respiring cells.

Question 29

How is the carbon dioxide released during the gas exchange of insects?

Answer 29

Carbon dioxide from the respiring cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.

Question 30

How do insects move air into and out of the spiracles?

Answer 30

Through rhythmic abdominal movements.

Question 31

What does gas exchange across the trachea of insects look like/

Answer 31

image

Question 32

What does gas exchange often lead to?

Answer 32

Water loss

Question 33

What adaptations do insects have that minimise water loss during gas exchange?

Answer 33

• They close their spiracles using muscles.

* They have a waterproof waxy cuticle over their body and tiny hairs (reducing evaporation).

Question 34

What adaptations do plants have that minimise water loss during gas exchange?

Answer 34

The opening and closing of their stomata:

• Stomatal pores stay open when water enters the guard cells, making them turgid
• Stomatal pores close when guard cells lose water, becoming flaccid, thus closing the pore (when plants are dehydrated).

Question 35

What are xerophytic plants?

Answer 35

Plants that are specially adapted for life in warm, dry or windy habitats, where water loss is a problem.

Question 36

What are some adaptations of xerophytic plants?

Answer 36

• Sunken stomata
• Layer of hairs around the epidermis
• Curled leaves with the stomata inside
• Reduced number of stomata
• Thicker, waxy, waterproof cuticles on leaves and stems

Question 37

Why do sunken stomata in xerophytes reduce water loss?

Answer 37

Because they trap water vapour, reducing the concentration gradient of water between the leaf and the air, reducing evaporation.

Question 38

Why do layers of hair around the epidermis in xerophytes reduce water loss?

Answer 38

This traps water vapour around the stomata, again reducing the concentration gradient between the leaf and air, redcuing evaporation.

Question 39

Why do curled leaves with the stomata inside in xerophytes reduce water loss?

Answer 39

This protects the stomata from the wind, decreasing diffusion and evaporation of water.

Question 40

Why does a reduced number of stomata in xerophytes reduce water loss?

Answer 40

Because there are less places for water to escape from.

Question 41

Why do thicker, waxy, waterproof cuticles on leaves and stems in xerophytes reduce water loss?

Answer 41

Because this reduces evaporation.