Bio 6 - Gas exchange

Question 1

What are the two things that most gas exchange surfaces have in common?

Answer 1

• they have a large surface area

- they’re thin

Question 2

By what process do single-celled organisms absorb and release gases?

Answer 2

Diffusion through their outer surface

Question 3

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

Answer 3

they have a relatively large surface area, a thin surface and a short diffusion pathway. So oxygen can take part in biochemical reactions as soon as it diffuses into the cell.

Question 4

In water, what is there a lower concentration of, air or oxygen?

Answer 4

theres a lower concentration of oxygen than air

Question 5

Where does water enter a fish?

Answer 5

Through the mouth and it passes through the gills

Question 6

What are filaments?

Answer 6

thin plates on each gill of a fish

Question 7

Why do fish have filaments?

Answer 7

They give the fish a big surface area for exchange of gases

Question 8

what are the gill filaments covered in?

Answer 8

lamellae

Question 9

what do lamellae do?

Answer 9

They increase the surface area even more

Question 10

What are lamellae?

Answer 10

they have lots of blood capillaries and a thin surface layer of cells to speed up diffusion

Question 11

What is a counter-current system?

Answer 11

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

Question 12

What does a counter-current system do?

Answer 12

It maintains a large concentration gradient between the water and the blood

Question 13

What do insects use to exchange gas?

Answer 13

A tracheae

Question 14

What is a tracheae?

Answer 14

Microscopic air-filled pipes

Question 15

Explain gas exchange for insects. (5 marks)

Answer 15

1) air moves into the tracheae through pores on the surface called spiracles
2) oxygen travels down the concentration gradient towards the cells
3) the tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells. this means that oxygen diffuses directly into respiring cells
5) carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
6) insects use rhythmic abdominal movements to move air in and out of the spiracles

Question 16

Dicotyledonous plants exchange gases where?

Answer 16

At the surface of the mesophyll cells

Question 17

Where is the main gas exchange surface in a leaf?

Answer 17

the surface of the mesophyll cells

Question 18

Where are the mesophyll cells?

Answer 18

Inside the leaf

Question 19

What are stomata?

Answer 19

Special pores in the epidermis that gases move in and out of

Question 20

Why do the stomata close at night?

Answer 20

To reduce the water loss

Question 21

If insects are losing too much water what do they do?

Answer 21

Close their spiracles

Question 22

Why do insects have a waxy cuticle all over their body?

Answer 22

to reduce evaporation

Question 23

List three ways that insects reduce water loss

Answer 23

• they close their spiracles
• waxy cuticle all over their body
• tiny hairs around their spiricles

Question 24

What opens the stomata?

Answer 24

Water enters the guard cells, making them turgid

Question 25

What closes the stomata?

Answer 25

If the plant gets dehydrated the guard cells lose water and become flaccid which closes the pore

Question 26

What new xerophytes?

Answer 26

plants that are specially adapted for life in warm, dry or windy habitats

Question 27

What happens during gas exchange when you breathe in? (5 marks)

Answer 27

1) as you breathe in air enters the trachea
2) the trachea splits into two bronchi, one bronchus leading to each lung
3) each bronchus then branches off into smaller tubes called bronchioles
4) the bronchioles end in small alveoli
5) the ribcage, intercostal muscles and diaphragm all work together to move air in and out

Question 28

What happens during inspiration (5 marks)

Answer 28

1) the external intercostal and diaphragm muscles contract
2) this causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity
3) as the volume of the thoracic cavity increases, the lung pressure decreases
4) air will always flow from an area of higher pressure to an area of lower pressure so air flows down the trachea and into the lungs
5) inspiration is an active process

Question 29

What happens during expiration (7 marks)

Answer 29

1) the external intercostal and diaphragm muscles relax
2) the ribcage moves downwards and inwards and the diaphragm becomes curved again
3) the volume of the thoracic cavity decreases causing the pressure to increase
4) air is forced down the pressure gradient and out of the lungs
5) normal expiration is a passive process

Question 30

where does gas exchange happen in humans?

Answer 30

alveoli

Question 31

What are alveolus made from?

Answer 31

a single layer of thin, flat cells called alveolar epithelium

Question 32

What are alveoli surrounded by?

Answer 32

Capillaries

Question 33

Why is there a large number of alveoli in the lungs?

Answer 33

theres a big surface area for exchanging oxygen and carbon dioxide

Question 34

What happens in the alveoli?

Answer 34

Oxygen diffuses out of the alveoli across the alveolar epithelium and the capillary epithelium and into haemoglobin in the blood. Carbon dioxide diffuses into the alveoli from the blood and is breathed out

Question 35

List 2 ways that alveoli are adapted for gas exchange

Answer 35

1) a thin exchange surface, its only one cell thick so theres a short diffusion pathway
2) a large surface area