(Paper 1 Content Knowledge) 2.1 Organisation: Animal gas exchange system

Question 1

List the levels of organisation in multicellular organisms in order of increasing complexity.

Answer 1

Cells → Tissues → Organs → Organ systems

Question 2

What is an organelle?

Answer 2

A specialised unit within a cell that performs a specific function.

Question 3

Define a cell.

Answer 3

The basic building block of all living organisms.

Question 4

What is a tissue?

Answer 4

A group of cells working together to perform a shared function, often with a similar structure.

Question 5

Define an organ.

Answer 5

A structure made up of groups of different tissues, working together to perform specific functions.

Question 6

What is an organ system?

Answer 6

A group of organs with related functions, working together to perform certain functions within the body.

Question 7

Why do organisms need exchange surfaces?

Answer 7

To take in essential substances (e.g., oxygen, food, water) and remove waste substances (e.g., carbon dioxide).

Question 8

How do small organisms exchange substances with their environment?

Answer 8

By diffusion directly across their body surface.

Question 9

What determines how quickly organisms can absorb substances?

Answer 9

Their surface area.

Question 10

What determines how much of a substance an organism needs?

Answer 10

Their volume.

Question 11

What happens to the surface area to volume ratio as organisms grow larger?

Answer 11

It decreases; volume increases faster than surface area.

Question 12

What issue arises as an organism’s surface area does not keep pace with its volume?

Answer 12

Insufficient surface area for exchange to meet the organism’s needs.

Question 13

How do larger organisms overcome having insufficient surface area for exchange?

Answer 13

They develop specialised exchange surfaces with increased surface area.

Question 14

What problem do organisms face as their volume increases?

Answer 14

Diffusion alone becomes too slow to transport substances throughout the organism’s body.

Question 15

How do larger organisms solve the problem of slow diffusion over large distances?

Answer 15

By developing transport systems (e.g., circulatory systems).

Question 16

Why do multicellular organisms need specialised exchange surfaces?

Answer 16

To efficiently exchange materials like gases, nutrients, and waste due to their size and complexity.

Question 17

What increases the effectiveness of exchange surfaces?

Answer 17

A large surface area, a short diffusion distance, and mechanisms to maintain a steep concentration gradient.

Question 18

Give two examples of structures with a large surface area for exchange.

Answer 18

Alveoli in lungs and villi in the small intestine.

Question 19

How do leaves provide a large surface area for gas exchange?

Answer 19

Their flattened shape maximises surface area.

Question 20

Why is a short diffusion distance important?

Answer 20

It allows substances to diffuse quickly across the surface.

Question 21

Give examples of structures with short diffusion distances.

Answer 21

Thin walls of alveoli, villi, capillaries, and cell membranes.

Question 22

How does an efficient blood supply improve exchange in animals?

Answer 22

It transports molecules to and from exchange surfaces, maintaining steep concentration gradients.

Question 23

Which two structures are surrounded by capillaries to aid exchange?

Answer 23

Alveoli (lungs) and villi (small intestine).

Question 24

What role does ventilation play in gas exchange?

Answer 24

It brings in fresh air and removes stale air from alveoli, helping maintain a concentration gradient.

Question 25

Why is maintaining a steep concentration gradient important?

Answer 25

It increases the rate of diffusion across exchange surfaces.

Question 26

What is the main function of the human lungs?

Answer 26

To provide an exchange surface for absorbing oxygen into the blood and removing carbon dioxide from the blood.

Question 27

What is ventilation?

Answer 27

The process of breathing air in and out to bring it into contact with the gas exchange surfaces in the lungs.

Question 28

Where does gas exchange occur in the lungs?

Answer 28

In the alveoli, which are surrounded by blood capillaries.

Question 29

What structures does air pass through to reach the alveoli?

Answer 29

Trachea → Bronchi → Bronchioles → Alveoli

Question 30

What keeps the trachea open during breathing?

Answer 30

Rings of cartilage in its walls.

Question 31

Name three features that make alveoli well adapted for gas exchange.

Answer 31

1. Very large surface area (about 70 m² total) 2. Walls are only one cell thick 3. Moist lining to dissolve gases

Question 32

How many alveoli are in the lungs?

Answer 32

Around 700 million (350 million per lung).

Question 33

What role do capillaries play in gas exchange?

Answer 33

They carry blood close to the alveoli, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out.

Question 34

Why is the diffusion path in the alveoli short?

Answer 34

Because both alveoli and capillary walls are only one cell thick.

Question 35

How is a steep concentration gradient maintained in the lungs?

Answer 35

Through constant ventilation (breathing) and blood flow, which continuously removes and delivers gases.

Question 36

What protects the lungs and helps with breathing?

Answer 36

The ribs, intercostal muscles, diaphragm, and pleural membranes.

Question 37

What carries air to and from the alveoli in the lungs?

Answer 37

The respiratory system (trachea → bronchi → bronchioles → alveoli).

Question 38

What causes air to enter the lungs during inhalation?

Answer 38

The diaphragm and external intercostal muscles contract, reducing pressure in the lungs below atmospheric pressure, so air rushes in.

Question 39

What is the main muscle used in normal inhalation?

Answer 39

The diaphragm.

Question 40

What happens during normal exhalation?

Answer 40

The diaphragm and external intercostal muscles relax, increasing lung pressure and pushing air out.

Question 41

Is normal breathing active or passive?

Answer 41

It is mostly a passive process, driven by pressure changes.

Question 42

What are the exchange surfaces in fish?

Answer 42

Gills

Question 43

How does water flow through a fish for gas exchange?

Answer 43

Water enters through the mouth, flows over the gills, and exits under the operculum.

Question 44

What is counter-current flow in fish gills?

Answer 44

Water flows over the gills in the opposite direction to blood flow, maintaining a steep concentration gradient.

Question 45

Why is counter current flow important?

Answer 45

It allows efficient oxygen absorption by maintaining a concentration gradient along the entire gill.

Question 46

Name three adaptations that make fish gas exchange efficient.

Answer 46

1. Large surface area of gill filaments 2. Thin diffusion pathway (one cell thick) 3. Rich blood supply and counter-current flow

Question 47

Why is gas exchange harder in water than air?

Answer 47

Water contains less oxygen (~1% at 15°C) than air (~21%).

Question 48

How efficient are fish gills at extracting oxygen?

Answer 48

They can extract 70–80% of available oxygen in water.

Question 49

What gas diffuses from alveoli into blood?

Answer 49

Oxygen (O₂).

Question 50

What gas diffuses from blood into alveoli?

Answer 50

Carbon dioxide (CO₂).

Question 51

What helps maintain a concentration gradient in human lungs?

Answer 51

Ventilation (breathing) and blood flow.

Question 52

What structures ensure the alveoli don’t collapse?

Answer 52

Surfactant lining and flexible connective tissue.

Question 53

What structure increases the surface area of fish gills?

Answer 53

Gill filaments and lamellae.

Question 54

What direction does blood flow in relation to water in fish gills?

Answer 54

In the opposite direction – this is called counter current flow.

Question 55

What is the advantage of counter-current flow in fish?

Answer 55

It maintains a constant concentration gradient along the entire gill surface.

Question 56

How do fish ventilate their gills?

Answer 56

By opening their mouths to let water flow over gills and closing them to force it out through the operculum.

Question 57

Why do land animals need moist gas exchange surfaces?

Answer 57

Gases must dissolve in moisture to diffuse across membranes.

Question 58

Which has more efficient gas exchange: fish gills or mammalian lungs?

Answer 58

Fish gills are extremely efficient due to counter current flow, but lungs are adapted for high oxygen availability in air.