Topic 3A: Exchange and Transport Systems

Question 1

Gas exchange in single called organisms

Answer 1

Substances are able to diffuse directly across the cell-surface membrane, into or out of the cell. The rate of diffusion is quick as the length of diffusion pathway is very small.

Question 2

Why can’t diffusion directly into multi-cellular organisms occur?

Answer 2

• Some cell’s are deep within body:
Large diffusion pathway.

• Some organisms are very large:
Small SA:Vol ratio.

Question 3

What affects the rate of heat exchange in an organism?

Answer 3

Body size and shape:

Animals with a larger SA:Vol ratio will have an increased rate of heat exchange.

Question 4

How are animals adapted to deal with heat exchange in their environment?

Answer 4

1) Hot climate:
Organisms will have a very large SA:Vol ratio in order to maximise heat exchange allowing them to cool down.

2) Cool climate:
Organisms will have a very small SA:Vol ratio in order to minimise heat exchange allowing them to remain warm.

Question 5

What are the features of a gas exchange surface?

Answer 5

1) Large surface area.
2) Very thin to reduce length of diffusion pathway.
3) Maintain a steep concentration gradient.
4) Moist.

Question 6

Gas exchange: Fish (the counter-current system)

Answer 6

1) Blood flows through the lamellae in an opposite direction to the flow of water across them.
2) Therefore, water with a high oxygen concentration always flows next to blood with a lower oxygen concentration.
3) This means a steep concentration gradient is maintained between the water and blood.
4) Consequently the rate of diffusion of oxygen from the water to blood is always high.

Question 7

Adaptations: Gills

Answer 7

• Each gill is made up of lots of gill filaments which provide a large surface area for the exchange of gasses.
• Gill filaments are covered in many tiny lamellae which increase the surface area further.
• The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion.

Question 8

Gas exchange: Plants

Answer 8

1) Gases move in and out of stomata found on the surface of the leaf.
2) These are controlled by guard cells which open during photosynthesis in order to let CO₂ into the plant, and then close in order to prevent water loss from the leaf.
3) The mesophyll cell’s are found inside the leaf and have a very large surface area in order to increase the rate of diffusion of CO₂ and O₂ inside the leaf.

Question 9

Gas exchange: Insects

Answer 9

1) The insect uses rhythmic abdominal movements to move air into the trachea through pores called spiracles.
2) Oxygen then travels down its concentration gradient towards the cells.
3) The trachea then branch off into tracheoles which have thin, permeable walls allowing oxygen to diffuse directly into every respiring cell.
4) Carbon dioxide moves down it’s concentration gradient from the cells to the spiracles where it is released into the atmosphere.

Question 10

What are the adaptations of xerophytes to control water loss?

Answer 10

• Stomata sunk in pits:
This traps water vapour, reducing the concentration gradient of water between the leaf and the air meaning less evaporation occurs.

• Thin layer of hairs on epidermis:
Trap water vapour around the stomata, reducing the concentration gradient of water between the leaf and the air meaning less evaporation occurs.

• Curled leaves with stomata inside:
Protects the stomata from the wind meaning water molecules are not blown from around the stomata.

• Reduced number of stomata:
Reduces the number of places where water can escape the plant.

• Thick, waxy cuticle:
Reduced evaporation in the leaves and stems.

Question 11

What are xerophytes?

Answer 11

Plants which are specially adapted to survive in warm, dry or windy habitats where there is lots of water loss.

Question 12

Structure of the human gas exchange system

Answer 12

1) Trachea
2) Bronhi
3) Bronchioles
4) Alveoli
5) Alveolar epithelium
6) Capillary endothelium
7) Haemoglobin in blood.

Question 13

What is the process of inspiration?

Answer 13

1) External intercostals and diaphragm muscles contract.
2) This causes the rib cage to move up and out, and the diaphragm to flatten.
3) Therefore the volume of the thoracic cavity increases.
4) Consequently the lung pressure decreases below atmospheric pressure.
5) Air flows from an area of higher pressure in the atmosphere, down it’s concentration gradient to an area of lower pressure in the lungs.

Question 14

What is the process of expiration?

Answer 14

1) External intercostals and diaphragm muscles relax.
2) This causes the rib cage to move down and in, and the diaphragm to become dome shaped.
3) Therefore the volume of the thoracic cavity decreases.
4) Consequently the lung pressure increases above atmospheric pressure.
5) Air flows from an area of higher pressure in the lungs, down it’s concentration gradient to an area of lower pressure in the atmosphere.

Question 15

What type of process is inspiration?

Answer 15

Active process as it requires energy for the muscles to contract.

Question 16

What type of process is expiration?

Answer 16

Normal expiration is a passive process as it doesn’t require energy as no muscles contract.

However, during forced expiration, the internal intercostal muscles contract, pulling the rib cage down and in further. This is therefore an active process as energy is used.

Question 17

Structure: Alveoli

Answer 17

The wall of the alveolus is made from a single layer of thin, flat cells called the alveolar epithelium which contain a protein called elastin.

This helps the alveoli to recoil to their normal shape after inhaling and exhaling air.

Question 18

Gas exchange: Alveoli

Answer 18

Oxygen diffuses out of the alveoli, across the alveolar epithelium and capillary endothelium, into haemoglobin compounds in the blood.

Carbon dioxide diffuses out of the blood, across the capillary endothelium and alveolar epithelium, into the alveoli.

Question 19

Adaptations: Alveoli

Answer 19

• Alveolar epithelium is one cell thick:
Reduces the length of diffusion pathway, increasing the rate of diffusion.

• Many alveoli:
Large surface area, increasing the rate of diffusion.

• Blood flow and ventilation:
Maintains a steep concentration gradient by constantly replacing blood with a high oxygen concentration with blood with a low oxygen concentration.

Question 20

Definition: Tidal volume

Answer 20

The volume of air in each breath.

Question 21

Definition: Ventilation rate

Answer 21

The number of breaths per minute

Question 22

Definition: Forced exploratory volume

Answer 22

The maximum volume of air which can be breathed out in one second.

Question 23

Definition: Forced vital capacity

Answer 23

The maximum volume of air it is possible to breath forcefully out of the lungs after a deep breath in.

Question 24

Lung disease: Tuberculosis

Answer 24

• The presence of bacteria causes the immune system to build a wall around bacteria in the lungs.
• This causes gaseous exchange surfaces to become damaged reducing tidal volume.

Question 25

Lung disease: Fibrosis

Answer 25

• Exposure to asbestos or dust causes scar tissue to form around the lungs.
• This increases the length of diffusion pathway, meaning diffusion is slower. Therefore, the ventilation rate increases to get enough oxygen into their blood.

Question 26

Lung disease: Asthma

Answer 26

• Allergic reactions to substances causes airways to become inflamed, meaning large amounts of mucus are produced.
• This causes construction in the airways meaning air flow is severely reduced.

Question 27

Lung disease: Emphysema

Answer 27

• Foreign particles in smoke become trapped in the alveoli, causing inflammation which attracts phagocytes to the area.
• These phagocytes produce an enzyme which breaks down elastin, meaning air cannot be forced out of the alveoli.

Question 28

Why do sufferers of lung disease often feel tired?

Answer 28

1) Their disease reduces the rate of gas exchange meaning less oxygen is able to diffuse into their blood stream.
2) Therefore, their body cells receive less oxygen, and the rate of respiration is reduced.
3) This means less energy is released, so sufferers feel tired.

Question 29

What is a risk factor?

Answer 29

Something that increases a person’s chance of getting a disease.

Question 30

What is a correlation?

Answer 30

A link between two things, e.g. smoking and cancer.

However, a correlation doesn’t mean the one thing causes the other, there may be other factors.

Question 31

Ethical issues with dissections

Answer 31

• It is wrong to kill animals just for dissections.

* Animals raised for dissections are not always done so in a humane way.