Exchange surfaces and breathing

Question 1

Explain the importance of specialised exchange surfaces in multicellular organims. (5)

Answer 1

• Metabolic activity is high. (1)
• When mobile, lots of energy is used. (1)
• Muscle cells demand more oxygen and more carbon dioxide is produced. (1)
• Diffusion is ineffective due to the distance between cells; gases cannot be exchanged fast enough or in high enough quantities. (1)
• Multicellular organisms have higher SA:V ratios. (1)

Question 2

How does a good blood supply makes an exchange surface more efficient? (1)

Answer 2

Maintains a steep concentration gradient; substances are constantly exchanged as they come; increases the rate of diffusion. (1)

Question 3

What is the adaptation that vili in the small intestine and root hair cells share to make exchange surfaces more efficient? (1)

Answer 3

Maximised surface area. (1)

Question 4

Describe the adaptations and structural features of the nasal cavity. (4)

Answer 4

• Large surface area. (1)
• Good blood supply; warms the air to body temperature. (1)
• Hairy lining secretes mucus to trap dust and pathogens. (1)
• Moist surfaces increase the humidity of the incoming air. (1)

Question 5

Fill in the gaps about the trachea:

The trachea is the main airway and carries clean, ___, warm air from the nose to the ___. It is supported by incomplete ___ of cartilage that is strong and ___. The trachea is lined with ___ epithelium with ___ cells under and between the cells in the tissue, that secrete ___. The cilia ___, moving the mucus away from the lungs. (8)

Answer 5

• Moist (1)
• Chest (1)
• Rings (1)
• Flexible (1)
• Ciliated (1)
• Goblet (1)
• Mucus (1)
• Beat (1)

Question 6

The trachea splits into two smaller airways called ___. (1)

Answer 6

Bronchi; left/right bronchus. (1)

Question 7

What is the role of smooth muscle in bronchioles?

Answer 7

• Smooth muscle contracts, bronchiole constricts; smooth muscle relaxes, bronchiole relaxes. (1)
• Controls the quantity of air entering the lungs. (1)

Question 8

Why are bronchioles lined with flattened epithelium? (1)

Answer 8

Allows for some gaseous exchange. (1)

Question 9

What is the advantage of having elastic fibres in alveoli? (1)

Answer 9

Allows alveoli to stretch as air is drawn in; air to be squeezed out as they return to their resting size (elastic recoil). (1)

Question 10

Fill in the blanks about alveoli:

There are hundreds of millions of alveoli in each lung, ensuring there is a ___ ___ ___ for diffusion to occur over. Alveoli and the ___ surrounding them have walls only one ___ cell thick, minimising the diffusion distance. The high amount of capillaries increases ___ ___, maintaining a steep ___ ___; good ventilation maintains the same effect, as carbon dioxide is constantly emptied out of the lungs and ___ drawn in. (6)

Answer 10

• Large surface area (1)
• Capillaries (1)
• Epithelial (1)
• Blood supply (1)
• Concentration gradient (1)
• Oxygen (1)

Question 11

Describe the movements of the diaphragm, ribs and muscles in inspiration. (3)

Answer 11

• The diaphragm contracts, flattening and lowering. (1)
• External intercostal muscles contract. (1)
• The ribs move upwards and outwards. (1)

Question 12

Explain how the volume and pressure in the thorax is affected by inspiration and how this brings in air. (3)

Answer 12

• The volume of the thorax is increased. (1)
• So, pressure in the thorax decreases. (1)
• Due to the pressure in the thorax being lower than the pressure of air outside the lungs, air is drawn in (equalising pressure). (1)

Question 13

Describe the movements of the diaphragm, muscles, ribs and alveoli in expiration. (4)

Answer 13

• The diaphragm relaxes, bringing it back up in its dome shape. (1)
• External intercostal muscles relax. (1)
• The ribs move downwards and inwards. (1)
• Elastic fibres in the alveoli return to their original length. (1)

Question 14

What does contracting your internal intercostal muscles result in? (1)

Answer 14

Forcible exhalation. (1)

Question 15

What is the difference between tidal volume and vital capacity?

Answer 15

• Tidal volume is the volume of air moved into (and out of) the lungs with each resting breath. (1)
• Vital capacity is the volume of air breathed in with the deepest possible inhalation (followed by the strongest possible exhalation). (1)
• Tidal volume is only a small fraction of vital capacity. (1)

Question 16

What is expiratory/inspiratory reserve volume?

Answer 16

The extra air that can be exhaled after a normal exhalation; the extra air that can be inhaled after a normal inhalation. (1)

Question 17

Residual volume is the volume of air that stays in your lungs at all times. Therefore, what does both the residual volume and vital capacity add up to? (1)

Answer 17

Total lung capacity. (1)

Question 18

Fill in the gaps of the following equation:

Ventilation rate = ___ volume x ___ rate (1)

Answer 18

• Tidal (1)
• Breathing (1)

Question 19

Insects have small openings where air can enter and water is lost. What are they called? (1)

Answer 19

Spiracles (1)

Question 20

The insect trachea is made up of tracheae and tracheoles. Describe the structure (and how this affects permeability) of each. (4)

Answer 20

• The tracheae lead away from the spiracles. (1)
• They are lined with chitin, preventing gaseous exchange before the tracheoles. (1)
• Tracheae branch into tracheoles, which are each an elongated cell. (1)
• They are freely permeable (no chitin), as they are the site of gaseous exchange. (1)

Question 21

How are tracheoles effective in gaseous exchange (including the changes made when demands for oxygen rise)?

Answer 21

• They are highly abundant and minuscule tubes, maximising surface area. (1)
• Walls of tracheoles are moist, allowing for oxygen to dissolve and then diffuse into surrounding cells. (1)
• Tracheal fluid limits diffusion, as oxygen cannot penetrate it. When oxygen demands rise, lactic acid builds up in the surrounding tissues and causes the water in the fluid to dissolve out of the tracheoles. (1)
• So, the surface area is maximised in the tracheoles. (1)

Question 22

Name two difficulties that bony fish have to overcome as they live in water. (2)

Answer 22

Water is much more viscous than air (1); water is much denser than air (1); water has a much lower oxygen content than air (1); oxygen diffuses slowly in water. (1)

Question 23

Gills are covered by a bony flap called the ___. (1)

Answer 23

Operculum (1)

Question 24

Fill in the gaps about the structure of gills:

Each ___ ___ is attached to two stacks of filaments. There are rows of ___ on each filament - they contain a network of blood ___. The blood flows in the opposite direction of ___, creating a ___-___ flow. This keeps the steep concentration ___ maintained over the length of the capillary. (6)

Answer 24

• Gill arch (1)
• Lamellae (1)
• Capillaries (1)
• Water (1)
• Counter-current (1)
• Gradient. (1)

Question 25

Describe the system that maintains flow over the gills. (5)

Answer 25

• The mouth opens (buccal cavity lowers), increasing the volume in the buccal cavity. (1)
• Increase in volume leads to drop in pressure, causing water to move into the buccal cavity (1)
• The floor of the buccal cavity slowly moves back up, causing volume to decrease; pressure to increase. (1)
• The change in pressure forces the water over the gills (1) and out of the operculum (the opercular valve is opened, previously shut). (1)