P1 Gas Exchange in Animals

Question 1

Structure of the trachea

Answer 1

1. Rings of cartilage surround the trachea to ensure it remains open.
2. Insides of the trachea is lined by a ciliated epithelium, which also contains goblet cells.
   - Goblet cells secrete mucus, which traps dust and mucus.
   - Cilia on the epithelium beat to move mucus away from the lungs.

Question 2

Structure of bronchi/bronchioles

Answer 2

1. Made of smooth muscle, which control air flow by dilating and constricting.
2. Elastic fibres inside the bronchi, bronchioles (and alveoli) enable the lungs to stretch and recoil.

Question 3

Describe inspiration

Answer 3

1. The diaphragm and external intercostal muscle contract.
2. The volume in the thorax increases, decreasing pressure in the thorax.
3. This forces air into the lungs.

Question 4

Describe expiration

Answer 4

1. Diaphragm relaxes and the internal intercostal muscles contract.
2. The volume in the thorax decreases, increasing pressure in the thorax.
3. This forces air out of the lungs.

Question 5

Structure of alveoli

Answer 5

• Have a one-cell thick layer of epithelial cells (the epithelium).
• Wrapped around each alveoli are capillaries, which have a one-cell thick layer of endothelium cells (the endothelium) - ensuring there is a short diffusion distance between the alveoli epithelium and the capillaries endothelium.
• The short diffusion pathway, steep concentration gradient (good ventilation to supply oxygen and good blood supply to supply carbon dioxide), large surface area (large numbers of alveoli) and moist linings (for diffusion gases) increase the rate of gas exchange.

Question 6

What is tidal volume?

Answer 6

The volume of air that is breathed in and out in one breath during normal breathing.

Question 7

What is vital capacity?

Answer 7

The maximum volume of air that can be breathed in and out in one breath.

Question 8

What type of circulatory system do fish have?

Answer 8

Single, closed - ventricles pump blood to the gills where gas exchange occurs.

Question 9

Structure of the gills

Answer 9

• Covered by a flap called the operculum. When closed the operculum provides protection to the gills, and when open it maintains constant water flow over the gills.
• Gills have gill arches, to which stacks of gill filaments are attached. The surface of the gill filaments is made of lamella (plate like structures).
• Each lamella contains many capillaries, that are attached to the blood vessels extending from the gill arch.

Question 10

Describe gas exchange in fish

Answer 10

• Water constantly moves through the lamella when the fish swims.
• Compared to the fish’s deoxygenated blood, the water contains a large amount of oxygen, so oxygen from the water diffuses into the capillaries. Carbon dioxide also diffuses from a high concentration in the capillaries, to a low concentration in the water.

Question 11

Describe ventilation in fish

Answer 11

• Ventilation in fish maintains a constant water flow from the buccal cavity (inside of the mouth) over the gills:
  1. The fish opens it’s mouth and lowers the buccal cavity floor, decreasing the pressure inside the cavity.
  2. Water flows down the pressure gradient into the buccal cavity, causing the operculum to close.
  3. The fish raises the floor of the buccal cavity and closes it’s mouth, increasing the pressure inside the buccal cavity.
  4. Water flows down the pressure gradient, outside of the fish. During this, water flows over the gills, then pushes the operculum open, allowing the water to exit the fish.

Question 12

What adaptations do fish have for efficient gas exchange?

Answer 12

1. Water and blood flow in opposite directions across the lamella (counter current mechanism), enabling the fish to maintain a steep concentration gradient of oxygen and carbon dioxide.
2. Fish contain a large number of gills, filaments, lamella and capillaries. This increases the surface area for the diffusion of oxygen and carbon dioxide.

Question 13

What circulatory system do insects have?

Answer 13

An open circulatory system - their heart pumps haemolymph (a blood-like liquid) to the surrounding organs, providing them with nutrients and removing waste products.

Question 14

Describe the tracheal system of insects

Answer 14

• Insects contain trachea, which are the main site of gas exchange.
• Trachea branch into trachioles, which extend into the insects muscle tissues.
• At the body’s surface tracheae end in tiny openings called spiracles, which open and close to control the entry and exit of gases.

Question 15

Where are tracheae found?

Answer 15

In the insects thorax and abdomen

Question 16

Describe ventilation in insects

Answer 16

• Ventilation from the spiracles to the trachea maintains a constant airflow.
• To draw air into the the tracheae, the insects expand it’s abdomen, increasing the volume of the thorax and creating a pressure gradient for air to flow into the trachea, all the way to the trachioles where gas exchange occurs.
• To remove air from the trachea, the insect squeezes it’s abdomen.

Question 17

What adaptations ensure efficient gas exchange in insects?

Answer 17

1. Wall at the end of each tracheole is only one cell thick (short diffusion pathway between tracheoles and the surrounding tissue).
2. Tracheoles are highly branched, and there are a large number of them, providing a large surface area for gas exchange, while also ensuring a short diffusion pathway.
3. Abdominal movement causes muscle contraction, which pumps large amounts of air through the tracheae and the tracheoles, maintaining a concentration gradient of oxygen and carbon dioxide.
4. The end of tracheoles are filled with fluid. Muscle contractions move this fluid into the surrounding tissue, causing air to be drawn in to the tracheoles (diffusion through air is quicker, allowing faster diffusion into the muscle tissue).

Question 18

What adaptations do insects have to limit water loss?

Answer 18

Insects have a large SA:V ratio, meaning their need for an efficient gas exchange system must be balanced with their need to limit water loss:
- have a waterproof exoskeleton
- spiracles can be open or closed to control water loss