Topic 4.3 Gas exchange

Question 1

Name three features of an efficient gas exchange surface

Answer 1

1. Large surface area, e.g. folded membranes in mitochrondria
2. Thin/short distance, e.g. wall of capillaries
3. Steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli

Question 2

Name and describe the main features of an insect’s gas transport system

Answer 2

• Spiricles = openings on the body’s surface
• Tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
• Tracheoles = smaller branches dividing off the tracheae

Question 3

How are insects adapted for gas exchange?

Answer 3

• Spiricles can be opened or closed to regulate diffusion
• Muscles in the trachea allow mass movement of air in and out
• Tracheoles highly branched to provide large surface area

Question 4

Name and describe the main features of a fish’s gas transport system

Answer 4

• Gills = made of filaments supported by arches
• Lamellae = folds that cover the filiments. Water passes over them due to preasure from the floor of the mouth

Question 5

How are fish adapted for gas exchange?

Answer 5

• Gills are made of numerous filaments and covered by lamellae, providing a high surface area
• Countercurrent exchange system means that water an blood flow in opposite directions, so water is always next to blood of a lower oxygen concentration; maintains a steep gradient

Question 6

How are mammels adapted for gas exchange?

Answer 6

Alveoli provide a large surface area and very thin diffusion pathway, maximising the amount of oxygen absorbed from one breath. They also have a plentiful supply of deoxygenated blood, maintaining a steep concentration gradient.

Question 7

How are plant leaves adapted for gas exchange?

Answer 7

1. Spongey mesophyll layer provides large surface area
2. Waxy cuticle is impermeable to gas, preventing excessive water loss
3. Lenticels (loosely arranged cells) allow gasses to enter and leave

Question 8

How do plants limit their water loss while still allowing gasses to be exchanged?

Answer 8

Stomata regulated by guard cells which allows them to open and close as needed. Most stay closed to prevent water loss while some open to let oxygen in.

Tracheoles have no chitin so are permeable to gasses and allow diffusion

Question 9

Why are tracheae lined with chitin?

Answer 9

Chitin (a structural polysaccaride) keeps the tracheae open and is impermeable to gasses

Question 10

Why are alveoli good at gas exchange?

Answer 10

• They provide a large surface area
• They are made of a single layer of flattened epithelial cells so provide a short diffusion pathway
• They are surrounded by capilliaries containing deoxygenated blood so there is a steep oxygen concentraion gradient

Question 11

Why must cartilaginous fish swim constantly?

Answer 11

To keep water contantly flowing over thier gills so concentration gradient is maintained and gas exchange still occurs

Question 12

Describe ventillation in fish

Answer 12

1. The preasure in the mouth cavtiy is reduced by the mouth of the floor being lowered and the operculum moved outwards
2. The operculum acts as a valve as it is pressed against the body wall by the higher outside preasure, thus water enters through the mouth and to equalise the preasure
3. The volume of the mouth cavity is now reduced and the preasure increased by raising the floor of the mouth. A valve inside the mouth prevents water from leaving
4. This increased preasure opens the operculum and water leaves. In doing so it passes te between the gill filaments where gas exchange occurs

Question 13

What are lenticils?

Answer 13

Thickened, woody plant stuctures (e.g. tree trunks) have no stomata, but the tissues underneath still need to respire.

Here, spongey lenticils develop, loosely arragned cells with many air spaces, linking the inner tissues with the outside enviorment.

Question 14

How do stomata open?

How do stomata close?

Why can this happen?

Answer 14

The guard cells lose water (due to K⁺ ions by active transport) and become flaccid, and closes

They gain water (due to K⁺ uptake) and become turgid, and opens

This happens because of the extra thickening on the side of the guard cell wall adjacent to the stomatal pore.

Question 15

What is mechanical ventilation in large insects?

Answer 15

In large very active insects, such as bees and flies, the abdomen can be pumped in and out to draw in more air.