3.1 Adaptations for Gas Exchange

Question 1

What are the 3 main adaptation for gas exchange?

Answer 1

• large SA:Vol
• short diffusion pathway
• steep concentration gradient

Question 2

What adaptations for diffusion do large organisms have?

Answer 2

• large variety of specialised cells, tissues, organs and gas exchange systems

Question 3

Why is specialised system for gas exchange required?

Answer 3

Problems of multicellular organisms:
- small SA:Vol
- long diffusion distance

Importance of a gas exchange system:
- supply of oxygen
- removal of carbon dioxide

Question 4

Why is diffusion NOT viable in larger multi-cellular organisms?

Answer 4

The time taken for oxygen to diffuse from the cell-surface membrane to the tissues would be too long.

Question 5

How does body mass relate to BMR?

Answer 5

The greater the mass of an organism, the higher the metabolic rate.

Question 6

Why is BMR higher per unit mass in smaller animals?

Answer 6

They have a greater SA:Vol so they lose more heat, so they have to use up more energy to maintain their body temperature.

Question 7

Explain why oxygen intake is a measure of BMR.

Answer 7

Oxygen is used in respiration which is a metabolic process.

Question 8

Adaptations in insects to prevent water loss

Answer 8

• waterproof exoskeleton
• small SA: V ratio: where water can evaporate from
• spiracles: can open and close to reduce water loss

Question 9

Outline the adaptations of insects’ tracheal system.

Answer 9

• large SA: large number of tracheoles
• Short diffusion distance: walls of tracheoles are thin & short distance between spiracles and tracheoles
• Concentration gradient: oxygen is used by respiring muscle fibres

Question 10

Gas Exchange within the tracheal system in insects

Answer 10

1. Diffusion: cells respire and use up O2 and produces CO2 → creates conc gradient from tracheoles to atmosphere
2. Abdominal pumping: air sacs on the tracheal system can be squeezed by muscles to push air in/ out
3. Tracheal fluid: cells undergo anaerobic respiration which produces lactic acid and lowers Ψ of the cells, causes water to move in cells via osmosis, reducing volume of tracheal fluid and allows for the diffusion of O2 and CO2

Question 11

Outline the adaptations of fish gills.

Answer 11

• SA: large number of filaments
• Short diffusion distance: surface of lamellae is a single layer of flattened cells + network of capillaries
• Concentration gradient: counter current system

Question 12

Describe the mechanism for gas exchange in fish.

Answer 12

• The capillary system within the lamellae ensures that the blood flow is in the opposite direction to the flow of water - it is a counter-current system
• The counter-current system ensures the concentration gradient is maintained along the whole length of the capillary
• The water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood

Question 13

Outline the adaptations of dicotyledonous plant leaves.

Answer 13

• SA: air spaces in spongy mesophyll
• Short diffusion distance: thin tissues within the leaf + stomata
• Concentration gradient: carbon dioxide used immediately by photosynthetic cells