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.
- Longer diffusion distance

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 → steep diffusion distance

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

Adaptations for efficient gas exchange in fish

Answer 11

• large SA: V ratio → created by many gill filaments covered in many gill lamellae
• Short diffusion distance: very thin lamellae + network of capillaries
• Concentration gradient: counter current flow 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

Question 14

What is the disadvantage for concurrent flow?

Answer 14

Blood and water flowing in the same direction so eventually reaches equilibrium
so no more diffusion
So won’t have O2 occurring across the whole lamellae

Question 15

The structure of the insect tracheal system

Answer 15

Order: spiracles, trachea, tracheoles
1. Spiracles: round valve like openings. O2 and CO2 enter and leave via the spiracles
2. Trachea: network of internal tubes, have rings around them to strengthen the tubes and stop them from collapsing
3. Tracheoles: smaller tubes branched from the trachea and extend throughout the tissues to deliver oxygen to respiring cells

Question 16

Advantage with counter current flow

Answer 16

Ensures equilibrium is not reached so a diffusion gradient is maintained across the entire length of the gill lamellae

Question 17

Structure of the gills

Answer 17

The gills are made up of stacks of gill filaments
Each gill filament is covered in gill lamellae (creates large surface area)

Question 18

Gas exchange at the stomata

Answer 18

• Photosynthesis: O2 diffuses out of the stomata, CO2 diffuses in
• Stomata close at night to reduce water loss by evaporation, as this is when photosynthesis would not be occurring
• CO2 diffuses in bc there is a lower conc of CO2 in spongy mesophyll compared to atmosphere

Question 19

Adaptations to xerophytic plants

Answer 19

• Curled leaves → to trap moisture and increase local humidity
• Hair → to trap moisture and increase local humidity
• Sunken stomata → to reduce water loss
• Thicker waxy cuticle → to reduce evaporation
• longer roots → network to reach more water
• Thicker leaves → low sa:v ratio
• Succulent leaves → sore water for dry periods