Gas excahneg and insects

Question 1

The scientist used units of μmol g–1 h–1 for the rate of oxygen uptake.

Suggest why he used μmol in these units.

This question think why use such a small value what are benefits

Answer 1

(Measures) small uptake / amount / quantity / volume / concentration / rate (of oxygen uptake);

OR

Avoids use of powers of ten / standard form

Question 2

The scientist decided to use the ratio of surface area to mass, rather than the ratio of surface area to volume. He made this decision for practical reasons.

Suggest one practical advantage of measuring the masses of frog eggs, tadpoles and adults, compared with measuring their volumes.

Answer 2

More accurate / less error (in measuring mass);

OR

Causes less distress / damage to animal (to measure mass);

OR

Easier / quicker (to find mass) because irregular shapes;

Question 3

Explain why oxygen uptake is a measure of metabolic rate in organisms.

Think what oxygen used for in organisms what process

Answer 3

(Oxygen used in) respiration, which provides energy / ATP;

OR

(Oxygen is used in) respiration, which is a metabolic process

Question 4

The adult damselfly uses a tracheal system for gas exchange.

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

Answer 4

. Tracheoles have thin walls so short diffusion distance to cells;

2. Highly branched / large number of tracheoles so short diffusion distance to cells;
3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);
5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;

Question 5

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.

Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water. These larvae do not actively hunt prey and do not have gills.

Explain how the presence of gills adapts the damselfly to its way of life.

Think it’s a hunter what does it need to do lots of to catch prey

Answer 5

Damselfly larvae has high(er) metabolic / respiratory (rate);

2. (So) uses more oxygen (per unit time / per unit mass);

Question 6

Abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. Explain why.

Answer 6

More air / oxygen enters / air / oxygen enters quickly / quicker;

1. Accept: converse for carbon dioxide
2. Can be in any correct context eg insect, tracheoles, muscle
3. Neutral: air / oxygen enters

(So) maintains / greater diffusion or concentration gradient;

Question 7

The ends of tracheoles connect directly with the insect’s muscle tissue and are filled with water. When flying, water is absorbed into the muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why.

Answer 7

Greater surface area exposed to air;

Neutral: shorter diffusion distance

2. Gases move / diffuse faster in air than through water;
3. Q Neutral: ‘harder to diffuse’
4. Accept gases diffuse directly, rather than through water
5. Increases volume / amount of air;

Question 8

Explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water.