Diffusion pathways

Question 1

Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish.

Answer 1

Water and blood flow in opposite directions which maintains concentration along whole/length of gill/lamellae

Question 2

Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. The disease causes the lamellae to become thicker and to fuse together. AGD reduces the efficiency of gas exchange in fish. Give two reasons why.

Answer 2

There is thicker lamellae so longer diffusion pathway and the lamellae fuse so reduced surface area;

Question 3

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves. 5 marks

Answer 3

In the root the active transport by the endodermis
of ions into xylem lower the water potential so water enters by osmosis.

Transpiration from the leaves creates cohesion between water whilst adhesion binds the water molecules to the xylem which creates a continuous watercolumn

Question 4

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

Answer 4

More oxygen enters so maintains a greater diffusion gradient

Question 5

Abdominal pumping is an adaptation not found in many small insects. These small insects obtain sufficient oxygen by diffusion. Explain how their small size enables gas exchange to be efficient without the need for
abdominal pumping

Answer 5

Large surface area to volume ratio

Question 6

The insect opens its spiracles at a lower frequency in very dry conditions. Suggest one advantage of this.

Answer 6

Less water lost

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 3 reasons why.

Answer 7

Greater surface area exposed to air;
Gases diffuse faster in air than through water
Increases volume/amount of air;

Question 8

Explain 3 way in which a palisade cell is adapted for photosynthesis.

Answer 8

Chloroplasts absorb light
Large vacuole pushes chloroplasts to edge (of cell)
Thin/permeable (cell) wall to absorb carbon dioxide

Question 9

The stomata on the leaves of pine trees are found in pits below the leaf surface.Explain how this helps to reduce water loss.

Answer 9

Water vapour accumulates around the stomata which the water potential gradient

Question 10

Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between body mass and oxygen uptake.

Answer 10

Smaller animals have larger surface area to volume ratio so lose more heat per gram of tissue so respire faster therefore need more oxygen.

Question 11

Explain how leaves lose mass through transpiration

Answer 11

Water evaporates out from open stomata as there is a high water potential inside the leaf