Paper 1 - Exchange And Transport

Question 1

Absorption of lipids

Answer 1

1. Micelles come to epithelial wall and release fatty acids and monoglycerides.
2. These monoglycerides simply diffuse into the epithelial cells.
3. They are then transported to the smooth ER where they form triglycerides.
4. The Golgi apparatus produces chylomicrons from these triglycerides.
5. Chylomicrons exit epithelial cells by exocytosis and enter lacteals and into the bloodstream.

Question 2

Capillaries

Answer 2

• Permeable wall allows for exchange of substances
• Endothelium wall is one cell thick = short diffusion pathway
• Endothelial cells are flattened = short diffusion pathway
• Pores = larger molecules can go through
• Narrow = RBCs pass through single file = short diffusion pathway
• Narrow = slows flow of blood = more time for diffusion

Question 3

Tissue fluid

Answer 3

1. Arterial end has high hydrostatic pressure of blood.
2. Water and soluble molecules pass out of capillaries
3. Proteins remain as they’re too large.
4. This lowers the WP of the blood.
5. Water moves back into venous end of capillary by osmosis.
6. Lymph vessels drain excess tissue fluid and returns fluid to blood

Question 4

Cohesion tension theory

Answer 4

1. Water evaporates from leaves through stomata - transpiration
2. Reduces WP in leaf cells
3. Water moves into leaf cells from xylem by osmosis
4. Negative pressure in top of xylem
5. Water is pulled up the xylem as a column due to cohesion
6. Adhesion of water molecules to walls of xylem
7. Water enters through roots by osmosis.

Question 5

Mass flow hypothesis (translocation)

Answer 5

1. At source, sucrose is actively transported into phloem by companion cells
2. WP is lowered in phloem
3. Water enters by osmosis
4. High hydrostatic pressure created
5. Sucrose is actively transported out of the phloem at the sink to be used for storage
6. Increases WP so water leaves by osmosis = low hydrostatic pressure
7. Mass flow of sucrose from source to sink down pressure gradient.

Question 6

Atrial systole

Answer 6

Decreased volume of atria = increase of pressure inside

Atrioventricular valves are open, semi lunar valves closed

Blood is pushed into ventricles

Question 7

Ventricular systole

Answer 7

Decreased volume of ventricles = increase of pressure

Atrioventricular valves shut - pressure higher in ventricles than atria which prevents back flow

Blood is forced up and out into arteries (semilunar valves open)

Question 8

Cardiac diastole

Answer 8

Higher pressure in arteries than ventricles - semilunar valves close to prevent back flow

Blood returns to heart, atria fill again

Atrioventricular valves open - allows blood to flow passively into ventricles from atria