Mass Transport

Question 1

cohesion-tension theory

Answer 1

1. Water lost from leaf due to transpiration
2. Lowers water potential of leaf cells
3. water is pulled up the xylem creating tension
4. Water molecules cohere
5. Forming continuous water columns
6. Adhesion of water molecules to walls of xylem

Question 2

Translocation

Answer 2

1. sucrose actively transported into phloem cell
2. By companion cells
3. Lowers water potential in phloem and water enters from xylem by osmosis
4. Produces higher hydrostatic pressure
5. Mass flow to respiring cells
6. Unloaded from phloem by active transport

Question 3

Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.
Explain the importance of the xylem being kept open as a continuous tube. {3}

Answer 3

1. This will ensure water Is pulled up to the leaves as a continuous column so no barrier to water movement
2. Cohesion from hydrogen bonds between water molecules
3. creates surface tension as water is pulled up the xylem

Question 4

Haemoglobin

Answer 4

• Quaternary structure protein 2 alpha chains
• 2 beta chains
• 4 associated haem groups in each chain containing Fe2+
• transports oxygen

Question 5

Structure of arteries relating to its function

Answer 5

• Thick muscle tissue - maintain blood flow
• thick elastic layer - can stretch and recoil in between surges
• thick wall - withstand the high pressure
• narrow luman - increases high pressure
• smooth endothelium - reduces friction
• no valves

Question 6

Capillary endothelium

Answer 6

• Extremely thin
• one cell thick
• contains small gaps for small molecules to pass through (e.g. glucose, oxygen)

Question 7

Tissue fluid

Answer 7

enables delivery of useful molecules to cells and removal of waste

Question 8

Tissue fluid formation

Answer 8

• At arteriole end, the smaller diameter results in high hydrostatic pressure
• small molecules forced out (ultrafiltration)
• red blood cells / large proteins too big to fit through capillary gaps so remain

Question 9

Re absorption of tissue fluid

Answer 9

• Large molecules remaining in capillary lower its water potential
• towards venule end there is
  lower hydrostatic pressure due to loss of liquid
• water reabsorbed back into capillaries by osmosis

Question 10

Role of the lymph in tissue fluid reabsorption

Answer 10

• Not all liquid will be reabsorbed by osmosis as equilibrium will be reached
• excess tissue fluid (lymph) is absorbed into lymphatic system and drains back into bloodstream and deposited near heart

Question 11

Cardiac muscle

Answer 11

• Walls of heart having thick muscular layer
• unique because it is:
• myogenic - can contract and relax without nervous or hormonal stimulation
• never fatigues so long as adequate oxygen supply

Question 12

Describe the structure of veins

Answer 12

• wider lumen- less resistance to blood flow
• thin elastic layer- lower blood pressure
• valves- prevent back flow of blood

Question 13

Structure of capillaries

Answer 13

• wall is a thin layer of endothelial cells - reduces diffusion distance
• has a large network of branched capillaries - increases surface area
• narrow lumen - reduces blood flow rate so more time for diffusion
• pores in walls between cells - allow larger substances through