B3.2 Transport

Question 1

What are the components of blood?

Answer 1

Plasma (55%):
- water
- salts
- plasma proteins
- substances transported by blood: eg. nutrients

Cellular elements (45%):
- RBC
- WBC
- platelets

Question 2

Function of arteries

Answer 2

• Carries blood away from heart to capillaries at high pressure.
• When blood is received under high pressure, wall of artery is pushed outwards which widens the lumen and stretches elastic fibres.
• At end of heartbeat, pressure falls & elastic fibres recoil, squeezing the blood in the lumen, pushing it forward.

Question 3

Structure of arteries

Answer 3

• Tunica intima: thin layer of smooth endothelium, sometimes with elastic fibres.
• Tunica media: many thick layers of smooth muscle and elastic fibres that stretch and recoil in synchrony with pulsating blood pressure.
• Tunica externa: tough layer of connective tissue and strong collagen fibres to withstand the changing high blood pressure without bursting.
• Narrow lumen
• Does not have valves bcs. blood is transported at high pressure in one direction.

Question 4

Function of veins

Answer 4

• Collects deoxygenated blood from capillaries and all organs and returns it to the heart under low pressure.
• Blood flow is assisted by gravity and pressures exerted by the muscles. When muscles contract, adjacent veins are squeezed like a pump.
• Valves prevent the backflow of blood from being transported at low pressure. When blood flows towards the heart, the valves push up allowing the blood to pass through. However, if blood were to flow back, the valves would push down hence, preventing backflow of blood.

Question 5

Structure of veins

Answer 5

• Tunica intima: thin layer of smooth endothelium, sometimes with elastic fibres
• Tunica media: thin, having fewer layers of smooth muscle and elastic fibres
• Tunica externa: tough layer of connective tissue and strong collagen fibres that withstands high blood pressure without bursting.

Question 6

Function of capillaries

Answer 6

• Connects arteries with veins
• Responsible for the exchange of material between blood and internal/external environment under low pressure.

Question 7

Structure and adaptations of capillaries

Answer 7

• One cell layer thick, providing a short diffusion pathway for the exchange of materials
• Branches and rejoins repeatedly to form a network of a huge total surface area for very efficient diffusion
• Coated by a thin protein gel which acts as a filter for substances
  • The fenestrations/pores allow greater volumes of tissue fluids to leak out through the gel-like basement membrane.
  • Tissue fluid is a part of the blood plasma with nutrients such as oxygen and glucose.

Question 8

What happens during pressure changes?

Answer 8

• Blood leaving the heart and going into the arteries is under high pressure and speeds, travelling in pulses.
• When the blood has reached the capillaries, it moves at a much lower pressure and speed without a pulse.
• Pressure reaches almost 0 mmHg, but increases in speed in the veins.

Question 9

How to measure pulse rate?

Answer 9

• A pulse is when a wave of blood under high pressure passes along the arteries.
• Measured using the wrist, neck or using digital devices.

Question 10

What is occlusion?

Answer 10

Happens when coronary arteries are blocked by atheroma, made up of lipids and cholesterol.

Question 11

Causes of occlusion

Answer 11

Unhealthy diet, smoking, diabetes

Question 12

Consequences of occlusion

Answer 12

1. Restricted blood flow to the heart muscle causing chest pain and shortness of breath, especially during exercise.
2. When calcium salts deposit in the atheroma and harden the artery, it increases the risk of a blood clot that can entirely block blood flow to the heart muscle and deprive it of oxygen, causing a heart attack.
3. Blockages that persist will cause tissue death and permanent damage

Question 13

Explain transport of water in plants

Answer 13

1. Water is absorbed by the roots, transported in the xylem and lost from the mesophyll in leaves via transpiration.
2. Capillary action, which brings the water up the roots and to the rest of the plant, is caused by the evaporation of water from the leaf mesophyll cells.
3. Adhesion of water molecules to the plant cell walls and cohesion between water molecules pulls it upwards in xylem vessels to generate tensions.

Question 14

Structure and adaptations of xylem vessels

Answer 14

• Lignin: hydrophobic polymers that cover the inside of vessel tubes which strengthen cell walls to withstand low pressure –> prevent it from collapsing.
• Tracheids:
  – Pits: gaps in the cell wall –> allows water to enter and exit
  – Long continuous columns of cells, arranged end-to-end to allow an unbroken water column.
• Perforated end walls: cell wall material between adjacent cells are removed & broken down –> minimal resistance to the flow of the sap.

Question 15

Distribution of tissues in a transverse section

Answer 15

• Dicotyledonous stem: vascular bundles are organized in rings around the stem
• Dicotyledonous root: xylem vessels are arranged in the form of a cross, and phloem cells are arranged throughout the cylinder
• Monocotyledonous stem: vascular bundles are scattered throughout the stem
• Monocotyledonous root: xylem vessels are arranged as a ring, and phloem cells are arranged throughout the cylinder