What are the key antigens for human blood groups and the structural differences between arteries and veins?

The antigens that determine human blood groups are:

• Antigen A
• Antigen B
• Rh antigen (D antigen)

Structural differences between arteries and veins:

• Arteries have thicker, more muscular, and elastic walls to withstand high pressure from the heart. Veins have thinner, less muscular, and less elastic walls.
• Arteries have a narrower lumen relative to their overall diameter, while veins have a wider lumen.
• Arteries generally do not have valves (except at the heart's exit), whereas veins contain valves to prevent the backflow of blood.
• Arteries maintain a more circular shape when cut, while veins tend to collapse.
• The tunica media (middle layer) is much thicker in arteries than in veins.

Reasons for carrying out the following procedures when making temporary slides:

• a) Making thin sections: To allow light to pass through the specimen, enabling clear observation of internal structures under a microscope.
• b) Adding water to the sections: To prevent the specimen from drying out and to provide a medium for viewing, maintaining its natural state.
• c) Placing coverslip over the plant section: To flatten the specimen, protect the objective lens from contact with the specimen, and hold the water/stain in place.

a) Distinguish between diffusion and osmosis:

• Diffusion is the net movement of particles (solutes or gases) from an area of higher concentration to an area of lower concentration. It can occur in any medium (gas, liquid, solid) and does not necessarily require a semi-permeable membrane.
• Osmosis is the net movement of water molecules across a selectively permeable membrane from an area of higher water potential (lower solute concentration) to an area of lower water potential (higher solute concentration).

b) The red blood cell "At end" is crenated (shrunken and spiky). This occurs when the red blood cell is placed in a hypertonic solution. Water moves out of the cell by osmosis into the surrounding solution, causing the cell to shrink.