BIOLOGY F4 CHAPTER: 3 MOVEMENT OF SUBSTANCES ACROSS PLASMA MEMBRANE

Question 1

What is the necessity of movement of substances across a plasma membrane?

Answer 1

1. Living cells require substances from the external environment to carry out living processes
2. At the time, metabolic process in the cells produce wastes that need to be disposed off from the cells
3. Cells must allow some substances move in and out of the cells to maintain living processes
4. The movement of substances into and out of the cell is regulated by the plasma membrane

Question 2

What are the structures of the plasma membrane? ( 1 )

Answer 2

1. According to the fluid mosaic model, protein molecules float within the phospholipid bilayer, forming a mosaic pattern
2. Each phospholipid consists of a polar head which is hydrophilic ( attracted to water ) and a non-polar tail which is hydrophobic ( repels water )
3. The heads of phospholipid molecules in the outer layer face extracellular fluid, whereas the heads in the inner layer face cytoplasm
4. The tails of the phospholipid molecules of the two layers face each other
5. There are various types of protein molecule embedded partially or fully within the membrane
6. The protein molecules are widely dispersed between the phospholipid bilayer
7. The protein molecules with channels or canals are known as channel protein, whereas the protein molecules that functions as carriers are called carrier protein

Question 3

What are the structures of the plasma membrane?

Answer 3

1. Some proteins and lipids have carbohydrate chains attach to them, known as glycoprotein and glycolipid respectively
2. Glycoprotein and glycolipid act as receptors to hormones such as insulin, stabilize the membrane by forming hydrogen bond with water and act as antigens for cell identification
3. Cholesterol makes phospholipid bilayer stronger, more flexible and less permeable to water-soluble substances such as ions
4. The phospholipid bilayer, protein and cholesterol are not static but form a dynamic and flexible structure
5. This contributes to the fluid characteristic of plasma membrane and makes the plasma membrane more flexible

Question 4

Explain the permeability of plasma membrane

Answer 4

1. A membrane is said to be permeable to a substances if the membrane allows the substance to pass through freely
2. On the contrary, a membrane is impermeable if a substance unable to move across it, The plasma membrane is a selectively permeable membrane
   3.