REMINDERS

Question 1

FICK’S LAW

Answer 1

RATE OF DIFFUSION=

(Surface Area x Difference in Concentration) / Length of Diffusion Path

Question 2

FACILITATED DIFFUSION

Answer 2

✅Net movement of charged ions and polar molecules, from a region of higher concentration to an area of lower concentration, down the concentration gradient through transmembrane channel and carrier proteins

✅Passive process

Question 3

ROLE OF IONS WITHIN THE BODY

Answer 3

Iron: involved in the transfer of electrons during respiration and photosynthesis, present in haemoglobin which allows oxygen to bind to it

Sodium: involved in the transport of glucose and amino acids across cell surface membranes

Phosphate: present in the phospholipid bilayer membrane, present in the formation of phosphodiester bonds between nucleotides in the formation of DNA

Question 4

TRANSPORT IN SMALL INTESTINE

Answer 4

Glucose enters the ileum epithelium with sodium ions:

1. Sodium ions are actively transported out of the epithelial cells into the blood by sodium potassium pump, this creates a concentration gradient
2. There is now higher concentration of sodium ions in the lumen of the ileum then inside the cells.
3. This causes the sodium ions to diffuse from the lumen of the ileum into the epithelial cells, down the concentration gradient, via sodium glucose co-transporter proteins
4. The co transporter carries glucose and amino acids into the cells with sodium, as a result the concentration of glucose inside the cells increases.
5. Glucose diffuses out of the cells into the blood, down the concentration gradient, through protein channels by facilitated diffusion

Question 5

PROPERTIES OF PHOSPHOLIPID BILAYER

Answer 5

Phospholipid bilayer allows the movement of non polar, lipid soluble substances and prevents the movement of polar, water soluble substances across the membrane.
The shape of the proteins determines which substances can move through the membranes.
Number of channels determines how quickly substances can diffuse across cell membranes.
Surface area or membrane determines the amount of diffusion that can occur

Question 6

RECEPTOR MEDIATED TRANSPORT

Answer 6

1. Specific molecules (Low Density Lipoproteins) bind to specific receptors on the plasma membrane.
2. Molecules enveloped to form coated vesicle.
3. Released into cytoplasm of cell

Question 7

SODIUM POTASSIUM PUMP

Answer 7

1. To begin, the pump is open to the inside of the cell and it has a high affinity for sodium ions, and will bind to
   three sodium ions
2. When the sodium ions bind, they trigger the pump to hydrolyse ATP. One phosphate group from ATP is attached to the pump which is phosphorylated and ADP is released as a by-product.
3. Phosphorylation makes the pump change form, re-orienting itself so it
   opens towards the extracellular space. In this shape the pump has a low affinity for sodium ions so the three sodium ions are released outside the cell.
4. In its outward-facing form, the pump now has a high affinity for potassium ions and will bind two of them, which triggers removal of the phosphate group attached to the pump
5. With the phosphate group gone, the pump will change back to its original
   form, opening towards the interior of the cell.
6. In its inward-facing shape, the pump has a low affinity for potassium ions, so the two potassium ions will be released into the cytoplasm.

The pump is now back to the form it was originally in and the cycle can be repeated.

Question 8

ROLR OF CHOLESTEROL IN PHOSPHOLIPID BILAYER

Answer 8

Cholesterol affects the fluidity and permeability of the cell membrane
• It disrupts the close-packing of phospholipids, increasing the flexibility of the membrane
• It acts as a barrier, fitting in the spaces between phospholipids preventing water-soluble substances from diffusing across the membrane
• Prevents membrane from solidifying