Cell Surface Membrane

Question 1

What are the components of the cell membrane?

Answer 1

• a phospholipid bilayer
• cholesterol molecules
• large embedded proteins
• glycoproteins and glycolipids

Question 2

Describe the structure and significance of phospholipids in the cell membrane.

Answer 2

-structure arranged in a phospholipid bilayer, hydrophilic polar heads face outwards and hydrophobic non-polar fatty acids tails point onwards
-significance allows non-polar substances to simply diffuse across membrane, and prevents water soluble substances from diffusing through, makes the membrane flexibel and self-sealing

Question 3

Describe the structure and significance of proteins in the cell membrane.

Answer 3

-structure are embedded in the membrane, they either span across both layers (intrinsic) or only one side of the membrane
-role channel proteins which allow facilitated diffusion of ions/ polar molecules , carrier proteins which bind ions or molecules like glucose and amino acids to move them across the membrane, receptors which identify cells.

Question 4

Describe the structure and role of Cholesterol in the cell membrane.

Answer 4

-structure binds to the hydrophilic tails of the phospholipids, makes them pack more closely together and restrict their movement
-role add strength and stability to the membrane, contribute to the hydrophilic nature of the cell membrane which prevents loss of water.

Question 5

Describe the structure and role of glycolipids in the cell membrane.

Answer 5

• structure carbohydrate covalently bonded to a lipid, carbohydrate extends outwards outside the cell
  -role recognition sites, maintain stability of membrane, help cells attach to one another to form tissues

Question 6

Name the different transport mechanisms across the plasma membrane

Answer 6

• simple diffusion
• active transport
• facilitated diffusion
• osmosis
• co-transport
• endocytosis/exocytosis

Question 7

Describe simple diffusion across the plasma membrane.

Answer 7

• particles move down the concentration gradient
• does not require energy (passive)
• no channel/carrier proteins needed
• transport of non polar substances (fatty acids, CO2)
• reaches a dynamic equilibrium

Question 8

Describe facilitated diffusion over the plasma membrane.

Answer 8

• particles move down the concentration gradient
• does not require ATP
• involves channel/carrier proteins
• transport of polar/charged substances
• reaches a dynamic equilibrium

Question 9

Describe osmosis over the plasma membrane

Answer 9

• particles move down the concentration gradient
• does not require ATP
• can involve aquaporins
• transport of water molecules
• reaches a dynamic equilibrium

Question 10

Describe active transport over the plasma membrane.

Answer 10

• particles move against a concentration gradient
• requires energy
• only carrier proteins involved
• transport of polar/charged substances (glucose/amino acids/ ions)
• does not reach a dynamic equilibrium

Question 11

What are the factors which affect the rate of diffusion?

Answer 11

• concentration gradient
• surface area
• length of diffusion pathway
• temperature
• size of molecule

Question 12

What is Fick’s law of diffusion?

Answer 12

Diffusion is directly proportional to
Surface area x concentration gradient=ans
Ans/ diffusion pathway length

Question 13

Factors affecting facilitated diffusion

Answer 13

• concentration gradient
• number of protein channels/carriers in membrane if there aren’t a many to carry the substance across they will quickly be saturated and the rate of facilitated diffusion will no longer increase

Question 14

Factors affecting active transport

Answer 14

• number of protein carriers in membrane
• amount of ATP available (aerobic respiration)