Biological Membranes

Question 1

Describe the fluid mosaic model of membranes ?

Answer 1

Fluid - Phospholipid bilayer in which individual phospholipids can move
Mosaic - Embeded with proteins of different shapes + sizes

Question 2

Explain the role of cholesterol & Glycolipids in membranes ?

Answer 2

Cholesterol - Steroid molecule in some plasma membrane, connects phospholipids & reduces fluidity
Glycolipids - Cell signalling & cell recognition

Question 3

Explain the functions of extrinsic proteins in membranes ?

Answer 3

• Binding sites/ receptors e.g. for hormones & drugs
• Antigens (glycoproteins)
• Bind cells together
• Involved in cell signalling

Question 4

Explain the functions of intrinsic proteins in membranes ?

Answer 4

• Channel proteins (facilitated diffusion).

- Carrier proteins (facilitated diffusion / active transport).

Question 5

Explain the functions of membranes within the cell ?

Answer 5

Provide internal transport
Partially permable to regulate passage of molecules in and out
Isolate organelles from cytoplasm

Question 6

Explain the function of plasma membrane

Answer 6

Isolate cytoplasm from extracellular environment
Partially permeable to regulate transport of substances
Involved in cell signalling

Question 7

Name and explain 3 factors that affect membrane permeability

Answer 7

• Temperature - high temperature denatures membrane proteins / phospholipid molecules have more kinetic energy & move further apart.
• pH - changes tertiary structure of membrane proteins.
• Use of a solvent - may dissolve membrane.

Question 8

What is osmosis ?

Answer 8

Water moving from a high water potential to an area of low water potential across a partially permeable membrane

Question 9

How does osmosis affect plant and animal cells ?

Answer 9

- osmosis INTO cell:
| plant: protoplast swells = cell turgid
_ animal: lysis
- osmosis OUT of cell:
| plant: protoplast shrinks = cell flaccid
| animal: crenation

Question 10

What is simple diffusion ?

Answer 10

The movement of particles from an area of high concentration to an area of low concentration. Passive princess no energy required

Question 11

What is facilitated diffusion ?

Answer 11

The movement of particles from a high to low concentration across a membrane protein

Question 12

What is active transport ?

Answer 12

The movement of particles from a low to high concentration across a carrier protein. Requires energy

Question 13

Define exocytosis and Endocytosis

Answer 13

• Active process
• Involved in bulk transport & transporting large particles
• Vesicles fuse with cell surface phospholipid membrane

Question 14

What 5 factors affect the rate of diffusion ?

Answer 14

• Temperature
• Concentration gradient
• Surface area
• Size of molecule
• Diffusion Distance