2.5 Biological Membranes

Question 1

What is the role of membranes at surface of cells?

Answer 1

• Partially permeable barrier between the cell and the environment- allows transfer of substances in and out of the cell.
• Site of chemical reactions
• Site of cell communication/signalling

Question 2

What is the role of membranes within cells

Answer 2

• Compartmentalisation
  -Controls what enters and leaves the organelle
• Allows for concentration gradients to be established and maintained
• Embedding of enzymes into the membrane

Question 3

Describe cell signalling

Answer 3

Communication between cells, cell recognition and identification, cells working together, to trigger a response

Question 4

Describe the phospholipid bilayer

Answer 4

Hydrophilic phosphate heads orientate themselves towards water and hydrophobic fatty acid tails orientate themselves away from water (in extracellular fluid and cytoplasm)

Question 5

Describe fluid mosaic

Answer 5

Fluid: components within the membrane move relative to each other (flexible)
Mosaic: embedded with proteins

Question 6

Describe the function of glycolipids and glycoproteins

Answer 6

Cell recognition and identification
Cell signalling
Act as antigens
Act as receptors
Involved in cell adhesion

Question 7

Describe the intrinsic proteins

Answer 7

Span the width of the membrane, usually transport proteins
Carrier proteins (transport large and polar substances), channel proteins (transport polar substances)

Question 8

What is the role of cholesterol?

Answer 8

Found between the tails of the phospholipids in the bilayer and regulates membrane fluidity

Question 9

How does temperature affect membrane fluidity?

Answer 9

As temperature increases the phospholipids gain kinetic energy
This causes gaps to appear between phospholipids
The membrane becomes more permeable
At high temperatures proteins in the membrane will denature

Question 10

How does freezing affect membrane fluidity

Answer 10

When water freezes it expands and forms ice crystals which pierce and break the cell membrane

Question 11

How do solvents (such as ethanol) and detergents affect fluidity?

Answer 11

Solvents and detergents dissolve the phospholipid bilayer increasing permeability

Question 12

Define diffusion

Answer 12

The net movement of molecules from an area of high concentration to an area of lower concentration down a concentration gradient

Question 13

Describe facilitated diffusion

Answer 13

Passive, requires a carrier/channel protein, molecules move down the concentration gradient

Question 14

Describe active transport

Answer 14

Movement of substances against the concentration gradient using carrier proteins and ATP

Question 15

Describe exocytosis

Answer 15

Cytoskeleton contracts to move a vesicle to the plasma membrane, the vesicle fuses with the plasma membrane releasing the contents

Question 16

Describe osmosis

Answer 16

The net movement of water molecules from a region of high water potential into a region of low water potential across a partially permeable membrane.

Question 17

What happens to animal and plant cells in a hypotonic solution

Answer 17

Animals: cytolysis
Plant: turgid

Question 18

What happens to animal and plant cells in a hypertonic solution

Answer 18

Animal: crenation
Plant: plasmolysis