1.3 Cell membranes and transport

Question 1

What are the similarities between the Fluid mosaic and the sandwich model of the plasma membrane?

Answer 1

• contains proteins
• contains phospholipids
• has a bilayer
• hydrophilic head outside
• hydrophobic heads inside

Question 2

What makes the Fluid mosaic different from the sandwich model?

Answer 2

• proteins span the layer
• proteins move with the layer
• glycolipids present
• cholesterol present

Question 3

What are the functions of membranes?

Answer 3

• keep cellular components inside the cell
• allow selective molecules to move in and out
• isolating organelles from cytoplasm
• site for biochemical reactions
• allow the cell to change shape

Question 4

What does the fluid mosaic model state?

Answer 4

membranes are composed of a phospholipid bilayer with various protein molecules floating around within it. the ‘fluid’ part represents how some parts of the membrane can move freely

Question 5

What are the components of the plasma cell membrane?

Answer 5

Phospholipids, extrinsic proteins, intrinsic proteins, cholesterol, glycolipids, channel protein pores.

Question 6

Why do phospholipids from a bilayer in plasma membranes?

Answer 6

because phosphate heads are hydrophilic so move towards water whilst fatty acid tails are hydrophobic and move away. they form this bilayer as both tissue fluid and cytoplasm contain water so the phospholipids from two layers the hydrophilic tails facing inwards and phosphate groups interacting with aqueous environment.

Question 7

What is the function of the PHOSPHOLIPID BILAYER?

Answer 7

Forms the basis of the cell membrane and allows transport of small non-polar molecules into and out of the cell by simple diffusion e.g. oxygen and carbon dioxide.

Question 8

What is the function of EXTRINSIC PROTEINS?

Answer 8

They are charged (polar) and associate with the hydrophilic heads of the phospholipids. They are found above or below the membrane. Many are receptor sites and bind with proteins such as hormones or neurotransmitters.

Question 9

What is the function of INTRINSIC PROTEINS?

Answer 9

They have polar and non-polar regions; which correspond with hydrophilic and hydrophobic regions of the bilayer. Their function is transport. Channels and carriers take part in facilitated diffusion. Pumps take part in active transport.

Question 10

Explain the meaning of FLUIDITY in a membrane?

Answer 10

The phospholipid layer is capable of movement. Components of the membrane are free to move with respect to each other.

Question 11

What is the function of CHOLESTROL?

Answer 11

It fits between the phospholipid molecules, increasing the rigidity and stability of the membrane.

Question 12

What is the function of GLYCOLIPIDS?

Answer 12

Glycolipids are lipids which have combine with polysaccharide; they are found in the outer layer of the membrane and are involved in cell to cell recognition.

Question 13

What is the width of a cell membrane?

Answer 13

7-8nm

Question 14

What are receptor molecules?

Answer 14

help cells to communicate with the environment through hormones.

Question 15

What is meant by compartmentalisation?

Answer 15

• divide cells into compartments for more efficiency
• isolates harmful enzymes
• large surface area for production of ATP
• allows molecules to be transported across the cell

Question 16

What affect does INCREASING TEMPERATURE have on permeability?

Answer 16

Increased heat energy leads to increases kinetic energy. The
phospholipids vibrate more and more and move further
apart. This increases the permeability of the membrane.

Question 17

What affect does INCREASING ETHANOL CONCENTRATION have on permeability?

Answer 17

Organic solvents such as ethanol dissolve phospholipids. The
greater the concentration of ethanol the more permeable
the membranes become.

Question 18

What affect does INCREASING NaCl CONCENTRATION have on permeability?

Answer 18

reduces mobility of the phospholipid molecules so less
betalain is released. As sodium chloride concentration
increases the permeability will decrease.

Question 19

What affect does INCREASING DETERGENT CONCENTRATION have on permeability?

Answer 19

reduce surface tension of phospholipids and
disperse the membrane. As the concentration of detergent
increases the permeability of the membranes increase.

Question 20

Describe the passage of Polar molecules across the membrane?

Answer 20

• the hydrophobic core of the membrane impedes transport of polar molecules
• charged particles cannot pass through as they are insoluble in lipids
• Intrinsic proteins allow these particles to cross the membrane

Question 21

Describe the passage of Non-Polar molecules across the membrane?

Answer 21

• pass through the membrane by simple diffusion
• Lipid soluble molecules can also pass through the bilayer

Question 22

Describe osmosis

Answer 22

the movement of water across along a concentration gradient through a semi-permeable membrane

Question 23

What is a Hypnotic solution?

Answer 23

a solution of high water potential, so water will leave the solution.
- plant cells: vacuole expands and becomes turgid
- red blood cells: burst, this is called haemolysis

Question 24

What is Hypertonic solution?

Answer 24

a solution of low water potential, so water will enter the solution.
- plant cells: lose water so cell becomes plasmolysed
- red blood cells: shrivel and become crenated