4. Cell Membranes & Transport

Question 1

Cell signalling

Answer 1

Communication between cells and coordination between action of different cells to trigger responses inside the cell

Question 2

Diffusion

Answer 2

The net movement of molecules or ions from a region of higher concentration to a region of lower concentration down a concentration gradient, as a result of their random movement

Question 3

Facilitated diffusion

Answer 3

The diffusion of a substance through transport proteins in a cell membrane

Question 4

Osmosis

Answer 4

The net movement of water molecules from a region of higher (less negative) water potential to a region of lower (more negative) water potential, through a partially permeable membrane, as a result of their random movement

Question 5

Active transport

Answer 5

The movement of molecules or ions through transport proteins across a cell surface membrane, against their concentration gradient, using energy from ATP

Question 6

Endocytosis

Answer 6

The bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell, by the infolding of the cell surface membrane to form vesicles containing the substance; it is an active process requiring ATP

Question 7

Exocytosis

Answer 7

The bulk movement of liquids or solids out of a cell, by the fusion of vesicles containing the substance with the cell surface membrane; it is an active process requiring ATP

Question 8

Describe the structure of a phospholipid.

Answer 8

• a hydrophilic PHOSPHATE head
• 2 hydrophobic fatty acid tails
• where the fatty acid can be saturated or unsaturated

Question 9

Explain how ions would move through the channel protein.

Answer 9

• ions move by diffusion
• down the concentration gradient
• channel protein has specific shape for particular ion…
• …and consists of a hydrophilic channel

Question 10

Explain why pressure potential curve is not linear.

Answer 10

• as water enters the cell, the protoplast pushes against the cell wall
• cell wall is relatively rigid
• water cannot be compressed
• therefore pressure builds up more and more rapidly

Question 11

As the cell changes volume, the change in solute potential is much less than the change in pressure potential. Suggest an explanation for this.

Answer 11

• only a small amount of water is needed to bring about a large change in pressure
• b/c the cell wall is relatively rigid
• this is not enough to significantly change the concentration of the cell contents

Question 12

Reasons why a LOW surface area to volume ratio could be a disadvantage to an organism [3m]

Answer 12

1. further diffusion distance
2. not enough oxygen/nutrients reaching the centre of the organism
3. limits the activity of the organism / larger organisms need a transport system