[OLD] Cells - Cell Membranes

Question 1

What do cell membranes do?

Answer 1

Control what enters and leaves the cell (plasma membrane) or organelle (if surrounding rER, Golgi etc)
They are selectively permeable.

Question 2

What does the fluid mosaic model contain?

Answer 2

Phospholipid bilayer
Proteins
Cholesterol
Glycoproteins / glycolipids

Question 3

What does the phospholipid bilayer do in the fluid mosaic model?

Answer 3

Hydrophobic tails to inside (away from water)

Hydrophilic heads to outside (in contact with water)

Question 4

What do proteins do in the phospholipid bilayer?

Answer 4

Act as receptors or enzymes
Spam membrane to transport ions and polar molecules
May bond to cytoskeleton for support

Question 5

What does cholesterol do in the fluid mosaic model?

Answer 5

It is a small molecule positioned within the phospholipid bilayer where it stabilises the membrane by regulating its fluidity

Question 6

What do glycoproteins / glycolipids do in the fluid mosaic model?

Answer 6

Act as antigens and receptors in surface of cell

Can form hydrogen bonds with water to help stabilise membrane

Question 7

How receptor molecules in the cell’s surface membrane work?

Answer 7

They are specific to one signal molecule only.
They will be complementary in shape to that signalling molecule.
They will bind to each other and the bring about a response within the cell.

Question 8

5 process that allow passage across a cell membrane

Answer 8

Simple diffusion
Facilitated diffusion
Active transport
Bulk transport
Osmosis

Question 9

2 transport proteins that allow passage across a cell membrane

Answer 9

Channel protein

Carrier protein

Question 10

What is simple diffusion?

Answer 10

Where molecules pass directly through phospholipid bilayer from high concentration to low concentration
No transport protein required
No energy requires
Example: O2, CO2

Question 11

What is facilitated diffusion?

Answer 11

Where molecules travel from high concentration outside cell to low concentration inside cell
Through carried or channel proteins
No energy required
Example: glucose, amino acid

Question 12

What is active transport?

Answer 12

Where molecules travel from low concentration outside cell to high concentration inside cell (against concentration gradient)
Carrier proteins used
Energy required
Example: Glucose, amino acid

Question 13

What is bulk transport?

Answer 13

Vesicle fuses with membrane to secrete substances out of the cell (exocytosis) or membrane surrounds and engulfs particles it take substances in (endocytosis)
No transport proteins used
Requires energy
Example: Hormones

Question 14

What is osmosis?

Answer 14

The transport of water through phospholipid bilayer or channel proteins (called aquaporins)
No energy required
Water passes down the water potential gradient (from high to low) into or out of cell

Question 15

What does channel protein carry?

Answer 15

Small, charged molecules e.g Na+

Question 16

What does a carrier protein carry?

Answer 16

Large, polar molecules (i.e have positive and negative areas) e.g glucose, glycerol, amino acids

Question 17

Which molecules require transport proteins?

Answer 17

Polar and charged molecules

Question 18

Which molecules will pass easily through the cell membrane by simple diffusion?

Answer 18

Very small polar molecules (e.g water only) and all non-polar molecules (large or small e.g steroid hormone)

Question 19

How does water travel by osmosis?

Answer 19

From an area of high water potential to low water potential.

Question 20

What is the highest water potential possible?

Answer 20

0kPa (pure water)

Question 21

What happens to the water potential as more and more solute is dissolved in the water?

Answer 21

It lowers

Question 22

Osmosis 3 mark phrase

Answer 22

Water travels by osmosis from an area of high water potential to an area of lower water potential down the water potential gradient.

Question 23

How to tell the water potential of a plant tissue using plasmolysis

Answer 23

Out samples of plant tissue in a variety of solutions of different water potentials.
If WP is much higher in the solution than the plant cells, all the plant cells will be turgid.
If WP is much lower in the solution than the plant cells, all the plant cells will become plasmolysed.
If WP is similar in the solution and the plant cells, about 50% of the plant cells will be plasmolysed.

Question 24

What is insipient plasmolysis?

Answer 24

When plasma membrane is just about to peel away from the inside of the cell wall.

Question 25

factors affecting the rate of active transport

Answer 25

speed of individual carried proteins - the faster they work the faster the rate of active transport.
the number of carrier proteins present - the more proteins there are, the faster the rate of active transport.
the rate of respiration in the cell and the availability of ATP. if respiration is inhibited, active transport can’t take place.