Topic 2 -Cell Membranes

Question 1

What are the functions of phospholipids in the phospholipid bilayer

Cell membranes

Answer 1

it allows lipid soluble substances to pass through but prevents water soluble substances from moving through. It also allows the membrane to be flexible and self sealing.

Question 2

Describe a cell surface membrane’s permeability

Cell membranes

Answer 2

Its selectively permeable as it allows lipid soluble substances to pass through but prevents water soluble substances from moving through

Question 3

What’s the model used for cell surface membranes ?

Cell membranes

Answer 3

The fluid mosaic model - its fluid because phospholipids are constantly moving and the size and pattern of the bilayer is mosaic like and proteins are scattered through like a mosiac.

Question 4

what are extrinsic proteins ?

Cell membranes

Answer 4

Proteins that do not span the whole bilayer, e.g. receptor proteins

Question 5

What are intrinsic proteins ?

Cell membranes

Answer 5

Proteins that span the whole bilayer, e.g. channel proteins/ carrier proteins

Question 6

What are channel proteins function ?

Cell membranes

Answer 6

They form pores in the membrane to allow charged particles (water soluble ions) to move(diffuse) through the membrane.

Question 7

What are carrier proteins functions ?

Cell membranes

Answer 7

Bind to larger molecules or ions like glucose and amino acids , then change shape in order to move these across the membrane.

Question 8

What are the functions of cholesterol in the cell membrane ?

Cell membranes

Answer 8

Adds strength. They’re very hydrophobic so prevent loss of water and dissolved ions from the cell. They fit in between the phospholipids and bind to the tails causing them to pack more closely together, making the membrane more rigid and less fluid by restricting movement. Maintains the shape animal cells (with no cell wall).

Question 9

What are the functions and structure of glycolipids ?

Cell membranes

Answer 9

Contain a carbohydrate chain covalently bonded with a lipid. This acts as a cell surface receptor for chemical. They help maintain the stability of the membrane. They act as recognition sites. Help cells attach to each other to form tissues.

Question 10

What’s the function and structure of glycoproteins ?

Cell membranes

Answer 10

Carbohydrate chains attached to extrinsic proteins covalently. Thy act as cell surface receptors, more specifically for hormones and neurotransmitters. They act as recognition sites, help cells attach to form tissues, and allow cells to recognise each other

Question 11

What happens to a cell surface membranes permeability in temperatures below 0 degrees ?

Cell membranes

Answer 11

Phospholipidss dont have much kinetc enegery so they cn’t move very much, they’re packed cloely together making the membrane rigid. Channel and carrier proteins deform, increasing permeability. Ice crystals may form and peirce the membrane, making permeability increase when it thaws.

Question 12

What happens to a cell surface membranes permeability in temperatures between 0 and 45 degrees ?

Cell membranes

Answer 12

Phospholipids can move around more as they aren’t packed as closely together-the membrane is partially permeable. As temperature increases, the phospholipids move more as they’re given more energy. This increases the permeability of the membrane.

Question 13

What happens to a cell surface membranes permeability in temperatures above 45 degrees ?

Cell membranes

Answer 13

The phospholipid bilayer begins to melt and the membrane becomes permeable. Water in the cell expands, putting pressure on the membrane. Channel and carrier proteins deform-they cannot control what enters of exits the cell so the permability increases.

Question 14

How would you investigate the permability of beetroot at different temperatures ?

Cell membranes

Answer 14

1. use a scapel to cut 5 identical peicies of beetroot and rinse them.
2. Place them each in their own test tube with 5cm3 of water (using a measuring cylinder).
3. Place each test tube in a different water bath of doffernt temperaures (10,20,30,40 and 50 degrees) for 20 minutes (using a stopwatch).
4. Remove the beetroot.
5. Use a colorimeter - a machine that passes light thorugh liquid and measures how much light is aborped, the more absorption, the more pigment, the more permeable the membrane.
6. connect the colorimetre to a computer to collect the data.

Question 15

What’s the definnitoin of diffusion ?

Cell membranes

Answer 15

The net movement of molecules or ions from an area of higher concentration to an area of lower concentation down the concentration graident.

Question 16

When does the process of diffusion stop ?

Cell membranes

Answer 16

Once equilobrium is reached - an even distibution of particles.

Question 17

What type of particles move across the membrane by simple diffsuion ?

Cell membranes

Answer 17

small and non polar molecules as it makes them lipid soluble.

Question 18

Is energy required for simple diffusion ?

Cell membranes

Answer 18

No, its passive.

Question 19

When is facilitated diffusion used and what happens ?

Cell membranes

Answer 19

For larger moleucle (like glucose and amino acids) and polar molecules as this makes them water soluble but the centre of the phospholipid bilayer is hydrophobic, so instead these particles diffuse through channel or carrier proteins.

Question 20

What does the rate of simple diffusion depend on ?

Cell membranes

Answer 20

• the higher the concentration gradient, the faster the rate of diffusion.
• The thinner the exchange surface the faster the rate as there’s less distance for particles to travel across.
• The larger the surface area, the faster the rate as more particles can diffuse at once.

Question 21

What are microvilli ?

Cell membranes

Answer 21

projections formed by the cell sirface membrane folding up on itself (e.g. eithelial cells), they give the cell a larger surface area so increase the rate of diffusion.

Question 22

What does the rate of simple diffusion depend on ?

Cell membranes

Answer 22

-The higher the concentration gradient, the faster the rate of diffusion.
-the more channel and carrier proteins the faster the rate as once all proteins are occupied the rate of diffusion cannot go any faster.
-the higher the concentration gradient, the faster the rate of diffusion.
-The thinner the exchange surface the faster the rate as there’s less distance for particles to travel across.
-The larger the surface area, the faster the rate as more particles can diffuse at once.

Question 23

What are aquaporins ?

Cell membranes

Answer 23

A type of channel prtiens that allow the facilitated difusion of water through the cell membrane, some kidney cells have these as it allows the reabprbtion of water that would otherwise be excreted.

Question 24

Why will the rate of diffusion slow down over time.

Cell membranes

Answer 24

The concentration of the particle insdie and outside of the cell will reach eqiilibrium.

Question 25

What’s osmosis ?

Cell membranes

Answer 25

The net diffusion of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane down the concentration gradient.

Question 26

What’s water potential ?

Cell membranes

Answer 26

The likelyhood (potential) pf water molecules diffusing into a solution.

Question 27

What solutioion has the highest water potential ?

Cell membranes

Answer 27

Water has a water potential of 0.

Question 28

Whats an isotonic solution ?

Cell membranes

Answer 28

Two solutions have the same water potential.

Question 29

What affects the rate of omosis ?

Cell membranes

Answer 29

the higher the water potential gradient, the faster the rate of osmosis
The thinner the exchange surface, the faster the rate of osmosis
The larger the surface area, the faster the rate of osmosis.

Question 30

How would you make serial dilutions ?

Cell membranes

Answer 30

1. line up 5 test tubes in a rack.
2. add 10cm3 of 2M of sucrose to the first test tube and 5cm3 of distilled water to the next 4 test tubes
3. transfer 5cm3 of the sucrose in the first test tube to the water in the second test tube using a pipette.
4. Mix
5. repeat for each test tube going in order to create solutions of 0.5,0.25 and 0.125M.

Question 31

What would happen to potato samples when out in a solution with higher water potential ?

Cell membranes

Answer 31

the potato’s will gain mass as water has been drawn in by osmosis from an area of higher water potential to an area of lower water potential through a partially permeable membrane.

Question 32

What is active transport?

Cell membranes

Answer 32

active transport uses energy to transport molecules or ions from an area of low concentration to an area of high concentration across a membrane against a concentration gradient.

Question 33

What proteins are used during active transport ?

Cell membranes

Answer 33

carrier proteins.

Question 34

How’s energy supplied for active transport?

Cell membranes

Answer 34

ATP is hydrolysed by ATP hydrolysis into ADP and Pi during respiration, this releases energy so that particles can be moved across the membrane in the carrier proteins.

Question 35

What are co transporters ? and what do they do ?

Cell membranes

Answer 35

a type of carrier protein that bind to 2 molecules,e.g. sodium ions and glucose. the sodium ions move down their concentration gradient into the cell by facilitated diffusion. this moves glucose into the cell, against its concentration gradient.

Question 36

What things affect the rate of active transport?

Cell membranes

Answer 36

the faster the carrier proteins work, the faster the rate of diffusion
the more carrier proteins the faster the rate
if respiration is inhibitors then ATP is not available active transport cannot take place

Question 37

How is glucose absorbed into the blood stream from the small intestine ?

Cell membranes

Answer 37

1. Sodium ions are actively transported out of the ileum epithelial cells into the blood by the sodium potassium pump, this creates a concentration gradient as there’s a high concentration of sodium ions in the lumen compared to the epithelial cells.
2. Sodium ions diffuse from the lumen into the epithelial cells down their concentration gradient via the co transporters
3. The co transporters bonded to glucose and sodium, meaning that glucose molecule is carried into the cell causing the concentration of glucose in the epithelial cells to increase.
4. glucose diffuses out of the cells into the blood stream down it’s concentration gradient in a protein channel by facilitated diffusion.