2B: Cell Membranes

Question 1

Structure of the Cell Membrane

Answer 1

Fluid Mosaic Model
phospholipid molecules form and continuous double layer (bilayer) and protein miolecules are scattered throughout it like a mosaic

Question 2

Function of Cholesterol in the Cell Membrane

Answer 2

Gives stability by binding to the hydrophobic tails of the phospholipids, causing them to pack together more closely
It also has hydrophobic regions which creates a further barrier

Question 3

How does the Cell Membrane act below 0 degrees celcius?

Answer 3

phospholipids don’t have much energy so can’t move very much
packed closely together so rigid membrane
channel and carrier proteins denature
ice crystals may form and pierce the membrane, making it highly permeable as it thaws

Question 4

How does the Cell Membrane act between 0 and 45 degrees celcius?

Answer 4

phospholipids can move around and aren’t as tightly packed together
membrane is partially permeable
as temperature increases, phodpholipids can move more as they have more energy which increases permeability

Question 5

How does the Cell Membrane act above 45 degrees celcius?

Answer 5

the phospholipid bilayer starts to melt and the membrane becomes more permeable
water inside the cell expands, putting pressure on the membrane
channel and carrier proteins denature so they can’t control what enters and leaves the cell which increases permeability

Question 6

How to investagate Cell Membrane Permeability

Answer 6

1. use a scalpel to carefully cut five equal pieces of beetroot. Rinse the pieces to remove any pigment released during cutting
2. Add the five pieces of beetroot to five different test tubes, each containing 5cm^3 of water.
3. Remove the pieces of beetroot from the tubes leaving just the coloured liquid
4. Use a calorimeter with a blue filter, obtaining readings for distilled water in the curvette

(not finished)

Question 7

Definition of Diffusion

Answer 7

the net movement of particles from an area of higher concentration to an area of lower concentration
passive process- it does not require energy

Question 8

Name 3 factors that affect diffusion

Answer 8

concentration gradient
thickness of exchange surface
surface area

Question 9

What is Facilitated Diffusion?

Answer 9

Diffusion with the helpp of a channel or carrier protein

Question 10

How do molecules diffuse through a carrier protein?

Answer 10

1. large molecule attaches to a carrier protein in the membrane
2. the protein changes shape
3. this releases the molecule on the opposite sie of the membrane

Question 11

What particles diffuse through carrier proteins?

Answer 11

large molecules

Question 12

How do molecules diffuse through a channel protein?

Answer 12

they move through the pore created

Question 13

What particles diffuse through channel proteins?

Answer 13

charged particles and polar molecules

Question 14

Name 2 factors affecting facilitated diffusion

Answer 14

concentration gradient
number of carrier or channel proteins

Question 15

Definition of Osmosis

Answer 15

The diffusion of water molecules accross a partially [ermeable membrane from an area of higher water potential to an area of lower water potential

Question 16

Definition of Water Potential

Answer 16

The potential of water molecules to diffuse out of or into a solution

Question 17

What does isotonic mean?

Answer 17

When two solutions have the same water potential, so net movmement is 0

Question 18

What does hypertonic mean?

Answer 18

The solution has lower water potential than the cell

Question 19

What does hypototic mean?

Answer 19

The solution has higher water potential than the cell

Question 20

Name 3 factors affecting the rate of Osmosis

Answer 20

Water Potential Gradient
Thicness of exchange surface
Surface Area

Question 21

How to investagate water potential

Answer 21

Making serial dilutions

1. Line up 5 test tubes in a rack
2. Add 10cm^3 of the initial 2mol sucrose to the first test tube and 5 cm^3 of distilled water to the other four test tubes
3. Then, using a pipette, draw 5cm^3 of the first solution, add it to the distilled water in the second test tube and mix thoroughly. You now have 10 cm^3 of solution thats half concentrated
4. Repeat this process three more times

OR

1. use the table below to make serial dilutions

Measuring change in mass

1. Use a cork borer to cut potatoes into identically sized chips about 1 cm in diameter. Divide chips into groups of three and measure the mass of each group using a mass balance
2. Place one group into each of your sucrose solutions and leave the chips in the solutions for at leats 20 minutes
3. Remove the chips and pat dry with paper towel. Weigh each group again and record results. Calculate percentage chage in mass for each group.

Producing a calibration curve

1. Plot percantage change in mass against concentration of sucrose solution
2. Use the calibration curve to determine the water potential of potato cells

Question 22

Definition of Active Transport

Answer 22

The movement of particles from an area of lower concentration to an area of higher concentration requiring energy, and carrier proteins or co-trasporters

Question 23

How do carrier proteins allow active transport?

Answer 23

ATP is used to supply the energy needed to change the shape of the carrier protein to allow a molecule bound to it to move against its concentration gradient

Question 24

What are co-transporters?

Answer 24

A type of carrier protein that bind to 2 molecules at a time

Question 25

How do co-transporters allow for active transport?

Answer 25

They allow 2 molecules to bind, one which is moving against its conc grad, the other moving with. the one moving with ‘brings’ the one moving against with it

Question 26

Describe co-transport and the absorption of glucose

Answer 26

1. Na+ are actively transported out of the epithelial cells in the ileum into the blood by the sodium-potassium pump
2. this causes Na + to diffuse from lumen of the ileum into the epithelial cell, down their concentration gradient whcih they do via sodium-glucose co-transporter molecules. the co-transporter molecule carries glucose into the cell with sodium and as a result, the concentration of glucose in the cell increases
3. glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel via facilitated diffusion

Question 27

Name 3 factors affecting active transport

Answer 27

Speed of individual carrier proteins
Number of carrier proteins
rate of Respiration (for ATP)