Cell membranes q

Question 1

Describe the model illustrated

Answer 1

Proteins are scattered amongst the phospholipids

The phospholipids are constantly moving so, the structure is fluid

Question 2

Explain the effect that a higher percentage of cholesterol would have on the model

Answer 2

The cholesterol molecules would restrict the movement of the phospholipids

Making the structure less fluid and more rigid

Question 3

Suggest and explain 2 ways in which the cell-surface membranes epithelial cells might be adapted to their function

Answer 3

Likely to have a high proportion of carrier or channel proteins

In order to carry nutrients via facilitated diffusion or active transport

Likely to have a large surface area/microvilli

To maximise the rate of absorption of nutrients

Question 4

Suggest and explain an adaption you might expect to observe in the cell membrane of a neurone cell

Answer 4

Large number of carrier or channel proteins

In order to allow cations to cross the cell membrane quickly

Question 5

When phospholipids come together to form a cell membrane, a bilateral structure is always formed. Explain why

Answer 5

Phospholipids have a hydrophobic tail and a hydrophilic head

The hydrophilic heads are attracted to the water molecules in the cytoplasm or cell surroundings

And the hydrophobic tails are repelled from them so, a bilayer is formed

Question 6

Describe the direction of movement of water across the cell membrane

Give a reason for your answer

Water potential = -2.4kPa

Answer 6

Water will move inside the cell

As the water potential outside the cell is higher than water potential inside the cell

Question 7

Explain how co-transport is used to transport sodium ions and glucose into cells in the mammalian ileum, across their cell membranes

Answer 7

Sodium ions are actively transported out of the ileum epithelial cells into the blood by the sodium-potassium pump

This creates a concentration gradient of sodium ions between the lumen of the ileum and the interior of the epithelial cells

Sodium ions diffuse down the concentration gradient into the epithelial cells via sodium-glucose co-transporter proteins

Question 8

Why were the cut sections of beetroot soaked in distilled water overnight

Answer 8

To make sure any pigments released by the cutting of the beetroot were washed away

Question 9

Suggest a negative control that could be used in this investigation

Answer 9

Colorimetry analysis of distilled water

Question 10

Use your knowledge of the structure of cell membranes to explain these results

Answer 10

Increasing the temperature from 20 to 40 increases the fluidity of the phospholipids in the beetroot cell membranes

At temperatures above 40, the membrane starts to break down with proteins in the membrane starting to denature

The membrane surrounding the vacuole therefore becomes more permeable with increasing temperature

Meaning the pigments leak out into the distilled water

The more pigment released, the higher the absorbance reading

Question 11

A second investigation found that membrane permeability increased as the pH increased

Suggest an explanation for this

Answer 11

Cell membranes contain channel proteins and carrier proteins

Proteins are denatured by high pHs as it interferes with the bonding in proteins, causing them to change shape

The proteins are then unable to function and control what goes in or out of the cell, membrane permeability will increase

Question 12

What type of polymer chain is attached to the lipid in a glycolipid

Answer 12

A polysaccharide (carbohydrate) chain is attached to the lipid in a glycolipid

Question 13

Name the lipid that restricts the movement of phospholipids in eukaryotic cell membranes

Answer 13

Cholesterol

Question 14

Cholesterol

Answer 14

Restricts the movement of phospholipids in eukaryotic cell membranes

Fit between phospholipids, binding to the hydrophobic tails and causing them to pack more closely.

This restricts their movement, making the membrane less fluid/more rigid

Question 15

Explain how the arrangement of phospholipids restricts the movement of water-soluble substances across cell membranes

Answer 15

Phospholipids are arranged in a bilayer with their heads facing outwards and their hydrophobic tails facing inwards

This means the centre of the bilayer is hydrophobic, so it acts as a barrier to substances that dissolve in water

Question 16

According to the fluid mosaic model, how are proteins arranged in the membrane surrounding a mitochondrion

Answer 16

Proteins are scattered through the phospholipid bilayer like tiles in a mosaic

Some proteins are able to move sideways through the bilayer

Question 17

Give one way the absorbance could have been measured

Answer 17

A colorimeter could have been used to pass light through the liquid and measure how much of that light was absorbed

Question 18

Give a conclusion that can be drawn from the results

Answer 18

As pH increases, absorbance decreases

This means that less pigment was released by the beetroot as the pH increased, so the beetroot cell membranes were less permeable at a higher pH

Question 19

The biconcave shape and resulting large surface area of the RBC allows a high rate of O2 diffusion across the cell-surface membrane

People with high blood cholesterol tend to have a high concentration of cholesterol in their RBC membranes

Suggest how this may affect O2 transport

Answer 19

High concentration of cholesterol will increase the rigidity of the RBC membranes

This may affect the biconcave shape of the cells and subsequently decrease their surface area

A decreased surface area would reduce the rate of diffusion of O2 across the RBC membrane and therefore, reduce O2 transport