Gas Exchange, Cell Membranes & Transport

Question 1

ficks law of diffusion

Answer 1

SA x Conc gradient / thickness of membrane

Question 2

role of lungs

Answer 2

maximise gas exchange while minimising the loss of water across the exchange surface

Question 3

what is trachea

Answer 3

tube that allows air to travel to the lungs
c-shaped rings of cartilage that ensure that the tube remains open

There is a layer of mucus covering the lining of the trachea that helps to trap dust and pathogens

Tiny hairs called cilia are also found on the lining of the airways, where they waft mucus towards the top of the trachea, removing any trapped particles and pathogens from the airways

Question 4

what is bronchi

Answer 4

Bronchi (singular bronchus) have a similar structure to the trachea but they have thinner walls and a smaller diameter

Question 5

bronchioles role

Answer 5

The larger bronchioles possess elastic fibres and smooth muscle that enable adjustment of the size of the airway to increase or decrease airflow

Question 6

How are lungs adapted to gas exchange

Answer 6

They have a large surface area due to the presence of many alveoli which increase the surface area

• Good supply of circulating blood to the lungs which carries carbon dioxide to the lungs and oxygen away from them ensures that the concentration gradient is steep - high concentration of oxygen and low concentration of carbon dioxide is maintained by mechanical ventilation
• They have a short diffusion distance as the alveoli are just one cell thick thus reducing the diffusion distance

Question 7

what do phospholipids consist of

Answer 7

A phosphate group
A molecule of glycerol
Two fatty acid tails, making up the lipid tail

Question 8

what part of phospholipid is polar and non polar

Answer 8

The phosphate head of a phospholipid is polar, meaning that it can interact with polar water molecules; the head is therefore described as being hydrophilic

The lipid tail is non-polar, meaning that it cannot interact with polar molecules; the tail is therefore described as hydrophobic

Question 9

what happens if phospholipids are spread over surface of water

Answer 9

form a single layer with the hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking up away from the water. This is called a phospholipid monolayer or phospholipid bilayer.

Question 10

where is cholesterol found

Answer 10

between the phospholipids, where it regulates membrane fluidity. Cholesterol increases the fluidity of the membrane at low temperatures, stopping it from becoming too rigid. stops the phospholipid tails packing too closely together

Question 11

what does interaction between cholesterol and phospholipid tails allow

Answer 11

stabilises the cell membrane at higher temperatures by stopping the membrane from becoming too fluid

Question 12

what does cholesterol increase in membranes

Answer 12

Cholesterol increases the mechanical strength and stability of membranes

Question 13

where are glycoproteins and glycolipids found

Answer 13

are present on the surface of the cell, where they aid cell-to-cell communication

some act like cell markers or antigens

Question 14

can mosaic of phospholipids and proteins move

Answer 14

they can move around within bilayer by diffusion

Question 15

what does it mean if the membrane is partially permeable

Answer 15

Small, non-polar molecules can pass through the gaps between the phospholipids

Large, polar molecules must pass through specialised membrane proteins called channel proteins and carrier proteins

Question 16

break down fluid mosaic model

Answer 16

The mosaic of phospholipids and proteins can move around within the bilayer by diffusion, hence the mosaic is said to be ‘fluid’

scattered pattern produced by the components within the phospholipid bilayer looks somewhat like a mosaic

Note that the fluid mosaic model is one model of membrane structure; other models have been considered and rejected

Question 17

what is the permeability of cell membrane affected by

Answer 17

Temperature
pH

Question 18

how can the factors temperature and PH on the permeability of cell membranes be investigated

Answer 18

Beetroot cells contain a dark purple-red pigment
The higher the permeability of the beetroot cell membrane, the more of this pigment leaks out of the cell

Question 19

what does a colorimeter do

Answer 19

amount of pigment in a sample can be measured using a piece of equipment known as a colorimeter

passes light through a coloured liquid sample and measures how much of that light is absorbed by or transmitted through the sample
less transmission both indicate a darker coloured solution

Question 20

how do you calibrate colorimeter

Answer 20

The colorimeter must be zeroed before each colorimeter is used; this can be done using distilled water in a small container called a cuvette
This process is known as calibrating the colorimeter

Question 21

Investigating the effect of temperature on membrane permeability

Answer 21

Using a cork borer and scalpel, cut five equal-sized sections of beetroot

Rinse the beetroot pieces

Add the beetroot pieces to five different test tubes, each containing the same volume of water, e.g. 5 cm3

Put each test tube in a water bath at a different temperature, e.g. 10 ℃, 20 ℃, 30 ℃, 40 ℃, and 50 ℃, for the same length of time
The time should be long enough to allow the pigment to diffuse into the water

Remove the beetroot pieces, leaving just the coloured liquid in the five test tubes
Use pipettes to transfer samples of the coloured liquid to colorimeter cuvettes

Use a colorimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid

The higher the absorbance, the more pigment must have been released due to a greater membrane permeability

Question 22

what should you look out for when investigating the effect of temperature on membrane permeability

Answer 22

The pieces must have the same dimensions so that they all have equal surface areas and volumes, as these factors could affect the rate at which the pigment leaks out

rinsing allows to remove any pigment released during cutting

The time should be long enough to allow the pigment to diffuse into the water, e.g. around 30 minutes

A different pipette should be used for each sample to avoid the transfer of pigment molecules between samples

Question 23

results of the effect of temperature on membrane permeability

Answer 23

as temperature increases, membrane permeability also increases

the phospholipids within the cell membrane move more because they have more kinetic energy; increased movement means the phospholipids are not as tightly packed together, increasing the permeability of the membrane. membrane proteins denature, increasing the permeability of the membrane

The volume of water inside the cells expands, putting pressure on the membrane and damaging membrane components; this can increase membrane permeability

Question 24

what type of molecules can move by simple diffusion

Answer 24

small and non-polar

Small molecules can fit between the phospholipids

Non-polar molecules are able to interact with the non-polar tails of the phospholipids

Question 25

what type of molecules cant diffuse

Answer 25

Large, polar molecules / water soluble such as glucose and amino acids
Ions

Question 26

what are the two types of facilitated diffusion

Answer 26

Channel proteins
Carrier proteins

Question 27

how do channel proteins work

Answer 27

pores that extend through the membrane from one side to another
allow charged substances to diffuse through the cell membrane they can open and close to control exchange of ions

Question 28

how are carrier proteins different to channel proteins

Answer 28

Unlike channel proteins which have a fixed shape, carrier proteins can switch between two shapes

Question 29

define active transport

Answer 29

movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration requires energy in the form of ATP from respiration

Question 30

what does active transport require

Answer 30

carrier proteins
Each carrier protein is specific to a particular type of molecule or ion
Energy is required to allow the carrier protein to change shape; this transfers the molecules or ions across the cell membrane
The energy required is provided by ATP

Question 31

explain endocytosis

Answer 31

a cell can surround a substance with a section of the cell surface membrane

The membrane engulfs the substance and pinches off inside the cell to form a temporary vacuole with the ingested substance contained inside

Endocytosis is an active process and requires a source of energy

Question 32

explain exocytosis

Answer 32

Some substances produced by the cell need to be secreted

Vesicles containing the substance pinch off from sacs of the Golgi apparatus
These vesicles are moved toward the cell surface and fuse with the cell surface membrane to be released outside the cell
Exocytosis is an active process and requires a source of energy

Question 33

define osmosis

Answer 33

net movement of water molecules from a region of lower solute concentration to a region of higher solute concentration through a partially permeable membrane

Question 34

what happens when cells are placed in pure water

Answer 34

water moves into the cells by osmosis and the cells swell
In animal cells this could lead to cell bursting
In plant cells the cell wall prevents bursting

Question 35

what happens when cells are placed into a solution that has smaller number of free water molecules

Answer 35

water moves out of the cells by osmosis and the cells shrink
In animal cells the entire cell shrivels
In plant cells the vacuole and cytoplasm shrink but the cell wall maintains the overall shape of the cell

Question 36

similarities between active transport and diffusion

Answer 36

both move molecules through the {phospholipid bilayer / cell surface membrane} (1)
* (in both) molecules can move through proteins (1)

Question 37

compare and contrast exocytosis and endocytosis

Answer 37

Similarities
both processes involve vesicles
(1)
both processes involve energy from ATP
(1)
Differences
exocytosis involves {molecules / substances} leaving the cell whereas endocytosis involves {molecules / substances} entering the cell
(1)
exocytosis involves vesicles fusing with cell surface membrane whereas endocytosis involves the formation of vesicles (from the cell surface membrane)

Question 38

how does glucose use carrier proteins to move into cells by facilitated diffusion

Answer 38

carrier protein (in cell surface membrane)
(glucose moves from) high to low concentration
glucose binds to (carrier) protein / (carrier) protein changes shape to move glucose (across the membrane)

Question 39

function of glycoproteins on cell surface membrane

Answer 39

cell signalling or cell recognition

Question 40

describe the three dimensional structure of a glycoprotein

split up protein and carbohydrate

Answer 40

proteins consist of amino acids joined together by peptide bonds;

credit reference to named bonds (between R groups) involved in holding {3D structure / eq} ;

carbohydrates consist of {monsaccharides / glucoses / eg};

reference to glycosidic {bonds / eq} between (adjacent)
{glucose / eq} molecules;

Question 41

describe thee structure of a cell membrane

Answer 41

reference to phospholipid bilayer;
2. correct orientation and structure of the phospholipids in the bilayer;
3. explanation of why the phospholipids are orientated the way they are e.g. heads attracted to water OR tails repelled by water;
4. proteins in the membrane (described / shown) ;
5. idea of two different locations of proteins e.g. extrinsic, intrinsic, transmembrane;
6. glycoproteins / glycolipids (described / shown) ;
7. idea of cholesterol within the membrane (described / shown);

Question 42

one similarity and one difference between facilitated diffusion and active transport

Answer 42

Similarity any one from:

1. use {ca ier / channel} proteins
   OR
2. transport {hydrophilic / eq} molecules / named molecule;
   Difference any one from:
3. dea that active transport requires {energy / ATP} / facilitated
   diffusion does not require {energy / ATP}

Question 43

difference between cellulose and starch

Answer 43

alpha glucose in starch and beta glucose in cellulose;
2. only {starch / amylopectin} can be branched / cellulose only a linear molecule;
3. starch contains two types of molecule, cellulose only one;
4. alternate monomers rotated through 180° in cellulose only;
5. only {amylopectin / starch} can have 1-6 glycosidic bonds / cellulose has 1-4 glycosidic bonds only;

Question 44

explain how rapid gaseous exchange take place in a mammal

Answer 44

1. idea that large surface area provided by alveoli;
2. idea that large surface area provided by capillary network;
3. idea that concentration gradient maintained by {ventilation of / air flow in / eq } the lungs;
4. idea that concentration gradient maintained by {circulation / mass flow / eq } of blood ;
5. idea that diffusion pathway is small because alveoli have a thin wall;
6. idea that diffusion pathway is small because capillaries { have a thin wall / are in contact with alveoli / are only one cell thick / eg } ;
7. idea that air is warmed because lungs are in core of body;
8. warmer air enables faster {movement / diffusion / eq } of gases / eq;
9. reference to { respiratory pigment / haemoglobin / red blood cells / eq } to carry oxygen;

Question 45

explain why people with cystic fibrosis have breathing difficulties

4MARKER

Answer 45

produces {thicker / stickier / more viscous / eq} mucus;

2. blocking { trachea / bronchi / bronchioles / airway / eq} / eq;
3. cilia are unable to move mucus out of lungs / eq;
4. idea of reduced flow of {air / oxygen } to alveoli;
5. idea of reduced concentration gradient for {oxygen / carbon dioxide} (in alveoli) ;
6. idea of loss of surface area / elasticity / eq;
7. idea of reduced gaseous exchange;
8. trapped bacteria may result in more respiratory infections

Question 46

Describe the function of carrier proteins in a cell surface membrane

Answer 46

involved in facilitated diffusion (1)

movement of { large molecules / polar molecules / ions } (1)

(facilitated diffusion) from a high concentration to a low concentration
(1)

involved in active transport (1)
needs ATP to move molecules against concentration gradient