CELLS : MARK SCHEME ANSWERS

Question 1

Explain why it is not possible to determine the identity of the structures
labelled X using an optical microscope. (2)

Answer 1

1. Resolution (too) low;
2. Because wavelength of light is (too) long.

Question 2

U. marinum cells ingest bacteria and digest them in the cytoplasm.
Describe the role of one named organelle in digesting these bacteria (3)

Answer 2

1. Lysosomes;
2. Fuse with vesicle;
3. releases hydrolytic enzymes

Question 3

Give two structures found in all prokaryotic cells and in all eukaryotic cells.(2)

Answer 3

1. Cell(-surface) membrane;
2. Ribosomes;
3. Cytoplasm;
4. DNA

Question 4

Describe how a sample of chloroplasts could be isolated from leaves. (4)

Answer 4

1.Break open cells/tissue and filter
OR
Grind/blend cells/tissue/leaves and filter;
2. In cold, same water potential/concentration, pH controlled solution;
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out;

Question 5

Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of
proteins from eukaryotic cells.
Do not include details of transcription and translation in your answer (4)

Answer 5

1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;
   OR
   Carbohydrate added/glycoprotein produced by Golgi apparatus;
   Accept body for ‘apparatus’
5. Vesicles transport

Question 6

Suggest why a nucleus is not visible in above image. (1)

Answer 6

A section/slice (so nucleus in another part of cell)
OR
(Nucleus) not stained;
1

Question 7

Give one advantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope. (1)

Answer 7

Higher resolution
OR
View internal structures;

Question 8

Name an organelle found in both a chloroplast and a prokaryotic cell. (1)

Answer 8

(70S) Ribosome;
Reject: (80S) Ribosome
1

Question 9

A biologist separated cell components to investigate organelle activity. She
prepared a suspension of the organelles in a solution that prevented
damage to the organelles.
Describe three properties of this solution and explain how each property
prevented damage to the organelles. (3)

Answer 9

1. (Ice) cold to prevent/reduce enzyme activity;
   For 1, 2 and 3 reject context of cell
2. Buffered to prevent denaturing of enzyme/protein;
   Accept description of buffer.
   Accept: prevent change of tertiary structure.
3. Same water potential/ Ψ to prevent lysis/bursting (of organelle);
   Accept: isotonic for same water potential.

Question 10

Contrast how an optical microscope and a transmission electron
microscope work and contrast the limitations of their use when studying
cells. (6)

Answer 10

1. TEM use electrons and optical use light;
2. TEM allows a greater resolution;
3. (So with TEM) smaller organelles / named cell structure can be
   observed
   OR
   greater detail in organelles / named cell structure can be
   observed;
4. TEM view only dead / dehydrated specimens and optical (can)
   view live specimens;
5. TEM does not show colour and optical (can);
6. TEM requires thinner specimens;
7. TEM requires a more complex/time consuming preparation;
   8.TEM focuses using magnets and optical uses (glass) lenses;

Question 11

Name two structures present in plant cells that are not present in animal
cells. (1)

Answer 11

1. Chloroplasts / plastids
2. Cell wall
3. Cell vacuole
4. Starch grains / amyloplasts;
   Any 2 for 1 mark

Question 12

Explain why the biologist used a blender and then filtered the mixture
(steps 2 and 3).

Answer 12

1. Break open cells / homogenise / produce homogenate;
2. Remove unbroken cells / larger debris;

Question 13

The second centrifuge tube was spun at a higher speed to obtain the
sample of organelles labelled C (mitochodria) in the diagram (step 5).
Suggest why. (1)

Answer 13

• Mitochondria / organelle C less dense than nucleus / organelle in first pellet;

Question 14

DNA and RNA can be found in bacteria.
Give two ways in which the nucleotides in DNA are different from the
nucleotides in RNA (2)

Answer 14

1. DNA contains thymine and RNA contains uracil;
2. DNA contains deoxyribose and RNA contains ribose.

Question 15

No organelles are visible in the cytoplasm of this red blood cell.
Suggest why. (1)

Answer 15

Cytoplasm of red blood cell filled with haemoglobin.

Question 16

Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface
membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane
as two dark lines. (3)

Answer 16

1. Membrane has phospholipid bilayer;
2. Stain binds to phosphate / glycerol;
3. On inside and outside of membrane.
   Accept phospholipid head / protein

Question 17

Describe and explain two features you would expect to find in a cell specialised for
absorption.(2)

Answer 17

Any of the 2:
1. Folded membrane/microvilli so large surface area (for absorption);
2. Large number of cotransport/carrier/channel proteins so fast rate (of
absorption)
3. Large number of mitochondria so make (more) ATP (by respiration) ( for active transport)
4. Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);

Question 18

Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end.
You may use a diagram in your answer

Answer 18

1. One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond;
2. (So in chain) there is a free amine/NH2 group at one end and a free
   carboxyl/COOH group at the other
3. Each amino acid is orientated in the same direction in the chain.

Question 19

The student kept constant:
* the mass of fresh blueberries
* the volume of extraction solvent
* the time for the mixture to stand.
Name two other variables the student should have kept constant during this investigation. (2)
investigation = A student investigated how to extract anthocyanins from blueberries

Answer 19

1. Temperature;
2. Agitation/mixing/stirring;
3. Source/age/type of blueberries;
4. Crushing of the blueberries;
5. Rinsing of the blueberries prior to mixing;
6. Concentration of ethanol/acid

Question 20

A different student did this investigation. He did not have a colorimeter.
Describe a method this student could use to prepare colour standards and use them to give
data for the total anthocyanin extracted. (3)

Answer 20

1. Use known concentration of blueberry juice/extract OR of anthocyanin/pigment (solution) OR of (extraction) solvent to be added to blueberries;
2. Prepare dilution series;
3. Compare (results) with colour standards to give score/value/concentration;

Question 21

Give two similarities in the movement of substances by diffusion and by osmosis. (2)

Answer 21

1. (Movement) down a gradient / from high concentration to low concentration;
2. Passive / not active processes;

Question 22

Explain the advantages of lipid droplet and micelle formation (3)

Answer 22

1. Droplets increase surface areas (for lipase / enzyme action);
2. (So) faster hydrolysis / digestion (of triglycerides / lipids);
3. Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to (intestinal epithelial) cell;

Question 23

suggest how the Golgi apparatus is involved in the absorption of lipids (3)

Answer 23

1. Golgi (apparatus);
2. Modifies / processes triglycerides;
3. Combines triglycerides with proteins;
4. Packaged for release / exocytosis
   OR
   Forms vesicles

Question 24

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these
cells have membranes with a carrier protein called NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen
ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how NHE3 does this. (3)

Answer 24

1. Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;
4. Protein changes shape (to move sodium ion and / or proton across the
   membrane);

Question 25

High absorption of salt from the diet can result in a higher than normal concentration of salt
in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid.
Explain how. (2)

Answer 25

1. (Higher salt) results in lower water potential of tissue fluid;
2. (So) less water returns to capillary by osmosis (at venule end);
3. (Higher salt) results in higher blood pressure / volume;
4. (So) more fluid pushed / forced out (at arteriole end) of capillary

Question 26

Describe how an ATP molecule is formed from its component molecules.(4)

Answer 26

mention these points:
1.2.: Accept for 2 marks correct names of three components adenine, ribose/pentose,
three phosphates;
3. Condensation reaction
4. ATP synthase

Question 27

Name and describe five ways substances can move across the cell-surface membrane into a cell(5)

Answer 27

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier protein;

Question 28

The movement of substances across cell membranes is affected by
membrane structure. Describe how (5)

Answer 28

Any 5 of these points:
1. Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances;
2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances
3. Carrier proteins allow active transport;
4. Channel/carrier proteins allow facilitated diffusion/co-transport;
5. Shape/charge of channel / carrier determines which substances move;
6. Number of channels/carriers determines how much movement;
7. Membrane surface area determines how much diffusion/movement;
8. Cholesterol affects fluidity/rigidity/permeability;