Cell Structure

Question 1

Eukaryotic (eg human) cells compared with
Prokaryotic (bacterium) (7)

Answer 1

1. Bacterial cell is much smaller than a human cell; (or human cell is much larger than a bacterial cell)
2. Bacterial cell has a cell wall but human cell does not;
3. Bacterial cell lacks a nucleus but human cell has a nucleus;
4. Bacterial cell lacks membrane-bound organelles but human cell has membrane-bound organelles;
5. Bacterial ribosomes smaller than human ribosomes / bacteria have 70S ribosomes whereas humans have 80S
6. Bacterial DNA is circular but human DNA is linear
7. Bacterial DNA is ‘naked’ whereas human DNA is bound to histones/proteins

Question 2

Eukaryotic - Describe the structure and
function of the nucleus.(4)

Answer 2

Any four from Structure
Nuclear envelope/double membrane
(Nuclear) pores (in the membrane)
Chromosomes/chromatin/(linear) DNA with histones
Nucleolus/nucleoli
Function
Holds/stores genetic information for production of proteins
DNA replication OR interphase
Production of mRNA/tRNA OR transcription
Production of rRNA/ribosomes;;;;

Question 3

Eukaryotic - Name the main polymer that
forms the following cell walls – plants
cells & fungal cells (1)

Answer 3

Cellulose (plant) AND
chitin (fungi);

Question 4

Eukaryotic - Describe the role
of one named organelle in digesting
these bacteria. (3)

Answer 4

1. Lysosomes;
2. Fuse with vesicle;
   Accept phagosome for vesicle
3. (Releases) hydrolytic enzymes;

Question 5

Eukaryotic - Identify two organelles in
cells that enable the production of
glycoproteins (1)

Answer 5

Rough endoplasmic reticulum/ribosomes and Golgi (apparatus/vesicles);

Question 6

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

Answer 6

1. Cell(-surface) membrane;
2. Ribosomes;
   Ignore 70S
3. Cytoplasm;
4. DNA;

Question 7

Eukaryotic – Give one feature of the
chloroplast that allows protein to be synthesised inside the
chloroplast and describe one difference
between this feature in the chloroplast
and a eukaryotic cell. (2)

Answer 7

Mark in pairs, 1 and 2 OR 3 and 4
1. DNA;
2. Is not associated with protein/histones but nuclear DNA is
OR
Is circular but nuclear DNA is linear
OR
Is shorter than nuclear DNA;
3. Ribosomes;
4. Are smaller than cytoplasmic ribosomes;

Question 8

Eukaryotic - Eukaryotic cells produce
and release proteins.
Outline the role of organelles in the
production, transport and release of
proteins from eukaryotic cells.(4)

Answer 8

1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
   Accept rER for ‘rough endoplasmic reticulum’
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
   OR
   Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane;

Question 9

Eukaryotic – state three differences
between DNA in the nucleus of a plant
cell and DNA in a prokaryotic cell.(3)

Answer 9

Plant v prokaryote
1. (Associated with) histones/proteins v no histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids;
Do not credit if suggestion that prokaryotic DNA only exists as plasmids.
4. Introns v no introns;
5. Long(er) v short(er);

Question 10

Eukaryotic – Name the main biological
molecule in the cell membrane (1)

Answer 10

Phospholipids;

Question 11

Eukaryotic – Describe the role of
mitochondria in secreting a protein (1)

Answer 11

(Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport;

Question 12

Eukaryotic – Describe the role of golgi
apparatus in secreting a protein (1)

Answer 12

(Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;

Question 13

Eukaryotic – Descirbe the role of the
golgi apparatus in lipid absorption

Answer 13

1. Modifies / processes triglycerides;
2. Combines triglycerides with proteins;
3. Packaged for release / exocytosis
   OR
   Forms vesicles;

Question 14

Prokaryotic - Name the main biological
molecule in a bacterial cell wall (1)

Answer 14

Murein / glycoprotein;

Question 15

Prokaryotic - Give two features
of all prokaryotic cells that
are not features of eukaryotic cells.

Answer 15

Cytoplasm with no membrane-bound organelles
Single, Circular DNA
DNA free in the cytoplasm
DNA that is not associated with proteins/histones
A cell wall that contains murein

Question 16

Viruses – Give 2 features of all viruses (2)

Answer 16

1. attachments proteins
2. capsid
3. nucleic acid

Question 17

Microscopes - How to measure objects
using an eyepiece graticule (3)

Answer 17

1. Use eyepiece graticule to measure the object e.g. nucleus or capillary
2. Calibrate eyepiece graticule against stage micrometer
3. Take a number of measurements and calculate the mean

Question 18

Microscopes - Advantages and Limitations
of Transmission Electron Microscope (TEM)
(6

Answer 18

Advantages:
1. Small objects can be seen;
2. TEM has high resolution as wavelength of electrons shorter;
Limitations:
1. Cannot look at living cells as cells must be in a vacuum;
2. Must be thin specimen;
3. Preparation may create artefact;
4. Does not produce colour image;

Question 19

Microscopes - Comparison of TEM and
optical microscope (8)

Answer 19

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
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 20

Microscopes – Advantage of electron
microscope over optical microscope (2)

Answer 20

1. High resolution;
2. Can see internal structure of organelles

Question 21

Microscopes - The resolution of an
image obtained using an electron
microscope is higher than the
resolution of an image obtained using
an optical microscope.
Explain why. (2)

Answer 21

Shorter wavelength between electrons;
OR
Longer wavelength in light rays;

Question 22

Microscopes - Describe and
explain one difference between TEM
and SEM (2)

Answer 22

1. 3D image (with SEM), not 2D image
   OR
   Lower resolution (with SEM)
   OR
   (Only) surface visible with SEM, but internal structures visible with TEM;
2. (Because) electrons deflected/bounce off (using SEM)
   OR
   Electrons transmitted/pass through (using TEM);

Question 23

Homogenisation – Conditions required for
cell homogenisation (3)

Answer 23

1. Ice-cold – Slows/stops enzyme activity to prevent digestion of organelles/mitochondria;
2. Buffered – Maintains pH so that enzymes/proteins are not denatured;
3. Same water potential – Prevents osmosis so no lysis/shrinkage of organelles/mitochondria;

Question 24

Homogenisation & Ultracentrifugation –
How to separate mitochondria? (4)

Answer 24

1. Break open cells/homogenise/produce homogenate;
2. Remove unbroken cells/larger debris by filtration;
3. Centrifuge highest density organelle nuclei obtained as pellet at slowest speed
4. Mitochondria in 2nd pellet as less dense than nucleus/organelle in first pellet;

Question 25

Suggest why scientists can use
detergent to break open cells instead of
homogenisation (2)

Answer 25

1. Cell membranes made from phospholipid;
2. (Detergent) dissolves membranes / phospholipid (bilayer);