3.2.1 Cell Structure

Question 1

Compare Eukaryotic (eg human) cells 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

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

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

Answer 3

Cellulose (plant) and
chitin (fungi);

Question 4

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

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

Answer 5

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

Question 6

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

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 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

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

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

Answer 10

Phospholipids;

Question 11

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

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

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

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

Answer 14

Murein / glycoprotein;

Question 15

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

Give 2 features of all viruses (2)

Answer 16

1. attachments proteins
2. capsid
3. nucleic acid

Question 17

Describe 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

Describe How to measure objects
using an eyepiece graticule (3)

Answer 18

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 19

Describe the Advantages and Limitations
of Transmission Electron Microscope (TEM)
(6)

Answer 19

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 20

Compare TEM and optical microscope (8)

Answer 20

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 21

Describe the Advantage of electron
microscope over optical microscope (2)

Answer 21

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

Question 22

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 22

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

Question 23

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

Answer 23

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 24

What are the Conditions required for
cell homogenisation (3)

Answer 24

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 25

Describe How to separate mitochondria (4)

Answer 25

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 26

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

Answer 26

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