unit 2 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
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.bacteria have 70S ribosomes whereas humans have 80S
5. Bacterial DNA is circular but human DNA is linear
6. 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

1.double membrane (Nuclear) pores (in the membrane) 2.Chromosomes/chromatin/(linear) DNA with histones Nucleolus/nucleoli Function Holds/
3.stores genetic information for production of proteins DNA replication OR interphase
4.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 chloroplast and

describe one difference between this

feature in the chloroplast and a eukaryotic cell. (2)

Answer 7

1. DNA;
2. Is not associated with protein/histones but nuclear DNA 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);
2. Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus; Accept body for ‘apparatus’
3. Vesicles transport OR Rough endoplasmic reticulum transports;
4. (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

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

1. Cytoplasm with no membrane-bound organelles
2. Single, Circular DNA
3. DNA free in the cytoplasm
4. DNA that is not associated with proteins/histones
5. 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

Why are viruses classed as non living?

Answer 17

have no metabolism/metabolic reactions; OR Cannot (independently) move/respire/replicate/reproduce/excrete OR (Have) no nutrition;

Question 18

Why are viruses classes as acellular?

Answer 18

no cell(-surface) membrane OR Not made of cells; Or Has no cytoplasm/organelles

Question 19

Microscopes - How to measure objects

using an eyepiece graticule (3)

Answer 19

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 20

Microscopes - Advantages and Limitations

of Transmission Electron Microscope (TEM)

(6)

Answer 20

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 21

Microscopes - Comparison of TEM and

optical microscope (8)

Answer 21

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 22

Microscopes – Advantage of electron

microscope over optical microscope (2)

Answer 22

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

Question 23

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 23

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

Question 24

Microscopes - Describe and

explain one difference between TEM

and SEM (2)

Answer 24

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 25

Homogenisation – Conditions required for cell homogenisation (3)

Answer 25

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 26

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

Answer 26

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 27

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

Answer 27

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