CELLS

Question 1

What is the function of the Ribsosomes

Answer 1

Site of Protein synthesis;

Question 2

What is the function of the Nucleus

Answer 2

Contains genetic material / DNA;
Controls cell activity;

Question 3

What is the function of the Mitochondria

Answer 3

Site of aerobic respiration;
ATP production;

Question 4

What is the function of the Smooth Endoplasmic Reticulum

Answer 4

Site of lipid synthesis;

Question 5

What is the function of the Rough Endoplasmic reticulum

Answer 5

Encrusted in Ribosomes;
Site of protein synthesis;
Transports and stores protein

Question 6

What is the function of Golgi Apparatus

Answer 6

Modifies/packages/sorts proteins;
Produces vesicles;

Question 7

What is the function of Lysosomes

Answer 7

Contains digestive enzymes;
Digests worn out organelles/autolysis;

Question 8

What is the function of Cell surface membrane

Answer 8

Made of a Phospholipid Bi-layer;
Controls what enters the cell/ is selectively permeable;
Can be folded to increase SA;

Question 9

What is the function of Chloroplasts

Answer 9

Contain thylakoids, stacked into Granum;
Site of photosynthesis;

Question 10

What is the function of Capsule

Answer 10

Protects cell from immune systems;
Aids bacteria sticking together;

Question 11

What is the function of Plasmid

Answer 11

Circular DNA;
Contains antibiotic resistance genes

Question 12

What is the function of Cell Wall

Answer 12

Provides rigid shape / structure;
Stops osmotic lysis;

Question 13

What is the function of Flagellum

Answer 13

Allows movement/propulsion;

Question 14

Compare and contrast Eukaryeotic and Prokaryotic cells

Answer 14

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

Question 15

State four differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

Answer 15

Plant v prokaryote
1. (Associated with) histones/proteins v no histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids;
4. Introns v no introns;
5. Long(er) v short(er);

Question 16

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is different

Answer 16

1. Cholera bacterium is prokaryote;
2. Does not have a nucleus/nuclear envelope/ has DNA free in cytoplasm/has loop of DNA;

3 and 4 Any two from: [No membrane-bound organelles/no mitochondria / no golgi/no endoplasmic reticulum];
5 Small ribosomes only;
6 and 7 Any two from [Capsule/flagellum/plasmid / cell wall]

Question 17

Give one advantage of using a TEM rather than a SEM

Answer 17

1. Higher resolution;
2. higher (maximum) magnification / higher detail (of image);
   OR
3. Allows internal details / structures within (cells) to be seen / cross section to be taken;

Question 18

Give one advantage of using a SEM rather than a TEM.

Answer 18

Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

Question 19

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure.

Answer 19

Principles:
1. Electrons pass through / enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present;
8. Complex staining method / complex / long preparation time;
9. Image not in 3D / only 2D images produced

Question 20

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:
a) Isotonic
b) Ice cold
c) buffered

Answer 20

a) Prevents osmosis / no (net) movement of water So organelle/named organelle does not burst/shrivel;
b) Reduce/prevent enzyme activity so organelles are not digested / damaged;
c) Maintain a constant pH so proteins do not denature;

Question 21

Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells.

Answer 21

1. Cell homogenisation to break open cells and release organelles;
2. Filter to remove (large) debris/whole cells using gauze
3. Use isotonic solution to prevent osmotic damage to organelles;
4. Keep cold to prevent damage to organelles by enzyme;
5. Use buffer to maintain pH and prevent enzyme denaturation;
6. Use high speed to separate heavy organelles;
7. Re-spin (supernatant after pellet removed) at highER speed to get mitochondria in pellet/at bottom;
8. Observe pellet with a microscope to identify mitochondria;

Question 22

Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).

Answer 22

1. Glycerol joined to two fatty acid tails Phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond).;
2. Phospholipid has hydrophilic head (phosphate and glycerol) and hydrophobic tails (fatty acid chains)
3. Arrange to form a phospholipid bilayer; (Hydrophilic head facing out. Hydrophobic fatty acid chains facing in)

Question 23

The structure of the organelles visible in the photograph could not have been seen using an optical(light) microscope. Explain why.

Answer 23

1.Has low resolution

2. (Because) wavelength of light not short enough / too long;

Accept larger wavelength

Question 24

Cells constantly hydrolyse ATP to provide energy.

(a) Describe how ATP is resynthesised in cells.

Answer 24

From ADP and phosphate;
2. By ATP synthase;
3. During respiration/photosynthesis;

Question 25

Give two ways in which the hydrolysis of ATP is used in cells.

Answer 25

To provide energy for other reactions/named process; (ion transport, muscle contraction,dna replication)
Reject ‘produce’ energy
2. To add phosphate to other substances and make them more reactive/change their shape;

Question 26

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. (5)

Answer 26

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;
5. Vesicles transport
Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane;

Question 27

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope.

Answer 27

1.Add drop of water to (glass) slide;
2. Obtain thin section (of plant tissue) float on drop of water;
3. Stain with iodine in potassium iodide.
3. Allow any appropriate method that avoids trapping air bubbles
4. Lower cover slip using mounted needle.

Question 28

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells.

Answer 28

1. Cell homogenisation to break open cells;
2. Filter to remove (large) debris / whole cells;
3. Use isotonic solution to prevent damage to mitochondria / organelles;
4. Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation;
5. Centrifuge (at HIGH speed to separate/ cell fragments / heavy organelles;
6. Re-spin (supernatant / after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom

Question 29

Actual width of plant is 3.4 cm using a ruler.
Calc width in micro metres

Answer 29

1. Convert cm into mm then into micrometers
   3.4x10
   X1000
   34000