Studying Cells

Question 1

What is the function of a Ribsosome?

Answer 1

Site of Protein synthesis;

(Translation)

Question 2

Describe the structure and function of the nucleus. [6]

Answer 2

Structure

1. Nuclear envelope and pores OR Double membrane and pores;
2. Chromosomes/chromatin OR DNA with histones;
3. Nucleolus/nucleoli;

Function
1. (Holds/stores) genetic information/material for polypeptides (production) OR (Is) code for polypeptides;
2. DNA replication (occurs);
3. Production of mRNA/tRNA OR Transcription (occurs);
4. Production of rRNA/ribosomes;

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

1. Encrusted in Ribosomes;
2. Site of protein synthesis;
3. Transports and stores protein within the cell

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 HYDROLYTIC enzymes;
• Digests worn out organelles/autolysis/apoptosis;

Question 8

What is the function of Cell surface membrane?

Answer 8

1. Made of a Phospholipid Bilayer;
2. Controls what enters the cell/ is selectively/partially permeable;
3. Can be folded to increase Surface Area;

Question 9

What is the function of Chloroplasts?

Answer 9

Contain thylakoids, stacked into Granum;

Site of photosynthesis;

Question 10

Prokaryote

What is the function of a Capsule?

Answer 10

Protects cell from immune systems;

Aids bacteria sticking together;

Question 11

What is the function of a Plasmid?

Answer 11

Circular DNA;

Contains antibiotic resistance genes;

Question 12

Eukaryotic cells produce and release proteins.

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. [6]

Answer 12

1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
3. Mitochondria produce ATP (for protein synthesis/ translation);
4. Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus;
5. Vesicles transport OR Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane

Question 13

Compare & Contrast between Eukaryotic and Prokaryotic cells [6]

Answer 13

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 14

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

Answer 14

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 15

Name two structures found in all bacteria that are not found in plant cells.

Answer 15

• Circular DNA (molecule in cytoplasm);
• Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
• Small(er)/70S ribosomes (in cytoplasm);

Question 16

Give one advantage of using a TEM rather than a SEM

Answer 16

Higher resolution;
higher (maximum) magnification / higher detail (of image);
OR

Allows internal details / structures within (cells) to be seen / cross section to be taken;

Question 17

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.

Answer 17

Electrons have shorter wavelengths

OR

Longer wavelength in light (rays);

Question 18

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

Answer 18

Thin sections do not need to be prepared
3-D images;

Question 19

Scientists use optical microscopes and transmission electron microscopes to investigate cell structure.

Explain the advantages and limitations of using a TEM to investigate cell structure. [6]

Answer 19

Advantages:

1 Small objects can be seen;

2 TEM has high resolution;

3 Electron wavelength is shorter;

Limitations:

4 Cannot look at living cells;

5 Must be in a vacuum;

6 Must cut section / thin specimen;

7 Preparation may create artefact;

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. [6]

Answer 21

1. Cell homogenisation to break open cells and release organelles;
2. Filter to remove (large) debris/whole cells;
3. Use isotonic solution to prevent osmotic damage to mitochondria / organelles;
4. Keep cold to prevent/reduce damage to organelles by enzyme;
5. Use buffer to maintain pH and prevent protein/enzyme denaturation;
6. Use differential Centrifuge (at high speed/1000 g) to separate nuclei / cell fragments / heavy organelles;
7. Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
8. Observe pellet with a microscope to identify mitochondria

Question 22

Bacteria are able to synthesis human proteins. Suggest why.

Answer 22

Mechanisms of Transcription and Translation are UNIVERSAL.