3.2 Cells:

Question 1

Uronema marinum is a single-celled eukaryotic organism. The diagram below is
a photograph of U. marinum taken through an optical microscope.

Explain why it is not possible to determine the identity of the structures
labelled X using an optical microscope. (2)

Answer 1

Optical microscopes produce (too) long wavelengths of lightwhich would result in (too) low resolution.

Question 2

U. marinum cells ingest bacteria and digest them in the cytoplasm.
Describe the role of one named organelle in digesting these bacteria. (3)

Answer 2

Lysosomes
Fuse with the vesicle (or phagosome)
Releasing hydrolytic enzymes called lysozymes

Question 3

What is the conversion of cm to millimeters to micrometers to nanometers?

(my own question relevant to a magnification question)

Answer 3

cm , mm , micrometers , nm
x10 , x1000, x1000, x1000
⟶

Question 4

All prokaryotic cells contain a circular DNA molecule and some prokaryotic cells
contain plasmids.

Scientists have found that the rate of plasmid replication is faster in cells
growing in a culture with a high concentration of amino acids than in a
culture with a lower concentration of amino acids.

Suggest one explanation for the faster rate of plasmid replication in cells growing in a culture with a high amino acid concentration. (2)

Answer 4

Amino acids are used in protein sythesis
A high conc. of amino acids would result in more protein sythesis occuring.
This means more enzymes for plasmid replication.

Question 5

What can you conclude from the figure above about a structural difference between the plasmids and the circular DNA? Explain your answer. (2)

Answer 5

The circular DNA molecules is heavier than the plasmids. This is because the band for the circular DNA molecules is moved further to the bottom of the tube once antibiotic X is added.

Question 6

Describe how a sample of chloroplasts could be isolated from leaves. (4)

Answer 6

Grind the leaves and filter
In a cold, same water potential and pH controlled solution
Centrifuge the sample and remove the cell debris
Centrifuge at a higher speed until the chloroplast settles out.

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 similar features in the rest of the cell. (2)

Answer 7

One feature: ribosomes
Structural difference: the ribosomes inside the chloroplast are smaller than the cytoplasmic ribosomes.

Another feature and difference:
F = DNA
D = Is not associated with proteins / histones but nuclear DNA is.

Question 8

Mass of protein / percentage of control 40
Mass of chlorophyll /percentage of control 10
The ratio of protein to chlorophyll in control plants is 9:1

Use the information in the table above to calculate the ratio of protein to chlorophyll in iron-deficient plants. (1)

Answer 8

control = P : Chloro
9:1
= 10
Iron defficient:
40/10 = 4
10/10 = 1
9 x 4 = 36
1 x 1 = 1

36 : 1

Question 9

The figure below shows transmission electron micrographs of two cells, one
animal cell and one prokaryotic cell.
Cell A = x 30000
Cell B = x 60000
Contrast the structure of the two cells visible in the electron micrographs
shown in the figure above. (5)

Answer 9

Magnification figures show that cell A is bigger than cell B.

A has a nucleus whereas B has free DNA.

A has no cell wall whereas B has a murein cell wall.

A has larger ribosomes than B.

A has no capsule whereas B has a capsule.

Question 10

IMMUNITY EXAM QUESTIONS

Explain the process of phagocytosis (non-specific)?

Acronym PPPLLL

Answer 10

1. Pathogen releases chemicals and this attracts the phagocyte
2. Phagocyte binds to pathogen by receptors on CSM
3. Phagocyte engulfs the pathogen which forms a phagosome vesicles
4. Lysosomes moves towards vesicle and fuse with it
5. Lysosomes contain hydrolytic enzymes= lysozymes which are released into phagosome
6. Lysosomes destroy bacteria by hydrolysis of cell wall

Question 11

How does the immune response lead to the production of antibodies?

Answer 11

• phagocytes stimulate t cells
• t cells form helper t cells
• t helper cells stimulate b cells
• b cells form plasma cells
• plasma cells form antibodies

Question 12

How do memory cells work (B/T)?

Answer 12

• made during specific immune response after a new infection by the pathogen (primary infection)
• B and T memory cells remain in blood
• if a person is reinfected by the same pathogen (secondary infection

Question 13

IMMUNITY EXAM QUESTIONS

Each type of labelled antibody binds specifically to one of the proteins. Explain why. (3 marks)

Answer 13

1. Each protein has a different tetiary structure.
2. Each antibody has a specific antigen binding site.
3. So each protein can only bind to its complementary protein.

Question 14

IMMUNITY EXAM QUESTIONS

Scientists use this antibody to detect an antigen on the bacterium that causes stomach ulcers. Explain why the antibody will only detect this antigen. (3 marks)

Answer 14

1. The antibody has a specfic amino acid sequence.
2. The shape of the binding site is complementary to these antigens
3. Forms an antigen-antibody complex.

Question 15

IMMUNITY EXAM QUESTIONS

Give two structures a bacterial cell may have that a white blood cell does not have. (2 marks)

Answer 15

1. Cell wall
2. Plasmid
3. Capsule
4. Flagellum