2. Cells

Question 1

Nucleus

Answer 1

1. chromosomes
2. protein-bound, linear DNA
3. one or more nucleoli

Question 2

Lysosomes

Answer 2

Membrane-bound organelle that releases hydrolytic enzymes (‘biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules’)

Question 3

Differences between prokaryotic and eukaryotic cells.

Answer 3

1. X nucleus- single, circular DNA molecules free in cytoplasm, X associated w/ proteins
2. Smaller ribosomes
3. Lack membrane-bound organelles in cytoplasm
4. Cell wall made of murein (glycoprotein)

• one or more plasmids
• one or more flagella
• capsule

Question 4

Key features of viruses

Answer 4

• genetic material
• capsid
• attachment protein

Question 5

Outline 2 main advantages of an electron microscope.

Answer 5

1. High resolution ∵ e- short wavelength
2. e- beam can be focused w/ electromagnets ∵ -ve charged

Question 6

Why does a near-vacuum have to be created within the chamber of an electron microscope?

Answer 6

e- are absorbed/ deflected by air molecules
∴ prevents e- from reaching specimen

Question 7

Explain why the homogenate was filtered before spinning at low speed in the centrifuge. (2)

Answer 7

• Remove debris
• Which may contaminate pellet 1

Question 8

Outline the 2 types of centrifugation techniques.

Answer 8

1. Differential centrifugation
   ** nuclei > mitochondria > lysosomes > ER > ribosomes
   ————————————————————————
2. Density gradient centrifugation
   
   • supernatant pipetted into sucrose solution
   • density gradient ∵ diff. conc. of sucrose (most dilute= least dense)
   • centrifuged
   • organelles settle at a level in density gradient that matches w/ their own
   • hole at the bottom- organelles collected in separate tubes
     ** cell debris > nuclei > chloroplasts > mitochondria > ribosomes

Question 9

Mitotic index

Answer 9

No. of actively-dividing cells in field of view
______________________________________________
Total no. of cells in field of view

Question 10

Describe cytokinesis of animal cell

Answer 10

• microfilament ring in the middle of the cell
• cleavage of cell membrane
• cytoplasm divides

Question 11

Describe cytokinesis for plant cells

Answer 11

• cell plate forms across equator
• new cell wall is laid

Question 12

What is cancer?

Answer 12

• uncontrolled growth of cells –> formation of tumour
• ∵ damage/ mutation to genes that regulate mitosis + cell cycle

Question 13

Malignant tumours

Answer 13

1. grow rapidly
2. ↓ compact
3. spread –> secondary tumours

Question 14

3 main stages of cell cycle

Answer 14

1. interphase
2. nuclear division
3. cytokinesis

Question 15

Explain why chemotherapy drugs are not given more frequently/ higher dose.

Answer 15

Frequency:
- frequency ↑ healthy cells x time to ↑ no. to near normal again between treatments
- no. declines rapidly after a few treatments–> kills the patient

Dose:
- kill ↑ healthy cells each time
- no. declines rapidly

Question 16

Give two processes which occur during interphase and which are necessary for nuclear division to take place. (2)

Answer 16

• replication of DNA
• ATP production
• protein synthesis