Chapter 3

Question 1

How do carry out ultracentrifugation for animal cells?

Answer 1

tube of filtrate placed in centrifuge and spun at low speed

• heaviest organelles (nuclei) forged to bottom of tube forming a pellet
• Fluid at top of tube (the supernatant) is removed leaving the pellet
• supernatant is transferred to another tube and spun faster than before
• process repeated with greater speed each time

Question 2

How do you work out magnification?

Answer 2

Size of image / size of real object

Question 3

Why cells were taken from the root tipped squashed to get images in a optical microscope of the cell cycle

Answer 3

Root tip- region where mitosis/cell division occurs

Squash - to allow light through

Question 4

Contrast the structure of a bacterial cell and the structure of a human cell

Answer 4

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. Bacterial ribosomes smaller than human ribosomes / bacteria have 70S ribosomes whereas humans have 80S ribosomes;
6. Bacterial DNA is circular but human DNA is linear;
7. Bacterial DNA is ‘naked’ whereas human DNA is bound to histones/proteins;