Mitosis

Question 1

Suggest and explain how two environmental variables could be changed
to increase the growth rate of these cells.

Answer 1

-Increased (concentration of) glucose; Increased respiration;
-Increased (concentration of) oxygen; Increased respiration;
- Increased temperature;
Increased enzyme activity;
-Increased (concentration of) phosphate;Increased ATP/DNA/RNA.

Question 2

Name the fixed position occupied by a gene on a DNA molecule.

Answer 2

Loci

Question 3

Describe the role of the spindle fibres and the behaviour of the chromosomes during each of these phases.

Answer 3

1-In prophase, chromosomes condense;
3. In prophase OR metaphase, centromeres attach to spindle fibres;
4. In metaphase, chromosomes of are at the centre of cell
5. (In) anaphase, centromeres divide
6. (In) anaphase, chromatids (from each pair) pulled to (opposite) poles of cell)
7. (In) prophase/anaphase, spindle fibres shorten.

Question 4

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

Answer 4

1-Examine large number of fields of view / many cells
2. To ensure representative sample
3. Repeat count
4. To ensure figures are correct

Question 5

Give two pieces of evidence from Figure 1 that this cell was undergoing mitosis. Explain your answer.

Answer 5

1-The (individual) chromosomes are visible because they have condensed
2-Each chromosome is made up of two chromatids because DNA has replicated
3-The chromosomes are not arranged in homologous pairs, which then they would be if it was meiosis.

Question 6

A scientist treated growing tips of onion roots with a chemical that stops roots growing. After 24 hours, he prepared a stained squash of these root tips.

Use all of this information to suggest how the chemical stops the growth of roots.

Answer 6

(By) stopping spindle fibres forming and attaching
Stops anaphase cell division prevents telophase,cytokinesis
3. Preventing separation of (sister) chromatids
4. So no new cells added (to root tip)

Question 7

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm.
So how does this procedure makes chromosomes more visible (move them apart)

Answer 7

-Cell/cytoplasm gets bigger
Water moves into the cells/cytoplasm by osmosis
-cell/cytoplasm has greater volume/swells/expands.