ALL CELLS ARISE FROM OTHER CELLS -The cell cycle

Question 1

state what cell cycle is and outline its stages?

Answer 1

cycle of division and intermediate growth period
1. interphase
2. mitosis or mieosis ( nuclear division)
3.cytokinesis ( division of the cytoplasm)

Question 2

Explain why the cell cycle may not occur in some cells?

Answer 2

After differentiation, some type of cells in multicellular organisms (eg neurons) no longer have the ability to divide.

Question 3

what happens during interphase?

Answer 3

G1: cell synthesises proteins for replication
S: DNA replicates = chromosomes consists of two sister chromatids joined at a centromere
G2: organelles divide

Question 4

State the purpose of mitosis

Answer 4

Produces 2 genetically identical daughter cells for:
- growth
- cell replacement
- asexual reproduction

Question 5

Name the stages of mitosis

Answer 5

Phrophase
Metaphase
Anaphase
Telophase

Question 6

What happens during prophase?

Answer 6

1. Chromosomes condense,becoming visible.
   ( X-shaped : 2 sister chromatids joined at the centromere)
2. Centrioles move to opposite poles of cell (animal cells) and mitotic spindle fibres form
3. Nuclear envelope and nucleolus break down = chromosomes free in cytoplasm

Question 7

What happens during metaphase?

Answer 7

Sister chromatids line up at all equator, attached to a spindle fibre by their centromeres.

Question 8

What happens during anaphase?

Answer 8

1. Spindle fibres contract = centromeres divide 2. Sister chromatids separate into 2 distinct chromosomes & are pulled to opposite poles of cell
2. Spindle fibres break down

Question 9

What happens during telophase?

Answer 9

1. Chromosomes decondense, becoming invisible again. (Becomes a chromatin)
2. New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosomes.

Question 10

What is cytokinesis?

Answer 10

When the cytoplasm divides to form 2 new daughter cells. The daughter cells are genetically identical.

Question 11

outline how to prepare a temporary mount of root tissue?

Answer 11

1. place root in HCl to stop division and hydrolyse the middle lamellae
2. stain the root tip with a dye that binds to chromosomes
3. macertate tissue in water using a mounted needle
4. press down coverslip and obtain single layer of cells. avoid trapping air bubbles

Question 12

name two dyes that bind to chromosomes?

Answer 12

toluidine blue
acetin orcein (red)

Question 13

why is only the root tip used when calculating a mitotic index?

Answer 13

meristematic cells at root tip are actively undergoing mitosis

Question 14

how do prokaryotic cells divide?

Answer 14

replication of the circular DNA and of plasmids.

division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.