2.2 All cells arise from other cells

Question 1

Cell theory states that all living things are made from cells, and all cells arise from other cells. What are the three ways cells arise from other cells?

Answer 1

All cells arise from other cells, by binary fission in prokaryotic cells and by mitosis and meiosis in eukaryotic cells.

Question 2

When does DNA replication occur?

Answer 2

DNA replication occurs during the interphase of the cell cycle, in a period called S phase.

Question 3

Mitosis is…

Answer 3

Mitosis is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication. Within multicellular organisms, not all cells retain the ability to divide.

Question 4

What happens in prophase?

Answer 4

Nuclear envelope breaks down, chromosomes shorten and supercoil (condensing tightly around histones), becoming visible (as two sister chromatids joined at the centromere) when viewed under optical microscope.

Question 5

What happens in metaphase?

Answer 5

Spindle forms and attaches to centromere

Chromosomes line up at equator of cell

Question 6

What happens in anaphase?

Answer 6

Centromere splits, chromatids separate and are pulled towards opposite poles / centrioles of cell.

Question 7

What happens in telophase?

Answer 7

Chromosomes uncoil / unwind / become longer / thinner.
Nuclear envelope forms around each group of chromosomes at each pole.

Question 8

After telophase, the cytoplasm divides. What is this called?

Answer 8

Cytokinesis

Question 9

Describe binary fission in bacteria.

Answer 9

1. Replication of circular DNA molecule;
   Reject chromosome
   Reject mitosis
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);

Question 10

Describe viral replication.

Answer 10

1. Attachment proteins attach to receptors;

For ‘attachment protein’ accept glycoprotein but ignore ‘receptor protein’ (as this is on the virus)

2. (Viral) nucleic acid enters cell;
3. Nucleic acid replicated in cell
4. Cell produces viral proteins (eg capsid/enzymes);
5. Virus assembled and released from cell;

Accept lysis OR burst OR bud off OR emerge for released

Question 11

Mitosis is a controlled process. What happens if it becomes uncontrolled?

Answer 11

Uncontrolled cell division can lead to the formation of tumours and of cancers.
Many cancer treatments are directed at controlling the rate of cell division.