All cells arise from another

Answer 1

Within multicellular organisms, not all cells retain the ability to divide.

Question 2

Eukaryotic cells that do retain the ability to divide show a cell cycle.

Answer 2

DNA replication occurs during the interphase of the cell cycle.
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.

Answer 3

The behaviour of chromosomes during interphase, prophase, metaphase, anaphase and telophase of mitosis. The role of spindle fibres attached to centromeres in the separation of chromatids.

Answer 4

Division of the cytoplasm (cytokinesis) usually occurs, producing two new cells.

Question 5

cell cycle: interphase, prophase, metaphase, anaphase and telophase (including cytokinesis)

Answer 5

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

Question 6

explain the appearance of cells in each stage of mitosis.

Answer 7

Mitosis is a controlled process. 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.

Question 8

Binary fission in prokaryotic cells involves:

Answer 8

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.

Answer 9

Being non-living, viruses do not undergo cell division. Following injection of their nucleic acid, the infected host cell replicates the virus particles.

Answer 10

Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index.

Students should measure the apparent size of cells in the root tip and calculate their actual size using the formula:

Answer 11

(During prophase)
1. Chromosomes
coil / condense / shorten / thicken / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the
centromere;
(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles /
ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes
uncoil / unwind / become longer / thinner.
No marks for naming the stages
Reject references to homologous chromosomes /
pairing of chromosomes
Ignore references to spindle formation during
prophase
5

Question 12

organells in eukarytoc cells work together to secrete an extracellular protein

Answer 12

• protein synthesis = at ribosomes - translation occurs (joining amino ascids toghether with peptide bomda is a specofic orxer to produce a poluypeptide chain). folded and processed insoide the RER (folded intoi its teritary structure), then the rer will package that protein into a vesicle, then to the golgi apparatures (fuse with it and the protein is now contained = to modify proteins + package them into a vesucle - secreteroy vesicle the fuse with cell surface membrane then protein get secrreted outside of the cell - exocytosis)