Everything Life Sciences Grade 10

FACT

Human cells have
46 chromosomes.
(23 from the mother
and 23 from the
father).

of cytokinesis:

1. prophase


2. metaphase


3. anaphase


4. telophase


5. cytokinesis


6. Prophase

During prophase, thechromatinmaterial shortens and thickens into individual chromo-

somes which are visible under the light microscope. Each chromosome consist of two strands

orchromatidsjoined by acentromere(Figure 4.2 ).

Figure 4.2: Chromosome structure showing (1) Chromatid, (2) Centromere, (3) Short and (4) Long

arms of chromosome.

As prophase progresses, the nuclear membrane and nucleolus disintegrates. In animal cells

thecentriolesseparate and move to opposite poles. The centrioles give rise to the spindle

fibres which form between the poles. In plant cells there are no centrioles to move to the

poles, so spindle fibres form in the cytoplasm.

Schematic diagram: animal cell Micrograph: plant cell

100 4.2. The cell cycle