CELLS AND MICROORGANISMSSTAGE 1 BIOLOGY

1.3 CELL DIVISION

Cells divide for a number of reasons:

1. To asexually reproduce(binary fission – prokaryotes)

2. To grow and repair tissues(mitosis – eukaryotes)

3. To form gametes (eggs and sperm) for sexual reproduction(meiosis – eukaryotes)

Cell Division

For bacteria (prokaryotes), cell division is a simple process.

Binary Fission Steps:

1. Single, circular chromosome replicates and fixes to themembrane

2. The membrane expands and grows apart

3. A new membrane forms between the two rings of DNA

4. Cells separate into two identical daughter cells, each with theirown circular chromosome

Binary Fission

Binary Fission

Binary Fission

Binary Fission

Binary Fission

Binary Fission

Describe Binary Fission in your own words. Include a diagram in your explanation.

Activity

INTENDED STUDENT LEARNING

Describe and represent binary fission in prokaryotic cells.

In eukaryotes, cell division occurs by mitosis.

Mitosis produces two identical daughter cells that are diploid(they each have two copies of each chromosomes 2n).

Mitosis is used for growth and repair (eg: new skin, bloodcells, stomach lining).

After fertilisation, the zygote grows into a ball of identical cellsby mitosis.

Mitosis

Mitosis

Mitosis Steps:

1. Interphase: Cell grows and chromosomes replicate

2. Prophase: Duplicated chromosomes condense

3. Metaphase: Chromosome pairs align in the centre of the cell(metaphase plate)

4. Anaphase: Spindle fibres pull chromosomes to opposite ends ofthe cell

5. Telophase: Cell pinches in the middle (cleavage furrow)

6. Cytokinesis: Cells separate, forming two identical daughter cells

Mitosis

Mitosis

Mitosis

Prophase

Animal Plant

Chromatin condenses, chromosomes visible, nuclear membrane breaks down, spindle forms, nucleoli disappear

Metaphase

Animal Plant

Replicated chromosomes align at the equator with sister chromatids facing opposite poles. They attach to the spindle at the centromere.

Anaphase

Animal Plant

Centromeres divide and sister chromatids separate.

Telophase and Cytokinesis

Animal Plant

Nuclear envelopes start to form around each new set of chromosome.Animals: The cell pinches in to separate the cytoplasm.

Plants: Cell wall forms between the two new cells.

Mitosis

Mitosis

Mitosis

Describe Mitosis in your own words. Include a diagram in your explanation.

Activity

INTENDED STUDENT LEARNING

Describe and represent mitosis.

Binary Fission vs Mitosis

Binary Fission MitosisProkaryotes Eukaryotes

No spindle formation Spindle formation

Chromosome attaches to membrane Chromosomes align at metaphase plate

Used for reproduction Used for growth and repair

INTENDED STUDENT LEARNING

Compare binary fission in prokaryotic cells with mitotic cell division in eukaryotic cells.

Homework

Independent content revision

Workbook questions

Being the gentlemen he was, Brian insisted on payingin restaurants even though he suddenly realised thatdating a bacterium was going to be more expensivethan he first thought.

Describe and represent binary fission in prokaryotic cells.

Describe and represent mitosis.

Compare binary fission in prokaryotic cells with mitotic celldivision in eukaryotic cells.

Knowledge Check