SACE Stage 2 Biology - Cell division

BINARY FISSION: In step 1,

DNA is copied, producing two identical chromosomes which attaches to the cell membrane

BINARY FISSION: In step 2,

Chromosomes separate and move to opposite poles as the cell elongates

BINARY FISSION: In step 3,

Cross wall is formed, and the membrane invaginates, dividing cytoplasm in two
The cross wall completes

BINARY FISSION: In step 4,

The daughter cells separate and are now independent organisms

BINARY FISSION: How is the DNA repliacted?

1. DNA in a circular chromosome must be cut and untwisted to allow enzymes to access the two strands, done by enzymes

2. Each single strand then acts as a template, forming two new strands

3. Corresponding single strands reform to produce two chromosomes

MITOSIS: What happens in PHROPHASE? (P for prep)

1. Chromosomes are normally indistinct, but can be viewed when they condense.

2. A pair of protein complexes called centrioles move to opposite poles, producing microtubules. This occurs in animal cells ONLY, as centrioles aren't in plant cells.

3. Nuclear membrane of nucleus breaks down, releasing chromosomes into the cytoplasm that move to the equator

4. Spindle fibres attach to centromeres of the chromosomes.

MITOSIS: What happens in METAPHASE? (M for middle)

The replicated chromosomes are arranged along the equator of the parent cell by centromeres

MITOSIS: What happens in ANAPHASE? (A for away)

1. Centromeres are broken down

2. Sister chromatids are pulled apart by the contracting of the spindle fibres

3. Parent cell beings to elongate in preparation for cytokinesis

MITOSIS: What happens in TELOPHASE? (T for two)

1. Spindle fibres and centrioles disappear

2. Chromosomes decondense and are no longer visible

3. Nuclear membrane reforms around the chromosomes on each side

4. Two daughter nuclei formed

MITOSIS: What happens in CYTOKINESIS in ANIMALS?

1. Facilitated by proteins called actin and myosin, that assemble at the equator during anaphase

2. They form a contractile ring at the equator, which condenses, forming an indentation called a cleavage furrow

3. Deepens until the cell is separated

MITOSIS: What happens in CYTOKINESIS in PLANTS?

1. Vesicles containing molecules for the synthesis of plant cell wall and membrane are assembled along the equator

2. Vesicles fuse, forming a structure called the cell plate

3. Completes the cell wall and membrane of the dividing daughter cells