Topic 1: The Cell Cycle

Unit 5: Cellular & Organismal Reproduction

Cell reproduction• How do cells reproduce?

• When does a cell reproduce?When a multicellular organism is growing or needs to replace dead or damaged cells (mitosis)

To make gametes for sexual reproduction in eukaryotes (meiosis)

When a single-celled organism reproduces asexually (mitosis or binary fission)

They divide into two cells!

First they copy all their parts (DNA, organelles, ribosomes)

Some Definitions• Parent Cell

• Daughter Cell

• Sexual Reproduction– Variation

• Asexual Reproduction

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4Figure 8.3A, p127

Asexual reproduction in bacteria (binary fission)

BinaryFission

Other forms of asexual reproduction• Budding

• Fragmentation

• Regeneration• Advantages:

– Don’t need to search for a mate

– Can reproduce if damaged

• Disadvantage:– No recombination

of genetic material

Chromatin

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Fun facts: number of chromosomes in a variety of organisms

Species # chromosomes

Humans 46

Kangaroo 12

Cat 38

Cow 60

Dog 78

Turkey 82

Algae 148

Shrimp 254Ophioglossum reticulatum (fern)

~1200! (highest known)

UNreplicated Chromosome

Replicated Chromosome

UNreplicated Chromosome

s

Sister Chromatids

10Figure 8.4, p128

Chromosome Anatomy

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Homologous chromosomes• Each chromosome has a homologue, or a chromosome that carries the same type of information as another chromosome

• The chromosomes may have different versions of the genes but the genes code for the same type of information

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Cell cycle

13Figure 8.5, p129

Mitosis inquiry

Cell cycle

15Figure 8.5, p129

The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase

16Figure 8.6, p130

The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.

17Figure 8.6, p131

Mitosis

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Mitosis in an onion root

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Cytokinesis in animal and plant cells

20Figure 8.7, p132

Cell turnover• The length of a cell cycle

depends on the type of cell and its function in the body.

• Some cells never divide after the first few months of life: brain, nerves

• Some cells never divide at all: red blood cells

• Some divide every 20 hours or so: cells of organ linings and skin cells

Chromosomes

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