5.4 Asexual Reproduction Roles of cell reproduction Replacement or repair of lost or damaged cells Growth of an organisms Produce offspring. Many organisms

5.4 Asexual Reproduction

Roles of cell reproduction Replacement or repair of lost or damaged cellsGrowth of an organismsProduce offspring.

Many organisms reproduce by cell division.

9.1 KEY CONCEPT Cells come from other cells


Asexual reproduction is the creation of offspring from a single parent

1. Binary fission is similar in function to mitosis.– Binary fission produces two daughter cells genetically

identical to the parent cell.– Binary fission occurs in

single celled organisms- examples

prokaryotes-bacteria. parent cell

DNA duplicates

cell begins to divide

daughter cells

Asexual Reproduction


• Environment determines what form of reproduction is most advantageous.

– Asexual reproduction is an advantage in consistently favorable conditions.

– Sexual reproduction is an advantage in changing conditions.


Some eukaryotes reproduce through mitosis.Mitosis is asexual reproduction

• Budding forms a new organism from a small projection growing on the surface of the parent.

bud

Hydra

Yeast

2. Budding


3. Regeneration: – Fragmentation is the splitting of

the parent into pieces that each grow into a new organism.

– examples

4. Vegetative propagation- Forms a new plant from

the modification of a stem or underground structure on the parent plant.

- examples

More Examples of Asexual Reproduction


Need two parents:

• Union of gametes- sex cells- egg and sperm.• Results in genetically different offspring.• Increases diversity in a species.• Important in species survival.• Occurs in most multicellular organisms

And some single celled organisms.

Sexual Reproduction


KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

9.2 Cell Cycle


• The cell cycle is a regular pattern of growth, DNA replication, and cell division.

The cell cycle is from the “birth” of a new cell until it completes cell division producing

daughter cells.


•

Interphase: 90% of time

3 stages

– Gap 1 (G1): cell grows, replicates organelles,normal functions

– DNA synthesis (S): DNA replicates.

– Gap 2 (G2): additional growth

Mitosis occurs only if the cell is large enough and the DNA undamaged.

Mitosis: 10% time

– division of the cell nucleus (mitosis)

– division of the cell cytoplasm (cytokinesis)

1. Interphase 2. Mitosis

2 main stages of the cell cycle


Cells divide at different rates.

• The rate of cell division varies with the need for those types of cells.

• Some cells are unlikely to divide (G0).

Cells divide at different rates.


Cell size is limited.

• Volume increases faster than surface area.• Which cell is more efficient?• Why is cell division important?

Cell division keeps cells a constant size:


• Surface area must allow for adequate exchange of materials.

– Cell growth is coordinated with division.

– Cells that must be large have unique shapes. Why?

Why do different cells have different shapes?


KEY CONCEPT Cells divide during mitosis and cytokinesis.

9.3 Cell Division


Chromosomes condense at the start of mitosis.

• DNA wraps around proteins (histones) that condense it.

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA


• One half of a duplicated chromosome is a chromatid.

• Sister chromatids are identical copies.

• Held together at the centromere.

• Telomeres –end of the chromsome• protect DNA and do not

include genes.• After 40-60 divisions they

are too short and the cell stops dividing.

Condensed, duplicated chromosome

chromatid

telomere

centromere

telomere

Chromatids:


Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

• Remember :– Interphase is not

part of Mitosis.– Interphase occurs

before Mitosis.- Interphase prepares

the cell to divide.- During interphase,

the DNA is duplicated.

Mitosis and cytokinesis produce two genetically identical daughter cells.

Occurs in body cells ( not egg or sperm cells)Asexual reproduction


• PMAT- acronym for the 4 phases:– Prophase, Metaphase, Anaphase and Telophase.

I. Prophase:

– chromosomes condense (become visible)

– spindle fibers form.

– nucleolus disappears.

– nuclear membrane disintegrates.

Mitosis has 4 distinct phases:


During metaphase, chromosomes line up in the middle of the cell.

2. Metaphase:


During anaphase sister chromatids separate to opposite sides of the cell.

3. Anaphase


During telophase, two new (identical) nuclei form.

Reverse of Prophase:– Nuclear membrane reforms– Nuceolus becomes visible.– Chromosomes uncoil

4. Telophase


Cytokinesis differs in animal and plant cells.

– In animal cells, the membrane pinches closed.

– In plant cells, a cell plate forms.

– Occurs almost simultaneously with telophase.

Cytokinesis: Division of cytoplasm

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5.4 Asexual Reproduction Roles of cell reproduction Replacement or repair of lost or damaged cells Growth of an organisms Produce offspring. Many organisms