1.1 Explain the term Asexual Reproduction
Asexual reproduction - the production of new individuals from a single parent without the production and fusion of gametes.
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Binary fission - the splitting of one cell into two. Example prokaryotes (bacteria)
N.B NOT mitosis because DNA in bacteria is circular with no production of spindle fibers but DNA does replicate by semi-conservative replication
Process of Binary fission
Cytokin
Gibberellin
kinetin
N.B NOT mitosis because DNA in bacteria is circular with no production of spindle fibers but DNA does replicate by semi-conservative replication
Process of Binary fission
- circular chromosome replicates
- two chromosomes separate
- two new cell membrane from across middle of cell
- cell wall material is formed between new membranes
- cell remain attached for a while then split
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Budding - small outgrowth enlarges and breaks off as a separate individual. Example yeast
Process of Budding
- linear chromosome replicate
- nucleus begins to divide by mitosis
- small swelling appears at the side of cell which forms a bud
- one daughter nuclei enter bud
- bud remains attached for a while then breaks off leaving bus scar on parent cell
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Asexual spore formation. Example Rhizopus
Spore - microscopic, reproductive bodies that contain cytoplasm and one or more nuclei
Process of spore formation
- hyphae known as sporangiophores grow up into air
- tip of sporangiophores swell up to form sporangium
- haploid nuclei move from hyphae to sporangium and divide by mitosis
- cytoplasm forms around a group of several nuclei to form a spore
- a wall form around each spore
- when spores are mature, the sporangium splits open and the spores dry and are blown away by air currents
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Fragmentation
In Spirogyra (algae)
- A short single chain of cell grow in length
- any cell in the chain enlarge, and divide by mitosis
- new filaments form when lines of weakness develop between cells then when a disturbance to the filaments occur they break apart.
In starfish
- reproduce sexually by allowing one arm or part of an arm to break off
- parent grows new arm to replace lost one
- part that broke off grow into a new individual
NB starfish can reproduce sexually
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Examples of asexual reproduction in plants. Example Ginger
Ginger reproduce using underground stems called rhizomes.
If a piece of rhizome is broken off a new plant is able to grow from the buds that occur along the rhizome. The roots of the rhizome are adventitious because they grow straight from a stem.
Buds - a group of cells that are able to undergo mitosis for growth.
Meristems - an area of a plant that has a collection of meristematic cells. eg. at tips of roots and stems
Ginger reproduce using underground stems called rhizomes.
If a piece of rhizome is broken off a new plant is able to grow from the buds that occur along the rhizome. The roots of the rhizome are adventitious because they grow straight from a stem.
Buds - a group of cells that are able to undergo mitosis for growth.
Meristems - an area of a plant that has a collection of meristematic cells. eg. at tips of roots and stems
Meristematic cells - plant cell which is able to divide by mitosis. It is undifferentiated.
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Hormone stimulation
Auxin
Hormone stimulation
Auxin
- located at shoot apex
- stimulates cell elongation
- used in rooting compound for cutting
Cytokin
- located at root apex
- stimulates cell division
Gibberellin
- located in roots and young leaves
- stimulates cell elongation and growth in length of stem
- sprayed on seedless grapes to increase grape size and distance between grapes
kinetin
- used in tissue culture to stimulate cell division
