Biology- Reproductive Strategies

Reproduction: The ability to produce other individuals of the same species.

Asexual reproduction: the 'cloning' of parent organisms.

Features:

• Genetically identical offspring
• Diploid cells produced by mitosis
• Binary Fission= CLONE.

Pros

• Very quick, produces a lot of a beneficial gene in a very short amount of time.
• only needs one parent
• encourages adaptation, a mutations occur a lot.

Cons

• Susceptible to disease and environmental change, as there is no genetic variation.
• a lot of competition between offspiring

Definition: The fusion of two haploid gametes to create a diploid zygote, producing genetically different offspring to the parent organisms.

Features

• genetically different offspring
• gametes are formed by meiosis

Pros

• genetic variation allows resistance to disease and environmental change.
• allows a resistant stage in life cycle to form
• Formation of spores/seeds etc allows intra-specific competition, and genetic variety.

Cons

• time consuming
• two parents needed
• less offspring
• open to mutation

e.g. fish

Female 'lays' eggs in the water, and the male releases sperm all over them.

pros

• many offspring produced
• little energy or time required

cons

• susceptible to predators
• less developed at birth- limited by yolk
• gametes are wasted
• environmental conditions change easily

e.g. mammals, birds

Sperm is released inside the femal during intercourse, where it meets the egg.

pros

• more protection from predators, including the opportunity to develop a hard shell
• less waste of gametes
• independent of water as a medium for sperm to swim in
• usually more parental care

cons

• less eggs, so less offspring
• expensive energywise for the mother who carries the eggs

The amniote is a fluid filled cavity surrounded by a membrane (shell). Yolk is the food source.

Why fluid filled?- to carry away waste products from the foetus. - gases can dissolve in it and reach foetus. -prevents the egg drying out.

e.g. mammals

mammals tak the internal fertilisation method further, and grow fully inside the mothers womb, before being born live.

pros

• very well protected throughout initial development
• well developed by birth, as their food source is not limited (they recieve nutrients through the placenta). this also means they are less susceptible to predators
• often much more parental care e.g training to become adults, provision of food, shelter

cons

• less offspring produced

INCOMPLETE METAMORPHOSIS

e.g. grasshoppers

Zygote develops into intermediate forms before becoming an adult.

Larvae ----> Nymph x5 -------> adult

To grow, the insect has to shed its exoskeleton, leaving it very vulnerable.

COMPLETE METAMORPHOSIS

e.g. butterflies, moths

Larvae are different from an adult; they go into a pupal phase, where all their consistuent ions and compounds are mixed up and reformed into the adult.

pros                                                                         cons

very specialised                                                       pupa/chrysallis is open to predation

Simple plant (algae) are contained to aquatic conditions.

Mosses have to stay in damp area because the male gamete needs moisture to swim.

Flowering plants adaptions:

• Pollen grains have a hard coat to prevent dessication. They contain the male gamete and travel by wind or insects.
• Brightly coloured flowers attract insects to carry the gametes. 
• The pollen grain easily reaches the female gamete through a pollen tube, so no water is needed.
• The zygote develops into a seed.

KEY: Exploit animals for pollination and seed dispersal. Enclosure of eggs in ovary. Seeds and pollen grains have hard shells

Why are flowering plants so successful?

• Interval between flower production and seed dispersal is short, so many offspring are produced.
• Seed has a food source to allow the sapling to develop before photosynthesis.
• Leaves are decidious and succelent, so they decay quickly. This encourages the production of 'humus' which recycles the ions for reuse.