Biology WJEC BY2 Notes for 2.4 Reproductive Strategies

I tend to find this topic quite easy.. not sure why, maybe because it just makes the most sense?

anyways i still have to do digestion notes.. the exam's tomorrow. Why on earth did I leave it this late....

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  • Created on: 20-05-12 13:50
Preview of Biology WJEC BY2 Notes for 2.4 Reproductive Strategies

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WJEC BY2.4 Reproductive Strategies
Two types of reproduction:
Asexual reproduction produces individuals that are genetically identical
Sexual reproduction produces offspring that are genetically different
Genetic variability enables a species to adapt to environmental change.
There are advantages and disadvantages to both asexual and sexual reproduction:
Sexual Reproduction Asexual Reproduction
Advantages o Genetic Variation o Rapid increase in numbers
o Produces variety to adapt o Where the environment is
to new environmental stable, already well
conditions adapted
Disadvantages o Need 2 individuals/parents o If one individual is effected
o Genetic mutation more by a disease, all in a
common population will be
Cells with the diploid number (full number)of chromosomes are produced by
Haploid cells/gametes are produced by meiosis (half the normal number of
Sexual reproduction is the production of a new individual from fusing two gametes
from two parents (fertilisation) which produces a single cell called the zygote
Males and females usually produce different sized gametes:

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Size Males: Small ­ approx 25um because: Females : Large ­ approx 130um because:
Contains smaller amount of cytoplasm, Contains lots of cytoplasm containing
therefore there is less resistance Yolk droplets (protein and lipid)
when moving needed for the development of the
More mitochandria embryo once the egg is fertilised
n = 23
o 2n meiosis n
o n mitosis n
o 2n mitosis 2n
o NEVER `halve' n!
o 2n is the normal number of chromosomes in any…read more

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Therefore fertilisation is external Gametes are `placed together', therefore higher chance
of fertilisation
This means that a lot of gametes are Lower chance of gametes being wasted
wasted as they fail to fuse
The developing embryo is entirely Eggs are not released, therefore fewer are produced
dependent on the yolk supply for its
The developing embryo is exposed to Internally developing young (in uterus) are not
hazards e.g.…read more

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Incomplete metamorphosis (e.g. dragonfly or locust)
Nymphs resemble the adult and progress through a series of moults to become the adult; they
undergo incomplete metamorphosis includes:
Egg stage
No larva or pupa
Complete metamorphosis (e.g.…read more

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Reproduction ­ Pollination
Male pollen (gametes) is deposited on the surface of a female stigma and travels through
the tissue to the ovary via a pollen tube to fertilise female's ovules (eggs)
The fertilised ovule develops into a seed
Sexual reproduction does not rely on gametes travelling through a thin film of water to reach the
Plants developed male pollen grains with a hard coat to withstand desiccation
Plants with small inconspicuous flowers are wind pollinated grasses
Plants with bright flowers/scent attract insect, and…read more

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Deciduous leaves fall to the ground and decay rapidly resulting in rapid recycling of mineral
ions to be reused by plants…read more


Hassan Arif

Really useful concise "to-the-point" notes for revision. Thanks you so much! :D

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