Complete set of IGCSE/GCSE Biology notes. Typed out, highly-detailed, contains plenty of diagrams, tables and illustrations for easy learning.
Topics (01-21):
01 Characteristics and Classification of Living Organisms
02 Organization of The Organism
03 Movement in and out of Cells
04 Biolog...
Reproduction
Asexual reproduction:
Asexual Reproduction: a process resulting in the production of genetically identical
offspring from one parent.
An example of asexual reproduction is Fungi and Potato Tubers.
The advantages and disadvantages of asexual reproduction are summarized in the table.
Advantages Disadvantages
Needs one parent cell only Competition is present
Asexual Reproduction
Faster than sexual reproduction Little to no variation in offspring
Less ability to adapt and less
Spreads rapidly
evolution
No need for gametes May all be killed by same disease
Less energy needed Converse of mp5 for asexual
Inherits adaptation from parent cells
Sexual reproduction:
Sexual Reproduction: a process involving the fusion of the nuclei of two gametes (sex
cells) to form a zygote and the production of offspring that are genetically different from
each other.
Fertilization: the fusion of gamete nuclei.
The nuclei of gametes are haploid and the nucleus of a zygote is diploid.
Haploid: containing a single set of unpaired chromosomes.
Diploid: containing two sets of chromosomes.
In a diploid cell, there is a pair of each type of chromosome and in a human diploid cell
there are 23 pairs.
The advantages and disadvantages of sexual reproduction are summarized in the table
below.
, Sexual Reproduction Advantages Disadvantages
Needs two plants or a pollinating
Variation
agent
Evolution or formation of new species Slow
Seed dispersal A lot of pollen or seeds wasted
Colonization or ability to adapt to change Fertilization may not happen
Loss of lots of energy
Sexual reproduction in plants:
A labeled flower is drawn in the figure below.
The table below summarizes the functions of each part.
Feature Function
Sepals Protect the flower when it is in the bud
Petals The color and scent of the petals attract insects to the flower
Anthers Pollen grains are produced in anthers by cell division
Stigmas Trap pollens and provide entrance to ovary
Ovaries Where fertilization takes place
, Fertilization
Pollination is complete when
stigma
pollen from an anther has landed pollen
style
on a stigma. If the flower is to ovule grain
produce seeds, pollination has to male nucleus
be followed by a process called
pollen tube
fertilization. nuclei fuse
female nucleus
In flowering plants, the male
gamete is in the pollen grain; the
female gamete, called the egg cell, ovary wall
is in the ovule.
pollen tube
For fertilization to occur, the enters micropyle
nucleus of the male cell from the
pollen grain has to reach the
female nucleus of the egg cell in
the ovule, and fuse with it.
The pollen grain absorbs liquid from the stigma and a microscopic pollen tube grows out
of the grain.
This tube grows down the style and into the ovary, where it enters a small hole, the
micropyle, in an ovule.
The nucleus of the pollen grain travels down the pollen tube and enters the ovule.
Here it combines with the nucleus of the egg cell.
Each ovule in an ovary needs to be fertilized by a separate pollen grain.
Pollination:
Pollination: the transfer of pollen grains from the anther to the stigma.
Self-pollination: as the transfer of pollen grains from the anther of a flower to the stigma
of the same flower or different flower on the same plant.
Cross-pollination: as transfer of pollen grains from the anther of a flower to the stigma of
a flower on a different plant of the same species.
The implications of self-pollination and cross-pollination are similar to those of asexual
and sexual reproduction.
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