Download Sexual Asexual Reproduction

Sexual Asexual Reproduction
Asexual reproduction in plants
• Asexual reproduction in plants can take a
number of forms:
Vegetative propagation:
• Many plants develop underground food
storage organs which overwinter and develop
into the following year's plant. Examples are
bulbs, tubers (eg potatoes or onions) and
rhizomes.
Plantlets:
• These can take the form of runners (eg
strawberries) or side branches (‘busy lizzy’).
Cuttings:
• We can make cuttings or grafts, which in the
right conditions will develop roots and grow
into a new plant.
Tissue culture:
• Tissue culture: We can take a few cells from a
plant and grow them into a complete
specimen. Tissue culture is a type of cloning
• As only one parent is involved in asexual
reproduction, all the offspring have exactly
the same genes as their parent. The offspring
are identical and they are called clones.
Because of this, any genetic problems there
may be will always be passed on to the new
generation.
Asexual reproduction in animals
• Asexual reproduction is found in many
invertebrate animals such as starfish, sponges
and worms. The hydra is a small tube-like
freshwater invertebrate which can reproduce
vegetatively as well as sexually.
• During vegetative reproduction, tiny 'buds'
grow out from the hydra's side, develop
mouth tentacles, and finally nip off at the base
to form a separate individual.
Sexual reproduction in plants
• Many plants reproduce sexually. The
advantage to the plant is that its offspring
have a selection of genes from two parents, so
each individual's genes are different. The
offspring are not identical, and there is variety
in the species.
A flowering plant's sexual organs
consist of:
• the stamen, or male sex structure, consisting
of a filament and a pollen-bearing anther at
the tip
• the pistil or female sex structure, consisting of
ovary and ovule, style, and stigma at the tip.
(The pistil is also sometimes called the carpel.)
Here's how it works:
• An insect or the wind carries pollen grains from
the anther of another flower.
• The pollen grains land on the stigma and a pollen
tube grows down through the style to the ovary.
• The nucleus of the pollen grain passes down the
tube. It fertilizes the egg cell inside the ovule.
• The fertilized egg cell develops into an embryo.
The ovary becomes the fruit and the ovule
becomes a seed - from which (once dispersed)
the offspring plant will grow.
Sexual reproduction in animals
• Most animals reproduce sexually. In sexual
reproduction male and female parents
produce sex cells or gametes, each containing
a mixture of the parental genetic material, but
only half the number of parental
chromosomes. Two gametes fuse together
during fertilization to make a new individual
with a full set of chromosomes.
Human ovum and sperm
In humans sexual reproduction has the
following stages:
• Once a month an egg cell is released from the
ovary. This is called ovulation.
• The egg cell moves into the oviduct.
• Many sperm are deposited in the vagina during
sexual intercourse. They pass through the cervix,
into the uterus and along the oviduct. A single
sperm meets the egg cell in the oviduct and
fertilization takes place here.
• The fertilized egg embeds itself in the uterus wall
and develops into a human embryo.