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.