Asexual Reproduction in Plants and Animals

Every living thing brings new living things of its own kind into the world. A hen hatches chicks, a maize plant carries a cob, and the grains on that cob grow into fresh maize plants. In well developed organisms the male and the female carry separate reproductive organs. Those organs make male and female sex cells, and a new life begins only after the two cells join. Reproduction of this kind needs two parents.

Not every organism follows that route. A fern carries no flower and no seed, yet new ferns keep appearing around an old one. In the pond animal called hydra a small bulge grows out from the side of the body, and within days that bulge separates and swims off as another hydra. No male cell and no female cell take part. In such organisms a specialised part of the body itself breaks away, sprouts, or makes special reproductive units, and a new organism develops from it.

This kind of reproduction is found in almost all living things, animals and plants alike. It is quick, because one parent is enough and many offspring can appear at the same time. Since the offspring grow out of the parent's own body, their build, colour and other features stay the same as the parent's. Asexual reproduction happens in several different ways.

• Fission: a single cell divides and the pieces become new organisms.
• Budding: a bud grows out from the side of the body and separates.
• Fragmentation: the body breaks into pieces and every piece grows.
• Regeneration: a broken off part grows back into a complete organism.
• Sporulation: spores are produced and each one grows into a new plant.
• Parthenogenesis: a new organism forms from an egg that was never fertilised.

Fission happens in two ways, binary fission and multiple fission. When the cell of a single celled organism divides into two equal parts and each part becomes a new organism, that is binary fission. The nucleus of the cell divides first, the cytoplasm divides next, and at the end two separate organisms are ready.

In binary fission the body splits either along its long axis or across it. A split along the long axis is called longitudinal binary fission, and a split across the body is called transverse binary fission. Amoeba, euglena and paramecium are animals that divide by binary fission, and the same process goes on in single celled plants such as bacteria, chlorella and anabaena.

In multiple fission the body, which is a single cell, divides into more than two parts, and every part grows into a new organism. This is seen mostly in protists and algae. Plasmodium, chlamydomonas and vorticella reproduce in this way. Because many offspring appear at once, it is a fast way of increasing numbers.

Laboratories keep permanent slides of these organisms. Looking at them through a microscope lets you pick out the stages of fission for yourself.

• Collect permanent slides of binary and multiple fission in amoeba, paramecium, euglena, plasmodium and chlamydomonas.
• Place each slide on the microscope and observe it.
• Draw what you see, show the drawings to your teacher, and discuss the asexual reproduction going on in those organisms.

Yeast, hydra, taenia, coral and jellyfish reproduce by budding. A small swelling first appears on the wall of the parent's body. That swelling keeps growing and slowly takes the shape of the parent. In hydra a tiny mouth and tentacles even appear on the bud itself. In the end the bud breaks away from the parent and starts living as an organism of its own. Sometimes the bud stays attached instead of breaking off, and that is how large colonies of animals like coral are built up.

It happens mostly in plants, for example in spirogyra, marchantia, ferns, lichens and mucor. The green thread of spirogyra that floats in a pond is broken easily by moving water or by animals brushing past it. If one thread breaks into three pieces, all three keep growing longer, and within a few days there are three separate spirogyra threads. The parent makes no special preparation here. The breaking itself is the start of reproduction.

It is found mostly in animals, for example in hydra, tapeworm, planaria, starfish, earthworm and leech. The part that has broken away from the parent starts growing again and takes the shape of a new organism. If a planarian is cut across the middle, the front piece grows a new tail and the back piece grows a new head, so two planarians are formed. If a starfish loses one arm, that arm can grow the rest of the body and become a whole starfish.

Ferns, mushrooms, mucor and marchantia reproduce asexually by producing spores. On the underside of a fern leaf you can see black, brown or yellow dots. Each dot is a cluster called a sorus, and the spore making parts lie inside it. For a plant that never bears a flower, this is the reproductive part.

When the spores are ripe the sporangium bursts and the spores scatter into the air. A spore carried by the air germinates and grows into a new plant if it lands on a damp place. Since thousands of spores leave a single leaf, ferns and mushrooms spread quickly wherever the ground stays wet. Reproduction that takes place through the production of spores is called sporulation.

Aim: to study the spores of a fern. Materials needed: a fern leaf carrying spores, a simple microscope, a slide and a brush.

• Collect a fern leaf that has black, brown or yellow dots of sori on its underside.
• Using the brush, shake the spores from those dots down onto the slide.
• Put the slide under the simple microscope and look at the shape and build of the spores.
• Discuss the build and the features of the spores you have seen with your friends, draw them, and present the drawings in class.

It is found both in animals and in plants. In plants such as apple, pineapple and cucumber the ovary and the ovule change directly into fruit and seed. In ants, termites and grasshoppers the young develop from eggs without any fertilisation. In other words the egg does not wait for a male cell. It simply begins to develop on its own.

• No sex cells are produced, and none are joined.
• There is no idea of male and female in it.
• It can take place from almost any part of the organism's body.
• Specialised reproductive units are produced in it.
• The offspring produced in this way show hardly any hereditary variation.

These features show both the strength and the weakness of asexual reproduction. No partner has to be found and numbers rise quickly, so such organisms spread fast when conditions suit them. But because every offspring is alike, a change in the surroundings or a new disease can put the whole group in danger at once.