LEARNING OBJECTIVES
By the end of this lesson, you should be able to:
Most living things live for many years. They eat, grow, move but finally die. They produce more of their kind in order to continue their race. Reproduction refers to the process through which living things produce offspring. Most animals reproduce in two ways:
Forms of reproduction
Reproduction can either be sexual or asexual. Sexual reproduction is the form of reproduction where two specialized organisms known as gametes must interact. These two gametes each contain half number of chromosomes of normal cells. The male gamete fuses or fertilizes the female gamete of an organism of the same species. The offspring produced bears genetic characteristics of both parental organisms. Examples of sexual reproduction include reproduction in higher organisms like human beings, and mammals.
In asexual reproduction, organisms reproduce without interaction with another organism. Cloning of an organism is an example of asexual reproduction. Asexual reproduction produces an organism that is genetically similar or an identical copy of itself. Note that asexual reproduction happens beyond single celled organisms only. Examples of asexual reproduction include bacteria, archaea, certain animals, and most fungi. In plants, it may take different forms such as; budding, binary fission, spore formation, vegetative propagation, parthenogenesis, apomixis, and fragmentation.
Animals that give birth to babies
Animals like cows, horses, tigers, goats and kangaroos, and many more, give birth to their babies. These animals feed their babies with their own milk. These animals are known as mammals. Mammals carry their babies inside their bodies. They get nutrients and oxygen and are born after a few months. After they are born, they cannot take care of themselves and the mother has to take care of them. Mothers feed the babies with their milk.
Some mammals like duck-billed platypus do not give birth to young ones, they lay eggs instead.
Animals that lay eggs
Animals such as birds, snakes, fishes, insects, and frogs lay eggs.
Birds
All birds reproduce through the laying of eggs. They make nests and lay their eggs. Let us start by looking at the structure of an egg.
Structure of an egg
An egg is made up of a hard outer covering known as the shell. The shell protects the egg and it also helps in developing the baby. In the middle of the egg is a yellow portion known as the yolk. It provides nutrition to the embryo that is developing. The yolk has a dark spot known as the embryo. A white substance called the albumen surrounds the yolk. It provides the embryo with water and protects it.
Birds lay their eggs in their nests. They then sit on the eggs to keep them warm. This process is known as incubation. When the embryo gets fully developed, the egg hatches and a chick comes out of it. This process is known as hatching. The parent bird feeds and looks after its chicks until they start searching for their own food.
Fishes
Most fishes lay their eggs in water. Fishes lay thousands of eggs at a time. The floating clusters of eggs are known as spawns. Only a few eggs survive as most of them are eaten by other fishes. Baby fish hatches out from the egg and grows into adult fish. A baby fish is called a fry.
Frogs
Most frogs lay their eggs in water or wet places. Like fishes, they also lay many eggs at a time. The floating clusters of eggs are known as spawns. The eggs are protected by a jelly-like substance that surrounds them. Eggs hatch tadpoles that later become frogs. Tadpoles have tales like those of fishes to help them swim in the water and eat water plants. They breathe with the help of the gills. After a few weeks, a tadpole develops legs and loses its gills. It also develops lungs as well as other organs. It later grows into an adult frog. Tadpole becomes an adult through the process of metamorphosis.
Insects
Insects also lay eggs. Most insects have four stages (egg, larva, pupa, and adult) in their development. Some insects have three stages (egg, nymph, and adult). They also show metamorphosis. An example of an insect is butterfly. A butterfly undergoes four stages in its cycle of life. The female butterfly lays a cluster of eggs mainly on leaves. When an egg hatches, it produces a worm-like larva. The larva is also called caterpillar. The caterpillar feeds on leaves and grows. After some time, it forms a shell around its body which is known as cocoon. The caterpillar now becomes a pupa. The pupa can also be referred to as chrysalis. In a week, the cocoon breaks open, and an adult fly comes out fully developed.
Reptiles
Snakes, crocodiles and turtles are some of the reptiles. Snakes lay their eggs on the ground. Their eggs have hard leather shell. Baby snakes emerge from the eggs by breaking the shell using a special egg tooth. Crocodiles dig shallow pit near river banks and lay there.
SUMMARY
We have learnt that;
