In this topic you will learn about patterns in the way living things reproduce and grow.
A kind of asexual reproduction in which one parent cell divides into two offspring cells is called fission. The chromosomes of the offspring are identical to the parent. Organisms that reproduce by fission include bacteria, some protists, and some yeast. A kind of asexual reproduction in which a new organism develops from a bump (bud) on the side of the parent is called budding. The chromosomes of the offspring match those of the parent. Hydra, sponges, and some yeast reproduce by budding. A kind of sexual reproduction in which two parent cells join and exchange material before they divide is called conjugation. The chromosomes of the offspring differ from each parent. Some protists reproduce by conjugation.
Members of the fungus kingdom, such as bread molds and mushrooms reproduce by forming spores. A spore is a cell that can develop into an adult organism without fertilization by another cell. Ferns, mosses, and even bacteria can reproduce by forming spores. The parts of the fungus seen on moldy bread are the reproductive structures that contain the spores. In a mushroom the spores are found beneath the cap.
The life cycle of most plants begins with the formation of a seed, which is the result of fertilization. Fertilization occurs when a pollen grain carrying sperm touches the egg-producing organ of a plant. The seed germinates and sprouts a root, a stem, and a leaf. The young plant pops through the ground. If the conditions are right, it grows and reproduces. Although reproduction is often the final stage of life for a mature plant, the seeds, spores, and new plants that a parent plant produces start the life cycle all over again.
Animals grow and develop in a pattern called a life cycle. Animals begin their life cycle with birth. Humans are all born looking like small adults. Childhood and adolescence in humans are periods of growth and development. As animals get bigger, they learn to survive. Adulthood is a time of reproduction and then aging. The final stage of the life cycle is death.
The changes of body form that some animals go through in their life cycle is called metamorphosis. Butterflies, mosquitoes, wasps, fireflies, bees, and ladybugs go through a complete metamorphosis in four distinct stages. In the first stage an egg is laid. Second, the egg hatches into a larva. The larva eats and gets larger. Third, the larva stops eating and enters the pupa stage. It covers itself with a special case. Larval tissues break down and adult structures begin to form. Finally, the animal comes out of the pupa and enters the adult stage.