Viruses and Classification of Living Things Study Guide for McGraw-Hill's ASVAB
Viruses are not alive in the strict sense of the word, but they reproduce and have a close relationship with all living organisms. Viruses are not plants, animals, or bacteria, although they may seem to be. A virus is basically a piece of hereditary material surrounded by a protein coating. Viruses do not have a nucleus or other organelles.
Viruses need a host cell in order to reproduce and function. They cannot generate or store energy, but take their energy from the host cell. They also take basic building materials from the host. All viruses contain nucleic acid, either DNA or RNA (but not both), and a protein coat, which encases the nucleic acid. Since viruses cannot penetrate plant cell walls, nearly all plant viruses are transmitted by insects or other organisms that feed on plants.
Viruses cause such conditions as the flu, the common cold, cold sores, measles, chicken pox, and AIDS.
Classification of Living Things
Scientists use an ordered taxonomy (classification system) to classify living things. The levels within this system are called, in descending order, kingdom, phylum/division, class, order, family, genus, and species.
All life is categorized into five kingdoms.
Human beings can be categorized according to the taxonomy in this way:
Within each kingdom, there are various phyla (the plural of phylum) for animals and divisions for plants.
How Organisms Obtain Energy There are many ways to classify living things. One way is to divide them into consumers and producers. Producers use an outside energy source, such as sunlight, to produce energy. Most producers have chlorophyll, and most, but not all, are plants. Consumers cannot make their own energy; to live, they need to eat other organisms. Consumers may eat only plants, only animals, or both. (See the classification of animals for more information.)
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