Life Science for Armed Services Vocational Aptitude Battery (ASVAB) Study Guide
Biology is the study of living things. We share the planet with over a million plants and animals. A Swedish scientist named Carl Linné, also known as Linnaeus, devised the classification system used in modern biological science. Every organism is grouped according to seven basic levels of classification, which are, from broadest to most specific: kingdom, phylum, class, order, family, genus, species.
Linnaeus's system describes organisms that have shared physical traits with a two-word, or binomial, name. The scientific name of an organism consists of a genus name and a species name. A genus name, always capitalized, precedes the species name, which is in lowercase. Both genus and species names are underlined or italicized.
- A human belongs to genus Homo, species sapiens, so it is Homo sapiens.
- A common frog belongs to genus Rana, species temporaria, so it is Rana temporaria.
- An African violet belongs to genus Saintpaulia, species ionantha, so it is Saintpaulia ionantha.
Most biologists divide all living things into five major types, each forming a kingdom: animals, plants, fungi, protists, and monerans. This chapter focuses on animals and plants because those kingdoms contain the majority of life. It is useful, however, to know a little about the other three kingdoms.
Monerans, such as blue-green algae and bacteria, are single-celled organisms containing no nuclei. Blue-green algae produce their own food through photosynthesis (defined later in this chapter). Many bacteria are parasites that cause diseases, or they are decomposers, meaning that they absorb food from decaying material.
Protists, such as protozoa and algae, are single-celled organisms that contain cell nuclei. Fungi, such as molds and mushrooms, are multiple-celled organisms that form spores and decompose other organic matter. Yeasts are unicellular fungi that form colonies.
Plants contain many cells and make their own food through photosynthesis. The two phyla, or large groupings within the plant kingdom, are the Bryophyta, such as mosses and hornworts, and the Tracheophyta, including flowering plants and pine trees. Bryophytes are tiny, grow on surfaces, and reproduce by spores. They are simply organized and lack the structural support of true roots, stems and woody tissue. Tracheophytes, or vascular plants, are the plants that we encounter every day. Almost all have roots, stems of woody tissue—which allow them to grow to great heights and in soil with a dry surface—and leaves.
The largest class of the Tracheophyta is composed of the following divisions:
- Filicophytes, or ferns
- Angiosperms (Magnoliophyta), flowering plants that produce seeds with protective coverings
- Gymnosperms (encompassing four divisions), which produce seeds without protective covering, though some produce seed cones, such as the pine cone
Angiosperms are further divided into monocots and dicots. Monocots bear seeds with only one cotyledon, a leaf within the embryo. Monocots, such as onions, tulips, and palms, are characterized by parallel leaf veins and flowers in groups of threes. Dicots bear two cotyledons. Dicots, such as potatoes, roses, and oaks, are characterized by net-like leaf veins and flower parts in fours, fives, or multiples of either four or five.
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