Life Science for Armed Services Vocational Aptitude Battery (ASVAB) Study Guide (page 3)
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.
Animals are many-celled, mobile organisms that cannot produce their own food. The animal kingdom is divided into approximately 26 phyla. Some of the major animal phyla are shown in the table on this page.
The vertebrates are a subphylum in the chordate phylum and include birds, fish, mammals, and reptiles. (All other animals are invertebrates.) Vertebrates have a spinal cord enclosed in a flexible, bony column that extends down the long axis of the body, providing skeletal support. There are eight classes of vertebrates. Four of the vertebrate classes are fish: agnatha (lamprey), chondrichthyes (shark), osteichthyes (trout), and the extinct placodermi. The other four classes of vertebrates and some of their characteristics are listed in the table on the next page.
Only the aves and mammalia are warm-blooded. Birds and humans generate and regulate their own body heat. Feathers on birds and fur on mammals help them retain body heat, and sweating (yes, birds sweat) helps them cool down. All of the other vertebrates are cold-blooded. This means that their body temperature is determined by the temperature of their surrounding environment.
All mammals share certain characteristics. They are warm-blooded, have a hair or fur covering for insulation, have a four-chambered heart, and breathe with lungs. In addition, females produce milk for their young. Mammals are divided further by body structures into 17 orders containing a total of only approximately 4,250 species. Some of the more important mammal orders are shown on the table at the bottom of this page.
Viruses are difficult to classify because scientists do not agree on the definition of a virus. Some scientists believe that a virus is nonliving because, alone, a virus is incapable of reproducing. However, viruses consist of a DNA or RNA core encapsulated in a protein coat (a capsid), which causes many to argure for its status as a life form. A virus has no true cell structure, and it isincapable of independent metabolism and reproduction without the aid of a host cell. Once inside another cell, a virus takes over and uses the host cell's resources to replicate viral DNA. Eventually the host cell dies and the (many) replicated viruses are released to infect new cells. Viral diseases in animals include the common cold, influenza, herpes, measles, polio, and rabies.
Basic Life Principles
All living organisms perform certain biochemical and biophysical activities to achieve homeostasis—a balanced internal environment. The life functions are as follows:
- Circulation: the transport of materials such as oxygen and nutrients throughout an organism
- Excretion: the elimination of metabolic waste products from an organism
- Growth: cell division and/or enlargement
- Nutrition: getting nutrients, or food molecules, from the environment via eating, absorption, or photosynthesis
- Regulation: the chemical control and coordination of life activities
- Reproduction: the production of new individuals
- Respiration: organic substances are broken down to simpler products with the release of energy, which is used to fuel other metabolic processes (in animals and plants)
Cells are the basic structural and functional unit of living things. One cell, alone, is the smallest unit of matter that is considered living. In general, plant and animal cells are similar, except that plant cells contain chloroplasts and cell walls. Chloroplasts contain chlorophyll, a food-generating substance. Cell walls, containing cellulose and other compounds, give plant cells a rigid structure and prevent desiccation, or drying out.
The size of cells varies, but most are microscopic (an average of 0.01–0.1 mm in diameter). They may exist independently, or they may form colonies or tissues—like those in plants and animals. Each cell contains a mass of protein, called protoplasm, that consists of jelly-like cytoplasm and a nucleus. The nucleus, in turn, contains deoxyribonucleic acid, or DNA, which is the genetic material of most organisms. The protoplasm is bound by a cell or plasma membrane, which controls the materials that pass in and out of the cell.
There are two types of cells, distinguished from one another by a number of characteristics, one being the way in which they reproduce. Bacteria are one example of prokaryotic cells. The nuclear material in prokaryotic cells is not bound by a membrane, and cell reproduction occurs by fission—asexual cell cleavage—the cell breaks apart to form another, identical cell. The other type of cell, found in most plants and animals, is a eukaryotic cell, in which the nucleus is separated from the cytoplasm by the nuclear membrane and there are separate organelles. In eukaryotic plant and animal cells, the major cell organelles are as follows:
- Cell membrane: partially permeable membrane that regulates flow of materials in and out of the cell and holds the structure of the cell together
- Cytoplasm: jelly-like material that encompasses the other cell structures
- Endoplasmic reticulum: a network of membranes extending from the nucleus into the cytoplasm, responsible for making lipids, proteins (in association with ribosomes), and transporting these products throughout the cell
- Golgi body/apparatus: stores and transports secretory products within the cell
- Lysosome: contains and releases enzymes within the cell
- Mitochondrion: the largest organelle and site of energy production, known as cellular respiration, in the cell (there are several mitochondria in each cell)
- Nucleus: contains genetic material and functions as the control center of the cell
- Ribosome: site of protein synthesis (there are many ribosomes in each cell)
Plant cells additionally have chloropoasts, where photosynthesis takes place, and a cell wall.
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