the thin outer shell of the earth and the inner layers of its atmosphere; the place where all living systems are found
the layer of a tree growth occurs, just under the bark
substances composed of long chains of oxgen, hydrogen, and carbon molecules. sugar, starch, and cellulose are all carbohydrates
in ecology, the number of living things that can exsit for long periods in a given area without damaging the environment
the basic unit of all living thing except viruses. In advanced organisms, cells consist of a necleus, cytoplasm, and organelles all of which are surrounded by a cell membrane
the development of different cells to perform different functions in complex organisms
the structure separating an animal cell from its environment or a plant cell from its cell wall. The cell membrane is a complex system that allows nutrients to enter the cell and waste products to leave, usually through osmosis
the rigid outer coverying of a typical plant cell, composed mainly of cellulose, and lying outside the cell membrane. Animal cells do not have cell walls.
a stringy, fibrous substance that forms the main material in the cell walls of plants. In an organic molecule, it is composed of carbon, hydrogen, and oxygen.
the complex chemical that gives a plant its green colors and plays an important role in the conversion of sunlight into energy for the plant.
animals that have a central nevre like the human spinal cord
the small bodies in the nucleus of a cell that carries the chemical 'instructions' for reproduction of the cell. they consist of strands of DNA wrapped in a double helix around a core of proteins. Each species of plant or animal has a characteristic number of these. For human beings it is 46
a way of organising living things. in biology plants and animals are usually classified by the structure of their bodies, in a descending hieranchy of categories: kingdom, phylum, class, order, family, genus, and species
a living system that is genetically identical to tis ancestor. since each cell contains the DNA molecules that characterize an individual, it is, in principle, possible to replicate, or reproduce, complex living systems in the laboratory
an ecosystem in which no materials can leave or enter, but through which energy from external sources can flow.