The number of hetrotrophic found in desert region in smaller . However they are found in greater numbers in the sea. Why is this so?
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The total number of species living on the planet is imprecisely known and published estimates vary from 12 million to over 100 million. This is because there are large numbers of species yet undiscovered and undescribed, and there is not always agreement on whether certain organisms should be regarded as separate species. The total number of known species including all animals, plants and micro-organisms is about 1.4 million, and over half of these are insects! Taxonomists have fairly complete records for the best known groups (e.g. birds with 9, 881 species world-wide). It is now also reasonably clear where the main gaps in our knowledge are, and intensive sampling of species-rich groups (e.g. insects) and species-rich areas (e.g. moist tropical forests) is now taking place to provide a more reliable picture of global and regional species richness, and a stronger basis for estimating the number of species.
In order to study the enormous diversity of organisms they need to be organised into manageable groups. This grouping of organisms is known as classification and the study of biological classification is called taxonomy. The usual method of classifying organisms, although not the only one in existence, follows the system originally proposed by the Swedish naturalist Carl Linnaeus (1707-1778) who gave each organism a two-part scientific name - a genus name and the species name (e.g. Homo sapiens). It is a hierarchical system of groupings based on evolutionary relationships. The sequence in the hierarchy is as follows: Kingdom-Phylum-Class-Order-Family-Genus-Species.
The five major groups, or kingdoms, are outlined below:
Bacteria Kingdom Only visible under the high power of the light microscope. Unlike other organisms (which have eukaryotic cells), they are single prokaryotic cells, i.e. without a proper nucleus (the DNA is not protected by a nuclear membrane), and live just about everywhere - air, water, soil, or inside animals and plants. They are often categorised according to their shape:
spherical (cocci) bacteria (e.g. Streptococcus, Staphylococcus) often mass together forming clumps or chains;
rod-shaped (bacilli) bacteria (e.g. Escherichia coli) also often form chains, some cells are curved or spiral and sometimes have flagella.
Many are beneficial, others cause disease.
Protoctist Kingdom A wide range of organisms divided into two main groups:
single-celled protoctists which are larger than bacteria and usually visible under the low power of the microscope. They may be plant-like, feeding by photosynthesis (e.g. Euglena in ponds; Pleurococcus on trees), or animal- like, taking in organic food (e.g. Amoeba and Paramecium in ponds). They live mainly in water or inside other organisms.
algae (e.g. seaweeds; Spirogyra blanket weed in ponds) are simple multicellular organisms without definite roots, stems or leaves. They are photosynthetic and live mainly in water.
Fungus Kingdom Single-celled (e.g. yeast), or multicellular (e.g. mushrooms, and moulds such as Penicillium and bread mould) which grow from a network (mycelium) of interwoven threads called hyphae. The hyphae have nuclei, and cell walls containing chitin, not cellulose. They have no chlorophyll and feed saprophytically absorbing organic substances.
[NB Viruses do not fit into any of the five kingdoms. They are smaller than bacteria and consist of genetic material (DNA or RNA) enclosed in a protein coat. They are able to replicate themselves inside other living cells, but are generally not considered living as they do not show many of the characteristics that define a living organism.]
Plant Kingdom The term plant, in everyday usage, generally refers to a complete, herbaceous specimen. Some children have difficulty assigning trees, or parts of plants (such as fruits, vegetables, flowers or seeds) to the plant kingdom. Plants are multicellular organisms able to photosynthesise. They have cells with cell walls, nuclei and chloroplasts. The largest, most highly evolved and most familiar group is the phylum of flowering plants (angiosperms). These have flowers for reproduction, produce seeds protected inside fruits, and range from small grasses to huge trees (e.g. oak, sycamore, fruit trees). The other phyla are non-flowering, often less conspicuous plants: the non-flowering trees (conifers) produce seeds in cones (e.g. pine, cypress); ferns (pteridophytes) can be large (e.g. bracken in woods) or small (e.g. water ferns in ponds), they have roots, stems and leaves (called fronds) and reproduce by spores; mosses and liverworts (bryophytes) are small plants with tiny leaves one cell thick and single- celled rootlets, reproduce by spores, common on trees, soil, walls, edges of ponds, etc.
In order to study the enormous diversity of organisms they need to be organised into manageable groups. This grouping of organisms is known as classification and the study of biological classification is called taxonomy. The usual method of classifying organisms, although not the only one in existence, follows the system originally proposed by the Swedish naturalist Carl Linnaeus (1707-1778) who gave each organism a two-part scientific name - a genus name and the species name (e.g. Homo sapiens). It is a hierarchical system of groupings based on evolutionary relationships. The sequence in the hierarchy is as follows: Kingdom-Phylum-Class-Order-Family-Genus-Species.
The five major groups, or kingdoms, are outlined below:
Bacteria Kingdom Only visible under the high power of the light microscope. Unlike other organisms (which have eukaryotic cells), they are single prokaryotic cells, i.e. without a proper nucleus (the DNA is not protected by a nuclear membrane), and live just about everywhere - air, water, soil, or inside animals and plants. They are often categorised according to their shape:
spherical (cocci) bacteria (e.g. Streptococcus, Staphylococcus) often mass together forming clumps or chains;
rod-shaped (bacilli) bacteria (e.g. Escherichia coli) also often form chains, some cells are curved or spiral and sometimes have flagella.
Many are beneficial, others cause disease.
Protoctist Kingdom A wide range of organisms divided into two main groups:
single-celled protoctists which are larger than bacteria and usually visible under the low power of the microscope. They may be plant-like, feeding by photosynthesis (e.g. Euglena in ponds; Pleurococcus on trees), or animal- like, taking in organic food (e.g. Amoeba and Paramecium in ponds). They live mainly in water or inside other organisms.
algae (e.g. seaweeds; Spirogyra blanket weed in ponds) are simple multicellular organisms without definite roots, stems or leaves. They are photosynthetic and live mainly in water.
Fungus Kingdom Single-celled (e.g. yeast), or multicellular (e.g. mushrooms, and moulds such as Penicillium and bread mould) which grow from a network (mycelium) of interwoven threads called hyphae. The hyphae have nuclei, and cell walls containing chitin, not cellulose. They have no chlorophyll and feed saprophytically absorbing organic substances.
[NB Viruses do not fit into any of the five kingdoms. They are smaller than bacteria and consist of genetic material (DNA or RNA) enclosed in a protein coat. They are able to replicate themselves inside other living cells, but are generally not considered living as they do not show many of the characteristics that define a living organism.]
Plant Kingdom The term plant, in everyday usage, generally refers to a complete, herbaceous specimen. Some children have difficulty assigning trees, or parts of plants (such as fruits, vegetables, flowers or seeds) to the plant kingdom. Plants are multicellular organisms able to photosynthesise. They have cells with cell walls, nuclei and chloroplasts. The largest, most highly evolved and most familiar group is the phylum of flowering plants (angiosperms). These have flowers for reproduction, produce seeds protected inside fruits, and range from small grasses to huge trees (e.g. oak, sycamore, fruit trees). The other phyla are non-flowering, often less conspicuous plants: the non-flowering trees (conifers) produce seeds in cones (e.g. pine, cypress); ferns (pteridophytes) can be large (e.g. bracken in woods) or small (e.g. water ferns in ponds), they have roots, stems and leaves (called fronds) and reproduce by spores; mosses and liverworts (bryophytes) are small plants with tiny leaves one cell thick and single- celled rootlets, reproduce by spores, common on trees, soil, walls, edges of ponds, etc.
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