B2: Classification

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  • Classification
    • Kingdoms
      • Organisms can be classified into groups depending on their characteristics.
      • Animals
        • Cells do not have a cell wall. They are multicellular and feed on other organisms.
        • All multicellular animals such as; Jellyfish, birds and mammals.
      • Plants
        • Cells have a cellulose cell wall. They use light energy to produce food through photosynthesis
        • All green plants including; Algae, ferns and mosses.
      • Fungi
        • Cells have chichin cell walls. Reproduce using spores rather than seeds.
        • Moulds, mushrooms and yeast.
      • Prokaryotes.
        • Have no cell wall but not made from cellulose.
        • Bacteria, blue-green algae
      • Protocists
        • Exists as a single cell or a colony of cells.
        • Amoeba, Paramecium.
    • Classification system
      • The first rank in the classification system is called kingdom. There are five cells based on what the organisms cells are like.
        • Animals (all multicellular animals). Plants (all green plants). Fungi (moulds, mushrooms, yeast). Prokaryotes (blue-green algae, bacteria). Protoctists (amoeba, paramecium).
      • There are several further ranks before we reach a specific species
        • In order: Kingdom, Plylum, Class, Order, Family, Genus and Species.
          • Kingdom (animal), Phylum (vertebrate), class (mammal), Order (carnivorous), Family (cat), Genus (big cat) and Species (lion).
    • Arthropods.
      • Invertebrates are animals without backbones. Arthropods are an important group of invertebrates.
      • There are four smaller group of Arthropods based on how many legs they have.
        • Insects (6 legs).
        • Arachnids (8 legs)
        • Crustaceans (10-14 legs)
        • Myriapods (more than 20 legs)
      • Classification systems can be artificial. They use obvious differences in features so that the organism can be identified.
        • Biologists often use field guides to work out what a plant or animal is. However these classification systems may not accurately reflect the evolutionary link between organisms.
          • To make links, natural classification systems using DNA are needed. Today, scientists can sequence the DNA of many organisms relatively easily.
            • Computer programmes compare the DNA sequences of different organisms to look for similarities and differences. This allows revolutionary trees to be made.
    • Species
      • A species is a group of organisms that can interbreed to create fertile offspring. Organisms of the same species have more in common with those of a different species.
        • Sometimes a group of the same species can have different kinds or breeds that show great variation but they still belong to the same species. Different breeds of pedigree dogs are like this.
      • Species and habitats.
        • Similar species tend to live in similar habitats. Closely related species share a relatively recent 'ancestor' - a 'common ancestor'.
        • If they live in a different kind of habitat, different species may have different features.
      • Binomial system.
        • In the 18th century Carl Linnaeus started the modern system for putting species of organism into different groups and giving them scientific names. Each species name is in Latin so that it can be used all over the world.
        • The scientific name for humans is homo sapien. The first part of the name tells you the genus while the second part of the name tells you the species.
      • It can be difficult to class some organisms into a species. For example, evolution is a continuing process.
      • Some organisms can only reporduce asexually while some species can interbreed to produce hybirds. For example the lyger is a hybrid, a cross between a male lion and a female tiger.



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