Topic outline

  • UNIT 2 Introduction to Classification

    Oral activity
    In groups, discuss these questions.
    1. How do we know that something is living?
    2. Make a guess about the number of different animals and plants in
    Rwanda. Do you think it is a large number or a small number?
    3. Th ink of ways in which you could put these organisms
    into groups.
    4. Do you know the scientific name for some of these organisms?

    Topic 1: Biodiversity and classification

    The importance of classification
    In the oral activity, you talked about how many different organisms there are
    in Rwanda. No doubt you realized that there are a large number of different
    living things in our country. In fact, there are more than 2,000 different types
    of plants and 500 different types of animals in our country.

    Activity 2.1
    Work in pairs. Look at the pictures below, and then answer the questions.

    Figure 2.2 Living and non-living things

    1. Draw a table with two columns. In one column, write down all the
    living things that you can see in the picture. In the other column, write
    down all the non-living things.
    2. How did you decide which things were living and which were not?
    3. Of the non-living things:
    a) Which were always dead?
    b) Which were once alive, but are now dead?
    4. Draw another table with two columns. In one column, write down
    the names of all the animals you can see in the picture. In the other
    column, write down the names of all the plants.
    5. How did you decide which things were animals and which were plants?

    Scientists need to sort all living things into groups so that they can recognise
    and study them more easily. When you were sorting the living things into
    plants and animals in the activity, you were classifying them. There are so
    many different organisms on Earth that scientists need to sort them into
    groups. Classification means sorting things into groups. Think back to how
    you sorted the living things. You put those that shared certain characteristics
    into the animal group, and those that shared certain other characteristics
    into the plant group.
    Sorting, or classifying, things into groups according to their similarities
    and differences is called classification, or taxonomy.
    Scientists sometimes change the way they classify an organism as they
    learn more about it. Taxonomists use information from many branches of
    Biology to classify organisms; for example, genetics, biochemistry and fossils.

    Unit 2: Introduction to classification

    The concept of hierarchical classification
    In Activity 2.1, you grouped different living organisms into two groups:
    animals and plants. However, there are thousands of different organisms
    in these two groups, so scientists must classify them into smaller groups.
    Taxonomists study more similarities and differences between different
    organisms so that they can classify them into smaller and smaller groups.
    Th is is called hierarchical classification.

    The five kingdom system
    Organisms are grouped into five big groups, called kingdoms. Th e
    kingdoms are Animals, Plants, Fungi, Protoctista and Monera.
    Th e features that are used to group organisms into these
    kingdoms are: body structure, method of getting food and method of
    Th e kingdoms are further divided into smaller groups called phyla,
    classes, orders, families, genera and species. See Figure 2.3.

    • Each kingdom is divided into phyla.
    • Each phylum is divided into classes.
    • Each class is divided into orders.
    • Each order is divided into families.
    • Each family is divided into genera.
    • Each genus is divided into species.

    Topic 1: Biodiversity and classification

    The diagram below shows two classification hierarchies. A hierarchy is a
    way of arranging groups from the biggest group to the smallest. The first is
    for a fig tree and the second is for a cat.
    Figure 2.4 The classification hierarchy for a fig tree (A) and a cat (B)