• 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
    reproduction.
    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)
    Kingdom






    Figure 2.4 The classification hierarchy for a fig tree (A) and a cat (B)

    Unit 2: Introduction to classification
    The binomial system
    Usually, we use an organism’s common name, for example, ‘cat’. However,
    the word for ‘cat’ is different in different languages. So, people in different
    parts of the world use different words to describe the same organism. This
    makes it difficult for scientists to accurately communicate their findings
    about an organism accurately.
    To solve this problem, the biologist Linnaeus developed a system
    accurately give an organism two Latin names. Using two names is called
    the binomial system. The first word in the name is the genus to which the
    organism belongs. So for a cat, this would be Felis. The second name is
    the species to which the organism belongs. A species is a group of closely
    related organisms that are able to breed with
    one another and produce offspring that can
    also reproduce. The species name for a cat
    is domesticus. So the scientific name for a
    domestic cat is Felis domesticus.
    Let us look at another example, one
    from the plant kingdom. Yellow commelina
    is a plant found commonly in Rwanda.
    Its scientific name is Commelina africana.
    The name Commelina is its genus name.
    All commelina plants have the same genus
    name. The africana part of the name is the
    species name. Only one kind of commelina
    plant has the species name. So Commelina
    africana is the scientific name for a particular
    kind, or species, of commelina plant.

    Figure 2.5 Yellow commelina, or Commelina africana


    Figure 2.6 A scientific name
    written by hand (A), and the
    same name in print (B)
    How to write scientific names
    Look again at the scientific names you have learnt about in this unit: Ficus
    carica, Felis domesticus and Commelina africana. What do you notice about
    how they are written?
    • The first name is the name of the genus the organism belongs to; it
    starts with a capital letter.
    • The second name is the name of the species the organism belongs to; it
    starts with a small letter.
    • When written by hand, the two names must be underlined separately;
    when they are printed, they must be in italics. See Figure 2.6.

    Characteristics of organisms in the five kingdoms
    Table 2.2 shows characteristics and examples of organisms in
    each kingdom.

    Topic 1: Biodiversity and classification

    Table 2.2 Characteristics of organisms in the five kingdoms


     KingdomCharacteristics Examples
     Animalia• The organisms’ cells do not have a cell
    wall.
    • The organisms are multicellular, feed
    on other organisms, and move around.
    Snail, mosquito, snake, bird

    forest cobra
     Plantae• The organisms’ cells have a cell wall.
    • The organisms contain a green
    substance called chlorophyll and make
    their own food through photosynthesis.
    Moss, fern, maize, fig tree

    fern
     Fungi â€¢ The organisms reproduce by means of
    spores and not seeds.
    • The organisms do not photosynthesise.
    Toadstool, mould, yeast

    toadstool
     Protoctista The organisms are single cells or colonies
    of single cells.
    Amoeba, paramecium

    paramecia
     Monera â€¢ The organisms are single cells that do
    not have a membrane-bound nucleus;
    they are prokaryotic.
    • They are the smallest and simplest of all
    organisms.
     Bacterium

    bacteria


    Exercise 2.1
    1. Name the five kingdoms of organisms.
    2. Identify the kingdom to which each of the organisms described
    belongs.
    a) It has a cell wall and chloroplasts.
    b) It is a single cell.
    c) It reproduces by means of spores.
    3. Arrange the classification groups below into the correct order. Start
    with the group that contains the smallest number of organisms.



    family species order genus phylum kingdom class


    Unit 2: Introduction to classification
    Exercise 2.2
    1. Give the correct name or word for each of the following:
    a) the biologist who developed the binomial system
    b) a system that groups things into smaller and smaller groups
    c) the naming and classification of organisms.
    2. Match each animal’s
    common name with
    its scientific name. To
    help you, here are some
    Latin words translated
    into English:
    mel = honey;
    taurus = bull;
    terra = earth;
    sapiens = wise


    Common name Scientific name
    2.1 Earthworm A. Homo sapiens
    2.2 Honeybee B. Bos taurus
    2.3 Rhinoceros C. Panthera leo
    2.4 Cow D. Apis mellifera
    2.5 Hippopotamus E. Diceros bicornis
    2.6 Lion F. Lumbricus terrestris
    2.7 Human G. Hippopotamus amphibius


    Homework
    Copy the table, and then complete it by putting the following animals into
    their correct groups:
    buffalo, earthworm,
    hyena, hare, cheetah,
    jellyfish, lynx.
    (Hint: all the
    animals belong to
    one group, but only
    some belong to
    other groups, too.)



    Kingdom Animalia
    Phylum Chordata
    Class Mammalia
    Order Carnivora  
    Family Felidae (cats)  

    Use simple identification keys
    Scientists use identification keys to help them to identify unknown
    organisms. A key is a list of characteristics. Scientists compare the
    characteristics of the unknown organism with the descriptions on the
    key, and so can classify the organism.
    You will use a dichotomous key in the next activity (‘di’ means
    ‘two’). A dichotomous key consists of pairs of statements about a
    characteristic of a particular organism.


     Topic 1: Biodiversity and classification

    Activity 2.2
    Work in pairs. Look at pictures A to D alongside, and read the example of a
    dichotomous key. Then, answer the questions.

    Example of a dichotomous key
    We can identify the animals A, B, C and D by using a dichotomous key
    like this one:
    1. Has legs ________________________ See 2
    Has no legs ____________________ Snake
    2. Has two legs _________________ Chicken
    Has more than two legs __________ See 3
    3. Has six legs _______________ Grasshopper
    Has eight legs __________________ Spider

    1. The key has three steps. Each step has a pair of statements which
    describe the animals. Notice that each pair of statements in the key
    divides the animals into two groups. What characteristic is used in this
    key to group and identify the animals?
    2. Step 1 of the key separates the animals that have legs (A, B and C) from
    those that do not have legs (D). The first statement in Step 1 says that if
    the animal has legs, we should move on to Step 2. The second statement
    says that if the animal has no legs, it is a snake. Therefore animal D is
    identified as a snake.
    3. Read Step 2 of the key. The first statement says that if the animal has
    two legs, it is a chicken. Of the three remaining animals (A, B and
    C), only B has two legs. Therefore, animal B is a chicken. This leaves
    two animals (A and C), which have more than two legs. The second
    statement tells us to go on to Step 3 to identify these
    two animals.
    4. Step 3 identifies an animal with six legs as a grasshopper. Therefore,
    animal C is a grasshopper. Using the second statement in Step 3, can
    you identify animal A?
    5. Your teacher will display some specimens or pictures of different
    organisms in the classroom. Identify their observable characteristics,
    and then try to make a dichotomous key using their characteristics so
    that someone else could identify them.


    Unit 2: Introduction to classification
    Checklist of learning:
    In this unit, I have learnt:
    There are many different organisms on Earth, and scientists classify them into groups.
    There are five groups, called kingdoms, which each have many organisms; the kingdoms are:
    Animalia, Plantae, Fungi, Protoctista and Monera.
    The kingdoms are further divided into smaller and smaller groups; this is called hierarchical
    classification.
    The groups in the kingdoms are: phyla, classes, orders, families, genera and species.
    Organisms have two names in the binomial system: a genus name and a species name.
    Animals have cells without a cell wall, are multicellular, can move around, and feed on other
    organisms.
    Plants have cells with cell walls, contain chlorophyll and can make their own food through
    photosynthesis.
    Fungi reproduce by spores instead of seeds and do not photosynthesise.
    Protoctista are single-celled organisms.
    Monera are single cells without a membrane-bound nucleus.
    To appreciate the need for classification of organisms.

    Self-assessment
    1. Copy the table, and then complete it by putting the following animals into their correct groups:
    cow, perch, locust, lion, donkey, leopard.
    (Hint: all the animals belong to one group, but only some belong to other groups, too.)


    Kingdom
    Animalia
    Phylum Animalia
    Class Chordata
    Class
    Mammalia
    Order
    Carnivora
    Family Felidae (cats)  



    Topic 1: Biodiversity and classification

    2. Figure 2.7 shows four animals: A, B, C and D. Construct a dichotomous key that can be used to identify the animals.

    A:
    B:
    C:
    D:
    3. In groups, discuss the dichotomous keys that you constructed.













































































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