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
| Kingdom | Characteristics |
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 | • 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 | • 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.
Oral activity
Topic 1: Biodiversity and classificationThe importance of classification
Figure 2.2 Living and non-living things1. Draw a table with two columns. In one column, write down all the
Topic 1: Biodiversity and classificationThe diagram below shows two classification hierarchies. A hierarchy is a
Figure 2.4 The classification hierarchy for a fig tree (A) and a cat (B)Unit 2: Introduction to classificationThe binomial systemUsually, we use an organism’s common name, for example, ‘cat’. However,
Figure 2.6 A scientific name
B
C
Figure 3.1 The flowering plants maize (A), sorghum (B) and cassava (C) are important food crops.Topic 1: Biodiversity and classificationThe external structure of a
C. Stem tuber D. CORM
Figure 3.3 Examples of
Leaves are attached to a plant’s stem at the nodes by a stalk called a petiole
Figure 3.5 Leaves can have different shapes and sizes.Topic 1: Biodiversity and classificationFunctions of leaf partsTable 3.2 describes the functions of the different parts of the leaf.Table 3.2 Parts of the leaf and their functions
Figure 3.6 Examples of leaf
Experiment 3.4Work in groups. Complete the experiment, and then answer