The environment is our surrounding including us. It consists of land, water bodies, houses, plants, animals etc.

Let’s do the following activity to find out the components of the environment.

You can observe many different things in the environment as well as in the classroom. Different environments consist of different components. Find out the things that you can see in the following environments. (Fig. 1.1)

Fig. 1.1 Different environments

Now, the size of your body is larger than earlier. The increase in size, height or amount is called growth.

Can you see a growth in everything in the environment? Let's do the following activity to find about it.

It is clear that there is a growth in some components while there is no growth in some components.

Components with a growth are called living things or living organisms.

The components without a growth are called non-living things.

Fig. 1.3 Living and non-living things

Let’s do the following activity to study more about living things/ organisms.

It is easily understood that the two categories are plants and animals. Therefore, it's clear that living things can be divided into two main groups as plants and animals.

Fig. 1.4 Some plants

Fig. 1.5 Some animals

Are there any other organisms except plants and animals?

When you observe the two water samples under the microscope, you will be able to observe some tiny organisms. These organisms that cannot be observed with the naked eye, are called micro-organisms. Some micro-organisms that can be observed in the water taken from a pond are shown in Fig 1.6.

Fig. 1.6 Some micro-organisms in a drop of water

The compound microscope is used to observe things that cannot be seen with the naked eye. A large number of micro organisms can be seen in water, soil, air and in rotten food.

Accordingly, organisms can be divided into three main groups. They are plants, animals and micro-organisms.

Growth

The above photographs show how the size of plants and animals is increased with age. This increase in size, height or amount is called growth. Growth is a common feature of organisms. There is no growth in non-living things.

Let’s do the following activity to understand further about the growth of organisms.

You can observe the growth of the plants with time. (Fig 1.9)

Nutrition

All organisms including humans need food for survival. Satisfying the food requirements of organisms is called nutrition. 

Most green plants produce food within themselves. Hence, these plants are called autotrophic. 

They use carbon dioxide from air, soil water and sun light to produce food. This process is called photosynthesis.

Animals can’t produce their own food. They depend on plants directly or indirectly. Therefore, animals are considered as heterotrophic.

Animals such as deer, cows etc. take plants as food. They depend on plants, directly. But animals such as tiger, lion take flesh as food. So, they depend on plants indirectly.

Movement

Showing different movements is a common feature of living organisms. Apart from movements, some animals can move from place to place. Animals moving from one place to another place is called locomotion. There are special appendages for animals for locomotion. Several locomotions of animals are shown in fig 1.12 below.

There are some animals that cannot move, but they show different movements. Sea anemone, Coral polyp living in oceans are such animals.(Fig 1.13)

When a Mimosa plant is touched, the leaves of the Mimosa plant shows a sleeping movement. Also, Albesia, Sesbenia (Kathurumurunga/ Agaththy), Tamarind leaves show sleeping movements in the evening. These are some examples of movements of plants.

Although, plants show many other movements, they cannot be observed during a short period of time.

Non-living things do not move on their own. Non-living things will move only when an external force is applied.

Respiration

When a person is lying in a relaxed position, you will see that his chest and the stomach move up and down. Why?

It is because we take air in (inhale) and release air out (exhale). Oxygen in the air, once breathed in, reacts with the food stored in the body and produces energy. This process is called respiration. In the process of respiration, oxygen is used and carbon dioxide is released.

Oxygen needed to breathe is taken in by inhaling while the produced carbon dioxide is released by exhaling.

The chest moves up and down because of the process of inhaling and exhaling. These movements are called respiratory movements.

Plants too breathe. But, they do not show respiratory movements as animals.

Respiration is a common feature of every organism. There is no respiration in non-living things.

Let’s do the following experiment to find out whether exhaled air contains carbon dioxide.

You will see that the colourless lime water changes into off white. This happens due to the presence of carbon dioxide. Hence, the exhaled air contains carbon dioxide.

Reproduction

It is obvious that every organism dies one day or the other. So, for the continuation of the living world it is essential to have new generations.

A matured living being producing new members of the same species is known as reproduction.

Fig 1.17 shows the reproduction of some plants and animals.

Reproduction of organisms occurs in different methods. Reproduction is essential for the existence of living organisms. It's common for all organisms. Reproduction does not occur in non-living things.

Diversity of Plants

There is a vast diversity among plants and animals in the environment.

• Based on the nature of plants, they can be categorized as plants, trees, shrubs and creepers.

• Also there is diversity among plants in relation to morphological features such as roots, stem, leaves, flowers, shape, size and colour of fruits and seeds.

• Plants grow not only on the terrestrial environments but also, on aquatic, coastal and mangrove environments.

Diversity of Animals

The following figure shows that there is a vast diversity among animals too.

You will learn more about the diversity among animals and plants in your upper grades. Diversity among animals and plants is a very important factor for the environment. It increases the beauty of the nature too. So, it is our responsibility to care for and conserve the animals and plants. You must not discharge harmful materials to the environment. Hence, you too can take part in protecting the wonder of the nature.

Compare the following table with the table you completed above.

Growth in animals visibly stops after a certain period of time.

Dichotomous Keys

It is very easy to use dichotomous keys to classify and identify organisms.

Categorization of organisms using the presence or absence of a characteristic feature is known as a dichotomous key. It is more suitable to use external features that can be easily observed.

Following figure shows how a dichotomous key is used to classify and identify some leaves.

Following dichotomous key shows a classification of some animals.

(iv) The gas emitted during the process of photosynthesis is

a) oxygen 

b) carbon dioxide

c) nitrogen 

d) hydrogen

(v)  The most suitable equipment to observe the micro-organisms in water is

a) telescope 

b) compound microscope

c) magnifying glass 

d) binocular

02  Select the most suitable word and fill in the blank.

(i) The energy needed for photosynthesis is supplied by ...................... (sun / man).

(ii)  There ...................... (is / isn’t) a limit of growth within plants.

(iii) Most of the animals are ................................. (autotrophic/ heterotrophic).

(iv) A characteristic which can be seen in animals but cannot be seen in most plants is ..................(locomotion / reproduction)

(v) An essential requirement for photosynthesis is............... (oxygen / carbon dioxide)

03. Use a dichotomous key to classify the given plants.

grass, mango, guava, hibiscus, coconut

04. Use a dichotomous key to classify the given animals.

cat, butterfly, cock, cow, rat snake, leech