ICSE Class 6 Biology Chapter 1 Life on Earth

Unit 1: Life on Earth

Learning Objectives

Characteristics of living beings

Unicellular and multicellular organisms

Differences in living and non-living things

Differences in plants and animals

Living and Non-Living Things

Biology is the science of life. In life science, we study the life processes of living organisms. Dogs, cats and plants are living while stone, milk, chalk are non-living. All life activities of an organism take place in a cell.

All organisms have certain characteristics by which they can be differentiated from non-living things. Let us study the characteristics of living beings.

1. Living Beings are Made up of Cells

The body of a living being is made up of tiny compartments called cells. A cell is the basic unit of life. If we examine an onion peal under a microscope, we will observe tiny compartments called cells. The term 'cell' was first coined by Robert Hooke. Each cell contains living substances called protoplasm. Protoplasm performs all the functions of a cell. Organisms may be made up of one or many cells. Organisms which are made up of a single cell are very small and can be seen under a microscope. They are called unicellular. Organisms which are made up of many cells are called multicellular. Amoeba, paramaecium and bacteria are unicellular organisms, while fish, earthworm, dog and man are multicellular organisms.

Some unicellular organisms are shown in a figure displaying Amoeba, Bacteria, and Paramaecium.

Activity 1.1: Animal cells

Open your mouth and lightly scrape the inner part of your cheek with a finger or toothpick. Put the scrapings on a glass slide. Add a drop of water and cover it with a cover slip. Observe it under a microscope. Draw the structure of cheek cells which you see on the slide (Fig. 1.2). These are animal cells.

A figure shows Human cheek cells with labels pointing to Nucleus and Cytoplasm.

Activity 1.2: Plant cells

Take an onion and cut it into several pieces. Take a fleshy part of it. You will see a thin paper layer on the concave side. Hold this side towards you and break the piece. Tear off the thin peel. Place a small piece of this peel on a glass slide. Put a drop of water and cover it with a cover slip. Observe it under a microscope. You will observe small chamber like structures which are called cells. These are plant cells.

A figure shows Cells of an onion peel with labels pointing to Nucleus and Cytoplasm.

Teacher's Note

Every living thing, from the tiniest bacterium to humans, is made of cells - the basic units that carry out all life functions in your body.

2. Growth and Changes

All living things grow. Growth is an irreversible change in size and mass. Animals and human beings grow to a certain size. Plants grow throughout their lifetime. A seedling grows into a plant. A puppy grows into a dog. Their growth is the result of cell division. As the number of cells increases, the organisms grow in size. The new cells also replace old cells resulting in the growth of a baby into a boy and a boy into an adult.

The growth in a non-living is due to the deposition of matter externally, e.g. growth of a crystal. A crystal grows in size due to deposition of more particles on the outer surface of the crystal.

A figure shows A child and an adult.

Teacher's Note

Just like a growing child gains height and weight, all living organisms increase in size through the process of cell division and growth.

3. Living Things Move

Movement is one of the important signs of life. Animals move from one place to another in search of food and shelter. They move to protect themselves from enemies.

All plants except some floating plants remain fixed to the soil at one place. They show movement in their parts. Roots of a plant always grow towards the soil while the shoots tend to grow towards light.

Non-living objects do not move on their own. They are moved from one place to another with the help of an external force.

Teacher's Note

Animals actively search for food by moving around, while plants stay rooted but their leaves and stems still grow toward light and water.

4. Nutrition

All living beings need food. Green plants manufacture green pigment called chlorophyll on their leaves. Plants make their own food in the presence of sunlight by using carbon dioxide from air and water from the soil. Green plants are called autotrophs or producers as they manufacture their own food. Since animals do not possess chlorophyll, they cannot manufacture their own food. Animals directly or indirectly depend on plants for their food. They are called heterotrophs or consumers.

A schematic diagram shows autotrophic nutrition in green plants, depicting CO2 from atmosphere, sunlight, water and minerals from soil through xylem, and glucose production.

Teacher's Note

Plants are nature's food makers - they capture sunlight to create their own food, while we as animals depend on eating plants or other animals for energy.

5. Living Things Excrete

All living organisms generate some wastes in their body in different forms. They get rid of these waste-products from their body through a system, called excretory system. Animals have special organs like kidneys, lungs, gills, and sweat glands to remove wastes from the body. The wastes are in the form of urine, sweat, exhaled air and solid wastes like faeces. Plants throw out their gaseous waste-products from the small openings in their leaves called stomata. The other excretory products of plants are gums and resins.

6. Respiration

All living things need energy for their activities. The energy is obtained from food. Living beings take in oxygen during breathing. Food is oxidised with the help of oxygen in the body to produce energy. The chemical process by which energy is released from food is called respiration. Living organisms give out carbon dioxide during respiration. Non-living things do not respire.

7. Response to Stimuli

All living beings respond to temperature, light, smell, etc. If we touch a hot object, we immediately withdraw our hand. Temperature is a stimulus. The change in the environment is called stimulus and the reaction of the organism is called response. When we feel hungry we eat. Plants also respond. The shoots of plants move towards light. Roots of plants respond to the gravity of the earth and therefore roots go deep into the earth. Leaves of a sensitive plant droop down and close on touching. Non-living things do not respond as they cannot feel anything.

Teacher's Note

When you touch something hot and quickly pull your hand away, that's your body responding to a stimulus - a reflex that living things do automatically.

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