Biologyfor students of class IX

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CONTENTS

Cell - Fundamental Unit Of Life 7Chapter 1

Tissues 33Chapter 2

Diversity in Living Organisms 59Chapter 3

Health and Diseases 97Chapter 4

Natural Resources 115Chapter 5

Food Resources - Improvement and Management

137Chapter 6

The following 2 pages will give you a

glimpse of how effectively we have used

illustrations along with simple language

to explain a concept. The following pages

are from the part of the biology book for

IX grade, these pages detail -

“The carbon cycle”

128

How is nitrogen added back to the atmosphere?Living organisms utilise nitrates and nitrites for their life process. For example, plants take up nitrates and nitrites to make proteins and also utilise these compounds for several other biochemical pathways. The plants are eaten by animals. Thus, these complex compounds reach the body of animals. Once the living organisms die, decomposers such as bacteria present in the soil convert all the nitrogen compounds into simpler nitrates and nitrites form. Another type of bacteria converts these nitrates and nitrites into elemental nitrogen. This process is called denitrification. Thus, the nitrogen passes from its elemental form in the atmosphere to the soil and water in the form of simpler compounds and back to the atmosphere in the form of nitrogen molecule. This is known as nitrogen cycle.

The carbon cycle: Carbon is the fundamental element found in all living forms. All the bio-molecules (proteins, lipids, carbohydrates etc) required for life process are made up of carbon. The endoskeleton and exoskeleton of various animals are also formed of carbonate salts. In nature, carbon is found in two basic forms which include

1. Elemental form ( diamonds and graphite) 2. Compound form (carbon dioxide, glucose etc.)

Carbon is incorporated into living forms through a fundamental process, called photosynthesis. Photosynthesis uses sunlight and atmospheric carbon dioxide (CO2) to produce a carbon compound glucose. These glucose molecules are utilised by other living organisms. Thus, atmospheric carbon is incorporated in living form.

How is carbon added back to the atmosphere? There are various processes by which carbon gets back into the nature in the form of carbon dioxide gas. The process of respiration breaks down glucose molecules to produce carbon dioxide gas. Combustion of fuels for domestic or industrial purposes also adds carbon dioxide gas in the atmosphere. In this way, carbon dioxide is again added to the atmosphere.

Decomposers are also known as saprotrophs. These organisms are also heterotrophs like herbivores and carnivores.Examples: Bacteria and Fungi

Know more

129

Figure 14: Carbon cycle

Rapid growth of industrialisation and increase consumption of fuels emit excessive amount of carbon dioxide gas in atmosphere. This has resulted in global warming or greenhouse effects.

What is meant by Global warming? What is meant by Greenhouse effects?

Global warming is the increase in the average temperature of earth’s surface. The Greenhouse effect is the overall increase in the average temperature of the earth due to the presence of greenhouse gases. Greenhouse gases are mainly carbon dioxide, water vapour and methane.

Greenhouse is actually a term used for a glass enclosure in which tropical plants are kept warm during winters. It works on the phenomenon that heat is trapped inside the glass enclosure making the temperature much warmer than outside.

How do greenhouse gases result in global warming? Solar radiation reaches the earth and heats its surface. In return, the earth also releases energy in the form of infrared radiation. This cools down the earth surface in night. In the presence of greenhouse gases, released heat from the earth surface cannot pass through the atmosphere. This increases the overall temperature of the earth. An increase in the amount of greenhouse gases in the atmosphere would cause more heat to be retained. Thus, it will lead to global warming.

The oxygen-cycle: Oxygen is also an essential requirement to sustain life on earth. Oxygen is found in elemental form in the atmosphere. 21% of the atmospheric constituent is

The average temperature of the world has increased by 0.8ºC since 1880.

This book contains expected learning objectives from a

chapter, simple content supported with lot of illustrations and

sectional assessments and comprehensive exercises at

the end of every chapter. To get this book delivered at

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