Class X Biology Chapter 6 | Life Processes | Notes And Text Book Answers

Class X Biology Chapter 6 deals with life processes. Here you can find notes that help you to understand the lesson better as well as expected questions and answers.

6.1 What are life processes?

1. What are life processes?

Living organisms need to repair and maintain their structures throughout their lives. Life processes are those processes which together perform the maintenance job.

2. Why are molecular movements needed for life?

Living organisms have well-organized structures. For example, they have tissues made up of cells. These cells are actually made up many smaller components. However, due to the effect of environment, the ordered nature of living structures will eventually break down. When the order breaks down, the organism will not be able to live. For this reason, living organisms must repair and maintain their structures all the time. Since all living structures are made up of molecules, they have to move molecules all the time. That means molecular movement is essential for life.

3. Why do living organisms need food?

Various maintenance processes are required to prevent living structures from breaking down. Energy is needed for performing these maintenance processes. This energy is transferred from outside the body of the organism to the inside through food. Growing organisms also need additional raw materials from outside to help their tissues grow. Since living organisms tend to have carbon-based molecules, these food sources are also carbon based.

4. Define life processes

a) Nutrition

Energy is needed for performing the various repair and maintenance processes required to keep an organism alive. This energy comes from outside in the form of food. Since living organisms on the earth have carbon-based molecules, the foods that they consume are also carbon-based. However, these outside sources of energy are quite varied. Before an organism can use this energy for performing various molecular movements, it has to be converted to a uniform source of energy. In order to achieve this, the body performs a variety of chemical reactions. Oxidising-reducing reactions are the most common chemical reactions performed to break down molecules.

b) Respiration

Respiration is the process of acquiring oxygen from outside the body for the purpose of using it to break down various foods consumed by the organism. The external sources of energy – foods – are very varied in nature. Hence, before the body can use them to perform various bodily processes, they have to be converted to a uniform source of energy. The body performs a variety of chemical reactions to break down food. The most common among them are oxidizing-reducing reactions. In order to perform these chemical reactions oxygen is sourced from outside the body through a process called respiration. With the help of this oxygen, the body breaks down food particles.

5. Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

Diffusion is sufficient in the case of single-celled organisms because the entire surface of the organism is in contact with the environment. Hence single celled organisms do not require any specific organs for taking in food or removing waste from the body. This is not the case with multi-cellular organisms that have large bodies. In these organisms, not all cells are in direct contact with the surrounding environment. Hence simple diffusion will not help.

6.2 Nutrition

Why do we need energy?

We need energy to perform various functions such as walking or jumping. We also need energy to maintain a state of order in our body and to grow, develop and synthesise protein. We get this energy from the food we eat.

What are autotrophs?

Some organisms obtain the energy needed for the functioning of their body from inorganic sources in the form of carbon dioxide and water. These organisms are called autotrophs. Examples are: green plants and some bacteria.

What are heterotrophs?

Heterotrophs obtain the energy required for the functioning of their body from complex substances. These complex substances have to be broken down into simpler substances before the body can use them for its growth and maintenance. In order to convert the complex food substances into simpler forms the body uses special bio-catalysts called enzymes. All animals and fungi are examples of heterotrophs.

Autotrophic nutrition

Autotrophic organisms perform photosynthesis to meet their energy requirements. They absorb carbon dioxide and water from outside and convert them into carbohydrates in the presence of sunlight and chlorophyll. The carbohydrates thus produced provide energy to the plant. During those times when water and other inorganic nutrients are available in abundance, plants often produce more carbohydrates than they need. The excess carbohydrates are then stored in the form of starch for use in the future. Thus starch is the internal energy reserve of the plant.

Define autotrophic nutrition

Autotrophic nutrition is the process in which organisms synthesise their own organic food with the help of the inorganic raw materials absorbed from the surroundings.

Inorganic nutrients are substances such as water (H2O), carbon dioxide (CO2) and minerals (iron, zinc, potassium, copper). Autotrophic organisms such as plants obtain these inorganic nutrients from the soil and from the atmosphere. Green plants convert these inorganic substances into starch which is an organic substance.

What are autotrophs?

Autotrophs are living organisms that can prepare their own food by converting inorganic raw materials obtained from the soil and atmosphere into organic food.

Differentiate between autotrophs and heterotrophs

Autotrophs prepare their own organic food with the help of inorganic nutrients obtained from the soil and atmosphere.
They possess photosynthetic pigments that allow them to trap light.
They convert light energy into chemical energy during a process called photosynthesis.
Using the chemical energy they split water molecules into hydrogen and oxygen and reduce carbon dioxide to carbohydrates.

Examples are: All green plants and cyanobacteria
Heterotrophs obtain their organic food from outside sources such as plants or animals.

They do not perform photosynthesis.
They obtain food from plants in the form of vegetables, cereals and fruits and from animals they obtain food in the form of milk, eggs or meat.

Examples are: animals, human beings, parasites

Nutrition in Human Beings

The human digestive system consists of the following parts:-

1. Mouth
2. Buccal cavity
3. Pharynx
4. Oesophagus
5. Stomach
6. Small intestine
7. Large intestine
8. Anus


It is the topmost part of the human digestive system. It consists of 2 soft movable lips on the top and bottom of the mouth. It helps in the ingestion of food into the body.

Buccal cavity

The lips open the mouth into the buccal cavity. It is located between the cheeks. It has the following parts:-

Salivary glands


The teeth serve a major function in the human digestive system. There are 2 sets of teeth in a human being. They are the milk teeth and the permanent teeth. The milk teeth are found in young children up to the age of 5-6. They are 20 in number. Then these are replaced by the permanent teeth. They are 32 in number. The teeth consist of 2 pair of incisors, 1 pair of canines, 2 pairs of pre-molars and 3 pairs of molars. The general dental formula is 2,1,2,3. The incisors serve the purpose of cutting of food. The canines are used to tear the food and the pre-molars and molars are used to grind the food.


The tongue performs an important function in the digestion of food. It mixes the food with the saliva. The tongue has taste buds that can experience four different types of tastes. They are sweet, salt, sour and bitter.

Salivary glands

The next part of the human digestive system is the salivary glands.

They perform a major function in our body.

The salivary glands secrete saliva which makes the food soft.

The saliva consists of an enzyme called salivary amylase or ptyalin. This enzyme breaks down starch into a sugar called maltose.

On chewing food for a long time we feel sweetness. This is because the starch content present in the food in converted into sugar (maltose) by the salivary amylase.

There are 3 pairs of salivary glands.

They are:- the parotid gland, the sub- lingual gland and the sub-maxillary gland.
The parotid glands are present on the sides of the face.
The sub-lingual glands lie below the frontal part of the tongue.
The sub-maxillary glands lie at the angles of the lower jaw.

Thus the digestion of carbohydrates begins in the buccal cavity itself. This partially digested food in the buccal cavity is called bolus.

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