NCERT Class 7 Science Curiosity Chapter 09 Life Processes in Animals PDF Download

Chapter 9: Life Processes in Animals

If your food is fully digested before you eat again, you won't need medicine for pain.

(Thirukkural 942)

In the Grade 6 Science textbook Curiosity, chapter 'Living Creatures: Exploring their Characteristics', we learnt about processes essential for survival of living beings like nutrition, respiration, excretion, and reproduction. These are collectively called life processes. In this chapter, we will learn about life processes such as nutrition and respiration in detail.

Observe your surroundings and notice what animals eat. Animals eat different types of food. Bees and sunbirds suck the nectar of flowers, while infants of humans and many other animals feed on their mother's milk. Snakes, like python, swallow the animals they prey upon. Some aquatic animals filter tiny food particles floating nearby and feed upon them.

Animals, including humans, obtain energy from food, which enables them to carry out various life processes. Animals consume food that contains complex components, such as carbohydrate, protein, and fat. These complex food components have to be broken down into simpler forms before the body can use them. But how does this process happen?

Breaking down of complex food components into simpler forms occurs in a long tube called the alimentary canal. This process starts in the mouth and ends at the anus (Fig. 9.1). As food moves through this canal, digestive juices secreted at different parts break it down into simpler forms. This simpler form of food is absorbed by different parts of our alimentary canal and transported to various parts of our body to carry out various functions.

[Figure 9.1: Human digestive system, See in your textbook]

9.1 Nutrition in Animals

How do the complex food components get broken down into simpler forms and used by the body in various animals? Is this process the same in all animals or does it vary? Let us first try to understand this process in humans.

9.1.1 Digestion in human beings

Let us trace the journey of food inside our body as it passes through different parts of the alimentary canal.

Beginning with the mouth cavity

The journey of the food you eat begins when it enters your mouth. Your teeth break down food you eat into smaller pieces by the processes of crushing and chewing. This process of initial breakdown of food into fine pieces is called mechanical digestion. Think about your favourite food. Does your mouth feel watery?

This happens because of more saliva that gets released when you recall your favourite food.

What do you think is the role of saliva in your mouth? What do you feel when you eat other types of food, such as chapati? Let us find out.

Take a small piece of chapati or a bite-sized portion of boiled rice and chew it properly for 30 - 60 seconds. At first, the chapati or rice has its usual taste, but as you continue chewing, do you notice a change in taste? The food begins to taste sweet! Have you ever wondered why this happens?

Teacher's Note

When you chew starchy food like rice or chapati for a long time and it tastes sweet, that's saliva at work breaking starch into sugar. This is a direct observation you can make yourself, and it shows chemical digestion happening in your mouth, not just mechanical digestion from your teeth.

Chapati or rice contains starch, which is a type of carbohydrate. Our saliva contains a digestive juice that helps break down starch into sugar. This explains why starchy food, like chapati, tastes sweet when you chew it for a long time. Saliva helps to break down components of food into simpler ones.

Science and Society

A healthy mouth requires good oral hygiene. We should brush our teeth and clean our tongue twice a day, and rinse our mouth with water after each meal to prevent tooth decay and bad smell in the mouth. Find out the ways our elders were maintaining oral hygiene.

Activity 9.1: Let us investigate

• Take two test tubes and label them as 'A' and 'B'.
• Take one teaspoonful of boiled rice in test tube A, and take a teaspoonful of boiled rice after chewing it for 30 - 60 seconds in test tube B.
• Add 3 - 4 mL of water in both the test tubes.
• Note the initial colour of the rice-water mixture in Table 9.1.
• Add 3 - 4 drops of iodine solution into each test tube with the help of a dropper. Mix the content of each test tube separately and observe.

Record your observations in Table 9.1.

Teacher's Note

In Activity 9.1, tube A (unchewed rice) will turn blue-black when iodine is added because starch is still present. Tube B (chewed rice) will show little or no colour change because saliva has already broken down most of the starch into sugar. This is how you know the enzyme in your saliva is actually working.

Key Points

• Animals eat different types of food, but all need to break down complex food components into simpler forms that the body can use for energy and other functions.
• Mechanical digestion happens in the mouth when teeth crush and chew food into small pieces, while chemical digestion begins when saliva breaks down starch into sugar.
• Saliva contains a digestive juice that breaks down starch into sugar, which is why starchy foods like rice and chapati taste sweet when chewed for a long time.
• The alimentary canal is a long tube running from the mouth to the anus, where food is digested and absorbed for the body to use.
• Good oral hygiene, such as brushing teeth twice a day and rinsing the mouth after meals, helps prevent tooth decay and maintain a healthy mouth.

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