Chapter at a Glance

Living beings need several important processes to stay alive. These are called life processes. In this chapter, we mainly learn about nutrition and respiration in animals.

• Nutrition: obtaining food and using its nutrients.
• Digestion: breaking complex food into simpler forms.
• Absorption: taking digested nutrients into the blood.
• Egestion: removing undigested waste from the body.
• Breathing: taking air in and sending air out.
• Respiration: using oxygen to break down glucose and release energy.

9.1 Nutrition in Animals

Animals obtain energy from food. Food contains complex substances such as carbohydrates, proteins and fats. These substances must be broken down into simpler forms before the body can use them.

This breaking down of food takes place in the long tube called the alimentary canal. It starts at the mouth and ends at the anus.

Human digestive system diagram. Image source: Wikimedia Commons, reusable open/public-domain educational image.

Beginning with the Mouth

Digestion begins in the mouth. Teeth crush and chew food. This initial breakdown is called mechanical digestion.

Saliva mixes with food. It contains a digestive juice that helps break down starch into sugar.

Important Experiment: Iodine Test

Iodine turns starch blue-black.

• Unchewed boiled rice contains starch, so iodine gives a blue-black colour.
• Chewed rice has some starch broken down by saliva, so the colour may be very light or may not appear.

Food Pipe or Oesophagus

The tongue helps push softened food into the oesophagus, also called the food pipe.

The walls of the food pipe contract and relax in a wave-like movement. This pushes food towards the stomach.

This wave-like movement continues through the alimentary canal and helps move food forward.

Stomach

The stomach walls contract and relax to churn the food.

The stomach lining releases digestive juice, acid and mucus.

• Digestive juice helps break down proteins.
• Acid helps in digestion and kills many harmful bacteria.
• Mucus protects the stomach lining from acid.

Food remains only partially digested in the stomach and becomes a semi-liquid mass.

Small Intestine

The partially digested food moves from the stomach into the small intestine.

The small intestine is almost 6 metres long and is the longest part of the alimentary canal.

It receives digestive secretions from:

• Liver – produces bile.
• Pancreas – produces pancreatic juice.
• Small intestine – produces digestive juices.

Bile neutralises acids and breaks fats into tiny droplets, making fat digestion easier.

Pancreatic juice helps break down carbohydrates, proteins and fats.

The digested nutrients pass through the wall of the small intestine into the blood. This process is called absorption.

The inner lining contains many finger-like projections that increase the surface area for absorption.

Large Intestine and Egestion

Undigested food moves into the large intestine.

The large intestine absorbs water and some salts. The remaining semi-solid waste is called stool.

The stool is stored in the rectum and finally removed through the anus.

This removal of undigested waste is called egestion.

9.1.2 Digestion in Other Animals

Ruminants

Animals such as cows and buffaloes partially chew grass and swallow it. Later, the partially digested food comes back into the mouth and is chewed again.

This process is called rumination. Animals that do this are called ruminants.

A cow may spend about 8 hours a day chewing food.

Digestion in Birds

Birds do not have teeth. They have a muscular chamber called the gizzard.

Food is broken down in the gizzard by its muscular movement, often with the help of small stones or grit swallowed by the bird.

9.2 Respiration in Animals

Respiration is the process by which nutrients are converted into usable energy.

In humans, oxygen helps break down glucose and release energy.

Human respiratory system. Public-domain image from the U.S. National Institutes of Health via Wikimedia Commons.

Breathing in Humans

Breathing is the process of inhaling and exhaling air.

Inhalation

• Ribs move upward and outward.
• Diaphragm moves downward.
• Space inside the chest increases.
• Air enters the lungs.

Exhalation

• Ribs move downward and inward.
• Diaphragm moves upward.
• Space inside the chest decreases.
• Air is pushed out of the lungs.

Simple Breathing Model

In the bottle model:

• Balloons represent the lungs.
• Rubber sheet represents the diaphragm.
• Pulling the rubber sheet down makes the balloons inflate.
• Moving the rubber sheet upward makes the balloons deflate.

Gas Exchange in the Lungs

The air reaches tiny balloon-like structures called alveoli.

The walls of alveoli are thin and surrounded by tiny blood vessels.

• Oxygen passes from the alveoli into the blood.
• Carbon dioxide passes from the blood into the alveoli.
• Carbon dioxide is then removed when we exhale.

Alveolus diagram. Source: Wikimedia Commons, openly licensed educational illustration.

Breathing and Respiration are Different

Circulatory System

The circulatory system transports nutrients, oxygen and other substances throughout the body.

It includes:

• Heart
• Blood
• Blood vessels

The heart pumps blood through blood vessels. Blood carries oxygen and nutrients to different parts of the body and also carries waste products away.

How Other Animals Breathe

Different animals have different breathing mechanisms because they live in different habitats.

In a Nutshell

• Life processes are essential for survival.
• Digestion changes complex food into simpler substances.
• The alimentary canal runs from mouth to anus.
• The small intestine is the main site of nutrient absorption.
• The large intestine absorbs water and some salts.
• Ruminants bring partially digested food back to the mouth for chewing.
• Breathing means inhalation and exhalation.
• Gas exchange occurs in the alveoli.
• Respiration releases energy from glucose.
• Breathing is physical; respiration is chemical.
• The circulatory system transports oxygen and nutrients.
• Different animals use different structures for breathing.

Let Us Enhance Our Learning

Textbook Questions with Easy Solutions

1. Complete the journey of food through the alimentary canal by fi lling up the boxes with appropriate parts—

Solution: The complete journey is:

Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus

2. Sahil placed some pieces of chapati in test tube A. Neha placed chewed chapati in test tube B, and Santushti took boiled and mashed potato in test tube C. All of them added a few drops of iodine solution to their test tubes—A, B, and C, respectively. What would be their observations? Give reasons.

Solution:

• Test tube A: Chapati contains starch, so it will turn blue-black.
• Test tube B: Chewing allows saliva to act on starch, so the colour may be lighter blue-black or may not appear.
• Test tube C: Boiled and mashed potato contains starch, so it will turn blue-black.

3. What is the role of the diaphragm in breathing?
(i) To fi lter the air
(ii) To produce sound
(iii) To help in inhalation and exhalation
(iv) To absorb oxygen

Solution: (iii) To help in inhalation and exhalation.

4. Match the following
Name of the part Functions
(i) Nostrils (a) fresh air from outside enters
(ii) Nasal passages (b) exchange of gases occurs
(iii) Windpipe (c) protects lungs
(iv) Alveoli (d) tiny hair and mucus help to trap dust and dirt from the air we breathe
(v) Ribcage (e) air reaches our lungs through this part

Solution:

(i) Nostrils → (a) fresh air from outside enters

(ii) Nasal passages → (d) tiny hair and mucus help to trap dust and dirt from the air we breathe

(iii) Windpipe → (e) air reaches our lungs through this part

(iv) Alveoli → (b) exchange of gases occurs

(v) Ribcage → (c) protects lungs

5. Anil claims to his friend Sanvi that respiration and breathing are the same process. What question(s) can Sanvi ask him to make him understand that he is not correct?

Solution: Sanvi can ask:

• Is breathing the same as breaking down glucose to release energy?
• Is breathing a physical process while respiration is a chemical process?
• Does respiration occur inside body cells?

These questions show that breathing and respiration are different processes.

6. Which of the following statements is correct and why?
Anu: We inhale air.
Shanu: We inhale oxygen.
Tanu: We inhale air rich in oxygen.

Solution: Tanu is correct. We inhale air, and this air is rich in oxygen. We do not inhale pure oxygen.

7. We often sneeze when we inhale a lot of dust-laden air. What can be possible explanations for this?

Solution: Dust irritates the lining of the nasal passages. The tiny hairs and mucus trap dust, and sneezing helps remove unwanted particles from the respiratory passage.

8. Paridhi and Anusha of Grade 7 started running for their morning workout. After they completed their running, they counted their breaths per minute. Anusha was breathing faster than Paridhi. Provide at least two possible explanations for why Anusha was breathing faster than Paridhi.

Solution: Possible reasons include:

• Anusha may have run faster or exercised more intensely.
• Anusha may have been less physically fit.
• Her body may have needed more oxygen after exercise.
• Individual breathing rates can be different.

9. Yadu conducted an experiment to test his idea. He took two test tubes, A and B, and added a pinch of rice fl our to the test tubes, half-fi lled with water and stirred them properly. To test tube B, he added a few drops of saliva. He left the two test tubes for 35–45 min. After that, he added iodine solution into both the test tubes. Experimental results are as shown in Fig. 9.15. What do you think he wants to test?

Solution: He wants to test whether saliva breaks down starch present in rice flour.

10. Rakshita designed an experiment taking two clean test tubes, A and B and fi lled them with lime water as shown in the fi gure. In test tube A, the surrounding air that we inhale was passed on by sucking air from the pipe, and in test tube B, the exhaled air was blown through the pipe (Fig. 9.16). What do you think she is trying to investigate? How can she confi rm her fi ndings?

Solution: She is investigating whether exhaled air contains more carbon dioxide than inhaled air.

She can confirm her finding because lime water turns milky when carbon dioxide reacts with it. The lime water receiving exhaled air should turn milky more clearly.

Quick Revision Table

Exploratory Projects

• Find good practices for maintaining oral hygiene and prepare a report.
• Find ways to maintain a healthy digestive system and suggest suitable foods.
• Prepare a 3-D model of the digestive system using coloured clay and label its parts.
• Find out what air quality and AQI mean and study their effects on respiratory health.
• Read about box-breathing and find out its benefits.
• Find out how the respiratory system of birds may help them fly at high altitudes where oxygen levels are low.

Chapter 9 Complete

Life processes keep animals alive. Nutrition provides nutrients, digestion makes food usable, respiration releases energy, and transport systems distribute important substances throughout the body.