Life Processes in Animals
Explore how animals obtain and digest food, how humans breathe and respire, and how nutrients and oxygen reach different parts of the body.
Chapter Snapshot
- Life processes are essential activities that keep living organisms alive.
- Animals obtain food from their surroundings and break complex nutrients into simpler forms.
- Digestion begins in the mouth and continues through the alimentary canal.
- Saliva starts the digestion of starch in the mouth.
- The stomach, small intestine, liver and pancreas play important roles in digestion.
- Most digested nutrients are absorbed through the wall of the small intestine.
- The large intestine absorbs much of the remaining water and some salts.
- Ruminants and birds show special adaptations for digesting food.
- Breathing is the physical process of taking air in and giving air out.
- Respiration is a chemical process in which nutrients such as glucose are broken down to release usable energy.
- Gas exchange takes place in tiny air sacs called alveoli inside the lungs.
- The circulatory system transports oxygen, nutrients and other substances around the body.
- Different animals use lungs, gills or skin for gas exchange depending on their habitat and body structure.
What You Will Learn
- Define life processes and explain why they are essential for survival
- Explain why complex food components need to be digested
- Trace the journey of food through the human alimentary canal
- Describe the roles of the mouth, oesophagus, stomach, small intestine and large intestine
- Explain the functions of saliva, bile and pancreatic juice in digestion
- Describe absorption of digested nutrients in the small intestine
- Explain rumination in grass-eating animals and digestion in birds
- Differentiate between breathing and respiration
- Identify the main parts of the human respiratory system
- Explain inhalation and exhalation using the movement of the ribs and diaphragm
- Describe gas exchange in the alveoli
- Explain the basic relationship between respiration and energy release
- Describe the role of the circulatory system in transporting nutrients and oxygen
- Compare breathing mechanisms in humans, fish, frogs and earthworms
Chapter Overview
Every living organism must perform certain essential activities in order to stay alive.
Animals need food. Food must be processed so that useful nutrients can be absorbed. Oxygen must reach body cells. Energy must be released from nutrients. Useful substances must be transported from one part of the body to another, and wastes must be removed.
These essential activities are known as life processes.
In this chapter, we will study two major life processes in greater detail:
nutrition and respiration.
We will also see how the circulatory system connects these processes by transporting nutrients and oxygen throughout the body.
Detailed Explanation
1. Nutrition in Animals
Animals cannot usually prepare their own food in the way green plants do.
They obtain food from:
- plants;
- other animals;
- or both.
Different animals have different feeding methods.
Examples include:
- bees sucking nectar;
- snakes swallowing prey;
- grazing animals eating grass;
- humans chewing food;
- some aquatic animals filtering food particles from water.
Although feeding methods differ, animals must obtain nutrients needed for:
- energy;
- growth;
- repair;
- maintenance of the body.
Food contains components such as:
- carbohydrates;
- proteins;
- fats;
- vitamins;
- minerals.
Many food components are too complex to be used directly by the body.
They must first be broken into simpler forms.
This process is called digestion.
Show answer
2. Human Digestive System
Digestion in humans takes place mainly in a long muscular tube called the alimentary canal.
The main parts are:
- mouth;
- oesophagus or food pipe;
- stomach;
- small intestine;
- large intestine;
- rectum;
- anus.
Important associated organs include:
- liver;
- pancreas.
3. Digestion Begins in the Mouth
The journey of food begins in the mouth.
The mouth performs both mechanical and chemical digestion.
Teeth and Mechanical Digestion
Teeth:
- cut food;
- tear food;
- crush food;
- grind food.
Breaking food into smaller pieces also helps digestive juices act more effectively.
Role of the Tongue
The tongue:
- helps move food during chewing;
- mixes food with saliva;
- helps in tasting;
- pushes softened food towards the throat for swallowing.
Role of Saliva
Saliva moistens food and makes swallowing easier.
It also begins chemical digestion of starch.
Foods such as:
- rice;
- chapati;
- potatoes
contain starch.
When starchy food is chewed for a long time, it may begin to taste slightly sweet because saliva helps break down starch into simpler sugars.
4. Oesophagus — The Food Pipe
After food has been chewed and mixed with saliva, it is swallowed.
It enters a muscular tube called the oesophagus.
Food does not simply fall into the stomach because of gravity.
The walls of the alimentary canal show coordinated muscular contractions and relaxations that move food forward.
5. Digestion in the Stomach
The stomach is a muscular, bag-like organ.
When food enters it:
- stomach walls contract and relax;
- food is churned;
- food mixes with secretions produced by the stomach lining.
The stomach secretion contains:
- digestive juice;
- acid;
- mucus.
Digestive Juice
Digestive substances in the stomach help break down proteins into simpler components.
Acid
The acid in the stomach:
- helps create suitable conditions for digestion;
- helps in the breakdown of food;
- kills many harmful bacteria entering with food.
Mucus
The stomach also produces mucus.
6. The Small Intestine
After partial digestion in the stomach, food enters the small intestine.
Despite its name, the small intestine is the longest part of the alimentary canal. In humans it is roughly several metres long.
It is called "small" because it is narrower, not because it is shorter than the large intestine.
The small intestine receives digestive secretions from:
- its own inner lining;
- the liver;
- the pancreas.
7. Role of the Liver and Bile
The liver is an important organ associated with digestion.
It produces bile.
Bile performs important functions.
It helps:
- neutralise acidic material entering the small intestine from the stomach;
- break large fat masses into tiny droplets, making fat digestion easier.
8. Role of the Pancreas
The pancreas releases pancreatic juice into the small intestine.
Pancreatic juice:
- is basic in nature;
- helps neutralise acidic material;
- helps digest carbohydrates;
- helps digest proteins;
- helps digest fats.
The inner lining of the small intestine also releases digestive juice that continues the breakdown of partially digested food.
By the time food has passed through the small intestine:
- complex carbohydrates are broken into simpler forms;
- proteins are broken into simpler components;
- fats are broken into simpler components;
- most useful nutrients are ready for absorption.
9. Absorption of Nutrients
Digestion alone is not enough.
The simpler nutrients must enter the body so that they can reach tissues.
Most nutrient absorption takes place in the small intestine.
Its inner lining contains thousands of tiny finger-like projections.
These projections greatly increase the surface area available for absorption.
After absorption, blood transports nutrients to different parts of the body.
These nutrients are then used for:
- energy;
- growth;
- repair;
- maintenance of tissues.
Show answer
10. The Large Intestine
After most nutrients have been digested and absorbed, the remaining undigested material moves into the large intestine.
Its major functions include:
- absorption of water;
- absorption of some salts;
- formation of semi-solid waste.
The remaining semi-solid waste is called stool.
The stool is stored temporarily in the rectum.
It is later expelled through the anus.
11. Fibre and Digestive Health
Dietary fibre is not digested in the same way as many nutrients, but it plays an important role in digestive health.
Fibre-rich foods include:
- fruits;
- vegetables;
- whole grains;
- pulses.
Fibre helps provide bulk to intestinal contents and supports regular movement of stool.
12. Digestion Is Different in Different Animals
Animals eat different types of food.
Their digestive systems therefore show adaptations suited to their diets.
Two useful examples are:
- ruminants;
- birds.
13. Digestion in Ruminants
Cows, buffaloes, goats and some other grass-eating animals are called ruminants.
The process is called rumination.
Basic sequence
- Grass is eaten and partly chewed.
- It is swallowed.
- Partial digestion occurs.
- Partially digested food returns to the mouth.
- The animal chews it thoroughly.
- The food is swallowed again for further digestion.
Remember:
Process → rumination
Animals → ruminants
Do not use the two terms interchangeably.
14. Digestion in Birds
Birds do not have teeth like humans.
How do they mechanically break down food?
Many birds possess a muscular chamber called the gizzard.
Some birds swallow small stones or grit.
The muscular walls of the gizzard contract and relax, and the grit can help grind the food.
Human, Ruminant and Bird Digestion
| Feature | Humans | Ruminants | Birds |
|---|---|---|---|
| Initial mechanical breakdown | Teeth chew food | Food is partly chewed and later chewed again | No teeth; gizzard helps grind food |
| Special feature | Complex alimentary canal with specialised digestive organs | Rumination | Muscular gizzard |
| Adaptation | Mixed diet | Suited to digestion of grass and plant material | Mechanical grinding without teeth |
15. From Digested Food to Energy
Digestion converts complex food into simpler nutrients.
But digestion itself is not the final step in obtaining usable energy.
Simple nutrients such as glucose can be broken down inside the body to release energy.
This process is called respiration.
Oxygen plays an important role in the form of respiration studied at this level.
Word Equation for Respiration
This represents the overall idea that glucose reacts with oxygen and releases energy.
The released energy supports activities such as:
- walking;
- running;
- growth;
- repair;
- movement;
- maintaining body functions.
16. Breathing Is Not the Same as Respiration
These two terms are often confused.
Breathing includes:
- inhalation — breathing in;
- exhalation — breathing out.
Respiration, on the other hand, is a chemical process occurring inside the body.
Breathing vs Respiration
| Feature | Breathing | Respiration |
|---|---|---|
| Type of process | Physical process | Chemical process |
| Main idea | Air enters and leaves the lungs | Nutrients are broken down to release energy |
| Oxygen | Brought into the respiratory system | Used in energy-releasing reactions |
| Carbon dioxide | Removed from the lungs during exhalation | Produced during the breakdown of glucose in the process studied here |
| Main outcome | Gas movement and exchange | Release of usable energy |
Show answer
17. Human Respiratory System
The human respiratory system provides a pathway for air and enables gas exchange.
The major parts include:
- nostrils;
- nasal passages;
- windpipe;
- branching air tubes;
- lungs;
- alveoli;
- diaphragm.
The lungs are protected by the rib cage.
18. Nostrils and Nasal Passages
Air normally enters through the nostrils.
It passes through the nasal passages.
Tiny hairs and mucus help trap:
- dust;
- dirt;
- some particles present in inhaled air.
19. Windpipe and Lungs
From the nasal passages, air travels down the windpipe.
The windpipe divides into branches that enter the two lungs.
Inside the lungs, these branches divide repeatedly into smaller passages.
The smallest passages lead to numerous tiny balloon-like air sacs called alveoli.
20. How Do We Breathe?
Breathing involves coordinated movements of:
- ribs;
- chest;
- diaphragm.
Inhalation
When we breathe in:
- ribs move upwards and outwards;
- the diaphragm moves downwards;
- space inside the chest increases;
- air enters the lungs.
Exhalation
When we breathe out:
- ribs move downwards and inwards;
- the diaphragm moves upwards;
- space inside the chest decreases;
- air is pushed out of the lungs.
Inhalation vs Exhalation
| Feature | Inhalation | Exhalation |
|---|---|---|
| Air movement | Air enters lungs | Air leaves lungs |
| Ribs | Move up and outward | Move down and inward |
| Diaphragm | Moves downward | Moves upward |
| Chest space | Increases | Decreases |
21. Gas Exchange in the Alveoli
Air reaching the lungs eventually fills the alveoli.
Alveoli have:
- very thin walls;
- a large combined surface area;
- a rich supply of tiny blood vessels around them.
These features make gas exchange efficient.
Oxygen
Oxygen present in the air inside the alveoli passes into the blood.
The blood carries oxygen to different parts of the body.
Carbon Dioxide
Blood returning from body tissues carries carbon dioxide.
Carbon dioxide passes from the blood into the alveoli.
It is then removed during exhalation.
22. Inhaled and Exhaled Air
The air we breathe in and the air we breathe out are not exactly the same.
Inhaled air contains approximately:
- 21% oxygen;
- about 0.04% carbon dioxide.
Exhaled air contains approximately:
- 16–17% oxygen;
- 4–5% carbon dioxide.
This shows two important things.
First, the body uses some of the inhaled oxygen.
Second, exhaled air contains much more carbon dioxide than inhaled air.
Inhaled Air vs Exhaled Air
| Gas | Inhaled Air | Exhaled Air |
|---|---|---|
| Oxygen | About 21% | About 16–17% |
| Carbon dioxide | About 0.04% | About 4–5% |
23. Testing Exhaled Air with Lime Water
Carbon dioxide can be detected using lime water.
When exhaled air is passed through lime water, the lime water becomes milky more readily because exhaled air contains a higher concentration of carbon dioxide.
Show answer
24. Why Does Breathing Become Faster During Exercise?
When we exercise:
- muscles work harder;
- more energy is required;
- respiration rate in active tissues increases;
- more oxygen is needed;
- more carbon dioxide is produced.
Therefore, breathing generally becomes faster and deeper.
25. Circulatory System — The Transport Link
Digested nutrients enter the blood from the small intestine.
Oxygen enters the blood from the alveoli.
How do they reach every part of the body?
They are transported by the circulatory system.
It includes:
- heart;
- blood;
- blood vessels.
Heart
The heart pumps blood.
Blood
Blood transports:
- oxygen;
- nutrients;
- carbon dioxide;
- other substances.
Blood Vessels
Blood vessels form pathways through which blood travels around the body.
26. Do All Animals Breathe in the Same Way?
No.
Different animals live in:
- air;
- water;
- soil;
- both water and land.
Their gas-exchange structures are adapted to their habitats.
27. Animals That Use Lungs
Humans use lungs.
Many other animals also use lungs, including:
- birds;
- elephants;
- cows;
- goats;
- lions;
- lizards;
- snakes.
Although all use lungs, the details of their respiratory systems differ.
28. Breathing in Fish
Most fish obtain oxygen dissolved in water using gills.
Gills are supplied with many blood vessels.
As water passes over them:
- oxygen from water enters the blood;
- carbon dioxide moves from blood into the water.
29. Breathing in Frogs
Frogs are amphibians.
They show different breathing mechanisms at different stages.
Tadpoles
Tadpoles live mainly in water and breathe using gills.
Adult Frogs
Adult frogs can use:
- lungs while on land;
- moist skin for gas exchange, especially while in water.
30. Breathing in Earthworms
Earthworms do not have lungs or gills like humans or fish.
They exchange gases through their moist skin.
Oxygen dissolves in moisture on the skin and passes into the body.
Therefore, keeping the skin moist is essential for effective gas exchange.
Breathing Structures in Different Animals
| Animal | Main Gas-Exchange Structure | Important Feature |
|---|---|---|
| Human | Lungs | Gas exchange occurs in alveoli |
| Fish | Gills | Uses oxygen dissolved in water |
| Tadpole | Gills | Aquatic stage of frog |
| Adult frog | Lungs and moist skin | Adapted for life on land and in water |
| Earthworm | Moist skin | Gas exchange occurs across skin |
31. Keeping the Respiratory System Healthy
Healthy lungs are essential for normal gas exchange.
Helpful habits include:
- avoiding smoking;
- avoiding second-hand smoke where possible;
- staying physically active;
- maintaining good air quality;
- following appropriate hygiene during respiratory infections.
Smoking exposes the respiratory system to harmful substances.
It can damage lung tissues and increase the risk of serious respiratory diseases.
Smoke also affects people nearby through passive smoking.
Avoiding tobacco smoke protects both the smoker and others.
32. Nutrition and Respiration — Putting Everything Together
The body needs both nutrients and oxygen.
Consider the complete sequence.
Step 1 — Food is eaten
Food enters the mouth.
Step 2 — Digestion occurs
Complex nutrients are broken into simpler substances.
Step 3 — Nutrients are absorbed
Most digested nutrients enter the blood through the small intestine.
Step 4 — Oxygen enters the body
Air enters through the respiratory system.
Step 5 — Gas exchange occurs
Oxygen passes from alveoli into blood.
Step 6 — Transport occurs
Blood carries:
- nutrients;
- oxygen
to different tissues.
Step 7 — Respiration releases energy
Cells use nutrients such as glucose and oxygen to release usable energy.
Step 8 — Carbon dioxide is transported away
Carbon dioxide produced during respiration is carried by blood to the lungs and removed in exhaled air.
Concept Map
Exam Focus
Important Exam Areas
- meaning of life processes;
- nutrition and digestion;
- human alimentary canal;
- mechanical digestion in the mouth;
- role of saliva in starch digestion;
- iodine test for starch;
- movement of food through the oesophagus;
- role of digestive juice, acid and mucus in the stomach;
- role of liver and bile;
- role of pancreas and pancreatic juice;
- small intestine as major site of digestion and nutrient absorption;
- finger-like projections and increased surface area;
- functions of the large intestine;
- egestion;
- rumination and ruminants;
- role of gizzard in birds;
- difference between breathing and respiration;
- parts of the human respiratory system;
- inhalation and exhalation;
- role of ribs and diaphragm;
- alveoli and gas exchange;
- composition of inhaled and exhaled air;
- respiration word equation;
- role of the circulatory system;
- breathing in fish, frogs and earthworms.
Key Terms
Key Terms
Quick Revision
Quick Revision
- Life processes are essential biological activities needed for survival.
- Nutrition provides the body with food and nutrients.
- Digestion breaks complex food into simpler forms.
- The alimentary canal extends from the mouth to the anus.
- Teeth carry out mechanical digestion by breaking food into smaller pieces.
- Saliva moistens food and begins digestion of starch.
- Iodine turns blue-black in the presence of starch.
- The tongue mixes food with saliva and helps in swallowing.
- The oesophagus carries food towards the stomach.
- Stomach walls churn food and mix it with digestive secretions.
- Stomach acid helps digestion and kills many harmful bacteria.
- Mucus protects the stomach lining.
- The small intestine receives secretions from the liver, pancreas and its own lining.
- Bile is mildly basic and helps neutralise acidic material and break fats into tiny droplets.
- Pancreatic juice helps digest carbohydrates, proteins and fats.
- Most digested nutrients are absorbed through the small intestine.
- The inner lining of the small intestine has many finger-like projections that increase surface area.
- The large intestine absorbs much of the remaining water and some salts.
- Egestion removes undigested material through the anus.
- Ruminants bring partially digested food back to the mouth and chew it again.
- Birds use a muscular gizzard to help grind food.
- Breathing involves inhalation and exhalation.
- Respiration releases usable energy from nutrients such as glucose.
- Breathing is physical; respiration is chemical.
- During inhalation, the ribs move upward and outward while the diaphragm moves downward.
- During exhalation, the ribs move downward and inward while the diaphragm moves upward.
- Gas exchange occurs in alveoli.
- Oxygen moves from alveoli into blood.
- Carbon dioxide moves from blood into alveoli.
- Exhaled air contains less oxygen and more carbon dioxide than inhaled air.
- The circulatory system transports nutrients and oxygen throughout the body.
- Fish use gills for gas exchange.
- Adult frogs use lungs and moist skin, while tadpoles use gills.
- Earthworms exchange gases through moist skin.
Important Biological Relationship
Formula / Key Relations
Respiration
Respiration releases usable energy from nutrients.
Practice Questions
A. Multiple Choice Questions
Digestion of food begins in the:
A. stomach
B. mouth
C. large intestine
D. anus
View Solution
Correct Answer: B. Mouth
Chewing begins mechanical digestion, while saliva begins the digestion of starch.
Which substance begins the digestion of starch in the mouth?
A. Bile
B. Saliva
C. Mucus
D. Blood
View Solution
Correct Answer: B. Saliva
Saliva contains substances that help break starch into simpler sugars.
Most digested nutrients are absorbed in the:
A. oesophagus
B. stomach
C. small intestine
D. rectum
View Solution
Correct Answer: C. Small intestine
The small intestine has a large absorptive surface and is the main site for nutrient absorption.
Bile is produced by the:
A. pancreas
B. liver
C. stomach
D. large intestine
View Solution
Correct Answer: B. Liver
The liver produces bile, which enters the small intestine and assists digestion.
Which animal is a ruminant?
A. Cow
B. Human
C. Eagle
D. Fish
View Solution
Correct Answer: A. Cow
Cows bring partially digested food back to the mouth and chew it again.
The muscular chamber that helps grind food in birds is the:
A. alveolus
B. gizzard
C. diaphragm
D. rectum
View Solution
Correct Answer: B. Gizzard
The gizzard mechanically grinds food, often with the help of swallowed grit.
Gas exchange in human lungs mainly occurs in the:
A. nostrils
B. windpipe
C. alveoli
D. rib cage
View Solution
Correct Answer: C. Alveoli
Alveoli have thin walls and are surrounded by blood vessels where oxygen and carbon dioxide are exchanged.
Which statement is correct?
A. Breathing releases energy from glucose.
B. Respiration is only movement of air into the lungs.
C. Breathing is physical while respiration is chemical.
D. Breathing and respiration are exactly the same process.
View Solution
Correct Answer: C. Breathing is physical while respiration is chemical.
Breathing moves air into and out of the lungs, while respiration releases energy from nutrients.
B. Very Short Answer Questions
-
What is digestion?
-
Name the main tube through which food passes in the digestive system.
-
What is the role of saliva?
-
Name the organ that produces bile.
-
Where are most nutrients absorbed?
-
What is rumination?
-
What is a gizzard?
-
Define breathing.
-
Define respiration.
-
What are alveoli?
-
Which organ pumps blood?
-
Name the respiratory organs of fish.
Answers
-
Digestion is the breakdown of complex food components into simpler absorbable forms.
-
The alimentary canal.
-
Saliva moistens food and begins the digestion of starch.
-
The liver.
-
Most nutrients are absorbed in the small intestine.
-
Rumination is the process in which partially digested food is returned to the mouth and chewed again.
-
A gizzard is a muscular digestive chamber in birds that helps grind food.
-
Breathing is the physical process of taking air into and giving air out of the lungs.
-
Respiration is the chemical process that releases usable energy from nutrients such as glucose.
-
Alveoli are tiny air sacs in the lungs where gas exchange occurs.
-
The heart.
-
Gills.
C. Short Answer Questions
Explain why chewed rice may give a weaker blue-black colour with iodine than unchewed rice.
View Solution
Rice contains starch.
Unchewed rice still contains a large amount of starch and therefore gives a strong blue-black colour with iodine.
When rice is chewed thoroughly, it mixes with saliva.
Saliva begins breaking starch into simpler sugars.
Therefore, less starch may remain and the iodine colour may be weaker.
What are the functions of acid and mucus in the stomach?
View Solution
The acid in the stomach:
- helps digestion;
- helps kill many harmful bacteria.
Mucus:
- forms a protective layer;
- protects the stomach lining from the acidic contents.
Explain two important functions of bile.
View Solution
Bile:
- helps neutralise acidic material entering the small intestine from the stomach;
- breaks fats into tiny droplets, making their digestion easier.
Why does the small intestine have many finger-like projections?
View Solution
The projections greatly increase the surface area of the inner lining.
A larger surface area allows digested nutrients to be absorbed more efficiently into the blood.
Differentiate between breathing and respiration.
View Solution
Breathing is a physical process involving movement of air into and out of the lungs.
Respiration is a chemical process in which nutrients such as glucose are broken down to release energy.
Breathing supplies oxygen needed for respiration and removes carbon dioxide from the lungs.
Explain the role of the diaphragm during inhalation and exhalation.
View Solution
During inhalation, the diaphragm moves downward.
This increases the space inside the chest and helps air enter the lungs.
During exhalation, the diaphragm moves upward.
This decreases the space inside the chest and helps push air out.
D. Long Answer Questions
Trace the journey of food through the human alimentary canal and describe what happens in each major part.
View Solution
Mouth
Food is chewed by the teeth.
Saliva moistens food and begins the digestion of starch.
Oesophagus
Swallowed food moves towards the stomach through wave-like muscular movements.
Stomach
Food is churned and mixed with digestive juice, acid and mucus.
Protein digestion begins or continues here.
Small Intestine
Food mixes with bile, pancreatic juice and intestinal secretions.
Digestion is largely completed.
Most nutrients are absorbed into the blood.
Large Intestine
Much of the remaining water and some salts are absorbed.
The waste becomes semi-solid.
Rectum
Stool is temporarily stored.
Anus
Undigested waste leaves the body by egestion.
Explain inhalation and exhalation.
View Solution
Inhalation
During inhalation:
- ribs move upward and outward;
- diaphragm moves downward;
- space inside the chest increases;
- air enters the lungs.
Exhalation
During exhalation:
- ribs move downward and inward;
- diaphragm moves upward;
- space inside the chest decreases;
- air leaves the lungs.
The coordinated movement of the ribs and diaphragm therefore helps produce breathing.
Explain how oxygen reaches body tissues and how carbon dioxide is removed.
View Solution
Air enters the lungs during inhalation.
It travels through the respiratory passages and reaches the alveoli.
At the alveoli:
- oxygen passes from the air into the blood;
- carbon dioxide passes from the blood into the alveoli.
The circulatory system carries oxygen-rich blood to body tissues.
Cells use oxygen during respiration to release energy from nutrients.
Carbon dioxide produced in the body is carried by blood back to the lungs.
It enters the alveoli and leaves the body during exhalation.
E. Application and HOTS Questions
Why does a person often breathe faster after running?
View Solution
Running increases muscular activity.
The muscles require more energy.
To release more energy:
- respiration increases;
- more oxygen is required;
- more carbon dioxide is produced.
The breathing rate therefore increases to bring in more oxygen and remove carbon dioxide more rapidly.
A student says, "The small intestine should actually be called the large intestine because it is longer." Explain why the name still makes sense.
View Solution
The terms small intestine and large intestine refer mainly to their width, not their length.
The small intestine is much longer but narrower.
The large intestine is shorter but wider.
Therefore, the names refer to their relative diameter.
Why would damage to the finger-like projections of the small intestine affect nutrition even if digestion of food were normal?
View Solution
These projections greatly increase the surface area available for nutrient absorption.
If they were damaged, digested nutrients might not be absorbed efficiently into the blood.
Therefore, a person could have difficulty obtaining enough nutrients even if food had been broken down correctly.
Why would it be incorrect to say that we inhale only oxygen and exhale only carbon dioxide?
View Solution
We inhale air, which is a mixture of gases.
Inhaled air contains about 21% oxygen and a very small amount of carbon dioxide.
Exhaled air still contains about 16–17% oxygen, but contains much more carbon dioxide than inhaled air.
Therefore, both inhaled and exhaled air contain several gases.
A fish is placed outside water for a long time even though plenty of oxygen is present in the surrounding air. Why may it still be unable to breathe normally?
View Solution
Fish are adapted to obtain oxygen dissolved in water using gills.
Their gills function effectively when water passes over the gas-exchange surfaces.
Outside water, the gill structures cannot function normally.
Therefore, simply having oxygen in the surrounding air does not mean that the fish can use it efficiently.
Assertion–Reason
Assertion: Chewing food properly helps digestion.
Reason: Chewing breaks food into smaller pieces and mixes it with saliva.
Choose the correct option:
A. Both Assertion and Reason are true, and Reason correctly explains Assertion.
B. Both are true, but Reason does not explain Assertion.
C. Assertion is true, but Reason is false.
D. Both are false.
View Solution
Correct Answer: A
Chewing increases mechanical breakdown and mixes food with saliva, which begins the digestion of starch.
Assertion: Alveoli are well suited for gas exchange.
Reason: They provide a large surface area and have thin walls surrounded by blood vessels.
Choose the correct option:
A. Both Assertion and Reason are true, and Reason correctly explains Assertion.
B. Both are true, but Reason does not explain Assertion.
C. Assertion is true, but Reason is false.
D. Both are false.
View Solution
Correct Answer: A
The large surface area, thin walls and blood supply make exchange of oxygen and carbon dioxide efficient.
Assertion: Breathing and respiration are exactly the same process.
Reason: Respiration releases energy from nutrients.
Choose the correct option:
A. Both are true.
B. Assertion is true, but Reason is false.
C. Assertion is false, but Reason is true.
D. Both are false.
View Solution
Correct Answer: C
Breathing is the physical movement of air into and out of the lungs.
Respiration is the chemical process that releases energy from nutrients.
Apply Your Learning
Construct a flowchart showing the journey from a meal to energy release.
Begin with:
Food
Then include:
Mouth → Oesophagus → Stomach → Small Intestine → Nutrient Absorption → Blood → Body Cells
Create a second flowchart for oxygen:
Air → Nose → Windpipe → Lungs → Alveoli → Blood → Body Cells
Finally, connect both pathways at:
Respiration
Use this relationship:
Then answer:
- Where does starch digestion begin?
- Where are most nutrients absorbed?
- Where does oxygen enter the blood?
- Which system transports nutrients and oxygen?
- Why are digestion, breathing, respiration and circulation interdependent?
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Final Chapter Summary
Chapter Summary
- Life processes are essential activities required to maintain life.
- Animals obtain nutrients through nutrition and release usable energy through respiration.
- Digestion converts complex food components into simpler absorbable forms.
- The human alimentary canal includes the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus.
- Digestion begins in the mouth through chewing and the action of saliva.
- Saliva begins breaking down starch into simpler sugars.
- The oesophagus moves food towards the stomach through muscular movements.
- The stomach churns food and mixes it with digestive juice, acid and mucus.
- Bile from the liver helps neutralise acidic material and assists fat digestion.
- Pancreatic juice helps digest carbohydrates, proteins and fats.
- The small intestine is the major site for completion of digestion and nutrient absorption.
- Finger-like projections increase the surface area available for absorption.
- The large intestine absorbs much of the remaining water and some salts.
- Egestion removes undigested material from the body.
- Ruminants return partially digested food to the mouth for further chewing.
- Birds use a muscular gizzard to grind food.
- Breathing is a physical process involving inhalation and exhalation.
- Respiration is a chemical process that releases usable energy from nutrients.
- During inhalation, the chest expands and the diaphragm moves downward.
- During exhalation, the chest space decreases and the diaphragm moves upward.
- Gas exchange occurs in the alveoli.
- Oxygen passes from alveoli into blood, while carbon dioxide passes from blood into alveoli.
- Exhaled air contains less oxygen and much more carbon dioxide than inhaled air.
- The circulatory system transports nutrients and oxygen around the body.
- Different animals possess breathing structures suited to their habitats.
- Fish use gills, adult frogs use lungs and moist skin, and earthworms exchange gases through moist skin.
- Digestive, respiratory and circulatory systems work together to sustain life.