CLASS 7 SCIENCE · CHAPTER 9 · STUDY NOTES
Life Processes in Animals
Follow food, air and blood through labelled structures to understand digestion and respiration.
01 / EXPLORE & UNDERSTAND
Food must become usable nutrients
Eating is only the first step in obtaining nutrients.
The food route and its helper organs
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1. Different ways to take in food
A nectar-feeding bird sucks liquid food; a python swallows prey; some aquatic animals filter food particles from water. These feeding methods differ, but nutrients still need to become available to the body.
2. Follow the human route
Food travels through the mouth, food pipe, stomach, small intestine, large intestine, rectum and anus. The liver and pancreas supply secretions into this route; swallowed food does not travel through those organs.
Your turn
Question
Does swallowed food pass through the liver on its way to the intestine?
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02 / EXPLORE & UNDERSTAND
Chewing and saliva begin digestion
Making smaller pieces and making simpler substances are different changes.
1. Chew and mix
Teeth crush and cut food. The tongue mixes it with saliva and helps swallowing. Smaller pieces provide more surface for digestive substances to act on, but cutting a piece alone does not turn starch into sugar.
2. Add chemical action
Saliva moistens food and contains an enzyme that starts breaking starch into sugars. That is why starchy food can taste sweeter after prolonged chewing. Digestion begins in the mouth but is not completed there.
Your turn
Question
Is cutting bread into tiny pieces the same as digesting its starch?
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03 / EXPLORE & UNDERSTAND
Use a test as evidence
Iodine tests for starch, not for every kind of food.
1. Compare before and after saliva
In a teacher-led comparison, rice containing starch gives a blue-black result. Rice exposed to saliva can give a weaker result because some starch has been broken down. Keep quantities, iodine and observation time comparable.
2. Avoid claiming too much
A weak colour does not measure an exact starch percentage. No visible blue-black means starch was not detected under those conditions, not that the sample contains no food. Do not taste tested samples or share saliva for experiments.
Your turn
Question
Can an iodine test tell whether protein is present?
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04 / EXPLORE & UNDERSTAND
Muscles push food along
The food pipe is more than a passive slide.
Read the three stages from left to right
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1. Squeeze behind the food
After swallowing, muscle behind the food contracts while the region ahead relaxes. This wave pushes the food along the oesophagus towards the stomach. The movement also occurs farther along the digestive tract.
2. Separate food and air routes
The oesophagus carries food towards the stomach. The windpipe carries air towards the lungs. These tubes have different jobs; a diagram showing them nearby does not mean food should enter the lungs.
Your turn
Question
What does the narrowed part behind the food show?
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05 / EXPLORE & UNDERSTAND
The stomach churns and adds secretions
Different parts of the stomach secretion do different jobs.
1. Mix and digest
Stomach muscles churn food into a semi-liquid mixture. Acid makes the surroundings suitable for stomach enzymes to begin protein digestion and kills many swallowed microbes. Acid alone does not perform all digestion.
2. Protect the wall
Mucus helps protect the lining from acid and digestive enzymes. Food then leaves gradually for the small intestine. The stomach is one stage, not the place where all nutrients are absorbed.
A little deeper: How knowledge develops
NCERT recounts Beaumont’s observations through Alexis St. Martin’s old stomach wound. Such historical observations helped explain digestion. Today, research with people requires informed consent and protection; this story is history, not a classroom method.
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Question
Why does the stomach need both acid and a protective lining?
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06 / EXPLORE & UNDERSTAND
Several secretions finish the breakdown
The small intestine receives help from the liver and pancreas.
1. Make fat easier to work on
Bile breaks large fat globules into smaller droplets. This increases the surface available to fat-digesting enzymes. It is physical emulsification: bile itself does not chemically turn fat into its final digestion products.
2. Combine digestive juices
Pancreatic and intestinal enzymes break down carbohydrates, proteins and fats into absorbable forms. Alkaline secretions help neutralise the acidic contents arriving from the stomach, creating suitable conditions for these enzymes.
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Question
Why do smaller fat droplets help digestion?
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07 / EXPLORE & UNDERSTAND
A folded lining gives more absorbing surface
Digestion makes nutrients small enough; absorption takes them into the body.
Many projections, a larger surface
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1. Look for the finger-like projections
The small intestine has many tiny projections called villi. They increase surface area. Their thin surface allows digested nutrients to cross; a smooth tube of the same size would offer less area.
2. Connect absorption with use
Blood carries many absorbed nutrients to body cells. Cells use them for growth, repair and energy release. Digestion, absorption and use by cells are connected stages, not three names for the same event.
A little deeper: The transport routes are not all identical
Most sugars and amino acids enter blood capillaries. Much absorbed dietary fat first enters lymph vessels before reaching the blood. The basic idea remains the same: nutrients cross a specialised absorbing surface and are transported onwards.
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Question
Why are many villi more helpful than a smooth inner surface?
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08 / EXPLORE & UNDERSTAND
Recover water, then remove undigested waste
“Large” describes width, not greater length.
1. Follow the remaining material
The large intestine absorbs remaining water and some salts. The material becomes stool, which is stored in the rectum and leaves through the anus. The small intestine is longer; the large intestine is wider.
2. Distinguish two kinds of removal
Egestion removes undigested material. Excretion removes wastes made by body processes, such as carbon dioxide from respiration. Fibre and gut microbes also play roles in digestive function; the intestine is not an empty waste pipe.
Your turn
Question
Is removing carbon dioxide from the lungs called egestion?
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09 / EXPLORE & UNDERSTAND
Different diets, different digestive structures
Animals do not all process food in the same way.
A cow’s digestive structures
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Find the gizzard
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1. Trace a ruminant’s route
Cows and buffaloes swallow partly chewed plant food. Food from the stomach is later brought back as cud, chewed again and swallowed. Microbes in specialised stomach chambers help process plant material.
2. Compare the bird’s gizzard
Birds have no teeth. A muscular gizzard grinds food, often with swallowed grit. It performs mechanical breakdown inside the body. A cow’s rumination and a bird’s gizzard solve food-processing needs in different ways.
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Question
Which structure helps a bird grind food without teeth?
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10 / EXPLORE & UNDERSTAND
Trace air to the lungs
Follow the labelled branches, not just the outline of the chest.
Airways, lungs and diaphragm
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1. Follow the route
Air enters the nostrils, passes through nasal passages and the windpipe, then through branching tubes in the lungs. These end at alveoli. Nose hairs and mucus trap some particles; they do not remove every harmful particle.
2. Locate support structures
The rib cage protects the lungs. The diaphragm is a muscle below them. The alveoli provide the gas-exchange surface; the diaphragm helps move air by changing chest volume. Their roles are different.
Your turn
Question
Does the diaphragm itself filter oxygen out of air?
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11 / EXPLORE & UNDERSTAND
Changing chest volume moves air
Lungs do not pull air in by acting like a mouth that sucks.
Compare inhaling and exhaling
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1. Make more space
During inhalation the diaphragm contracts and moves down; the ribs move up and out. Chest volume increases and pressure in the lungs falls slightly below outside pressure, so air flows in.
2. Let the volume decrease
During quiet exhalation the muscles relax; the diaphragm rises and the chest recoils. Volume decreases, pressure rises and air flows out. The bottle-and-balloon model demonstrates volume change, but its rigid bottle cannot show moving ribs.
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Question
In the model, which part stands for the diaphragm?
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12 / EXPLORE & UNDERSTAND
Oxygen and carbon dioxide cross opposite ways
Breathing brings air close to blood; gases then cross a thin surface.
Exchange across a thin wall
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1. Read both arrows
Oxygen crosses from alveolar air into the blood. Carbon dioxide crosses from blood into the alveolus and is breathed out. Thin walls and nearby blood vessels make the exchange effective.
2. Compare mixtures, not pure gases
Inhaled and exhaled air both contain oxygen and carbon dioxide. Exhaled air has less oxygen and more carbon dioxide. A teacher’s lime-water comparison can show the extra CO2; ordinary outside air is not CO2-free.
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Question
Is all oxygen removed from a breath before it leaves the lungs?
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13 / EXPLORE & UNDERSTAND
Cells release energy from food
Breathing and cellular respiration cooperate but are different processes.
1. Connect food and oxygen
Digestion supplies simple nutrients such as glucose. Blood transports nutrients and oxygen to cells. In aerobic respiration, glucose and oxygen are used, producing carbon dioxide and water while releasing energy.
2. Connect the three systems
The digestive system provides absorbed nutrients; the respiratory system exchanges gases; the circulatory system links them with cells. The heart pumps blood through vessels. Energy is needed even while resting, not only during sport.
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Question
Where does the energy-releasing chemical process happen: only in the lungs or in body cells?
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14 / EXPLORE & UNDERSTAND
Different animals exchange gases differently
Living in water does not mean using water itself instead of oxygen.
Water passes across the gills
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1. Compare fish and land animals
Water flows across a fish’s gills. Oxygen dissolved in the water crosses into blood; carbon dioxide crosses out. Birds and many land animals use lungs, although their lung structures are not all identical.
2. Include moist skin and life stages
Earthworms exchange gases through moist skin. Tadpoles commonly use gills; adult frogs use lungs and moist skin. Skin exchange is not restricted to being underwater. Body structures and life stage both matter.
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Question
Does a fish obtain oxygen by splitting water molecules?
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Sign inNew here? Sign up freeCHAPTER RECAP
Take these ideas with you
- Digestion makes complex food simpler; absorption moves nutrients across the gut lining.
- Food passes along the alimentary canal, not through the liver or pancreas.
- Villi increase absorbing area.
- Breathing changes air movement; alveoli exchange gases.
- Cells use nutrients and oxygen to release energy.
- Circulation connects digestion, gas exchange and cells.
Use your understanding in a new situation
Question
Explain why a thin, folded intestinal lining is useful.
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Trace oxygen from outside air to its use in a cell.
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Sign inNew here? Sign up freeNCERT · Chapter source PDF, pages 13, 14 · Original Learnijoy explanations and practice.