The Journey Food Takes Through Your Body
Learn the different ways animals take in food, the parts of the human digestive system, the five steps of nutrition, and how a cow's digestion differs from yours.
How do different animals take in their food?
Animals take in food in ways that suit what they eat and how they live. A butterfly sucks nectar, a calf feeds on its mother's milk, a snake swallows prey whole, a blue whale filters tiny food particles from sea water, and humans and cattle chew their food.
This page covers everything in the CBSE Class 7 Science chapter on life processes in animals: the modes of taking food, the parts of the human digestive system, the five steps of nutrition, and how digestion differs in ruminants and birds.
This page covers everything in the CBSE Class 7 Science chapter on life processes in animals: the modes of taking food, the parts of the human digestive system, the five steps of nutrition, and how digestion differs in ruminants and birds.
What are the parts of the human digestive system?
The digestive system is essentially one long tube, the alimentary canal, with glands attached along it.
The buccal cavity (mouth) takes in food, where teeth chew it and the tongue mixes it. The oesophagus (food pipe) carries it down to the stomach, a muscular bag that churns it. The small intestine is a long coiled tube where most digestion is completed and absorption happens. The large intestine absorbs water from the remaining material, which is stored in the rectum and passed out through the anus.
Three glands add their juices: the salivary glands in the mouth, the liver, which produces bile, and the pancreas, which produces pancreatic juice.
The small intestine is far longer than the large intestine — several metres, coiled to fit — despite the names. "Small" refers to its narrower width, not its length, which is a common source of confusion in diagrams.
The buccal cavity (mouth) takes in food, where teeth chew it and the tongue mixes it. The oesophagus (food pipe) carries it down to the stomach, a muscular bag that churns it. The small intestine is a long coiled tube where most digestion is completed and absorption happens. The large intestine absorbs water from the remaining material, which is stored in the rectum and passed out through the anus.
Three glands add their juices: the salivary glands in the mouth, the liver, which produces bile, and the pancreas, which produces pancreatic juice.
The small intestine is far longer than the large intestine — several metres, coiled to fit — despite the names. "Small" refers to its narrower width, not its length, which is a common source of confusion in diagrams.
What are the five steps of nutrition in humans?
Nutrition runs through five steps in order.
Ingestion is taking food into the body through the mouth.
Digestion is breaking complex food into simpler substances the body can use. Saliva begins it in the mouth by acting on starch. The digestive juice of the stomach contains acid and acts on proteins. In the small intestine, bile from the liver breaks fat into tiny droplets, and pancreatic juice acts on carbohydrates, proteins and fats.
Absorption is the passage of digested food into the blood, and it happens through the villi — thousands of tiny finger-like projections lining the small intestine. Their shape gives an enormous surface area for absorbing food quickly.
Assimilation is the use of that absorbed food by the body's cells for energy, growth and repair.
Egestion is the removal of undigested waste through the anus.
Note that bile does not digest fat chemically — it breaks large fat globules into small droplets so that other juices can act on them faster. Questions test that distinction.
Ingestion is taking food into the body through the mouth.
Digestion is breaking complex food into simpler substances the body can use. Saliva begins it in the mouth by acting on starch. The digestive juice of the stomach contains acid and acts on proteins. In the small intestine, bile from the liver breaks fat into tiny droplets, and pancreatic juice acts on carbohydrates, proteins and fats.
Absorption is the passage of digested food into the blood, and it happens through the villi — thousands of tiny finger-like projections lining the small intestine. Their shape gives an enormous surface area for absorbing food quickly.
Assimilation is the use of that absorbed food by the body's cells for energy, growth and repair.
Egestion is the removal of undigested waste through the anus.
Note that bile does not digest fat chemically — it breaks large fat globules into small droplets so that other juices can act on them faster. Questions test that distinction.
How is digestion in a cow different from digestion in a human?
Ruminants such as cows, buffaloes, goats and deer eat grass, which contains cellulose — something humans cannot digest at all.
A cow swallows grass quickly and stores it partly digested in a part of the stomach called the rumen, where it becomes cud. Later, resting, the animal brings the cud back into its mouth and chews it slowly — this is chewing the cud, or rumination. Bacteria in the rumen break down the cellulose, which the cow's own body could not.
Birds have no teeth, so they swallow grain whole. It passes to a muscular gizzard, where swallowed grit and small stones grind the food — the bird's substitute for chewing.
For example, you can watch a buffalo sitting still and chewing steadily long after it has finished grazing; that is rumination, not a second meal.
So the same problem — breaking food down — is solved three different ways: our teeth and juices, a cow's bacteria, a bird's swallowed grit.
A cow swallows grass quickly and stores it partly digested in a part of the stomach called the rumen, where it becomes cud. Later, resting, the animal brings the cud back into its mouth and chews it slowly — this is chewing the cud, or rumination. Bacteria in the rumen break down the cellulose, which the cow's own body could not.
Birds have no teeth, so they swallow grain whole. It passes to a muscular gizzard, where swallowed grit and small stones grind the food — the bird's substitute for chewing.
For example, you can watch a buffalo sitting still and chewing steadily long after it has finished grazing; that is rumination, not a second meal.
So the same problem — breaking food down — is solved three different ways: our teeth and juices, a cow's bacteria, a bird's swallowed grit.
Why does the small intestine need villi?
Because absorption depends on surface area, and a smooth tube would not have nearly enough.
The villi are tiny finger-like projections covering the inner lining of the small intestine. Each one contains fine blood vessels, so digested food passing into a villus enters the blood directly. Having thousands of them multiplies the absorbing surface many times over compared with a plain tube of the same length.
The blood then carries the absorbed food to every cell in the body, which is the assimilation step.
For example, the inside of the small intestine works like a towel rather than a sheet of plastic — the tiny loops give it far more surface to soak things up with.
This is also why damage to the villi, from certain illnesses, causes weakness even when a person is eating normally: the food is digested but cannot be absorbed properly.
The villi are tiny finger-like projections covering the inner lining of the small intestine. Each one contains fine blood vessels, so digested food passing into a villus enters the blood directly. Having thousands of them multiplies the absorbing surface many times over compared with a plain tube of the same length.
The blood then carries the absorbed food to every cell in the body, which is the assimilation step.
For example, the inside of the small intestine works like a towel rather than a sheet of plastic — the tiny loops give it far more surface to soak things up with.
This is also why damage to the villi, from certain illnesses, causes weakness even when a person is eating normally: the food is digested but cannot be absorbed properly.
Exam tip
Exam tip: keeping the five steps in the right order
Students list the steps out of order, or merge absorption with assimilation.
Hold on to the sequence by following the food: it goes in (ingestion), is broken down (digestion), passes into the blood (absorption), is used by cells (assimilation), and the leftovers go out (egestion).
The pair most often confused is absorption and assimilation. Absorption is food entering the blood through the villi; assimilation is cells using that food. Write both definitions in terms of where the food is, and the distinction stays clear.
In diagram questions, label parts in the order food meets them — buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum, anus — so nothing is missed.
Hold on to the sequence by following the food: it goes in (ingestion), is broken down (digestion), passes into the blood (absorption), is used by cells (assimilation), and the leftovers go out (egestion).
The pair most often confused is absorption and assimilation. Absorption is food entering the blood through the villi; assimilation is cells using that food. Write both definitions in terms of where the food is, and the distinction stays clear.
In diagram questions, label parts in the order food meets them — buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum, anus — so nothing is missed.
Did you know
Why can a cow digest grass when we cannot?
Grass is largely cellulose, and neither a cow nor a human produces a juice that can break it down.
The difference is that a cow houses bacteria in its rumen that can, and it gives them time to work by storing the food and chewing it again later. The cow is not digesting the grass alone — it is providing a place for the bacteria that do.
The difference is that a cow houses bacteria in its rumen that can, and it gives them time to work by storing the food and chewing it again later. The cow is not digesting the grass alone — it is providing a place for the bacteria that do.
Key takeaways
Digestion in animals: quick revision
- Animals take food by sucking, feeding on milk, swallowing whole, filtering or chewing, according to what they eat.
- The alimentary canal runs buccal cavity → oesophagus → stomach → small intestine → large intestine → rectum → anus, with salivary glands, liver and pancreas adding juices.
- The five steps are ingestion, digestion, absorption, assimilation and egestion.
- Villi in the small intestine give a huge surface area so digested food can pass into the blood; bile breaks fat into droplets rather than digesting it chemically.
- Ruminants store food as cud and use rumen bacteria to break down cellulose, while birds grind grain in a gizzard using swallowed grit.
You will remember all of this far better after answering five questions on it than after reading it twice.
- The alimentary canal runs buccal cavity → oesophagus → stomach → small intestine → large intestine → rectum → anus, with salivary glands, liver and pancreas adding juices.
- The five steps are ingestion, digestion, absorption, assimilation and egestion.
- Villi in the small intestine give a huge surface area so digested food can pass into the blood; bile breaks fat into droplets rather than digesting it chemically.
- Ruminants store food as cud and use rumen bacteria to break down cellulose, while birds grind grain in a gizzard using swallowed grit.
You will remember all of this far better after answering five questions on it than after reading it twice.