Section outline

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    Introduction

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    • In this chapter, we will explore about how animals & humans get their nutrition.

      We will learn:

      1. Human digestive system.
      2. Organs that comprise the digestive system.
      3. Role played by all the digestive organs and glands in the process of digestion.
      4. Ways in which animals get their nutrition.
      5. Digestion in animals like starfish, ameoba & ruminants.

      So learner's, let's begin!

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    Digestive system

    • Digestion:

      Digestion is the process of breaking down complex nutrients into simpler form that can be absorbed & used by the body.

      Explanation:
      1. The nutrients (components of food) such as carbohydrates, fats & proteins are complex substances.
      2. These complex substances cannot be utilized or absorbed directly by the body.
      3. So they are broken down into simpler substances. 
      Steps in digestion:

      Steps

    • Digestive system in humans:

      The digestive tract (or the alimentary canal) &  accessory organs (secretory organs) together form the digestive system.

      List of the organs in the digestive system:

      digestive system

      Functioning of the digestive system:
      1. The digestive system has many compartments that form the alimentary canal.
      2. Food passes gradually through these compartments & food components get digested.
      3. Digestive juices are secreted by the inner walls of the stomach & small intestine and various associated glands like the salivary glands, live & pancreas.
      4. These digestive juices convert complex food components into simple substances.
      5. This is the overview of the functioning of the digestive system.

      Let's study in detail the digestive system & the journey of food through this system. 

    • Diagram of digestive system

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    Digestion in Humans

    • Alimentary canal or digestive track

      It is a long tube of organs through which the food enters & leaves the body starting from the mouth & ending at the anus.

      Features:
      1. The food passes through a long continuous canal which begins at the buccal cavity & ends at the anus.
      2. It is also called the digestive track.
      3. There are various compartments in this canal which gradually digest the various food components.

      The alimentary canal is divided into:

       

      Let's understand the function of each organ in detail.

    • Buccal cavity or mouth
      1. Food is taken into the body through the mouth or buccal cavity.
      2. The process of taking food into the body is called ingestion.
      3. When we chew the food, the teeth break it into small pieces.
      4. Saliva secreted by the salivary glands gets mixed with the food.
      5. The saliva breaks down the starch into sugars.
      6. The process of digestion begins in the mouth.

    • Teeth
      1. Teeth are located in the mouth.
      2. We chew the food in the mouth with the help of teeth.
      3. Teeth break the food into small pieces in the mouth.
      Milk teeth:
      1. They are the first set of teeth.
      2. They grow during infancy & fall off between the age of six to eight years.
      3. There are a set of 20 milk teeth.
      4. They are also called baby teeth or primary teeth.
      Permanent teeth:
      1. The second set that replaces the milk teeth are the permanent teeth.
      2. They may last throughout life or fall off during old age or due to some dental disease
      3. Most adults have 32 permanent teeth, 16 in the upper jaw & 16 in the lower jaw.
      4. They vary in appearance & perform different functions.
      5. Each tooth is rooted in a separate socket in the gums.
      Types of permanent teeth:
      Type of teeth Number Location Function
      Incisors 8 Front Cutting & biting
      Canines 4 Next to incisors Piercing & tearing
      Premolars 8 Behind canines Chewing & grinding
      Molars 12 Back of the mouth
      Diagram:

      Tooth Decay:
      1. If the teeth & mouth are not kept clean after eating food, some harmful bacteria begin to grow.
      2. These bacteria break down the sugars present from the leftover food & release acids.
      3. The acids gradually damage the teeth leading to tooth decay.
      4. Tooth decay can lead to severe toothache & tooth loss in extreme cases.
      5. Hence, tooth decay should be treated immediately.
      6. Chocolates, sweets, soft drinks & other sugar products lead to tooth decay.
      7. To prevent tooth decay we should brush our teeth & dental floss at least twice a day & rinse the mouth after every meal.
      8. Also prevent putting dirty fingers or any unwashed object in the mouth.

    • Tongue 
      1. The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity.
      2. It is free at the front & can be moved in all directions.
      3. It is used for talking.
      4. It mixes saliva with the food during chewing & helps in swallowing food.
      5. It has taste buds that detect different tastes of food. 
      Diagram:

    • Oesophagus:
      1. Oesophagus is also called the food pipe.
      2. It is a muscular tube that runs along the neck & chest.
      3. It carries swallowed food from the mouth to the stomach.
      4. Food is pushed down by movement of the wall of the food pipe.
      5. Hence it is an important part of the alimentary canal.
      6. At times the food is not accepted by our stomach and is vomited out.
      Why do we get hiccups?
      1. The windpipe or trachea carries air from the nostrils to the lungs.
      2. The windpipe runs adjacent to the food pipe.
      3. Inside the throat, they both share a common passage.
      4. There is a flap-like valve, called the epiglottis that closes the passage of the windpipe when we swallow food or liquids.
      5. This ensures that the food enters the food pipe only.
      6.  Sometimes when we eat in a hurry, talk or laugh while eating, the food particles enter the windpipe.
      7. Hence, we feel choked or get hiccups or cough.

    • Stomach
      1. It is a muscular organ that connects the oesophagus at the top & small intestine at the bottom.
      2. It is a thick-walled bag which has a shape like a flattened J.
      3. It is the widest part of the alimentary canal.
      4. The inner lining of the stomach secretes mucous, hydrochloric acid & digestive juices.
      5. In 1822, Doctor William Beaumont, discovered the process of digestion in the stomach.
      Functioning:
      1. The stomach receives the food from the food pipe.
      2. The food that enter the stomach contains many bacteria.
      3. The acid in the stomach kills these bacteria & makes the medium in the stomach acidic.
      4. The digestive juices break down the proteins into simpler substances.
      5. The mucous protects the lining of the stomach from the acid.
      6. Stomach holds food & then pushes the partly digested food in the small intestine.
    • Liver:
      1. The liver is a reddish brown gland situated in the upper part of the abdomen on the right side.
      2. It is the largest gland in the body.
      3. It secretes bile juice that is stored in a sac called as the gall bladder.
      4. The bile helps in the digestion of fats.
      Pancreas:
      1. The pancreas is a large cream coloured gland located just below the stomach.
      2. The pancreatic juice acts on carbohydrates, fats & proteins to change them into simpler forms.

      3. The pancreas also produces insulin, which helps regulate blood sugar levels.

      Thus, the liver, gall bladder & pancreas are secretory glands that help in the process of digestion.

    • Small Intestine
      1. It is the longest part of the alimentary canal.
      2. It is highly coiled & about 7.5 metres long.
      Digestion:
      1. It receives digestive juices from the liver & pancreas.
      2. The partly digested food reaches the lower part of the small intestine. 
      3. Here the intestinal juice completes the digestion of all components of the food.
      4. It converts complex food components into simple substances.

      Cabohydrates = Simple sugar (i.e. glucose)

      Fats = Fatty acids & Glycerol

      Proteins = Amnio acids

      Absorption:
      1. It is the process in which the digested food is taken in by the blood vessels present in the wall of the intestine.
      2. The inner walls of the small intestine have thousands of finger-like outgrowths called as villi.
      3. Each villus has a network of thin & small blood vessels close to its surface. 
      4. Thus the villi increases the surface area for absorption of the digested food.
      Assimilation:
      1. The absorbed substances are transported via the blood vessels to different organs of the body.
      2. There they are used to build complex substances such as proteins required by the body.
      3. This is process is called assimilation.
      4. In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water & energy is released.

      The food that remains undigested & unabsorbed enters into the large intestine.

    • Large Intestine
      1. It is wider & shorter than small intestine.
      2. It is about 1.5 metre in length.
      Function:
      1. It absorbs water & some salts from the undigested food.
      2. The remaining waste is passed into the rectum where it remains as semi-solid faeces.
      Anus:

      The faecal matter is removed through the anus. 

      This process is called egestion.

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    Animal Nutrition

    • Animal nutrition includes:
      • Nutrient requirement.
      • Mode of intake of food.
      • Its utilisation in the body.
      Mode of nutrition:

      Animals get their food from plants, either directly or indirectly. Depending upon the mode of nutrition, the animals are of three types:

      1. Herbivores: animals that eat only plants, eg: cows. rabbits, deer, etc.
      2. Carnivores: animals that eat only animals, eg: lions, tigers, wolfs, etc.
      3. Omnivores: animals that eat both plants & animals, eg: humans, bears, etc.

      The mode of taking food into the body varies in different organisms.

      Examples:

      1. Bees & humming-birds suck the nectar of plants.
      2. Infants of human and many other animals feed on mother’s milk.
      3. Snakes like the python swallow the animals they prey upon.
      4. Aquatic animals filter tiny food particles floating & feed upon them.

       

       

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    Digestion in Animals

    • Starfish
      1. It eats animals that are covered by hard shells of calcium carbonate.
      2. After opening the shell, the starfish pops out its stomach through its mouth.
      3. It eats the soft animal inside the shell.
      4. The stomach then goes back into the body and the food is slowly digested.

    • Amoeba 
      1. It is a microscopic single celled organism. 
      2. It has a cell membrane, a rounded nucleus & many small food vacuoles in its cytoplasm.
      3. It has finger-like temproary projections of cell membrane called pseudopodia or false feet.
      4. It uses pseudopodia to move, capture of food or change its shape & position.
      Digestion:
      1. Amoeba feeds on some microscopic organisms.
      2. When the amoeba senses food, it pushes out one or more pseudopodia around the food to capture it.
      3.  The food becomes trapped in a food vacuole where digestive juices are secreted.
      4. They act on the food & break it down into simpler substances that can be abosorbed.
      5. The absorbed substances are used for growth, maintenance & multiplication.
      6. The undigested residue of the food is expelled outside by the vacuole.
      Diagram:

       

    • Rumination:

      All grass eating animals are called ruminants.

      Ingestion:

      1. The ruminats continuously swallow grass without chewing it much.
      2. This partly chewed food is swallowed through the esophagus to the first chamber of the stomach.
      3. The stomach of the ruminants has four chambers.

      Rumen:

      1. It is the first & largest chamber of the stomach.
      2. It receives the food swallowed through the esophagus.
      3. The food is stored here & broken down.
      4. The partly digested is called as cud.
      5. Cellulose, an important plant based carbohydrate is broken down & digested  by the cellulose digesting bacteria present in the rumen.

      Reticulum:

      1. It is the second chamber of the stomach.
      2. From the rumen the cud enters the reticulum.
      3. Here, the cud is brought back to the mouth in small lumps to chew it properly. This process of rechewing of cud is called as rumination.
      4. Saliva is mixed with the food & the food is rechewed.
      5. The food enters the third chamber.

      Omasum:

      1. It is the third & smallest chamber of the stomach.
      2. Here, the food is broken down into small pieces.

      Abomasum:

      1. It is the fourth chamber of the stomach.
      2. Here, hydochloric acid & gastric juices are secreted to digest the food.
      3. From here the food reaches the caecum.

      Caecum:

      1. It is a sac like structure present between small and large intestine.
      2. in some animals like horses, rabbits, cellulose may be digested here. 

      Small Intestine:

      The digested food now passes into the small intestine for absorption and assimilation.

      Large intestine:

      The undigested food passes through the large intestine, where water & minerals are abosrbed.

      The undigested food is stored as waste & egested from the body.

      *Humans caanot digest cellulose as they don't have cellulose digesting bacteria.

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    Text Book Exercises

    • Q1. Fill in the blanks:

      Ans:

      (a) The main steps of nutrition in humans are ingestion, digestion, absorption, assimilation, and egestion.

      (b) The largest gland in the human body is the liver.

      (c) The stomach releases hydrochloric acid and digestive juices which act on food.

      (d) The inner wall of the small intestine has many finger-like outgrowths called villi.

      (e) Amoeba digests its food in the food vacuole.

      Q2. Mark ‘T’ if the statement is true and ‘F’ if it is false:

      Ans:

      (a) Digestion of starch starts in the stomach. - (F)

      Explanation: The digestion of starch actually starts in the mouth with the help of saliva, which contains enzymes that break down starch into simpler sugars.

      (b) The tongue helps in mixing food with saliva. - (T)

      Explanation: The tongue is a muscular organ that plays a crucial role in mixing food with saliva during chewing. This mixing helps in the initial digestion of food.

      (c) The gall bladder temporarily stores bile. - (T)

      Explanation: The gall bladder is responsible for storing bile produced by the liver. Bile is released into the small intestine to help digest fats.

      (d) The ruminants bring back swallowed grass into their mouth and chew it for some time. - (T)

      Explanation: Ruminants, such as cows, bring back food to the mouth in the form of cud.

      Q3. Tick (bold) mark the correct answer in each of the following:

      Ans:

      (a) Fat is completely digested in the (i) stomach (ii) mouth (iii) small intestine  (iv) large intestine

      Explanation: Fat digestion is completed in the small intestine, where bile & pancreatic enzymes work together to break down fats into fatty acids & glycerol.

      (b) Water from the undigested food is absorbed mainly in the (i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine 

      Explanation: The large intestine is primarily responsible for absorbing water from undigested food, which helps in forming solid waste.

      Q4. Match the items of Column I with those given in Column II:

      Ans:

      Food Components Product(s) of Digestion
      Carbohydrates Sugar
      Proteins Amino acids
      Fats Fatty acids and glycerol

       

      Q5. What are villi? What is their location and function?

      Ans:

      1. Villi are tiny, finger-like projections located in the inner walls of the small intestine.
      2. Function: is to increase the surface area for the absorption of nutrients from digested food. 
      Q6. Where is the bile produced? Which component of the food does it help to digest?

      Ans:

      1. The bile is produced in the liver.
      2. It is stored in a sac called gall bladder.
      3. It helps in digestion of fats.
      Q7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.

      Ans:

      1. Cellulose is the carbohydrate that can be digested by ruminants.
      2. The ruminants have a sac called rumen between the esophagus & small intestine.
      3. The rumen has special cellulose digesting bacteria that help in the digestion of cellulose.
      4. These are not present in humans, hence humans cannot digest cellulose.
      Q8. Why do we get instant energy from glucose?

      Ans:

      1. Glucose is a simple carbohydrate which is easily broken down in the cell with the help of oxygen to release a lot of instant energy.
      2. Glucose gets quickly absorbed in the blood after digestion providing instant energy. 
      Q9. Which part of the digestive canal is involved in:

      Ans:
      (i) absorption of food small intestine.
      (ii) chewing of food buccal cavity or mouth.
      (iii) killing of bacteria stomach.
      (iv) complete digestion of food small intestine.
      (v) formation of faeces large intestine.

      Q10. Write one similarity and one difference between the nutrition in amoeba and human beings.

      Ans:

      Similarity: 

      In both ameoba & human beings, digestive juices are secreted which convert complex food into simple & absorbable substances that can be used by the body.

      Differences:

      The amoeba captures the food with the help of pseudopodia whereas humans take in the food through the mouth or buccal cavity.

      Q11. Match the items of Column I with suitable items in Column II

      Ans:

      Column I Column II
      (a) Salivary gland (iii) Saliva secretion
      (b) Stomach (iv) Acid release
      (c) Liver (i) Bile juice secretion
      (d) Rectum (ii) Storage of undigested food
      (e) Small intestine (v) Digestion is completed
      (f ) Large intestine (vi) Absorption of water

       

      Q12. Label Fig. 2.11 of the digestive system.

      Ans:

      Q13. Can we survive only on raw, leafy vegetables/grass? Discuss.

      Ans:

      1. No, we cannot survive only on raw, leafy vegetables or grass.
      2. Because they contain cellulose.
      3. We cannot digest cellulose as we don't have cellulose digesting bacteria.
      4. Also, leafy vegetables have only one type of nutrition & we require a balanced diet with all other nutrients to live a healthy life.

       

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    Objective Q & A

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    Additional Q & A

    • Q1. Explain how assimilation is different from absorption.

      Ans:

      1. The process by which the nutrients in the digested food is absorbed by the blood vessels present in the wall of the intestine is called as absorption. 
      2. The process by which the absorbed nutrients are utilised by the body for repair, growth and energy generation is called as assimilation.
      Q2. What is the action of the intestinal juice on carbohydrates, fats and proteins?

      Ans:

      The intestinal juice does the following action:

      1. Carbohydrates is broken into simple sugars.
      2. Fats is broken into fatty acids & glycerol.
      3. Protein is broken into amino acid.
      Q3. Why do stomach ulcer occur? What will happen if they are not treated?

      Ans:

      1. The stomach has a protective mucous lining to protect it from its own digestive juices & acid present in the stomach.
      2. When this protective mucus lining gets reduced or damaged it causes stomach ulcer
      3. If not treated, stomach ulcers can cause pain in the upper abdomen, heart burn, nausea, indigestion or gas.
      Q4. Rohan was eating his food quickly without chewing it properly during the lunch break as he wanted to go to play cricket. Suddenly he started coughing severly. Why do you think this happened?

      Ans:

      1. The wind pipe runs adjacent to the food pipe & they share a common passage in the throat.
      2. There is a flap-like valve, called the epiglottis that closes the passage of the windpipe when we swallow food or liquids.
      3. When we are eating food quickly or talking or laughing while eating food this valve remains open.
      4. As Rohan was eating quickly, the food must have entered the windpipe.
      5. Hence, he started coughing to clear the wind pipe of the food.
      Q5. Differentiate between milk teeth and permanent teeth.

      Ans:

      Milk teeth Permanent teeth
      They are the first set of teeth. They are second set of teeth which grow after the milk teeth fall off.
      These teeth are smaller & fall off at the age of 6. They are stronger and larger.
      They are 20 in number. They are 32 in number.
      They are replaced by permanent teeth when they fall. They are replaced by artificial teeth when they fall.

       

      Q6. Explain the function of the tongue in the digestive process?

      Ans:

      1. The tongue helps to move, chew & mix saliva with the food in the mouth.
      2. It has different taste buds which helps us to taste different flavours.
      3. It helps to swallow the food by pushing it into the oesophagus.
      Q7. How does the digestive system of humans differ from that of ruminants?

      Ans:

      1. The humans have a single chambered stomach while ruminants have a stomach with four chambers.
      2.  The ruminants can digest cellulose, a comples carbophydrate obtained from plants with the help of cellulose digesting bacteria in their rumen. While humans cannot digest cellulose.
      Q8: Name the four chambers of stomach present in ruminants with their functions.

      Ans:

      The four chambers of the stomach in ruminants are:

      1. Rumen: It is the first chamber where food is stored here & broken down in the form of cud after swallowing. 
      2. Reticulum: It is second chamber which sends the cud back to the mouth for chewing.
      3. Omasum: it is the third chamber where food in broken down into pieces.
      4. Abomasum: It is last chamber where the aic & digestive juices are mixed with the food.
      Q9. What is ORS? When should it be given?

      Ans:

      1. ORS means oral rehydration solution.
      2. It should be given to anybody suffering from diarrhoea.
      3. Diarrhoea is when a person is passing watery stool frequently due to infection, food poisoning or indigestion.
      4. This causes excessive loss of water and salts from the body.
      5. ORS is made by boiling & cooling plenty of water with a pinch of salt & sugar dissolved in it.
      Q10. How does the food reach the stomach?

      Ans:

      1. When the food is ready to be swallowed, the tongue pushes food into the throat.
      2. The epiglottis, a flap like valve covers the windpipe & food food enters the oesophagus.
      3.  The muscles of the esophagus contract & relax in a wave-like motion called peristalsis.
      4. This motion pushes the food into the stomach.
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    MCQ's

    • Welcome to the Quiz!🎯

      Before you start, please take a moment to go through the important rules so you can make the most of this quiz.

      📌 Quiz Format:

      • Marks per Question: 1 🎯
      • No Negative Marking! 😀

      🔄 Attempts & Scoring:

      • You can take the quiz as many times as you want—no limits! 🚀
      • Your final score will be the average of all your attempts.

      🏆 Passing Criteria:

      You need to score at least 70%  average marks to pass of all your attempts.

      🚀 Pro Tips for Success:

      • 💡 Read each question carefully before selecting your answer.
      • 💡 Manage your time wisely—you go back to previous questions!
      • 💡 Stay focused, and most importantly, have fun!

      Once you’re ready, click the "Start Attempt" button and let’s go! 🎯🎉

    • Set 1 Quiz
      Students must
      Receive a grade
      Receive a passing grade

      Total 10 Questions

    • Set 2 Quiz
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      Total 10 Questions

    • Set 3 Quiz
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      Total 10 Questions

    • Set 4 Quiz
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      Total 9 Questions With Multiple Right Answers

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    Objective Questions

    • Welcome to the Quiz!🎯

      Before you start, please take a moment to go through the important rules so you can make the most of this quiz.

      📌 Quiz Format:

      • Marks per Question: 1 🎯
      • No Negative Marking! 😀

      🔄 Attempts & Scoring:

      • You can take the quiz as many times as you want—no limits! 🚀
      • Your final score will be the average of all your attempts.

      🏆 Passing Criteria:

      You need to score at least 70%  average marks to pass of all your attempts.

      🚀 Pro Tips for Success:

      • 💡 Read each question carefully before selecting your answer.
      • 💡 Manage your time wisely—you go back to previous questions!
      • 💡 Stay focused, and most importantly, have fun!

      Once you’re ready, click the "Start Attempt" button and let’s go! 🎯🎉

    • Give one word answer Set 1 Quiz
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      Total 10 Questions

    • Give one word answer Set 2 Quiz
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      Total 11 Questions

    • True or False Quiz
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      Total 7 Questions

    • Arrange the steps Quiz
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      Total 1 Questions with 5 steps