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Revision Notes for Class 7 Science Chapter 2 Nutrition in Animals
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Chapter 2 Nutrition in Animals Notes Class 7 Science
DIGESTION IN HUMANS
Humans have a well developed digestive system. This consists of the gut or alimentary canal, along with the associated digestive glands.
Parts of alimentary canal and accessory glands
The food that we take in can provide energy only if it is digested, absorbed and assimilated to be distributed to all parts of the body.
During digestion large insoluble pieces of food are broken down into soluble substances which are small enough to be absorbed through the walls of the intestine and into the bloodstream. This, process involves certain physical and chemical reactions, as follows:
Physical Action
• Chewing the food with teeth, so as to break the solid food into smaller pieces.
• Churning by the stomach to mix the food with the gastric juices.
Chemical Action
• Carbohydrates to simple sugars.
• Fats to fatty acids and glycerol
• Proteins to amino acid.
Enzymes are the digestive juices prepared by cells in various part of the digestive system. Table 1. Lists the details of the source, their substrates, affects and the resultant products.
The alimentary canal is a long tube of varying diameter which begins from the mouth and ends at the anus. It consists of mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
Mouth: Food is ingested by us through the mouth. The mouth contains tongue, teeth and salivary glands. They work together in chewing (masticating) the food. The chewed food is mixed with saliva, a watery fluid secreted by the salivary glands. This process is called mastication. Saliva contains the enzyme amylase, which converts starch into sugar, so it tastes sweet to us.
Teeth: Our teeth cut, tear and grind the food before we swallow it. We can feel the different shapes of our teeth with our tongue. There are four types of teeth in our mouth.
a) Incisors: These are the front 8 teeth, four on upper and four on lower jaw. These are flat, chisel - shaped teeth, well adapted for cutting and biting of food item
b) Canines: One incisor each is found on either side of each jaw. These round, sharp and pointed teeth are well adapted to hold and tear the food.
c) Premolars: There are two premolars on each side of each jaw. They have flat surfaces bearing small grooves and ridges, and are well adapted to crush and grind food.
d) Molars: These are the last three teeth on both sides in both the jaw They have almost flat surfaces with small projections for effective grinding of the food. (Fig. 7)
The white substance that covers our teeth is called enamel. It is the hardest substance in the body. All of us have two sets of teeth in our lifetime. The first set erupts when we are babies and lasts until we are about 8 years old. These are known as the milk teeth or temporary teeth. A child has only 20 such teeth –10 in each jaw. These teeth fall out one by one and are replaced by permanent teeth. A human adult has 32 teeth in all –16 in each jaws.
Structure of a tooth: Each tooth remains buried in the jaw bone by its root and the crown remains outside the gum. Incisors and canines have single root, while premolars and molars have two roots each. The crown is formed of dentine and has a layer of enamel outside.
Enamel forms the shining white part of the crown of each tooth. It is deposited on the surface of crown of the tooth.
Enamel is the hardest substances in our body, even harder than bones. It is also chemically the most stable substance. (Fig. 8).
Tongue: The tongue is a muscular organ and helps to mix saliva in the food. It pushes food towards our teeth. The tongue rolls the food into a bolus which is easy to swallow. It is pushed down the food pipe or oesophagus, by means of a series of rhythmic muscular contractions that go by the name ‘peristalsis’.
The tongue is the main organ of taste. Different sets of taste buds located in specific areas of the tongue, distinguish whether the food is sweet, salty, sour, bitter, etc. Thus, taste buds help us to select the right quality of food. The tongue also helps us to speak
Oesophagus: It is the tube connecting the mouth and the stomach, and is about 30 cm long. It takes about six second for solid food to reach the stomach after it is swallowed. Liquids travel faster down the oesophagus.
The powerful muscles in the oesophagus gently push food down to the stomach in a wave like action, called peristalsis as mentioned earlier.
Stomach: It is a J-shaped muscular bag. It can hold upto two litres of food at a time. Food stays in the stomach from a few minutes to a few hours depending on the type of food. Gentle movements of the stomach wall churn the food up with digestive juices like hydrochloric acid and gastric juices and change it into a semi-liquid state called chyme. The enzymes present in the gastric juices break down proteins. The hydrochloric acid kills the harmful bacteria and also helps the enzymes to work. In the stomach, the milk is changed to curd. Thus, food gets partly digested in the stomach.
Sometimes, we experience vomiting. It is nothing but antiperistaltic movements of the stomach wall and oesophagus.
Q1.What is nutrition?
A. The process by which living beings take in food and use it to obtain energy for growth and development is called nutrition
Q2.Why do we call animals heterotrophs?
A. Animals are called heterotrophs as they do not prepare their own food and derive their nutrition from some other organisms.
Q3.Mention 5 steps in the process of animal nutrition.
A. 1. Ingestion 2. Digestion 3. Absorption 4. Assimilation 5. Egestion
Q4. Name three glands associated with the alimentary canal in man. Mention their secretions.
A. 1. Salivary glands- secrete digestive juice that digests starch.
B. Liver- secretes bile juice.
C. Pancreas- secretes digestive juices that digest carbohydrates and proteins.
Q5.What is ingestion?
A. The process of taking in of food is called ingestion.
Q6. Name different types of teeth in our mouth and write their functions.
A. 1. incisors- cutting and biting
2. canines- tearing
3. pre molars- crushing and grinding
4. molars- finer grinding
Q7.Why is not advisable to not to talk while swallowing food?
A. When we talk while eating our wind pipe is open and food can enter in it leading to choking and hiccupping.
Q8.What are the secretions in stomach and their role in nutrition process?
A. It secretes- 1. HCl- provides acidic medium and kills microorganisms.
2. mucous- protects stomach lining from the action of acid and lubricates food.
3. Digestive juice- digests proteins.
Q9.What happens to food in small intestine?
A. 1. Small intestine receives digestive juices from pancreas, liver and its own wall.
2. Bile from liver emulsifies fats.
3. Pancreatic and intestinal juices break down carbohydrates, fats and proteins.
4. Nutrients are absorbed.
Q10. How is digested food absorbed?
A. Absorption of food occurs through small projections in the inner lining of the part of small intestine. These projections are called Villi.
Q11. What is large intestine and how does it function?
A. It is the extension of small intestine in the alimentary canal with a wider diameter. It helps in reabsorption of water from the waste to be thrown out.
Q12. Explain the process of digestion in ruminants.
A. cattle animals quickly swallow their food and store it in a part of stomach called Rumen. The food gets partially digested there called Cud. This cud returns to the mouth for further chewing and the process is called rumination. Their food is rich in cellulose which is digested in caecum.
Q13. What are the products of digestion of carbohydrates, fats and proteins?
A. the products of digestion of carbohydrates, fats and proteins are glucose, fatty acids and glycerol and amino acids respectively.
Q14. Although large intestine is not involved in the process of digestion, yet it has an important function. Justify.
A. It helps in absorption of water.
Q15. Write a note on the nutrition of amoeba.
A. Amoeba ingests food by pseudopodia and traps food in a vacuole. Food is digested with the help of digestive juices within it. The undigested food is thrown out by the vacuole only.
Q16. What is egestion?
A. it is the process of throwing out of undigested food.
Q17. What is the role of gall bladder in human digestive system?
A. gall bladder stores the secretion of liver temporarily.
Q18. Why are cattle animals known as ruminants?
A. They are called so as the partially digested food comes back in the miuth for further chewing.
Q.19: What is mastication?
Ans: Mastication is a process in which chewing of food and mixing of saliva with it is done in mouth.
Q.20: What is the role of tongue in our mouth? Ans: The tongue has following roles in our mouth:
=> It helps in talking.
=> It helps in mixing of saliva with the food during mastication.
=> It helps to swallow the food.
=> It gives us sensation of taste of food.
Q21: What is peristalsis?
Ans: The powerful muscles in oesophagus gently push food down to the stomach in a wave - like action, called peristalsis.
Q.22 What are secreted inside the stomach?
Ans: Gastric juice is secreted by the walls of stomach which contains HCl and Pepsin.
Q.23 What are the functions of HCl stomach?
Ans:Functions of HCl:
=> It helps to kill the germs present in the food.
=> After mixing with the food it makes an acidic medium which is essential for the activation of digestive juice.
Q.24 What is secreted from liver?
Ans: Bile juice is secreted from liver.
Q.25 What is digestion?
Ans: Digestion is a process which include crushing of the food into smaller particles by chewing and then breakdown of its complex components into simpler substances with the help of enzymes in a liquid medium which can be absorbed by our body.
Q.26: Write short notes (1 or 2 sentences) on -
(a) Pancreas (b) Liver (c) Oesophagus (d) Rumination (e) Pseudopodia
Ans:
(a) Pancreas: Pancreas is a large cream coloured gland located or present just below the stomach. Pancreatic juice acts on carbohydrates and protein and changes them into simpler forms.
(b) Liver: Liver is a reddish brown gland present in the upper part of our abdomen on the right side. It is the largest gland in our body. It secretes bile juice stored in sac - like structure called gall bladder.
(c) Oesophagus: It is along, narrow, muscular tube which directly leads to the stomach. It is about 25 cm long and passes downwards through the neck, the thorax and the abdominal cavity.
(d) Rumination: A process in which partially digested food returns to the mouth in small lumps and the animal chews it. This type of process is called Remination or Rumination and such types of animals are called Ruminants.
(e) Pseudopodia: The unicellular organism like amoeba constantly changes its shape and position. It catches food by pushing out a finger - like projection called Pseudopodia.
Q.27: What are digestive enzymes?
Ans: There are different types of enzymes which are used for the digestion of different food materials like - carbohydrates, fats, protein etc into their usable form.
Q28. Draw a labeled diagram of human digestive system.
A.
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CBSE Class 7 Science Chapter 2 Nutrition in Animals Notes
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