NCERT Text book Solutions and other Questions and Answers
Q1: Fill in the blanks:
(a) The main steps of digestion in humans are ingestion, digestion, absorption , assimilation and egestion.
(b) The largest gland in the human body is 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:
(a) Digestion of starch starts in the stomach. (T/F) : False. It starts in the mouth
(b) The tongue helps in mixing food with saliva. (T/F) : True
(c) The gall bladder temporarily stores bile. (T/F) : True
(d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F) : True
Q3: Tick (√) mark the correct answer in each of the following:
(a) Fat is completely digested in the(i) stomach
(iii) small intestine (√)
(iv) large intestine
(b) Water from the undigested food is absorbed mainly in the
(iii) small intestine
(iv) large intestine (√)
Q4: Match the items of Column I with those given in Column II:
Carbohydrates - Sugar
Proteins - Amino acids
Fats - Fatty acids and glycerol
Q5: What are villi? What is their location and function?Answer:
The inner walls of the small intestine have thousands of finger-like outgrowths.These are called villi
The villi increase the surface area for absorption of the digested food. Each villus has a network of thin and small blood vessels close to its surface. The surface of the villi absorbs the digested food materials. The absorbed food is then transported to various organs via blood vessels.
Here is a nice and funny video posted by makemegenius.com about digestive system.
Q6: Where is the bile produced? Which component of the food does it digest?
Liver secretes bile juice that is stored in a sac called the gall bladder. The bile plays an important role in the digestion of fats.
Q7: Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Cellulose, a type of carbohydrate present in grass and it can be digested by ruminants but not by humans. Ruminants have a large sac-like structure between the small intestine and large intestine called caecum. The cellulose of the food is digested here by the action of certain bacteria which are not present in humans.
Q8: Why do we get instant energy from glucose?Answer:
Glucose is the simplest form of sugar. It can directky be absorbed by intenstine and can easily be transported by blood to various cells of the body. Cells directly act on glucose along with oxygen to given energy.
While carbohydrates are complex forms of sugars and they need to be further broken down into simpler substances like glucose before absorption. Hence it requires extra time as compared to glucose which provides instant energy.
Q9: 10. Which part of the digestive canal is involved in:
(i) absorption of food __villi in small intestine__.
(ii) chewing of food __mouth (buccal cavity)__.
(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.
- Similarity: The basic process of digestion of food and release of energy is the same in amoeba as well as in human beings. In amoeba, Digestive juices are secreted into the food vacuole. They act on the food and break it down into simpler substances. Gradually the digested food is absorbed. Similarly, in human beings various digestive juices (mouth, stomach, intestine etc.) act on food and break it down to simpler substances.
- Difference: The digestion process in amoeba is simple while in human beings it s a complex process. The process of ingestion and egestion are also quite different. Amoeba engulf its food by surrounding the food particle with its pseudopodia. The undigested food which is largely carbon dioxide gas is expelled outside by the vacuole. While in human beings, the food (which is complex substance) is taken inside the mouth and undergoes a complex process of digestion and absorption. Finally the undigested food it expelled in the form of faeces.
(a) Salivary gland - (iii) Saliva secretion
(b) Stomach - (iv) Acid release
(c) Liver - (i) Bile juice secretion
(d) Rectum - (vii) Release of faeces
(e) Small intestine - (v) Digestion is completed
(f) Large intestine - (vi) Absorption of water, (ii) Storage of undigested food
Q12: Label the following fig of digestive system.
|Human Digestive System|
Q13: Can we survive only on raw, leafy vegetables/grass? Discuss.
Answer: Raw leafy vegetables and grass are rich in cellulose, a type of carbohydrate. Many animals, including humans, cannot digest cellulose, because they do not have enzymes and certain type of bacteria which can digest cellulose.
We cannot survive by taking vegetables in raw form. That's why we boil or cook vegetables which breaks down cellulose into simple carbohydrates. We can only survive by taking in vegetables in boiled/cooked form.