Class 7 Nutrition in Animals - NCERT Important Q&A
Complete topic-wise questions and answers from CBSE Class 7 Science Chapter 2
Introduction to Animal Nutrition
Q. What is meant by animal nutrition?
A. Animal nutrition includes nutrient requirement, mode of intake of food, and its utilisation in the body.
Q. What is digestion?
A. The breakdown of complex components of food into simpler substances is called digestion.
Different Ways of Taking Food
Q. What are the different ways of taking in food? Describe them with example of organism.
A. Different ways of taking food include:
- Scraping - In this method, food is scraped off a surface by the jaw or an organ. Examples of animals that use this method include snails and ants.
- Chewing - This mode involves the biting and grinding of food in the mouth by teeth. Examples of animals that chew their food include humans and dogs.
- Siphoning -It is a mode of nutrition in which animals suck food from the substratum using a siphon, which is a long hollow tube. This method is commonly observed in certain insects and animals that feed on liquid food. For example, butterflies and hummingbirds use siphoning to feed on nectar
- Capturing and swallowing - This involves capturing the food and then swallowing it whole. Examples of animals that use this method include lizards and snakes, which often swallow their prey whole.
- Sponging - This involves dissolving food particles using saliva and then drawing the liquid into the mouth. Examples of animals that use this method include houseflies and butterflies.
- Sucking - This involves piercing the food and then sucking the liquid out of it. Examples of animals that use this method include mosquitoes and leeches.
Q. Why does a starfish pop out its stomach through its mouth?
A. A starfish feeds on animals that have hard calcium carbonate shells. After opening the shell, it pops out its stomach through its mouth to reach and eat the soft animal inside. Then it pulls the stomach back into its body and digests the food slowly.
Digestion in Humans
Q. What is alimentary canal (digestive tract)?
A. Alimentary canal is a long, muscular tube that runs from mouth to anus through which food passes and gets digested.
Q. What is digestive system?
A. Digestive system consists of the alimentary canal and associated glands that help in digestion.
Q. What are the various compartments of alimentary canal?
A. The alimentary canal has these compartments:
- Mouth and buccal cavity
- Oesophagus (food pipe)
- Stomach
- Small intestine
- Large intestine
- Rectum and anus
Q. What are the various glands associated with the alimentary canal?
A. Glands associated with digestion include:
- Salivary glands
- Liver
- Pancreas
- Gastric glands in stomach
- Intestinal glands in small intestine
The Mouth and Buccal Cavity
Q. What is ingestion?
A. The process of taking food into the body is called ingestion.
Q. Where does the process of digestion start?
A. The process of digestion starts in the mouth.
Q. What are milk teeth?
A. Milk teeth are the first set of teeth that appear in babies. They start falling around 6 years of age.
Q. What are permanent teeth?
A. Permanent teeth replace milk teeth and last throughout life.
Q. What are different types of teeth? What are their numbers?
A. Types of teeth and their numbers in adults:
- Incisors (8) - for biting
- Canines (4) - for tearing
- Premolars (8) - for grinding
- Molars (12) - for crushing
Q. What are salivary glands?
A. Salivary glands are glands in the mouth that produce saliva.
Q. What is secreted by salivary glands?
A. Salivary glands secrete saliva.
Q. What does saliva do to starch?
A. The saliva breaks down the starch into sugars.
Q. What is the tongue?
A. The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity. It is free at the front and can be moved in all directions.
Q. What are the functions of the tongue?
A. Functions of tongue:
- Tasting food
- Mixing food with saliva
- Swallowing food
- Speaking
Q. What is tooth decay?
A. Tooth decay is the damage of teeth caused by bacteria producing acid that destroys tooth enamel.
Q. How does tooth decay happen?
A. Bacteria in the mouth act on sugars in food to produce acids. These acids damage the tooth enamel causing cavities.
Q. What type of food causes tooth decay?
A. Sugary foods like sweets, chocolates, and cold drinks cause tooth decay.
Q. Sometimes when we eat in a hurry, talk or laugh while eating, we may cough, get hiccups or a choking sensation. Why?
A. This happens because food may enter the windpipe instead of the food pipe.
Q. How is food prevented from entering the windpipe?
A. A flap called epiglottis closes the windpipe opening during swallowing to prevent food from entering it.
The Foodpipe/Oesophagus
Q. How does food move in the foodpipe?
A. Food moves through the foodpipe by wave-like muscle movements called peristalsis.
Q. What is peristalsis?
A. Peristalsis is the wave-like contraction and relaxation of muscles in the alimentary canal that pushes food forward.
Q. Why do we vomit?
A. Vomiting occurs when the stomach expels harmful or unwanted food through the mouth.
Q. How does food move in the opposite direction during vomiting?
A. During vomiting, the muscles of the stomach and oesophagus contract in reverse direction to push food upward.
The Stomach
Q. What is stomach?
A. Stomach is a J-shaped muscular bag that stores and digests food.
Q. What is the shape of the stomach?
A. The stomach is J-shaped.
Q. Which is the widest part of the alimentary canal?
A. The stomach is the widest part of the alimentary canal.
Q. What are secreted by the stomach? What are their functions?
A. The inner lining of the stomach secretes:
- Mucous - protects stomach lining
- Hydrochloric acid - kills bacteria, makes medium acidic
- Digestive juices - break down proteins
Q. What do the digestive juices in the stomach break down?
A. The digestive juices break down the proteins into simpler substances.
The Small Intestine
Q. What is the length of small intestine? How is such a long structure accommodated in a small space within our body?
A. The small intestine is about 7.5 meters long. It is coiled and folded to fit in the abdominal cavity.
Q. What are the secretions received by the small intestine?
A. The small intestine receives secretions from the liver and the pancreas. Its wall also secretes juices.
Q. Which is the largest gland in the body?
A. Liver is the largest gland in the body.
Q. What does the liver secrete and where is it stored? What is its function?
A. The liver secretes bile juice that is stored in the gall bladder. Bile helps in the digestion of fats.
Q. Where is the pancreas located and what does it do?
A. The pancreas is a large cream coloured gland located just below the stomach. It secretes pancreatic juice which acts on carbohydrates, fats and proteins.
Q. What does the intestinal juice do?
A. The intestinal juice completes the digestion of all food components:
- Carbohydrates → simple sugars (glucose)
- Fats → fatty acids and glycerol
- Proteins → amino acids
Q. Where does the process of digestion get completed?
A. The process of digestion gets completed in the small intestine.
Absorption in the Small Intestine
Q. What is absorption?
A. Absorption is the process by which digested food passes through the intestinal wall into the blood vessels.
Q. What are villi? What are their functions?
A. Villi are finger-like projections in the inner walls of the small intestine. They increase the surface area for absorption of digested food.
Q. What is assimilation?
A. Assimilation is the process by which absorbed nutrients are used by the body for energy, growth and repair.
Large Intestine
Q. What is the length of the large intestine?
A. The large intestine is about 1.5 meters long.
Q. Why is the large intestine called so, even though it is shorter in length?
A. It is called large intestine because it is wider than the small intestine.
Q. What is the function of the large intestine?
A. Its function is to absorb water and some salts from the undigested food material.
Diarrhoea
Q. What is diarrhoea? How is it caused?
A. Diarrhoea is a condition where frequent loose, watery stools are passed. It is caused by infection, food poisoning or indigestion.
Q. What is ORS?
A. ORS (Oral Rehydration Solution) is a solution of sugar and salt in clean water. It prevents dehydration during diarrhoea.
Digestion in Grass-Eating Animals
Q. Why do cows, buffaloes and other grass-eating animals chew continuously even when they are not eating?
A. They are chewing the cud, which is partially digested food brought back from stomach to mouth for re-chewing.
Q. Why can't these animals chew food properly at the time they take it in?
A. They swallow grass quickly to avoid predators while grazing, storing it in rumen for later chewing.
Q. Why can't we digest cellulose like cattle do?
A. Humans lack the special bacteria and enzymes needed to break down cellulose.
Q. What is cellulose?
A. Cellulose is a complex carbohydrate that forms the cell walls of plants.
Q. What is cud?
A. Cud is partially digested food that ruminants bring back to the mouth for re-chewing.
Q. What is rumination?
A. Rumination is the process of re-chewing the cud.
Q. What are ruminants?
A. Ruminants are animals (like cows, buffaloes) that have a four-chambered stomach and chew cud.
Q. How do animals like horses and rabbits digest cellulose?
A. Animals like horses, rabbits, etc., have a large sac-like structure called caecum between the oesophagus and small intestine. Cellulose is digested there by bacteria.
Q. What are the parts of digestive system of the ruminants?
A. Ruminant digestive system parts:
- Mouth
- Oesophagus
- Four-chambered stomach (rumen, reticulum, omasum, abomasum)
- Small intestine
- Large intestine
Q. There are many small organisms which do not have a mouth and a digestive system. Then, how do they acquire and digest food?
A. They take in food through their body surface or form food vacuoles where digestion occurs.
Feeding and Digestion in Amoeba
Q. What is amoeba?
A. Amoeba is a microscopic single-celled organism found in pond water.
Q. What is pseudopodia?
A. Pseudopodia are temporary finger-like projections of Amoeba's cell membrane used for movement and feeding.
Q. What does Amoeba feed on?
A. Amoeba feeds on some microscopic organisms like bacteria and algae.
Q. What are food vacuoles?
A. Food vacuoles are bubble-like structures in Amoeba where food is stored and digested.
Q. Explain the process of digestion in amoeba.
A. Digestion in Amoeba:
- Amoeba captures food using pseudopodia
- Food is engulfed forming a food vacuole
- Digestive juices are secreted into the vacuole
- Food is broken down into simpler substances
- Digested food is absorbed
- Undigested material is expelled
Extra Questions
Q. Create a table for what is secreted by which organ or gland.
| Organ/Gland | Secretion |
|---|---|
| Salivary glands | Saliva |
| Stomach | mucus, Hydrochloric acid, digestive juices |
| Liver | Bile |
| Pancreas | Pancreatic juice |
| Small intestine | Intestinal juice |
Q. Create a table for what is broken down by which enzymes?
| Component | Action | Target | Result |
|---|---|---|---|
| Saliva | Breaks down | Starch | Sugars |
| Digestive juices | Breakdown | Proteins | Simpler substances |
| Bile | Digests | Fats | - |
| Pancreatic juice | Acts on | Carbohydrates, Fats, Proteins | Simpler forms |
| Intestinal juice | Completes digestion | All food components | - |
| Final Breakdown Products: | |||
| Carbohydrates → | Simple sugars (glucose) | ||
| Fats → | Fatty acids and glycerol | ||
| Proteins → | Amino acids | ||
Q. Fats in goat's milk are much simpler than those in cow's milk. Therefore, the goat's milk is much easier to digest than the cow's milk.
A. This statement is correct. Goat milk has smaller fat molecules and different protein structure making it easier to digest.
Q. What are the five stages of digestion the human body?
A.
Five Stages of Digestion in the Human Body:
- Ingestion – The process of taking food into the mouth.
- Digestion – The breakdown of food into simple, soluble forms (starts in the mouth and continues in the stomach and small intestine).
- Absorption – The process where digested food is absorbed into the blood, mainly in the small intestine.
- Assimilation – The absorbed nutrients are used by body cells for energy, growth, and repair.
- Egestion – The removal of undigested and unabsorbed food from the body through the anus.
Note: All answers are based on NCERT Class 7 Science textbook "Nutrition in Animals" chapter. Diagrams mentioned should be practiced from the textbook.
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