Chapter- 2 Nutrition in Animals
NOTES
1. The nutrition of living beings involves the need for nutrients, the method of food intake (eating), and the way it is utilized in the body.
2. Digestion- The breakdown or conversion of complex food substances into simpler substances is called decomposition, and this process is known as digestion.
3. The method of food intake varies among different organisms. In bees and some other animals, the young ones feed on the mother's milk. Creatures like pythons from the serpent family swallow their prey whole. Some aquatic animals filter food particles floating in the water around them and consume them.
4. Digestion in Humans- In humans, food passes through a continuous tube that starts from the oral cavity and extends to the anus. This tube can be divided into various parts: 1. Oral cavity, 2. Esophagus, 3. Stomach, 4. Small intestine, 5. Large intestine, 6. Rectum or anus.
- The inner lining of the stomach, the small intestine, and various glands associated with the alimentary canal, such as the salivary glands, liver, and pancreas, secrete digestive juices. These digestive juices convert complex substances into their simpler forms. The alimentary canal and the associated glands together form the digestive system.
A. Mouth and Oral Cavity- The intake of food occurs through the mouth. The process of taking food into the body is called ingestion.
- We chew food with the help of teeth and grind it into small pieces using a mechanical process. Each tooth is embedded in a separate cavity within the gums. The shape and functions of our teeth vary. Types of teeth: 1. Incisors (for cutting), 2. Canines (for tearing and shredding), 3. Premolars, 4. Molars (for chewing and grinding).
- Salivary Glands- The salivary glands are present in our mouth and secrete saliva. Saliva converts the starch in rice into sugar.
- The tongue is a muscular and flexible organ, attached at the back to the floor of the oral cavity. Its front part is free and can move in any direction. We use the tongue for speaking. Additionally, it mixes saliva with food and aids in swallowing. The tongue helps us detect taste. It has taste buds that enable us to identify different types of flavors.
C. Stomach- The stomach is a thick-walled, pouch-like structure. It is flat and J-shaped, and it is the widest part of the alimentary canal. The inner lining of the stomach secretes mucus, hydrochloric acid, and digestive juices. The mucus protects the inner lining of the stomach. The acid destroys many bacteria that reach the stomach with food. The digestive juices (gastric juice) break down proteins into simpler substances.
D. Small Intestine- The small intestine is a highly coiled tube approximately 7.5 meters long. It receives secretions from the liver and pancreas, and in addition, some digestive juices are also secreted from its walls.
- Liver- The liver is the largest gland in the body. It is a dark red-brown gland. It secretes bile, which is stored in a sac called the gallbladder. Bile plays an important role in the digestion of fats.
- Pancreas- The pancreas is a large, light yellow gland. It secretes pancreatic juice, which acts on carbohydrates and proteins, converting them into their simpler forms. Carbohydrates are converted into simple sugars like glucose. Fats are converted into fatty acids and glycerol, while proteins are converted into amino acids.
- Absorption in the Small Intestine- The digested food passes into the blood vessels located in the walls of the small intestine. This process is called absorption. The inner lining of the small intestine has finger-like projections called villi or intestinal villi.
- Assimilation- The transfer of absorbed substances through the blood vessels to different parts of the body, where they are used to form complex substances, is called assimilation.
E. Large Intestine- The large intestine is shorter and wider than the small intestine. It is approximately 1.5 meters long. Its main function is to absorb water and some salts. The remaining undigested material moves into the rectum and remains in the form of semi-solid feces.
- From time to time, the feces are expelled through the anus. This process is called excretion.
- Partial digestion of food occurs in the rumen, which is called rumination.
- Later, the animal brings the food back into the mouth in the form of small lumps and continues to chew it. This process is called remastication, and such animals are called ruminants.
6. Cecum- In animals like horses, rabbits, etc., there is a large pouch-like structure between the small intestine and the large intestine, which is called the cecum.
7. Reproduction and Digestion in Amoeba- Amoeba is a unicellular organism found in water bodies. The cell of an amoeba has a cell membrane, a dense spherical nucleus, and several vacuoles in the cytoplasm that resemble bubbles.
- Amoeba constantly changes its shape and position. It extends one or more finger-like projections called pseudopodia, which help it in movement and capturing food.
8. Food Vacuole- Digestive juices are secreted in the food vacuole. These digestive juices act on the food and convert it into simpler substances. Undigested waste is expelled by the food vacuole.
EXERCISE
(a) The main steps of nutrition in humans are ______, ________, ________, _________ and _______.
(b) The largest gland in the human body is ________.
(c) The stomach releases hydrochloric acid and _______ juices which act on food.
(d) The inner wall of the small intestine has many finger-like outgrowths called______.
(e) Amoeba digests its food in the _______.
Answer- (a) The main steps of nutrition 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 (Villus).
(e) Amoeba digests its food in the Stomach.
Question- 2. Mark 'T' if the statement is true and 'F' if it is false:
(a) Digestion of starch starts in the stomach. (T/F)
(b) The tongue helps in mixing food with saliva. (T/F)
(c) The gall bladder temporarily stores bile. (T/F)
(d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F)
Answer- (a) - False, (b) - True, (c) - Ture, (d) - True.
Answer- (a) - False, (b) - True, (c) - Ture, (d) - True.
Question- 3. Tick (✓) mark the correct answer in each of the following:
(a) Fat is completely digested in the
(1) Stomach (2) Mouth (3) Small intestine (4) Large intestine
(b) Water from the undigested food is absorbed mainly in the
(1) Stomach (2) Foodpipe (3) Small intestine (4) Large intestine
Answer- (a) Small intestine (b) Large intestine
Question- 4. Match the items of Column 1 with those given in Column 2:
Question- 5. What are Villi? What is their location and function?
Answer- The inner wall of the small intestine has finger-like projections called villi (or intestinal villi). Villi increase the surface area for the absorption of digested food.
Digested food is absorbed through the surface of the villi and then passes into the blood vessels.
Question- 6. Where is the bile produced? Which component of the food does it helps to digest?
Answer- The liver secretes bile juice. Bile juice is stored in a sac-like structure called the gall bladder. Bile juice plays an important role in the digestion of fats.
Question- 7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Answer- Cellulose requires more time for digestion. The alimentary canal of ruminants is larger than that of humans. Therefore, cellulose can be digested by ruminants but not by humans.
Question- 8. Why do we get instant energy from glucose?
Answer- We get energy quickly from glucose because, in the cells, glucose easily breaks down into carbon dioxide and water with the help of oxygen, releasing energy.
Question- 9. Which part of the digestive canal is involved in:
(1) absorption of food _____.
(2) Chewing of food ______.
(3) Killing of bacteria _______.
(4) Complete digestion of food ______.
(5) Formation of faeces _______.
Answer- (1) Small intestine, (2) Buccal cavity (mouth cavity), (3) Stomach, (4) Small intestine, (5) Large intestine.
Question- 10. Write one similarity and one difference between the nutrition in amoeba and human beings.
Answer- Similarity: The basic process of digestion of food and the release of energy from it is the same in both Amoeba and humans. In humans, different digestive juices mix with the food and break it down into simpler substances. Similarly, in Amoeba, digestive juices are secreted into the food and act on it, breaking it down into simpler substances.
Difference: The process of digestion in Amoeba is very simple, whereas in humans it is very complex. In humans, food is taken in through the mouth and passes through a complex process of digestion and absorption. Finally, the undigested matter is excreted in the form of feces. In Amoeba, food is captured with the help of pseudopodia, and after absorption, the undigested food is expelled from the food vacuole.
Question- 11. Match the items of Column 1 with suitable items in Column 2:
Question- 12. Label Fig 2.11 of the digestive system.
Question- 13. Can we survive only on raw, leafy vegetables/grass? Discuss.
Answer- Humans can digest vegetables only when they are eaten in a boiled or cooked form because raw leafy vegetables and grass contain cellulose. Humans and many animals cannot digest cellulose-rich food because they lack certain specific enzymes and do not have special types of bacteria that can digest cellulose. Therefore, we boil or cook vegetables, which breaks cellulose into simpler carbohydrates.