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.
