NCERT Solutions for Class 7 Science - Nutrition in Animals

Nutrition in humans is a multi-step process to obtain and utilize food for energy and growth. The five main steps are:

• Ingestion: Taking in food through the mouth.
• Digestion: Breaking down food into smaller, absorbable molecules.
• Absorption: Nutrients from the food pass into the blood from the digestive tract.
• Assimilation: Cells in the body use these absorbed nutrients for various functions.
• Egestion: Expelling the undigested waste from the body.

• The liver is the largest gland in the human body. 
• It plays a crucial role in digestion by producing bile, which helps break down fats. 
• It also performs various other functions, such as detoxifying the blood and storing vitamins and minerals.

• The stomach releases hydrochloric acid and digestive juices. 
• These juices contain enzymes like pepsin that help break down proteins into simpler forms, aiding in the overall process of digestion.

• The inner wall of the small intestine has finger-like outgrowths called villi. 
• Villi increase the surface area for absorption, allowing nutrients to pass efficiently into the bloodstream.

• Amoeba digests its food in the food vacuole. 
• Amoeba engulfs food by forming a vacuole around it, where enzymes break down the food for absorption and energy.

• The digestion of starch actually starts in the mouth, not the stomach. 
• Saliva contains an enzyme called amylase, which begins breaking down starch into simpler sugars as soon as food is chewed and mixed with saliva.

• The tongue is essential in the process of mixing food with saliva, which moistens the food and starts the breakdown of starch. 
• The tongue also helps move the food around the mouth, making it easier to swallow.

• The gallbladder is a small organ that temporarily stores bile produced by the liver. 
• Bile is released from the gallbladder into the small intestine to help digest fats.

• Ruminants, such as cows and goats, have a unique digestive process called "rumination." 
• After swallowing grass, they bring it back into their mouth to chew it again thoroughly, which helps break down the food further and aids in digestion.

• The small intestine is where fat digestion is completed. 
• Bile, produced by the liver and stored in the gallbladder, is released into the small intestine to emulsify fats, breaking them down into smaller droplets. 
• Pancreatic enzymes then act on these droplets, allowing for complete digestion and absorption.

• The large intestine is responsible for absorbing water from undigested food material. 
• As the undigested food passes through the large intestine, most of the water is absorbed back into the body, leaving a more solid waste product for elimination.

 Carbohydrates - Sugar

• Carbohydrates are broken down into simpler sugars, primarily glucose, during digestion. 
• This breakdown begins in the mouth with the enzyme amylase and is completed in the small intestine. 
• Glucose serves as the primary energy source for the body's cells.

Proteins - Amino acids

• Proteins are digested into amino acids, which are their basic building blocks. 
• Protein digestion begins in the stomach with enzymes like pepsin and continues in the small intestine. 
• Amino acids are then absorbed and used for growth, repair, and various cellular functions.

Fats - Fatty acids and glycerol

• Fats are broken down into fatty acids and glycerol in the small intestine. 
• Bile from the liver emulsifies fats, while pancreatic enzymes break them down further. 
• These smaller molecules are absorbed and used as an energy source or stored for future use.

• The small intestine is the primary site for the absorption of nutrients. 
• Its inner walls have villi and microvilli, which increase the surface area, allowing nutrients from digested food to be absorbed efficiently into the bloodstream.

• The buccal cavity, or mouth, is where food is initially broken down by chewing (mastication) with the help of teeth. 
• Saliva mixes with the food, softening it and beginning the digestion of carbohydrates.

• The stomach secretes hydrochloric acid (HCl), which creates an acidic environment. 
• This acid not only aids in digestion but also kills bacteria and other pathogens present in food, providing protection against infections.

• The small intestine is where complete digestion occurs. 
• Digestive enzymes from the pancreas and bile from the liver further break down food, allowing all nutrients to be fully digested and absorbed.

• In the large intestine, undigested food residue and waste are processed. 
• Water is absorbed, and the remaining material solidifies, forming faeces, which are stored until elimination from the body.

(a) Salivary gland - (iii) Saliva secretion

• The salivary glands, located in the mouth, produce and release saliva. Saliva contains enzymes like amylase that begin the digestion of starches in food.

(b) Stomach - (iv) Acid release

• The stomach secretes gastric acid (hydrochloric acid), which helps in breaking down food, creating an acidic environment that activates digestive enzymes and kills harmful bacteria.
  

(c) Liver - (i) Bile juice secretion

• The liver produces bile, a digestive fluid that helps in emulsifying fats. Bile is stored in the gallbladder and released into the small intestine to aid fat digestion.
  

(d) Rectum - (vii) Release of faeces

• The rectum is the last part of the large intestine, where faeces are stored temporarily until they are expelled from the body through the anus.
  

(e) Small intestine - (v) Digestion is completed

• In the small intestine, enzymes and bile work to complete the digestion of food. Nutrients are then absorbed through the intestinal walls into the bloodstream.
  

(f) Large intestine - (vi) Absorption of water

• The large intestine absorbs water and salts from undigested food, turning it into a more solid form, which becomes faeces, before it moves to the rectum for elimination.