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• Animals take food inside the body by chewing, swallowing, sucking, nibbling, lapping, filtering, scraping.
• Human digestive system
  • Human digestive system is a complex system consisting of Alimentary Canal and Digestive Glands. Alimentary canal is long, tube like structure extending from mouth to Anus.
  • Food material is broken down in smaller particle by teeth, mixed with saliva containing salivary amylase, which breaks starch into sugar called maltose
  • Food material reaches to stomach and receives Hydrochloric Acid , Enzyme Pepsin and Mucus from the gastric glands present in the wall of stomach.
  • The movements of the wall of stomach churn the food and help in mixing the gastric juice in food. Sphincter Muscle present at the end of stomach regulates the passage of food into small intestine.
  • In small intestine digestion of carbohydrates, Fats and Proteins takes place. Walls of small intestine have large number of finger like projections called Villi. Villi absorbs the food. It is then carried to other parts of the body by blood. Unused glucose is stored as Glycogen in the liver. The unabsorbed food is then sent to large intestine.
  • Walls of large intestine have villi which absorbs the water and salt from the digested food. The Waste Material is then removed from the body through Anus
• Food and mouth –
• Teeth – Hardest substance which breaks down food material into smaller substances. There are 32 teeth in a healthy human body. The upper jaw and lower jaw consists of 16 teeth each. These are molars, premolars, incisors
• Salivary Glands secrete enzymes which convert complex food material i.e. starches present in food, into simpler substances i.e. sugars. That means the digestion itself starts in mouth.
• Tongue is a fleshy muscular organ in the mouth which has taste buds. it helps to understand the taste of the food. There are five basic tastes, sweet, salty, sour, bitter and umami.
• Digestion in herbivores
  • Herbivores eat food with the help of Mouth. Teeth breaks the food partially. However herbivores swallow the food quickly. It passes through esophagus into the largest part of the stomach called rumen.
  • There are four parts of the stomach, these are, rumen, reticulum, omasum, and abomasum.
  • Rumen is the temporary storage of food. The microorganisms present in rumen breaks down complex plant material into Volatile fatty acids i.e. VFA’s. This process is called fermentation. Rumen wall absorb most of the VFA’s.The partly digested food or cud is brought again in their mouth and they starts chewing it again. This process is called rumination.
  • During rumination, food is converted into fine particles and saliva is mixed in it.
  • Later food is passed into reticulum, where bigger food particles are separated from smaller and bacterial fermentation continues. Fine particles are sent forward and bigger particles are sent back to rumen
  • In omasum, water and other nutrients present in the food get absorbed. From omasum the food passes into true stomach called abomasum.
  • Here, the enzymes and acids causes further breakdown of the food into simpler substances. The food then passes to small intestine. It is a long tube having three main parts duodenum, jejunum and ileum. It receives secretions from various glands so as to break down the food further. It absorb most of the nutrients from the food.
  • Small intestine is connected to large intestine through a pouch like structure called caecum. It is a storage organ where microorganisms helps to digest cellulose. The food then passes to large intestine. Here most of the water is absorbed. The waste is thrown out of animal body.
• Digestion in amoeba takes in 5 steps ingestion, digestion, absorption, assimilation, egestion
  • Ingestion – it is the method of taking food inside the body. Amoeba takes food inside the body through pseudopodia. It encircles food and engulf it inside the body.
  • Digestion – digestive enzymes are secreted into food vacuole, which converts food particle into simple substance
  • Absorption – diffusion of simpler substance into cytoplasm.
  • Assimilation: The food entering in cytoplasm is used for energy, growth, maintenance and multiplication. Excess food is stored as glycogen and fats.
  • Egestion: The undigested waste is taken near the cell membrane and then thrown outside the cell body by rupturing i.e. cutting the membrane. It is called egestion.