NCERT Class 7 Science Chapter 1: Nutrition in Animals YouTube Lecture Handouts

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  • Animal nutrition includes nutrient requirement, mode of intake of food and its utilization in the body

  • Digestion: Breaking down of complex substances into simpler substances

  • Bees – suck nectar

  • Snakes – swallow prey

  • Starfish eats soft animal inside the shell of – it pops out the stomach to eat and then moves back again

  • Some mode of intake includes scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.

Digestive Tract (Alimentary Canal)

  • Buccal cavity

  • Foodpipe or oesophagus

  • Stomach

  • Small intestine

  • Large intestine ending in the rectum

  • Anus

Walls of stomach, salivary glands, liver and pancreas secrete digestive juices (convert complex food to simple food)

Image - 1 of Digestive Tract

Image - 1 of Digestive Tract

Image - 1 of Digestive Tract

Image - 2 of Digestive Tract

Image - 2 of Digestive Tract

Image - 2 of Digestive Tract

Buccal Cavity

Ingestion – taking in of food, chew with teeth and break into smaller pieces – teeth are rooted in gums

  • Permanent teeth – 32 (in human)

  • Milk teeth – 20 (in human) – till 6 to 8 years

Image of Buccal Cavity

Image of Buccal Cavity

Image of Buccal Cavity

  • Incisor – to cut

  • Canine – to tear

  • Premolar and molar – grind

Saliva breaks down starch into sugar (chewed rice will not change in color with iodine)

Bacteria break down the sugars present from the leftover food and release acids & acids gradually damage the teeth causing tooth decay – chocolates, soft drinks, sweets and sugar products

Tongue – fleshy muscular organ – free at front and can move in all directions – used for talking, chewing and swallowing – has taste buds

Image of Basic Tastes

Image of Basic Tastes

Image of Basic Tastes

  • If food particle enters wind pipe – choke, cough or hiccup

  • Windpipe carries air from the nostrils to the lungs. It runs adjacent to foodpipe. Inside the throat, air and food share a common passage. During swallowing a flap-like valve closes the passage of the windpipe and guides food into foodpipe.

Foodpipe

  • Runs along neck and chest till stomach

  • Peristalsis - wave-like muscle contractions that moves food

Stomach

  • Thick wall J Shaped

  • Widest part of alimentary canal

  • Inner lining secretes mucous (protects lining of stomach), hydrochloric acid and digestive juices (break down the proteins into simpler substances)

  • In 1822, a man named Alexis St. Martin was badly hit by a shot gun - brought to an American army doctor William Beaumont – found stomach was churning food

Small Intestine

  • Digested food is absorbed in blood vessels – absorption – inner walls have outgrowths called villi (increase surface area for digestion)

  • Absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as proteins – Assimilation

  • Highly coiled and 7.5 mt long

  • Gets secretions from liver and pancreas

  • Carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol, and proteins into amino acids.

    • Duodenum is the former part - receives partially digested food or chyme from the stomach. It also receives bile from the gallbladder and digestive enzymes from the pancreas.

    • Jejunum is the middle part - absorbs fully-digested carbohydrates and proteins

    • Ileum is the final part - absorbs the non-absorbed particles from the jejunum.

Liver – largest gland of body – secretes bile which is stored in gall bladder. Bile helps in digestion of fats.

Pancreas – below stomach & cream colored - pancreatic juice acts on carbohydrates, fats and proteins and changes them into simpler forms

Large Intestine

  • Undigested and unabsorbed food reaches here

  • Water and salts are absorbed

  • Wider and shorter – 1.5 mt long

  • Rectum & Anus

  • Remain waste goes to rectum and semi-solid faeces is removed by anus by egestion

Diarrhea

  • Watery stool frequently

  • It may be caused by an infection, food poisoning or indigestion.

  • Boiled and cooled water with pinch of salt and sugar as ORS

Digestion in Grass Eating Animals

Rumen – grass-eating animals swallow food and store it in stomach (rumen) – partial digestion takes place and is called as cud. Cud enters mouth again and rumination occurs.

  • The cow has four stomachs

    • Unchewed food travels to the first two stomachs - rumen and reticulum

    • Cow coughs up bits of the unchewed food called cud

    • Cud then goes to the third and fourth stomachs, the omasum and abomasum, where it is fully digested.

  • Grass is rich in cellulose (humans cannot digest it)

  • Ruminants: Grazing animals like cows, buffaloes and deer quickly ingest, swallow their leafy food and store it in the rumen. Later, the food returns to the mouth and the animal chews it peacefully.

  • Animals like horses, rabbit, etc., have a large sac-like structure called Caecum between oesophagus and small intestine (cellulose is digested by action of bacteria)

Amoeba

Image of Amoeba

Image of Amoeba

Image of Amoeba

  • Single cellular organism in pond water

  • Amoeba has a cell membrane, a rounded, dense nucleus and many small bubble-like vacuoles

  • Ingestion by its false feet or pseudopodia. The food is digested in the food vacuole.

  • Digestive juices are secreted into the food vacuole

  • The absorbed substances are used for growth, maintenance and multiplication

  • Nutrition is a complex process & involves:

    • Ingestion

    • Digestion

    • Absorption

    • Assimilation

    • Egestion

  • Fats in goat’s milk are much simpler than those in cow’s milk.

  • Therefore, goat’s milk is much easier to digest than cow’s milk