Why does a cow keep chewing even when it isn't eating? Why does chewed rice start tasting sweet the longer you chew it?
Key idea
The Alimentary Canal
Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Anus
Key idea
The Mouth and the Stomach
1
The mouth
Teeth crush food (mechanical digestion), while saliva chemically breaks starch into sugar — which is why chewed starchy food tastes sweet.
→
2
The stomach
Digestive juice, acid, and mucus break down proteins, kill harmful bacteria, and protect the stomach's own lining.
Key idea
The Small and Large Intestine
1
Small intestine
About 6 metres long. Receives bile (from the liver) and pancreatic juice (from the pancreas), and its own wall absorbs nutrients into the blood through finger-like projections.
→
2
Large intestine
Absorbs water and salts from undigested food, forming stool — stored in the rectum and expelled through the anus.
Key idea
Rumination in Cows
Ruminants like cows and buffaloes chew grass partially, swallow it, partially digest it, then bring it back to the mouth to chew thoroughly.
8 hours a dayThat's roughly how much time a cow spends chewing — including food it already swallowed once.
Key idea
The Bird's Gizzard
Grinding without teeth. Birds have a muscular gizzard that grinds food by contracting and relaxing — often with the help of swallowed grit (small stones).
Key idea
Breathing
1
Inhalation
Ribs move up and outward, the diaphragm moves down — chest space increases, and air enters the lungs.
→
2
Exhalation
Ribs move down and inward, the diaphragm moves up — pushing air back out.
Key idea
Respiration
The body uses oxygen to break down glucose from digested food, releasing energy.
Glucose + Oxygen → Carbon dioxide + Water + Energy
This exchange happens at the alveoli — tiny air sacs in the lungs — where oxygen enters the blood and carbon dioxide leaves it.
Key idea
Breathing Is Not the Same as Respiration
1
Breathing
A physical process — the movement of air in and out of the lungs.
→
2
Respiration
A chemical process — releasing energy from glucose, using oxygen, inside cells.
Key idea
How Other Animals Breathe
Animal | Breathing organ
Most land animals (birds, mammals, reptiles)
Lungs
Fish
Gills
Frog (tadpole → adult)
Gills → lungs and skin
Earthworm
Moist skin
Chapter · Key terms to remember
Key Terms
Alimentary canal
The tube from mouth to anus where digestion happens.
Digestion / Absorption
Breaking food down / nutrients entering the blood.
Egestion
Expelling undigested waste as stool.
Chapter · Key terms to remember
More Key Terms
Rumination
Bringing food back up to chew again.
Gizzard
A bird's muscular food-grinding chamber.
Breathing
The physical movement of air in and out.
Chapter · Key terms to remember
More Key Terms
Respiration
The chemical release of energy from glucose.
Gills
Organs for exchanging gases with water.
Questions for your notebook
Write these down, then discuss
1
Complete the journey of food through the alimentary canal: Food → Mouth → ___ → Stomach → ___ → ___ → Anus.
2
Unchewed chapati, chewed chapati, and boiled mashed potato are each tested with iodine solution. What would you observe in each, and why?
3
What is the role of the diaphragm in breathing? (i) Filtering air (ii) Producing sound (iii) Helping inhalation and exhalation (iv) Absorbing oxygen
Project as-is — students copy the questions, then the class discusses answers together.