Page 17 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

v Saliva also contains another enzyme called lysozyme, which helps in killing germs and

bacteria that may have entered the mouth along with food. It also helps in the lubrication
of the food so that it can move through the alimentary canal smoothly.

v Humans grow two sets of teeth in their life time—milk teeth and permanent teeth.
v Milk teeth are set of 20 teeth that develop between the ages of 6 months and 6 years. These
are also known as deciduous teeth.

v After 6 years, milk teeth start falling & are gradually replaced by permanent teeth. An adult
has a set of 32 permanent teeth.

v Adult humans have four types of teeth – Incisors, Canines, Premolars and Molars.
v There are 8 incisors that are used for cutting and biting. There are 4 canines used for holding

and tearing the food. There are 8 premolars that help in crushing and grinding of food.
There are 12 molars used for fine grinding of food.

v Tooth decay occurs due to improper cleaning of teeth. Food particles get stuck between the
teeth and the bacteria present in our mouth break these down and produce acids which
damages the teeth. Severe tooth ache and tooth loss may also occur if not treated in time.

v Tongue helps in talking, chewing and swallowing food by mixing saliva in it. Taste buds are
present in the tongue that detect four basic tastes–sweet, salty, sour and bitter.

v The food pipe or the oesophagus is a tube-like structure that connects the mouth to the
stomach.

v Food from the mouth, called bolus, is carried down to the stomach with the help of wave
like contraction in the walls of alimentary canal and pushed downwards. This movement is

known as peristaltic movement.
v In the throat, there is a common passageway for air and food. So, when we swallow food,
epiglottis, a flap-like structure, closes the passage of wind pipe and food enters into the

food pipe.
v Stomach is a muscular J-shaped, bag-like structure whose one end is connected to the food

pipe and the other end to the smaller intestine.
v Mucous produced by the walls of the stomach protects its inner walls from hydrochloric
acid, which is also produced by the walls of the stomach.

v Hydrochloric acid kills the harmful bacteria that enter the stomach with food.
v Food is partially digested in the stomach with the help of digestive juices and hydrochloric

acid. These help in breaking down the proteins in the food to simpler forms. This partially
digested food is called chyme.

v Small intestine is a narrow, coiled tube about 7.5 m long and 2.5 cm wide. Complete
digestion and absorption of food takes place here with the help of intestinal juice secreted

by the walls of small intestine.

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