CLASS 7

OBTAINING AND UTILIZING FOOD

Q1. What is the role of chlorophyll in photosynthesis?
Ans. Chlorophyll absorbs light energy from the sun and supplies this energy to the leaves to enable them to
carry out photosynthesis for making food.
Q2. Give the overall equation of photosynthesis.
Ans.

Q3. What are the conditions required for photosynthesis? Draw diagram.
Ans. 1. Water –from soil
2. Carbon dioxide- from air
3. Chlorophyll- contained in leaf
4. Energy- from sunlight

PHOTOSYNTHESIS

Q4. How does photosynthesis occur?

Ans. In plants and most algae, it occurs in the chloroplasts and there are two
principle reactions:
(i) Light reaction (light-dependent) bring about the photolysis of water

(ii) Dark reaction (light-independent) during this reaction carbon dioxide is reduced to carbohydrates in a
metabolic pathway known as the Calvin cycle.
Q5. What is the stored form of sugar in plants and animals?
Ans. Starch in plants and glycogen in animals
Q6. Draw a well labeled diagram of open stomata.
Ans
Q7. How is atmospheric nitrogen made available to the plants?
Ans. Plants cannot absorb the nitrogen from the air. Soil has certain bacteria that convert gaseous nitrogen
into a usable form and release it into the soil. These soluble forms are absorbed by the plants along with
water.
Q8. Define the following terms.
Ans. (a) Alimentary Canal- The tubular passage that extends from mouth to anus and functions in digestion
and absorption of food and elimination of residual waste and that in most mammals includes the mouth,
pharynx, esophagus, stomach, intestine, and anus—called also called digestive tract.
(b) Digestive system-The system by which ingested food is acted upon by physical and chemical means to
provide the body with absorbable nutrients and to excrete waste products; in mammals the system includes
the alimentary canal extending from the mouth to the anus, and the hormones and enzymes assisting in
digestion.
(c) Digestion- It is the conversion of complex non-absorbable constituents of food into simple absorbable
form with the help digestive juices.
(d) Mastication- The process of chewing food into small pieces and its conversion into pulpy mass is called
mastication.
(e) Peristalsis- The wavelike muscular contractions in the organs of the digestive system such as the
esophagus and the intestines. It is characterized by alternate contraction and relaxation, which pushes
ingested food through the digestive tract towards its release at the anus.

(f) Anti-peristalsis- a wave of intestinal contraction in a direction the reverse of normal, by which the
contents of the intestine are forced backward.
(g) Villi- The inner wall of the small intestine has millions of finger-like folds, called villi.
(h) Epiglottis- A thin, triangular plate of cartilage at the base of the tongue that covers the glottis during
swallowing to keep food from entering the trachea.
Q9. Where does mechanical digestion of food take place?
Ans. Mechanical digestion of food takes place at three places in the alimentary canal: -
(i) mouth (by teeth)
(ii) stomach (churning movement)
(iii) small intestine (rhythmic movement)
Q10. Differentiate between milk teeth and permanent teeth.
Ans.
Milk teeth (Deciduous teeth) Permanent teeth
1. These teeth are replaced by permanent teeth 1. They are those teeth which once broken cannot
naturally. be replaced naturally.
2. The first milk teeth appear between the age of 6- 2. Their formation begins at the age of 6 years.
11 months.
3. All the temporary teeth develop by the age of 2 3. Their formation is completed by the age of 12
years. years.
4. Their number is 20 with 8 incisors, 4canines and 4. Their number is 32 with 8 incisors, 4 canines, 2
8 molars. Premolars are absent. premolars and 3 molars.
Q11.Explain the different types of human permanent teeth with proper diagram.
Ans.
Type of teeth Location Number Shape Function
Incisors Front at the middle of 2 Flat and blade-like Biting and cutting
each jaw
Canines on either side of the 1 Pointed Tearing food
incisors
Premolars On each side of canine in 2 Broad grinding Crushing and
each jaw surfaces grinding food
Molars On each side of 3 Broad uneven Finer crushing and
premolars in each jaw grinding surface grinding

4 DIFFERENT TYPES OF TEETH IN HUMANS

Q12. What are the functions of tongue?

Ans. The tongue helps us in several ways: -
1. Manipulates the food while chewing.
2. Helps in tasting the food.
3. Helps in mixing the saliva with the food.
4. Helps in cleaning the teeth.
5. Helps in speaking.
Q13. What is saliva? What does it contain?
Ans. Saliva is a fluid containing water, salts and a slimy mucus.
It contains a substance, an enzyme called amylase which convert starch into maltose.
Q14. Why does a piece of bread or boiled rice starts tasting sweet when you chew it for a while?
Ans. A piece of bread or boiled rice when chewed thoroughly starts sweet. The tasteless starch changes into
sweet maltose.
Q15. What is the function of epiglottis?
Ans. When we swallow food, the epiglottis folds over the glottis to stop liquid and food from entering the
trachea (wind pipe). Thus, food goes right to the esophagus so that one would not get choked. It also serves
to produce speech sounds in some languages.

Q16. What is the function of villi?

Ans. The villi increase the surface area for absorption of digested food. Each villus has a network of thin and
small blood vessels close to its surface. The surface of the villi absorbs the digested food materials.
Q17. Name the secretion, content and function of stomach, pancreas and liver.
Ans.
Organ Secretion Content Function
Stomach Gastric juice Mucous Protects the lining of
the stomach
HCl Kills germs, makes the
medium acidic
Enzyme-Pepsin Break down protein
Pancreas (small intestine) Pancreatic juice Starch-digesting enzyme Break down starch
Protein-digesting enzyme Break down protein
Fat-digesting enzyme Break down fat
Liver (small intestine) Bile (stored in gall No enzyme Emulsification of fat
bladder) Makes the medium
alkaline

Q18. What is emulsification of fat?

Ans. The breakdown of fat globules in the small intestine into tiny droplets, which provides a larger surface
area on which the pancreatic enzyme can act to digest the fats.
Q19. What are the final molecules of digestion of all the components of food?
Ans. The carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol, and
proteins into amino acids.
Q20. What is the function of the large intestine?
Ans. The large intestine absorbs water and some salts from the undigested food material
Q21.What is the difference in the type and arrangement of teeth of herbivores and carnivores?
Ans. Most of the teeth of herbivores are on the sides of the jaws, or their ‘cheeks’. Only the sharp-edged
incisors, meant for vegetable matter, are in front. The canines are absent and there is a big gap between the
incisors and premolars. Canines are present and the gap between the incisors and premolars is present in
carnivores.
Q22. Define diastema. Why is it important for herbivores?
Ans. A space separating teeth of different functions, especially that between the biting teeth (incisors and
canines) and grinding teeth (premolars and molars) in herbivores.
It would allow food to be pushed between the upper and lower jaw through the gap, to be stored briefly in
the cheek. Thus, it is possible for the animal to eat more food without stopping to chew and swallow each
mouthful.
Q23. Write a short note on ruminant stomach.
Ans. The animals like cows and buffaloes quickly eat the fodder. Then they relax leisurely and chew what
they have eaten. This act of chewing is called as chewing cud. Animals like sheep and deer also chew cud.
All the animals who chew cud are called ruminants.
The stomach of ruminants has 4 chambers- Rumen, Reticulum, Omasum and Abomasum. Such a
stomach is called compound stomach.
The food enters the first chamber, the Rumen. This is the largest chamber. From here the food enters
into the second chamber, the Reticulum. In these two chambers, the food is partially digested and converted
into a soft pulp, called cud. When the animal is relaxing, the soft pulpy food or cud from the second
chamber is brought back to the mouth and is again chewed. This is known as chewing the cud. The process
of chewing cud is called rumination. During rumination, cud mixes with saliva and becomes a semi-liquid
paste.
From the mouth, food is put directly into the third chamber i.e., the Omasum. From the third
chamber, it moves into the fourth chamber, where the ultimate digestion takes place. The semi-liquid food is
acted upon by enzymes and the digestion is completed here. After this, the food moves into intestine.