Model Questions and Answers

Answer: Nutrition is the process of intake, as well as utilization of nutrients by an organism. The different modes of nutrition are saprophytic nutrition, parasitic nutrition and holozoic nutrition.

Answer: Saprophytic nutrition is the mode of nutrition that is seen in fungi.

Answer: Chlorophyll is the pigment, which can absorb solar energy.

Answer: The two stages in photosynthesis are
(i) Light reaction and
(ii) Dark reaction.

Answer: The factors which affect photosynthesis, are light, water, temperature, humidity, age of the leaf and carbon dioxide.

The animals that feed only on plants are called herbivores.
The animals that feed only on flesh are called carnivores.

Answer: Amoeba engulfs its food by extending pseudopodia. This process is known as Phagocytes.

Answer: The parts of the digestive system of a grasshopper are the pharynx, salivary glands, hepatic caeca, malpighian tubules, ileum, colon, rectum and anus

Answer: Breathing is a process by which organisms inhale oxygen. The inhaled oxygen gets diffused into the blood and the carbon dioxide from the blood diffuses back into the alveoli from where it is exhaled.

Answer: The liver secretes bile, which contains bile pigments and bile salts. The bile secreted by the liver cells is normally stored in the gall bladder until needed in the duodenum. The pancreas lies parallel to and beneath the stomach. It is a large gland, which secretes digestive enzymes as well as hormones, insulin and glucagons. Both bile and pancreatic juice enter the duodenum through a common duct. Bile emulsifies fat present in the food. Pancreatic juice contains trypsin, for digesting proteins and pancreatic amylase for the breakdown of starch.

Answer: Respiration is a complex process, which includes breathing, the mechanism of exchange of gases, oxygen and carbon dioxide and oxidation of digested food occurring in the cells in order to release energy. The main outcome of respiration is the release of energy through the oxidation of simple food molecules such as glucose.

Answer: In aerobic respiration more energy is released

Answer: Root hair is the part of the root which is involved in the exchange of respiratory gases.

(i) Stomata are tiny apertures found on the surface of the leaf, which regulate the exchange of respiratory gases and transpiration.

(ii) Lenticels are the raised pores in the woody plants that allow the exchange of gases between the atmosphere and the internal tissues.

The respiration in plants differ from respiration in animals in two respects, they are

(i) There is minimal transport of gases from one part of the plant to another, unlike the animals.
(ii) Plant respiration occurs at a much slower rate than animal respiration.

The respiratory organs of
(i) fish – gills
(ii) mosquito – tracheoles
(iii) earthworm – skin
(iv) dog – lungs.

(i) Prawns take in oxygen that is dissolved in water.
(ii) Rat takes in oxygen from the atmosphere.

Answer: Epiglottis prevents the food from entering into the trachea.

Answer: The phenomenon of breaking down water in the illuminated chloroplast is known as photolysis.

Answer: The living organisms that cannot make their own food called heterotrophs.

Chemotrophs are organisms, which do not require light. They manufacture their food from inorganic substances in the presence of energy derived from the oxidation of simple inorganic compounds of iron, sulphur, etc.
e.g. bacterium Nitrosomonas

Answer: Digestion begins from the mouth.

The name given to the process of using the absorbed food for producing energy is assimilation.

The visible light of the Sun consists of seven colours, namely, violet, indigo, blue, green, yellow, orange and red. Chlorophyll absorbs mainly blue, violet, red and orange lights out of these lights of different wavelengths but does not absorb the green light. Due to the reflection of green light by the chlorophyll, the plant looks green in colour.


Enzymes are biological catalysts. Catalysts are proteins that increase the rate of chemical reactions without being used up. For example, Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine

Unicellular organisms can absorb sufficient oxygen because of their complete contact with the atmosphere, but in multicellular organisms, the rate of absorption and diffusion becomes very less because all cells are not in direct contact with the atmosphere. Multicellular organisms require a greater amount of oxygen to sustain life processes that cannot be fulfilled by the process of diffusion.

Unicellular organisms can absorb sufficient oxygen because of their complete contact with the atmosphere, but in multicellular organisms, the rate of absorption and diffusion becomes very less because all cells are not in direct contact with the atmosphere. Multicellular organisms require a greater amount of oxygen to sustain life processes that cannot be fulfilled by the process of diffusion.

(i) Digestive enzymes – Foods need to be broken into their small or simpler molecules so that they can be absorbed into the bloodstream. However, the physical breakdown of food is not enough. Enzymes are hence needed for the chemical breakdown of food and speeding up the digestive process. The products of digestion can hence be small enough to be absorbed.

(ii) Hydrochloric acid – Hydrochloric acid helps to kill the germs which might have entered into the system through food. It creates an acidic medium for the pepsin to act on food to break down proteins.

(iii) Villi – Villi are finger-like projections in the small intestine. They help to increase the surface area for absorption of the digested food. Villi are richly supplied with blood vessel which helps to absorb digested food into the bloodstream.

(a) In plants, there are tiny pores called stomata on leaves and lenticels in the stem, facilitating the exchange of gases. Carbon dioxide is taken in and oxygen given out {during photosynthesis} and vice versa during respiration.

(b) Water and minerals are transported within the plant by the Xylem vessels (mainly in an upward direction); these are part of the vascular system, including Phloem vessels.
Phloem transports the products of photosynthesis within the plant, to all parts like the stem, roots, fruits etc. in all directions.

Take a healthy leaf from the potted plant.
Remove a part of the peel from the lower surface of the leaf. You can do this by folding the leaf over and gently pulling the peel-apart using forceps. Keeps the peel in a watch glass containing water.
Put a few drops of safranin stain in a watch glass.
After 2-3 minutes take out the peel and place it on a clean glass slide.
Put a drop of glycerin over the peel and place a clean coverslip gently over it with the help of a needle.
Remove the excess stain and glycerin with the help of blotting paper.
Observe the slide under magnifications of the compound microscope.

These features particularly make our lungs efficient for gas exchange. 1.Thin: the air sac walls are very thin so that gases can quickly diffuse through them. Oxygen is absorbed into the blood and carbon dioxide is given out into the lungs to be exhaled out.
2.Moist: the air sacs are moist with mucus so that gases can dissolve before diffusing.
3.Large surface area: the surface area for gases to diffuse through in human lungs is roughly the same as a tennis court. The alveoli help to increase the surface area for the absorption of oxygen.

(a)(i) It sterilises food by killing pathogens and other microbes.
(ii) It has a pH of 2, which is perfect for entyaus such as pepsin to break down proteins as effectively as possible.
(iii) Helps emulsify food (digestion of protein and stimulates the pancreas to produce digestive enzymes and bile) and protects against harmful bacteria.

(b) Breakdown of large globule fats into smaller fats droplets is known as emulsification.

(c) Trypsin is the enzyme secreted by the pancreas which aids in the digestion of proteins.

In the small intestine, complete digestion of various components of food takes place. The process of digestion of food in the mouth, stomach and small intestine in human body are as follows:

Mouth: Digestion of food begins in the mouth. Saliva present in the mouth contains a digestive enzyme, called salivary amylase, maltose and dextrins, which breaks down starch into sugar.

Stomach: Stomach stores and mixes the food received from the oesophagus with gastric juices. The main components of gastric juice are hydrochloric acid, mucus and pepsinogen. Hydrochloric acid dissolves bits of food and creates an acidic medium. In this medium, pepsinogen is converted to pepsin which is a protein-digesting enzyme. Mucus protects the inner lining of the stomach from the action of HC1.

Small Intestine: Small intestine is the site of the complete digestion of carbohydrates, proteins and fats. The small intestine produces intestinal juice from the glands present in its wall. The intestinal juice helps in the further digestion of food. The small intestine also obtains digestive juices from the liver and pancreas. The liver produces bile juice that causes emulsification of fats and the pancreas produces pancreatic juice for digesting proteins and emulsified fats. This digested food is finally absorbed through the intestinal walls.

The quantity of dissolved oxygen is fairly low in the water as compared to the amount of oxygen in the air. Aquatic organisms, therefore, have to breathe faster than terrestrial organisms to absorb the required amount of oxygen from the water.

The process of breakdown of glucose in a cell are as follows:

The first step in the breakdown of glucose both in presence of 02 and in absence of O2 is the same. In this step, glucose is broken down into pyruvate.
The second step which involves the further breakdown of private into simple compounds can take place in two different ways:

(i) In presence of O2: In the presence of 02, private is converted into C02 and water. The energy released during aerobic respiration is much greater than that released during anaerobic respiration.
(ii)In absence of O2: In the absence of 02 in yeast, pyruvate is converted into ethanol and C02 and the process is called fermentation. In absence of 02, in our muscle cells, pyruvate is converted into lactic acid. The build-up of lactic acid in muscle cells causes cramps.

(a) The process of taking in oxygen from the air into the lungs and expulsion of carbon dioxide out of the lungs is called breathing. The rate of breathing during vigorous exercise increases by about 20 to 25 times per minute. It is because during vigorous exercise the demand for oxygen increases. Breathing occurs involuntarily but its rate is controlled by the respiratory centre of the brain.

(b) Translocation is the transport of food from the leaves to other parts of the plant and occurs in the part of the vascular tissue known as phloem.
It is essential for plants because every part of the plant needs food to build its parts and maintain its life.
(i) Sugar is synthesised in the leaves of the plant.
(ii) Hormones are synthesised at the tips of the roots and stems of a plant.