CBSE Class 10 Biology Life Processes MCQs Set 16

Answer: (b) nutrition

Explanation:
1. Nutrition covers both intake of food and its utilisation.
2. Respiration releases energy, transportation distributes materials and excretion removes wastes, so they do not describe intake of food.

Teacher's Note:
1. Remember the four basic life processes: nutrition, respiration, transportation and excretion.
2. Each one has its own job, so match the job to the term.

Answer: (d) autotroph

Explanation:
1. Autotrophs take in carbon dioxide and water and build organic food.
2. Heterotrophs, saprotrophs and parasites all depend on ready-made food from other organisms.

Teacher's Note:
1. Auto means self and troph means nourishment.
2. Green plants and some bacteria are autotrophs.

Answer: (c) \(6CO_2+12H_2O\xrightarrow{\text{light, chlorophyll}}C_6H_{12}O_6+6H_2O+6O_2\)

Explanation:
1. Carbon dioxide and water are converted into glucose in presence of light and chlorophyll, with oxygen released.
2. The equation with glucose on the left is respiration, which is the reverse process, and the others are not balanced.

Teacher's Note:
1. The oxygen released comes from water, which is why 12 molecules of water are written on the left.
2. Six molecules of water are formed on the right side, so the net water used is 6.

Answer: (b) remove the starch already stored in the leaves

Explanation:
1. In darkness the plant cannot photosynthesise and uses up its stored starch.
2. This destarching makes sure that any starch found later was made during the experiment.

Teacher's Note:
1. The process is called destarching.
2. Without destarching you cannot be sure that the starch was newly made.

Answer: (d) starch

Explanation:
1. Iodine reacts with starch to give a blue-black colour.
2. It does not give this colour with glucose, protein or fats.

Teacher's Note:
1. Blue-black colour with iodine is the standard test for starch.
2. A leaf that turns blue-black has carried out photosynthesis.

Answer: (b) absorbs carbon dioxide

Explanation:
1. KOH removes carbon dioxide from the air inside the bell jar.
2. The leaf in this jar cannot photosynthesise, so it gives no blue-black colour with iodine.

Teacher's Note:
1. The experiment shows that carbon dioxide is necessary for photosynthesis.
2. The second plant in a jar without KOH is the control.

Answer: (a) Guard cells

Explanation:
1. Each stoma is bordered by two kidney shaped guard cells.
2. When they swell with water the stoma opens, and when they lose water it closes.

Teacher's Note:
1. Guard cells also contain chloroplasts.
2. Do not confuse the stomatal pore with the guard cells that regulate it.

Answer: (b) chloroplast

Explanation:
1. Chloroplasts contain chlorophyll and carry out photosynthesis.
2. Mitochondria release energy in respiration, so they are not the site of food making.

Teacher's Note:
1. Chloroplast is sometimes called the kitchen of the cell.
2. Mesophyll cells of the leaf contain most chloroplasts.

Answer: (a) grana of the chloroplast

Explanation:
1. Light energy is absorbed by chlorophyll in the grana (thylakoid membranes).
2. The dark reaction, in which carbon dioxide is fixed into sugar, takes place in the stroma.

Teacher's Note:
1. Light reaction gives ATP, NADPH2 and oxygen.
2. Dark reaction does not need light directly but uses ATP and NADPH2 made in the light reaction.

Answer: (d) photolysis

Explanation:
1. Photo means light and lysis means breaking, so photolysis is breaking of water by light.
2. Hydrolysis uses water to break something else, and glycolysis splits glucose.

Teacher's Note:
1. Photolysis releases hydrogen and oxygen from water.
2. The oxygen given out by plants comes from this step.

Answer: (c) their stomata open at night to reduce water loss

Explanation:
1. Opening stomata at night reduces loss of water by transpiration in the hot day.
2. The carbon dioxide is stored in an intermediate form and used during the day when light energy is available.

Teacher's Note:
1. This saves water in dry habitats.
2. Stomata of most other plants are open in the daytime.

Answer: (d) Cuscuta (Amarbel)

Explanation:
1. Cuscuta lives on a host plant and takes nourishment from it.
2. Mushroom and yeast are saprotrophs and Amoeba is holozoic.

Teacher's Note:
1. Other parasites are lice, ticks, leeches and tapeworm.
2. A parasite does not usually kill its host quickly.

Answer: (c) pseudopodia

Explanation:
1. Amoeba forms finger like pseudopodia that surround the prey and form a food cup.
2. Cilia are found in Paramecium, which moves food to a fixed spot by ciliary action.

Teacher's Note:
1. The food then lies in a food vacuole, which acts as a temporary stomach.
2. Undigested matter is thrown out from any point of the body surface.

Answer: (b) salivary amylase

Explanation:
1. Salivary amylase (ptyalin) begins the digestion of starch in the mouth.
2. Pepsin acts in the stomach on proteins and trypsin acts in the small intestine.

Teacher's Note:
1. Starch is broken down to maltose in the buccal cavity.
2. Saliva has no enzyme to digest proteins.

Answer: (a) rhythmic contraction and relaxation of muscles of the alimentary canal

Explanation:
1. Waves of muscular contraction push the food forward along the digestive tube.
2. They are involuntary and occur all along the oesophagus, stomach and intestines.

Teacher's Note:
1. Peristalsis moves food even when you are upside down.
2. It is not caused by ciliary movement.

Answer: (d) digests proteins directly into amino acids

Explanation:
1. HCl does not digest proteins itself; pepsin starts digestion of protein into peptides.
2. HCl activates the inactive enzymes and makes the medium acidic (pH about 2).

Teacher's Note:
1. Mucus protects the stomach lining from the acid.
2. Too much acid secretion can cause peptic ulcers.

Answer: (c) pepsinogen

Explanation:
1. Gastric glands secrete pepsinogen, which is changed into pepsin by HCl.
2. Pepsin is the active form, and trypsin and amylase are pancreatic enzymes.

Teacher's Note:
1. Releasing enzymes in inactive form protects the cells that make them.
2. Prorennin is another inactive enzyme, activated to rennin.

Answer: (b) emulsifying fats and making the medium alkaline

Explanation:
1. Bile salts break large fat globules into small droplets.
2. This increases the surface area for lipase to act, and the alkaline medium suits pancreatic enzymes.

Teacher's Note:
1. Bile has no enzymes, so it does not chemically digest food.
2. Bile is made in the liver and stored in the gall bladder.

Answer: (a) Trypsin - digests proteins into peptides

Explanation:
1. Trypsin of pancreatic juice acts on proteins and converts them into peptides.
2. Amylase acts on starch and lipase acts on fats, so the other pairs are wrong.

Teacher's Note:
1. Amylase for starch, protease for protein, lipase for fat.
2. Pancreatic juice contains all three kinds of enzymes.

Answer: (c) increase the surface area for absorption

Explanation:
1. Finger like villi greatly increase the absorbing surface.
2. They also have a rich blood supply and lacteals to carry away the absorbed food.

Teacher's Note:
1. Villi are found only in the small intestine.
2. A longer small intestine is found in herbivores because cellulose is hard to digest.

Answer: (a) destruction of enamel by acids made by bacteria

Explanation:
1. Bacteria in plaque act on sugars to make acids that demineralise the enamel.
2. If untreated the decay spreads to the dentine and pulp, causing pain.

Teacher's Note:
1. Brushing after meals removes plaque.
2. Sugary sticky food increases the risk.