CBSE Class 10 Biology Life Processes MCQs Set 26

Answer: (b) H₂O

Explanation:
1. Oxygen is released when water is split in the light reaction.
2. The oxygen in CO₂ ends up in the sugar and in water formed, not in the gas released.

Teacher's Note:
1. This was shown using water labelled with heavy oxygen.
2. Remember: the oxygen comes from water, the carbon from carbon dioxide.

Answer: (b) Stroma

Explanation:
1. The dark reaction uses ATP and NADPH made in the light reaction to fix CO₂.
2. It occurs in the stroma, the fluid part of the chloroplast.

Teacher's Note:
1. The light reaction occurs in the grana (thylakoids).
2. The stroma contains the enzymes for fixing carbon.

Answer: (b) Light-independent reactions

Explanation:
1. CO₂ is reduced to carbohydrate in the light-independent (dark) reaction.
2. The reducing power (NADPH) and energy (ATP) come from the light reaction.

Teacher's Note:
1. Reduction of carbon means CO₂ gains hydrogen to form sugar.
2. This is done by the enzymes in the stroma.

Answer: (b) O₂

Explanation:
1. Photosynthesis needs CO₂ and water as raw materials, and ATP and NADP in the reactions.
2. Oxygen is a product of photosynthesis and is not required.

Teacher's Note:
1. Oxygen is released, not used, in photosynthesis.
2. Plants use oxygen in respiration, not in photosynthesis.

Answer: (c) Photosynthesis

Explanation:
1. Anabolism builds complex molecules from simple ones using energy.
2. Photosynthesis builds glucose from CO₂ and water.

Teacher's Note:
1. Respiration and digestion break down molecules, so they are catabolic.
2. Transpiration is loss of water vapour, not a synthesis.

Answer: (a) Starch

Explanation:
1. Plants store extra glucose as starch.
2. Glycogen is the reserve carbohydrate of animals, and cellulose is a structural material.

Teacher's Note:
1. Starch is detected by the blue-black colour with iodine.
2. Animals store carbohydrate as glycogen in liver and muscles.

Answer: (d) Saprotrophs

Explanation:
1. They feed on dead and decaying organic matter by secreting enzymes outside and absorbing the digested food.
2. Organisms that feed in this way are saprotrophs.

Teacher's Note:
1. Saprotrophs are fungi that act as decomposers.
2. Holozoic nutrition means taking in solid food and digesting it inside the body.

Answer: (b) (ii) and (iii)

Explanation:
1. Plants absorb nitrogen as nitrates and nitrites dissolved in soil water.
2. They cannot use proteins directly, and most plants cannot use atmospheric nitrogen.

Teacher's Note:
1. Nitrogen-fixing bacteria change atmospheric nitrogen into usable forms.
2. Legume roots have such bacteria in nodules.

Answer: (a) Liver

Explanation:
1. The liver weighs about 1.2 to 1.5 kg and is the largest gland.
2. It secretes bile and does many metabolic jobs.

Teacher's Note:
1. The pancreas is the second largest digestive gland.
2. The liver lies in the upper right of the abdomen.

Answer: (c) 20

Explanation:
1. Humans have 20 milk teeth that are replaced by permanent teeth.
2. The 12 molars of an adult are not replacing any milk teeth.

Teacher's Note:
1. Permanent teeth number 32 in total.
2. Milk teeth are shed from about 6 years of age.

Answer: (b) Beta cells

Explanation:
1. Beta cells of the islets of Langerhans secrete insulin.
2. Alpha cells secrete glucagon.

Teacher's Note:
1. Insulin lowers blood sugar.
2. Lack of insulin causes diabetes mellitus.

Answer: (c) Lysozyme

Explanation:
1. Lysozyme is an enzyme in saliva that breaks the cell walls of many bacteria.
2. Cerumin is ear wax, chyme is partly digested food, and secretin is a hormone.

Teacher's Note:
1. Tears also contain lysozyme.
2. Saliva also contains salivary amylase for starch.

Answer: (b) Below the ear

Explanation:
1. The parotid glands lie just below and in front of the ears.
2. They are the largest salivary glands.

Teacher's Note:
1. Mumps is an infection of the parotid glands.
2. The other two pairs are submaxillary and sublingual.

Answer: (b) Bile

Explanation:
1. Bilirubin and biliverdin are bile pigments formed from the breakdown of haemoglobin.
2. They give bile its colour.

Teacher's Note:
1. Bile pigments are waste products excreted through bile.
2. Excess bilirubin in blood causes jaundice.

Answer: (d) Liver

Explanation:
1. Bile is made by liver cells and stored in the gall bladder.
2. It reaches the small intestine through the bile duct.

Teacher's Note:
1. The gall bladder only stores and concentrates bile.
2. The bile duct joins the pancreatic duct before opening into the duodenum.

Answer: (a) Acidic

Explanation:
1. Gastric glands secrete hydrochloric acid, making gastric juice strongly acidic (about pH 2).
2. The acid kills bacteria and activates pepsin.

Teacher's Note:
1. Mucus protects the stomach wall from the acid.
2. Ulcers form when this protection fails.

Answer: (a) Proteins

Explanation:
1. Pepsin is a protease in gastric juice.
2. It breaks proteins into smaller peptides in an acidic medium.

Teacher's Note:
1. Pepsin is secreted in the inactive form pepsinogen.
2. HCl converts pepsinogen to pepsin.

Answer: (a) Providing an acidic medium for pepsin

Explanation:
1. Pepsin works only in a strongly acidic medium, which HCl provides.
2. HCl also kills bacteria taken in with food.

Teacher's Note:
1. HCl itself does not digest proteins; pepsin does.
2. It also activates pepsinogen.

Answer: (b) Emulsification

Explanation:
1. Bile salts break large fat globules into tiny droplets.
2. This is called emulsification and gives lipase a larger surface to act on.

Teacher's Note:
1. Emulsification is a physical change, not a chemical one.
2. It is similar to the action of soap on grease.

Answer: (c) Bile, pancreatic juice, succus entericus

Explanation:
1. Bile and pancreatic juice enter the duodenum through ducts.
2. The intestinal wall itself secretes intestinal juice (succus entericus).

Teacher's Note:
1. Saliva acts in the mouth and gastric juice in the stomach.
2. The small intestine is where digestion is completed.

Answer: (d) Lipase

Explanation:
1. Lipase hydrolyses fats into fatty acids and glycerol.
2. Amylase acts on starch, and trypsin and pepsin act on proteins.

Teacher's Note:
1. Enzyme names often end with -ase.
2. Lipase comes from lipos, meaning fat.

Answer: (d) Saliva

Explanation:
1. Ptyalin is salivary amylase and begins the digestion of starch in the mouth.
2. It turns starch into maltose.

Teacher's Note:
1. Ptyalin works in a nearly neutral medium.
2. It stops working in the acidic stomach.

Answer: (b) Salivary glands

Explanation:
1. Ptyalin (salivary amylase) is secreted by the salivary glands.
2. It mixes with food during chewing.

Teacher's Note:
1. Pancreatic amylase is called amylopsin.
2. Bile is not a gland but a secretion of the liver.

Answer: (b) An almost neutral medium

Explanation:
1. Saliva has a pH of about 6.8, which is almost neutral.
2. Ptyalin works best at this pH.

Teacher's Note:
1. In the stomach the acid inactivates it.
2. Different enzymes have different optimum pH values.