Biology and Human Welfare Questions and Answers

Answer: C

The process not carried out by microorganisms is Preservation of food items in homes.

Food preservation in homes, by salting, adding sugar or oil, pickling, refrigeration or heating, works by preventing the growth of microorganisms, because microbes are what spoil food. So preservation is protection against microorganisms, not something they do.

Microorganisms do the other three. Bacteria and fungi decompose organic wastes. Nitrogen-fixing bacteria and blue-green algae increase soil fertility. Antibiotics such as penicillin and streptomycin, and many vaccines, are made with the help of microorganisms.

Answer: C

The smallpox vaccine was discovered by Edward Jenner.

In 1796 the English physician Edward Jenner showed that inoculating material from cowpox sores protected a person against smallpox. The word vaccine comes from the Latin vacca, cow. Mass vaccination later led to the eradication of smallpox, declared in 1980.

Ronald Ross showed that mosquitoes transmit malaria, Robert Koch identified the bacteria causing tuberculosis and cholera, and Alexander Fleming discovered penicillin.

Answer: A

Yeast is used for the production of alcohol.

Yeast is a unicellular fungus that respires anaerobically. It converts sugar into alcohol and carbon dioxide by fermentation, a process discovered by Louis Pasteur. This is used to make wine, beer and industrial alcohol, and the carbon dioxide also makes bread dough rise.

Curd is made by the bacterium Lactobacillus, not yeast. Sugar is the raw material that yeast consumes, not its product, and common salt has nothing to do with microorganisms.

Answer: B

The disease is malaria.

Malaria, spread by the female Anopheles mosquito, causes high fever with shivering and chills. Quinine, obtained from the bark of the Cinchona tree, was for centuries the main medicine against it.

Typhoid is a bacterial infection spread through contaminated food and water, and dengue and chikungunya are viral fevers spread by Aedes mosquitoes. None is treated with cinchona bark.

Answer: B

Bacteria are not used in baking of bread.

Bread is made to rise by yeast, a fungus. Yeast respires the sugar in the dough and releases carbon dioxide, whose bubbles make the dough spongy.

The other processes do use bacteria: Lactobacillus turns milk into curd, bacteria such as Rhizobium in root nodules (and free-living forms in soil) fix atmospheric nitrogen, and the souring and conversion of fermenting sugarcane juice into vinegar involves bacteria such as Acetobacter (as NCERT notes, yeast also takes part in fermenting sugars into alcohol).

Answer: C

The statement that is not an advantage of manure is it fixes atmospheric nitrogen.

Nitrogen fixation, turning nitrogen gas from the air into compounds plants can use, is done by microorganisms such as Rhizobium in the root nodules of legumes and by some free-living bacteria and blue-green algae, and by lightning. Manure itself does not fix nitrogen; it returns nutrients already in the plant and animal waste.

The other three are real advantages of manure over fertilizers: its humus makes the soil porous and loose, it adds to and feeds the useful soil microbes, and it improves the soil's water-holding capacity. Chemical fertilizers supply nutrients but do none of these.

Answer: A

The key gives growth of bacteria in the wheat dough.

Dough left in the open is moist and rich in nutrients, so microbes from the air multiply in it. A foul, putrid smell is the mark of bacterial decomposition: bacteria break down the proteins and other matter in the dough and release foul-smelling products.

Saprophytic fungi (moulds) do grow on stale food, usually seen as fuzzy coloured patches, but the option ties them to breaking down carbohydrates, which does not account for a foul smell, and the key treats bacteria as the cause. The two options about bran are not real processes: bran is not oxidised to lactic acid, and 'reduction of bran particles' does not produce a smell.

Answer: A

The set of communicable diseases is tuberculosis, cholera, measles.

Communicable diseases are caused by microbes and spread from person to person: tuberculosis (a bacterium, through the air), cholera (a bacterium, through contaminated water and food) and measles (a virus, through the air).

Each other set includes a non-communicable disease: hypertension, asthma and cancer do not spread from one person to another. Common cold, common flu and chickenpox are communicable, but a set containing even one non-communicable disease is not a set of communicable diseases.

Answer: C

The incorrect statement is shearing is done after scouring.

Wool is processed in this order: shearing (removing the fleece), scouring (washing it to remove grease, dust and dirt), sorting (separating hair of different textures), picking out the burrs, dyeing, and finally straightening, combing and rolling into yarn.

Scouring washes the fleece, so it can only be done after the fleece has been sheared off. The other statements fit the order: sorting comes after shearing, shearing comes before picking out the burrs, and dyeing follows the removal of burrs.

Answer: C

The correct matching is (a)-(iv), (b)-(v), (c)-(i), (d)-(ii).

Yeast is used in baking bread: it ferments sugar and the carbon dioxide released makes the dough rise (a-iv). The protozoan Plasmodium causes malaria (b-v). The bacterium Vibrio cholerae causes cholera (c-i). HIV, a virus, causes AIDS (d-ii).

'Producing antibodies' is the distractor: antibodies are made by the body's own white blood cells, not by bacteria, so option 2 is wrong. Options 1 and 4 also pair the protozoan with cholera, which is caused by a bacterium.