Your Answer : (Not Answered)

Correct Answer : B

The pea experiments were done by Gregor Johann Mendel.

Mendel, an Austrian monk, crossed pea plants in his monastery garden in the 1850s and 1860s. He studied traits that come in contrasting pairs, such as tall or short, round or wrinkled seeds, yellow or green seeds, and found the laws by which they are inherited. He is called the father of genetics.

Dr. M.S. Swaminathan is the Indian agricultural scientist associated with the Green Revolution. George de Mestral, a Swiss engineer, invented Velcro after noticing burrs sticking to his dog. Charles Darwin proposed the theory of evolution by natural selection.

Your Answer : (Not Answered)

Correct 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.

Your Answer : (Not Answered)

Correct 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.

Your Answer : (Not Answered)

Correct 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.

Your Answer : (Not Answered)

Correct 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.

Your Answer : (Not Answered)

Correct Answer : A

Nose bleeding happens because the pressure in blood vessels exceeds outside pressure.

Air pressure falls with altitude. At great heights the pressure of the blood inside the body becomes much greater than the air pressure outside, and the thin, delicate blood vessels in the nose can burst. The dry, cold air of high mountains adds to the effect.

The blood pressure does not fall below or equal the outside pressure, and blood thickening is not the reason given for nosebleeds.

Your Answer : (Not Answered)

Correct Answer : D

The correct statements are (i) and (ii).

William Beaumont, an American army surgeon, studied digestion through a wound in the stomach of Alexis St. Martin that never fully closed after a gunshot accident in 1822. Through it he observed that the stomach churns food and digests it with juices it secretes, so (i) and (ii) are true. This story appears in the NCERT Class V EVS book.

Statement (iii) is false: Beaumont found that the gastric juice is acidic, not basic; it contains hydrochloric acid. Statement (iv) overstates the time: his experiments ran from 1825 to 1833, well under ten years, not nineteen. Every option including (iii) or (iv) is therefore wrong.

Your Answer : (Not Answered)

Correct Answer : C

The answer is 2 hours.

The figure comes from the NCERT Class V Environmental Studies chapter 'From Tasting to Digesting'. It draws on the observations the army surgeon William Beaumont made on a man with a permanent opening in his stomach, which gave the time different foods stay in the stomach before they are digested. In that table boiled milk takes about 2 hours, and unboiled milk a little longer, 2 hours 15 minutes.

The options 3, 4 and 5 hours are not the NCERT figure for boiled milk; a figure of about 3 hours appears in a different study of raw milk and is not in the NCERT table. I checked the figure against secondary pages that reproduce the table, not the textbook itself.

Your Answer : (Not Answered)

Correct Answer : B

Ozone depletion is caused by chlorofluorocarbons.

CFCs, once used in refrigerators, air conditioners and aerosol sprays, are stable enough to reach the stratosphere. There ultraviolet light breaks them down and releases chlorine atoms, and each chlorine atom can destroy thousands of ozone molecules in a chain reaction. This is why the Montreal Protocol phased them out.

Carbon dioxide and methane are greenhouse gases linked to global warming, not ozone depletion, and carbon monoxide is a poisonous gas from incomplete combustion. Acid rain is caused by sulphur and nitrogen oxides and damages buildings, soil and lakes, not the ozone layer.

Your Answer : (Not Answered)

Correct Answer : C

Species restricted to a particular area are called endemic species.

An endemic species is found naturally only in one region and nowhere else, for example sal and wild mango, which the NCERT Class VIII textbook names as endemic flora of the Pachmarhi Biosphere Reserve, or the Nilgiri tahr of the Western Ghats.

The other terms mean different things. Endangered species are those at risk of extinction, wherever they live. Extinct species no longer exist anywhere. Migratory species move between regions, often seasonally, which is the opposite of being restricted to one area.

Your Answer : (Not Answered)

Correct Answer : D

The one different from the rest is conservation.

Deforestation (clearing forests), desertification (fertile land turning into desert) and soil erosion (removal of the top soil by wind and water) are all forms of damage to land and the environment, and each can lead to the others: cutting forests exposes soil to erosion and can eventually turn land into desert.

Conservation is the protection and careful use of forests, wildlife, soil and other resources, a remedy for these problems rather than one of them.

Your Answer : (Not Answered)

Correct Answer : D

The practice not likely to increase soil fertility is maintaining minimum distance between the crops while sowing.

Sowing seeds too close together does not add anything to the soil. It causes overcrowding, so plants compete for the same nutrients, water and sunlight, and the soil is drained faster rather than enriched.

The other practices all help restore fertility. Organic manure adds humus and nutrients and improves soil texture. Leaving a field fallow between crops lets the soil recover its nutrients. Crop rotation, especially with legumes, replenishes nitrogen.

Your Answer : (Not Answered)

Correct Answer : A

Both (A) and (R) are true but (R) is not the correct explanation of (A).

The assertion is true: the nucleus is a distinct, usually spherical structure, typically near the centre of the cell. The reason is also true: the nucleus lies in the cytoplasm, the jelly-like substance between it and the cell membrane.

But being surrounded by cytoplasm is not why the structure is called the nucleus or why it is spherical and central. The two statements are separate facts, so (R) does not explain (A).

Your Answer : (Not Answered)

Correct Answer : A

The only correct statement is D: all cells have a cell membrane.

The cell (plasma) membrane surrounds every cell, plant, animal or bacterial, and controls what enters and leaves it.

The others have exceptions. Not all cells are microscopic: a hen's or ostrich's egg is a single cell visible to the naked eye, and some nerve cells are very long. Animal cells have no cell wall. Bacteria and blue-green algae are prokaryotes and have no nuclear membrane. So 'A and D', 'B and C' and 'Only A' are wrong.

Your Answer : (Not Answered)

Correct Answer : C

The organelles with their own DNA are A, B and C: plastids, mitochondria and the nucleus.

The nucleus holds most of the cell's DNA in its chromosomes. Mitochondria and plastids (such as chloroplasts) also have their own small, circular DNA and ribosomes and can make some of their own proteins, which is evidence that they descend from free-living bacteria.

The vacuole is a membrane-bound sac storing water, food and wastes; it has no DNA. So options naming D are wrong, and 'B and C' leaves out the plastids.

Your Answer : (Not Answered)

Correct Answer : A

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

• Rose: vegetative propagation, by stem cuttings.
• Yeast: budding, a small bud growing from the parent cell.
• Ferns: spore formation.
• Spirogyra: fragmentation, the filament breaking into pieces that each grow.

Pollination is not a mode of asexual reproduction at all; it is a step in sexual reproduction, so options matching any plant to pollination are wrong, and option C swaps the yeast and Spirogyra methods.

Your Answer : (Not Answered)

Correct Answer : D

The set in which all show external fertilisation is Frogs, fish, starfish.

In external fertilisation eggs and sperm are released into water and fuse outside the body. Frogs and most fish release eggs and sperm in water, and starfish shed their gametes into the sea.

Hens, lizards and butterflies all have internal fertilisation, so any set containing one of them fails.

Your Answer : (Not Answered)

Correct Answer : A

The common method is Spore formation.

Fungi such as bread mould (Rhizopus) produce spores in sporangia. Mosses and ferns are non-flowering plants that also reproduce by spores, released from the capsule of a moss and from the sori on the underside of fern leaves.

Regeneration is typical of animals like Planaria and Hydra. Budding is seen in yeast and Hydra, not in mosses and ferns. Fragmentation is typical of filamentous algae such as Spirogyra, and is not the method these three groups share.

Your Answer : (Not Answered)

Correct Answer : D

The blanks are: ovaries enlarge, they produce estrogen, the testes produce testosterone, and production is controlled by the pituitary gland.

At puberty the ovaries enlarge, eggs begin to mature and the ovaries secrete the female sex hormone estrogen. The testes secrete the male sex hormone testosterone. The release of these hormones is controlled by hormones from the pituitary gland, which stimulate the ovaries and testes.

The ovaries do not reduce in size, which rules out two options. Thyroxine is made by the thyroid gland and is not a sex hormone, and the adrenal gland does not control the production of the sex hormones, which rules out the others.

Your Answer : (Not Answered)

Correct Answer : C

The correct sequence is (D) → (A) → (B) → (C).

1. (D) Bacteria such as Rhizobium and blue-green algae fix atmospheric nitrogen into compounds in the soil.
2. (A) Plants take up these nitrogen compounds through their roots.
3. (B) Plants use them to build proteins and other compounds, which pass to animals through food.
4. (C) When plants and animals die, bacteria and fungi convert their nitrogenous wastes back into nitrogen compounds.

Option A puts decomposition before uptake, option B starts with uptake before any fixation, and option D has plants making proteins before they absorb nitrogen.