996 practice questions for CBSE Class 12 Biology, organised by NCERT chapter (13 chapters). Every question includes a written explanation. Pick a chapter below, or try the samples first.
Bacteria that grow without oxygen on cellulose-rich material and give off large amounts of methane are called
Amethanogens
Blactic acid bacteria
Cnitrogen-fixing bacteria
Dcyanobacteria
Show answer and explanation
Correct answer: A - methanogens
Methanogens, such as Methanobacterium, are the group named for the methane they produce. Lactic acid bacteria such as Lactobacillus make lactic acid and set curd. Cyanobacteria are photosynthetic and serve as biofertilisers, while nitrogen-fixing bacteria such as Rhizobium convert atmospheric nitrogen into a usable form.
Q2
easy
The red blood cells of a person with blood group AB carry both the A sugar and the B sugar on their surface. Which pattern of inheritance does this illustrate?
AComplete dominance
BIncomplete dominance
CCo-dominance
DPolygenic inheritance
Show answer and explanation
Correct answer: C - Co-dominance
Both alleles are fully expressed in the heterozygote and each makes its own sugar, which is co-dominance. Incomplete dominance would give a single new sugar of intermediate character rather than both sugars side by side. Complete dominance would let only one of the two sugars appear. Polygenic inheritance needs several genes adding small effects, but blood group here depends on one gene.
Q3
hard
Consider these statements about the discovery of penicillin.
(i) The mould that produced it was Penicillium notatum.
(ii) Fleming was working with Staphylococci when he noticed its effect.
(iii) Fleming himself established the full potential of penicillin as an antibiotic.
Which of these are correct?
AOnly (i) and (ii)
B(i), (ii) and (iii)
COnly (i) and (iii)
DOnly (ii) and (iii)
Show answer and explanation
Correct answer: A - Only (i) and (ii)
The mould was Penicillium notatum and Fleming was culturing Staphylococci when he saw that they could not grow near it, so the first two statements are true. The full potential of penicillin as an antibiotic was established later by Ernest Chain and Howard Florey, so the third statement is false and any answer that includes it must be wrong.
Q4
hard
Assertion (A): When an exotic species is introduced into a new region it usually stays rare, because the predators of that region begin to feed on it at once. Reason (R): Predators keep the populations of their prey under control.
ABoth A and R are true, and R is the correct explanation of A
BBoth A and R are true, but R is not the correct explanation of A
CA is true, but R is false
DA is false, but R is true
Show answer and explanation
Correct answer: D - A is false, but R is true
(A) is false. An introduced species commonly turns invasive and spreads fast precisely because the new land holds no predator adapted to feed on it, as the prickly pear did in Australia. (R) is true, and it is the general rule whose absence in the invaded land explains the runaway spread. So a true reason sits beside a false assertion here.
Q5
easy
In a forest, tall trees form the topmost layer, shrubs grow beneath them, and herbs and grasses cover the ground. What is this vertical arrangement of species in an ecosystem called?
AStratification
BHumification
CMineralisation
DFragmentation
Show answer and explanation
Correct answer: A - Stratification
The vertical distribution of different species at different levels of an ecosystem is called stratification, and a forest shows it as a tree layer, a shrub layer and a ground layer. Fragmentation is the breaking of dead matter into small pieces by detritivores, humification is the build-up of humus in soil, and mineralisation is the release of inorganic nutrients from humus. All three are steps of decomposition, not patterns of layering.
Q6
medium
Why do assisted reproductive technologies remain beyond the reach of most infertile couples in India?
AThey work only for women below the age of eighteen years, and most women seek treatment later than that
BThey need highly trained specialists and costly equipment, and emotional, religious and social factors also discourage couples
CThey have been banned by law throughout the country
DThey may be used only by couples who already have one child, under rules meant to limit family size, so childless couples are left out
Show answer and explanation
Correct answer: B - They need highly trained specialists and costly equipment, and emotional, religious and social factors also discourage couples
These procedures demand extremely precise handling by specialists and expensive instruments, and emotional, religious and social attitudes keep many couples away even where clinics exist. The techniques are legal in India. No rule limits them to couples with an existing child, and there is no such age ceiling, 18 years being the legal marriageable age for women rather than an upper limit for treatment.
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