Reproduction in flowering plants and humans
A mature embryo sac in a typical angiosperm contains: (a) 8 cells, 8 nuclei (b) 7 cells, 8 nuclei (c) 8 cells, 7 nuclei (d) 7 cells, 7 nuclei
(b) 7 cells and 8 nuclei. The central cell holds two polar nuclei, which is why the nucleus count exceeds the cell count. This exact distinction is asked repeatedly.
Which part of the ovule develops into the seed coat? (a) Nucellus (b) Integuments (c) Funicle (d) Hilum
(b) Integuments. The nucellus provides nutrition, the funicle is the stalk, and the hilum is the junction between funicle and ovule body.
The fusion of a male gamete with the two polar nuclei produces: (a) Zygote (b) Primary endosperm nucleus (c) Embryo (d) Suspensor
(b) The primary endosperm nucleus, which is triploid. This second fusion, alongside syngamy, is what makes the process double fertilisation - a phenomenon unique to angiosperms.
In humans, fertilisation normally occurs in the: (a) Uterus (b) Cervix (c) Ampullary region of the fallopian tube (d) Ovary
(c) The ampullary-isthmic junction of the fallopian tube. The fertilised egg then travels to the uterus for implantation.
Ovulation is triggered by a surge of which hormone? (a) FSH (b) LH (c) Progesterone (d) Oestrogen
(b) The LH surge in mid-cycle. The corpus luteum that forms afterwards secretes progesterone, which maintains the endometrium.
How many functional gametes are produced from one primary oocyte and from one primary spermatocyte?
One ovum from a primary oocyte, along with three polar bodies that degenerate, but four sperms from a primary spermatocyte. The asymmetry of oogenesis conserves cytoplasm for the future zygote.
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Genetics and inheritance
Mendel's law of independent assortment holds for genes located: (a) On the same chromosome (b) Close together on one chromosome (c) On different chromosomes (d) On the X chromosome
(c) On different (non-homologous) chromosomes. Genes close together on the same chromosome are linked and tend to be inherited together, which is why linkage was the first major exception discovered to Mendel's results.
The phenotypic ratio of a dihybrid cross in the F₂ generation is: (a) 3:1 (b) 1:2:1 (c) 9:3:3:1 (d) 1:1:1:1
(c) 9:3:3:1. The 1:2:1 ratio is the genotypic ratio of a monohybrid cross, and 1:1:1:1 is the result of a dihybrid test cross.
ABO blood grouping in humans is an example of: (a) Incomplete dominance (b) Multiple alleles and codominance (c) Polygenic inheritance (d) Pleiotropy
(b) Multiple alleles with codominance. Three alleles exist in the population - I^A, I^B and i - with I^A and I^B codominant to each other and both dominant over i.
Colour blindness is inherited as: (a) Autosomal dominant (b) Autosomal recessive (c) X-linked recessive (d) Y-linked
(c) X-linked recessive, which is why it is far more common in males - a single affected X is enough, since there is no second X to mask it.
Down's syndrome is caused by: (a) Trisomy of chromosome 21 (b) Monosomy of X (c) XXY condition (d) Deletion in chromosome 5
(a) Trisomy 21 - an extra copy of chromosome 21. Turner's syndrome is 45,XO and Klinefelter's is 47,XXY.
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Molecular basis of inheritance
In B-DNA, the pitch of the helix and the number of base pairs per turn are: (a) 3.4 nm and 10 (b) 0.34 nm and 10 (c) 3.4 nm and 20 (d) 2.0 nm and 10
(a) A pitch of 3.4 nm with about 10 base pairs per turn, giving a rise of 0.34 nm per base pair. All three numbers get asked, so learn them together.
Semi-conservative DNA replication was experimentally demonstrated by: (a) Griffith (b) Hershey and Chase (c) Meselson and Stahl (d) Avery, MacLeod and McCarty
(c) Meselson and Stahl, using heavy nitrogen (¹⁵N) labelling in E. coli. Griffith showed transformation, Avery's group identified DNA as the transforming principle, and Hershey and Chase confirmed DNA as the genetic material using bacteriophages.
Splicing removes which part of the primary transcript? (a) Exons (b) Introns (c) The poly-A tail (d) The cap
(b) Introns - the non-coding regions - after which the exons are joined. Capping and tailing are separate processing steps, not removals.
How many codons exist, and which are the stop codons?
There are 64 codons; UAA, UAG and UGA are stop codons, and AUG both starts translation and codes for methionine. The code is degenerate because 61 codons specify only 20 amino acids.
In the lac operon, the inducer is: (a) Glucose (b) Lactose (c) The repressor protein (d) RNA polymerase
(b) Lactose, which binds the repressor and prevents it from blocking the operator, so transcription can proceed. In the absence of lactose the repressor binds the operator and the operon is switched off.
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Evolution and human health
Darwin's finches on the Galapagos islands are an example of: (a) Convergent evolution (b) Adaptive radiation (c) Genetic drift (d) Industrial melanism
(b) Adaptive radiation - one ancestral stock diversifying into many forms suited to different habitats and diets on the same island group.
The Hardy-Weinberg principle is expressed as: (a) p + q = 1 only (b) p² + 2pq + q² = 1 (c) p² + q² = 1 (d) 2pq = 1
(b) p² + 2pq + q² = 1, where p and q are allele frequencies summing to 1. Deviation from this equilibrium indicates that evolution is occurring in the population.
The infective stage of Plasmodium that enters the human body through a mosquito bite is the: (a) Gametocyte (b) Sporozoite (c) Trophozoite (d) Merozoite
(b) Sporozoite, injected by a female Anopheles mosquito. It multiplies in liver cells and then infects red blood cells, whose rupture releases the toxin haemozoin that causes the characteristic fever.
An antibody molecule is represented as: (a) H₂L₂ (b) HL (c) H₄L₂ (d) H₂L₄
(a) H₂L₂ - two identical heavy chains and two identical light chains, giving the familiar Y shape with variable regions at the tips.
Which of these provides innate, non-specific protection against viral infection? (a) Antibodies (b) Interferons (c) T-lymphocytes (d) Memory cells
(b) Interferons, secreted by virus-infected cells to protect neighbouring uninfected cells. Antibodies, T-cells and memory cells belong to the acquired, specific immune response.
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Microbes and biotechnology
Organism-to-product matching is the most reliably asked question type in these chapters. The table is worth memorising outright.
| Organism | Product or role |
|---|---|
| Lactobacillus | Curd formation from milk |
| Saccharomyces cerevisiae | Bread, beer and ethanol (brewer's yeast) |
| Aspergillus niger | Citric acid |
| Penicillium notatum | Penicillin (discovered by Fleming) |
| Streptococcus | Streptokinase, a clot buster |
| Trichoderma polysporum | Cyclosporin A, an immunosuppressant |
| Monascus purpureus | Statins, which lower blood cholesterol |
| Bacillus thuringiensis | Bt toxin used in insect-resistant crops |
A high BOD value of a water sample indicates: (a) Clean water (b) High dissolved oxygen (c) Heavy organic pollution (d) High salinity
(c) Heavy organic pollution. Biochemical oxygen demand measures the oxygen microbes need to break down organic matter, so a high value means a large pollutant load.
Restriction enzymes cut DNA at: (a) Random sites (b) Palindromic recognition sequences (c) The 5' end only (d) Every adenine
(b) Specific palindromic recognition sequences, producing staggered cuts that leave single-stranded 'sticky ends' - which is exactly what allows a foreign fragment to be joined into a vector.
In gel electrophoresis, DNA fragments move towards the: (a) Cathode (b) Anode (c) Neither (d) Both ends
(b) The anode, because DNA is negatively charged due to its phosphate backbone. Smaller fragments travel further, and the bands are visualised with ethidium bromide under UV light.
PCR requires which heat-stable enzyme? (a) DNA ligase (b) Taq polymerase (c) Restriction endonuclease (d) Reverse transcriptase
(b) Taq polymerase, isolated from a thermophilic bacterium so that it survives the repeated denaturation step at around 95 °C. The three steps are denaturation, annealing and extension.
Bt cotton is resistant to bollworm because it expresses genes named: (a) nif (b) cry (c) rop (d) Ti
(b) cry genes from Bacillus thuringiensis - cryIAc and cryIIAb control bollworms. The toxin is an inactive protoxin that becomes active only in the alkaline gut of the insect.
ADA deficiency, the first disorder treated by gene therapy, is caused by the absence of: (a) Adenosine deaminase (b) Amylase (c) Alanine dehydrogenase (d) Aldolase
(a) Adenosine deaminase, an enzyme essential to immune function. Early treatment involved introducing a functional gene into the patient's lymphocytes.
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Ecology and environment
The 10% law of energy transfer between trophic levels was proposed by: (a) Odum (b) Lindeman (c) Tansley (d) Ehrlich
(b) Lindeman. Only about 10% of the energy at one trophic level is available to the next, which is why food chains rarely exceed four levels.
Which ecological pyramid is typically inverted in an aquatic ecosystem? (a) Energy (b) Number (c) Biomass (d) None
(c) The pyramid of biomass, because the phytoplankton at the base have a small standing biomass but reproduce very rapidly. The energy pyramid is always upright.
The species-area relationship is expressed as: (a) S = CA^Z (b) S = C + AZ (c) S = A/Z (d) S = ZA²
(a) S = CA^Z, where Z is the slope of the regression line. Z usually lies between 0.1 and 0.2 for smaller areas, and is steeper for very large areas such as whole continents.
An age pyramid with a broad base and narrow top represents a population that is: (a) Declining (b) Stable (c) Expanding (d) Extinct
(c) Expanding, since it has proportionally many young individuals. A stable population shows a bell-like shape, and a declining one is narrow at the base.
Which of these is an alien invasive species in India? (a) Water hyacinth (b) Lantana (c) Parthenium (d) All of these
(d) All of these. Water hyacinth (terror of Bengal), Lantana and Parthenium are the standard examples, along with the African catfish Clarias gariepinus.
The 'rivet popper hypothesis' about biodiversity loss was proposed by: (a) Paul Ehrlich (b) Edward Wilson (c) Charles Elton (d) Robert May
(a) Paul Ehrlich, who compared species in an ecosystem to rivets in an aircraft - losing a few may be survivable, but losing rivets from a critical part is not.
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How to use this set
- ✓Answer before reading the explanation. An MCQ you did not commit to teaches you nothing.
- ✓For every miss, write the NCERT line that would have answered it. Class 12 Biology MCQs are line-level recall questions.
- ✓Learn the numbers as a group: 7 cells and 8 nuclei, 64 codons, 3.4 nm pitch, 10% energy transfer, 47 XXY.
- ✓Memorise the organism-product table and the scientist-experiment pairs - they are almost free marks.
- ✓Then drill the same units as timed quizzes, because both the board paper and NEET measure speed as well as recall.
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