Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
BioNotesBioNotesCreated by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Online
Practice question paper (70 marks, 3 hours) for ISC Class XII Biology Paper 1 Theory, 2027 pattern.
Maximum Marks: 70 | Time Allotted: Three Hours | Reading Time: Additional Fifteen Minutes
This is a practice paper prepared on the ISC 2027 specimen pattern. Syllabus coverage follows the CISCE ISC 2027 Biology (863) Class XII syllabus.
Answer the following questions briefly.
(i) Cleistogamous flowers are advantageous to a plant because they: (Understand) [1]
(a) ensure seed set only through outcrossing
(b) ensure seed set even in the absence of pollinators
(c) increase genetic variability in the offspring
(d) are always pollinated by insects
(ii) Assertion: Okazaki fragments are formed on the lagging strand during DNA replication.
Reason: DNA polymerase can synthesise a new strand only in the 5′→3′ direction. (Understand) [1]
(a) Both Assertion and Reason are true, and Reason is the correct explanation for Assertion.
(b) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
(c) Assertion is true and Reason is false.
(d) Both Assertion and Reason are false.
(iii) A double-stranded DNA molecule has 1200 nucleotides, of which 20% are guanine. The number of adenine nucleotides in the molecule is: (Apply) [1]
(a) 240
(b) 360
(c) 480
(d) 720
(iv) Identify the mismatched pair. (Recall) [1]
(a) Rhizobium – symbiotic nitrogen fixer
(b) Trichoderma – biocontrol agent
(c) Bacillus thuringiensis – biofertiliser
(d) Lactobacillus – curd formation
(v) In which of the following ecosystems is the pyramid of numbers inverted? (Understand) [1]
(a) Grassland
(b) Pond
(c) A forest with a single large tree supporting many herbivorous insects
(d) Open ocean
(vi) Assertion: The forelimbs of a human, a bat and a whale are examples of divergent evolution.
Reason: They have the same basic structural plan but perform different functions. (Analyse) [1]
(a) Both Assertion and Reason are true, and Reason is the correct explanation for Assertion.
(b) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
(c) Assertion is true and Reason is false.
(d) Both Assertion and Reason are false.
(vii) DNA fingerprinting is based on the variation in: (Recall) [1]
(a) single nucleotide polymorphisms (SNPs)
(b) variable number of tandem repeats (VNTRs)
(c) expressed sequence tags (ESTs)
(d) ribosomal RNA genes
(viii) A seed in which the endosperm is completely consumed by the developing embryo is called ______. Give one example. (Recall) [1]
(ix) Name the type of immunoglobulin (a) present in colostrum and (b) responsible for allergic reactions. (Recall) [1]
(x) State one way in which oral contraceptive pills prevent pregnancy. (Understand) [1]
(xi) In a population of 2000 individuals, in one year there were 40 births, 20 deaths, 10 individuals immigrated and 5 emigrated. Calculate the population size at the end of the year. (Apply) [1]
(xii) In the grazing food chain Grass → Grasshopper → Frog → Snake, the grass fixes 10,000 J of energy. Using the 10% law, calculate the energy available at the snake's trophic level. (Apply) [1]
(xiii) DNA polymerase : replication :: ______ : transcription. (Understand) [1]
(xiv) The template strand of a gene has the sequence 3′–TAC GGA TTC–5′. Write the sequence of the mRNA transcribed from it (5′→3′). (Create) [1]
(xv) In a population of 1500 individuals, 60 individuals are born in a year. Calculate the natality rate per individual per year. (Apply) [1]
(xvi) (a) Expand the abbreviation ADA. (Recall) [1]
(b) Name the scientists who proposed the chromosomal theory of inheritance. (Recall) [1]
(xvii) State the role of Taq polymerase in the polymerase chain reaction (PCR). (Recall) [1]
(xviii) Give a reason for each of the following: (Understand)
(a) The stigma of wind-pollinated flowers is often large and feathery. [1]
(b) X-linked recessive disorders are more common in human males than in females. [1]
Describe any two contrivances adopted by flowering plants to prevent self-pollination. (Recall)
In the Hershey–Chase experiment, one batch of bacteriophages was labelled with ³²P and another with ³⁵S. (i) In which batch was the radioactivity found inside the infected bacterial cells? (Recall) (ii) What conclusion was drawn from this experiment? (Understand)
When pure-breeding red-flowered snapdragon (Antirrhinum) plants are crossed with pure-breeding white-flowered plants, all F₁ plants have pink flowers. (i) Name the phenomenon. (Recall) (ii) State the phenotypic ratio expected in the F₂ generation. (Apply)
(i) Name one primary and one secondary lymphoid organ in the human body. (Recall) (ii) Where do T-lymphocytes mature? (Recall)
(i) A child suffers from Severe Combined Immunodeficiency (SCID). (a) Name the enzyme whose deficiency causes SCID. (Recall) (b) Briefly state how gene therapy is used to treat the child. (Understand)
OR
(ii) A man with blood group A (heterozygous) marries a woman with blood group B (heterozygous). (a) Write the genotypes of all possible children. (Apply) (b) What is the probability of a child with blood group O? (Apply)
In Miller and Urey's experiment on the origin of life, (i) name the gases that were used in the apparatus, and (ii) name the organic compounds that were formed. (Recall)
Differentiate between in situ and ex situ conservation of biodiversity, giving one example of each. (Understand)
(i) Draw a neat, labelled diagram of a mature embryo sac (female gametophyte) of a flowering plant. (Recall)
OR
(ii) Draw a neat, labelled diagram of a human sperm. (Recall)
A DNA sample is amplified by PCR.
(i) Name the three steps of one PCR cycle in the correct sequence. (Recall)
(ii) State the role of primers in PCR. (Understand)
(iii) If the reaction begins with a single copy of the target DNA, how many copies will be obtained after 5 cycles? (Apply)
In a population in Hardy–Weinberg equilibrium, the frequency of the recessive allele (q) for a trait is 0.3.
(i) Calculate the frequency of the dominant allele (p). (Apply)
(ii) Calculate the frequency of heterozygous individuals. (Apply)
(iii) How many homozygous dominant individuals are expected in a population of 1000? (Apply)
(i) Define Net Primary Productivity (NPP). (Recall)
(ii) In a grassland ecosystem the NPP is 1200 g/m²/year and 40% of the Gross Primary Productivity (GPP) is lost in respiration. Calculate the GPP and the amount of energy lost in respiration. (Apply)
Draw a neat, labelled diagram of a typical antibody (IgG) molecule. (Recall)
Describe the Meselson and Stahl experiment under the following headings:
(i) isotopes of nitrogen used and the organism used (Recall)
(ii) the observation after the first generation (Understand)
(iii) the conclusion drawn (Understand)
A patient is diagnosed with AIDS.
(i) Name the causative agent and the type of cell it mainly infects. (Recall)
(ii) Name the enzyme which the virus uses to convert its RNA into DNA. (Recall)
(iii) Name the test used for the diagnosis of the disease. (Recall)
A colour-blind man marries a woman of normal vision whose father was colour-blind.
(a) Write the genotypes of the man and the woman. (Apply) [1]
(b) Using a Punnett square, show the genotypes of all possible children. (Apply) [2]
(c) What is the probability of a colour-blind daughter? (Apply) [1]
(d) What is the probability of a colour-blind son? (Apply) [1]
(a) Differentiate between a true fruit and a false fruit, giving one example of each. (Understand) [2]
(b) Explain the events of double fertilisation in a flowering plant. (Understand) [2]
(c) What is perisperm? (Recall) [1]
(i) Describe the hormonal control of the human menstrual cycle with reference to the menstrual, follicular, ovulatory and luteal phases. (Understand) [5]
OR
(ii) Describe the process of translation (protein synthesis) in prokaryotes under the headings: charging of tRNA, initiation, elongation and termination. (Understand) [5]