BioNotesISC Class XII Biology Practice Paper 2 - Marking Scheme
Marking scheme and model answers for ISC Class XII Biology Practice Paper 2, 2027 pattern.
2017 Biology Science Paper - 3
Complete biology examination paper covering cell biology, physiology, genetics, human anatomy, and environmental science with two sections totaling 80 marks
Created 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) Which of the following is not a function of Sertoli cells? (Understand) [1]
(a) Providing nourishment to developing sperm
(b) Secretion of inhibin
(c) Secretion of testosterone
(d) Phagocytosis of residual cytoplasm of spermatids
(ii) Assertion: Wind-pollinated plants produce an enormous number of pollen grains.
Reason: The chances of a pollen grain reaching a stigma are low because wind is a non-directed pollinating agent. (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.
(iii) A segment of B-DNA has 200 base pairs. If there are 10 base pairs in each complete turn of the helix, the number of complete turns in the segment is: (Apply) [1]
(a) 10
(b) 20
(c) 40
(d) 200
(iv) Identify the incorrect statement about restriction enzymes. (Recall) [1]
(a) They recognise specific palindromic nucleotide sequences.
(b) EcoRI produces sticky ends.
(c) They are exonucleases that remove nucleotides from the ends of DNA.
(d) They are isolated from bacteria.
(v) A cuckoo lays its eggs in the nest of a crow, which then incubates and raises the cuckoo's young. This is an example of: (Understand) [1]
(a) commensalism
(b) amensalism
(c) brood parasitism
(d) mutualism
(vi) Assertion: Taq polymerase is preferred for PCR.
Reason: It is thermostable and remains active at the high temperatures required for denaturation of DNA. (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) Assertion: A patient suffering from malaria shows recurring bouts of chills and fever.
Reason: Haemozoin released on rupture of infected red blood cells causes the chills and fever. (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.
(viii) Name the type of tumour whose cells spread from the primary site to other parts of the body, and name the process by which this happens. (Understand) [1]
(ix) In the name EcoRI, what do the letters 'Eco' and 'R' indicate? (Recall) [1]
(x) State the principle on which vaccination is based. (Understand) [1]
(xi) Why can a pyramid of energy never be inverted? (Understand) [1]
(xii) A fish population in a pond initially has 400 individuals. During one year, 60 fish are born, 20 die, 10 immigrate and 30 emigrate. Calculate the population size at the end of the year. (Apply) [1]
(xiii) Exon : expressed sequence :: Intron : ______. (Understand) [1]
(xiv) A codon on an mRNA has the sequence 5′–GCU–3′. Write the sequence (5′→3′) of the anticodon of the tRNA that will bind to it. (Create) [1]
(xv) A pea plant with genotype TtRr is self-pollinated. What fraction of the offspring is expected to be homozygous recessive for both traits? (Apply) [1]
(xvi) (a) Expand the abbreviation ZIFT. (Recall) [1]
(b) Who is known as the 'Father of Indian Ecology'? (Recall) [1]
(xvii) In gel electrophoresis, towards which electrode do DNA fragments move? Give a reason. (Recall) [1]
(xviii) Give a reason for each of the following: (Understand)
(a) Banana is a seedless fruit. [1]
(b) Mycorrhizal association improves the growth of plants. [1]
Differentiate between exponential growth and logistic growth of a population, giving the equation for each. (Understand)
Explain industrial melanism as an example of natural selection. (Understand)
State any two features of the genetic code. (Recall)
Tobacco plants are protected from the root-knot nematode Meloidogyne incognita by using RNA interference (RNAi). Briefly explain how RNAi works in this case. (Understand)
(i) Define cleistogamy and state one advantage of it. (Recall)
OR
(ii) Define apomixis and state its significance in agriculture. (Recall)
Name the hormone responsible for (i) milk synthesis and (ii) milk ejection from the mammary glands after childbirth. (Recall)
Define a biodiversity hotspot. Name any two biodiversity hotspots that include regions of India. (Recall)
(i) Draw a neat, labelled diagram of a T.S. of a young microsporangium (pollen sac) showing its wall layers. (Recall)
OR
(ii) Draw a neat, labelled diagram of a mature human ovum. (Recall)
The packaging of DNA in eukaryotes involves nucleosomes.
(i) Define a nucleosome. (Recall)
(ii) Name the histone proteins that form the histone octamer. (Recall)
(iii) State the function of histone H1. (Understand)
The plasmid pBR322 is a commonly used cloning vector.
(i) Name the two antibiotic-resistance genes present in pBR322. (Recall)
(ii) State the role of the ori site. (Understand)
(iii) Name one restriction site present within the tetracycline-resistance gene. (Recall)
Bt cotton is resistant to cotton bollworms.
(i) Name the gene/protein responsible for the resistance. (Recall)
(ii) Explain how the toxin kills the insect. (Understand)
(iii) Why does the toxin not kill the Bacillus thuringiensis bacterium that produces it? (Understand)
The Human Genome Project (HGP) was a landmark scientific effort.
(i) State the goal of the HGP. (Recall) [1]
(ii) Name the two major methodologies used in the project. (Recall) [1]
(iii) State one application of the knowledge gained from the HGP. (Recall) [1]
Differentiate between active immunity and passive immunity on the basis of any three points. (Understand)
The species–area relationship is expressed as: log S = log C + Z log A.
(i) What do S, A, Z and C represent? (Recall) [2]
(ii) State the range of Z values for smaller areas and for very large areas such as continents. (Recall) [1]
The following family history of a disease was recorded.
Generation I: I-1 (male, unaffected) and I-2 (female, unaffected) are married.
Generation II: Their children are II-1 (male, affected), II-2 (female, unaffected) and II-3 (male, unaffected).
Generation III: II-2 marries an unaffected man; their son III-1 is affected.
(a) Identify the most likely mode of inheritance. (Understand) [1]
(b) Write the genotypes of I-2 and II-2. (Apply) [2]
(c) What is the probability that a son born to II-2 and her husband will be affected? (Apply) [1]
(d) Give one reason why the disease cannot be autosomal dominant. (Analyse) [1]
(a) Differentiate between spermatogenesis and oogenesis on the basis of any three points. (Analyse) [3]
(b) Define (i) spermiogenesis and (ii) spermiation. (Recall) [2]
(i) Describe the steps involved in the formation of recombinant DNA and its introduction into a host, and explain how recombinants are selected by insertional inactivation. (Understand) [5]
OR
(ii) Explain the flow of energy in an ecosystem with reference to PAR, the 10% law and the grazing food chain. Explain why a pyramid of energy is always upright. (Understand) [5]
ISC Class XII Biology Practice Paper 2 - Marking Scheme
Marking scheme and model answers for ISC Class XII Biology Practice Paper 2, 2027 pattern.
2017 Biology Science Paper - 3
Complete biology examination paper covering cell biology, physiology, genetics, human anatomy, and environmental science with two sections totaling 80 marks