NEB Class 12 · Past paper
The complete NEB Class 12 2080 exam paper for Biology, all 22 questions with solved model answers.
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Which tissue is called a living mechanical tissue? A) Parenchyma B) Aerenchyma C) Collenchyma D) Chlorenchyma
Correct option: C) Collenchyma. Collenchyma is a living tissue with cells thickened at the corners by cellulose/pectin; it provides mechanical support and flexibility to young growing organs.
What is the genetic material composed of in most organisms? A) Proteins B) Carbohydrates C) Lipids D) Nucleic acids
Correct option: D) Nucleic acids. In most organisms the genetic material is a nucleic acid (DNA, and RNA in some viruses).
Which of the following tissue has the light and dark bands alternately arranged? A) Striped B) Unstriped C) Involuntary D) Unstriated
Correct option: A) Striped. Striped (striated/skeletal) muscle shows alternate light (I) and dark (A) bands, giving a striped appearance.
What is the main end product of photosynthesis? A) ATP B) Carbon dioxide C) Water D) Glucose
Correct option: D) Glucose. Photosynthesis fixes $CO_2$ and water using light energy to form glucose (carbohydrate) and releases oxygen.
What is meant by heterozygous genotype? A) Having two different alleles for a gene B) Having no alleles for a gene C) Having a dominant allele and a recessive allele for a gene D) Having two identical alleles for a gene
Correct option: A) Having two different alleles for a gene. A heterozygous genotype (e.g. $Tt$) carries two different (contrasting) alleles of the same gene.
Which of the following functions is related to sertoli cells? A) Formation of ova B) Nutrition to sperms C) Movement of sperms D) Formation of sperms
Correct option: B) Nutrition to sperms. Sertoli (nurse) cells of the seminiferous tubules nourish and support the developing sperms.
Which of the following is the organ transplantation between two genetically identical individuals? A) Autograft B) Xenograft C) Isograft D) Allograft
Correct option: C) Isograft. A graft between two genetically identical individuals (identical twins) is an isograft.
How can the accurate age of a tree be determined? A) Counting the number of branches B) Measuring the diameter of stem C) Counting the number of annual rings in the tree trunk D) Measuring the height of the tree
Correct option: C) Counting the number of annual rings in the tree trunk. Each annual (growth) ring represents one year's secondary growth, so their number gives the tree's age (dendrochronology).
Which of the following sequence is in correct order? A) Malleus, stapes, incus B) Incus, stapes, malleus C) Malleus, incus, stapes D) Incus, stapes, malleus
Correct option: C) Malleus, incus, stapes. The ear ossicles from the eardrum inward are malleus → incus → stapes.
If a woman is not able to produce the baby, what technique is used to solve this problem? A) Amniocentesis B) In-vitro fertilization C) Vaccination D) In-vivo-fertilization
Correct option: B) In-vitro fertilization. IVF (test-tube baby technique) helps infertile women conceive by fertilizing the ovum outside the body and implanting the embryo in the uterus.
Why is it rare for a girl to be colourblind? A) Her mother and maternal grandfather were colourblind B) Her father and maternal grandfather were colourblind C) Her mother is colourblind and father has normal vision D) Parents have normal vision but grandparents were colourblind
Correct option: B) Her father and maternal grandfather were colourblind. Colour blindness is X-linked recessive, so a girl is colourblind ($X^c X^c$) only when she receives $X^c$ from both parents. This needs the father to be colourblind...
What is the difference between hypertonic, hypotonic and isotonic solutions and how do they affect the movement of water across a selectively permeable membrane? [3+2]
Thus, across a selectively permeable membrane water always moves osmotically from the hypotonic (high water potential) side to the hypertonic (low water potential) side until equilibrium.
What is incomplete dominance? Provide an example of a trait that shows incomplete dominance and explain how it is inherited. [1+4]
Incomplete dominance is the phenomenon in which neither allele is completely dominant, so the heterozygote shows an intermediate (blended) phenotype.
Example - flower colour in Mirabilis jalapa (4 o'clock plant): a cross between red (RR) and white (rr) flowers gives F1 that are all pink (Rr). On selfing the pink F1:
$$Rr \times Rr \rightarrow 1,RR : 2,Rr : 1,rr$$
giving 1 red : 2 pink : 1 white. Here the genotypic and phenotypic ratios are the same ($1:2:1$) because each genotype has its own distinct phenotype, unlike the $3:1$ ratio of complete dominance.
What is plasmolysis? Point out its significances. [1+4]
Plasmolysis is the shrinkage of the protoplasm away from the cell wall when a plant cell is placed in a hypertonic solution and loses water by exosmosis.
Significances:
Draw a labelled diagram of T.S. of dicot stem and compare it with that of monocot stem. [3+2]
Comparison of dicot and monocot stem: - Dicot stem: vascular bundles are arranged in a ring, are conjoint, collateral and open (with cambium, so secondary growth occurs); has a distinct cortex, endodermis and central pith with medullary ...
Digestive, respiratory and circulatory systems in human beings are interrelated. Applying your understanding, how do all these systems work together for normal physiology? [5] (Or) Identify the hormones released by adrenal cortex. In what ways are these hormones useful to the human body. [2+3]
The three systems work together to supply energy to every cell: - The digestive system breaks down food into simple absorbable nutrients (glucose, amino acids, fatty acids) and passes them into the blood. - The respiratory system takes i...
Compare and contrast areolar and adipose tissues. [2.5+2.5]
Both are loose connective tissues with cells in a matrix, but they differ: - Areolar tissue: a soft, packing/connective tissue found beneath the skin and between organs; matrix contains collagen and elastic fibres with cells like fibrobl...
What is diffusion? Compare it with that of osmosis. [1+4]
Diffusion is the net movement of molecules (of a gas, liquid or solute) from a region of higher concentration to a region of lower concentration until evenly distributed.
Comparison with osmosis:
(Osmosis is thus a special kind of diffusion of water across a semipermeable membrane.)
How can biotechnology be applied in medicine and agriculture, and analyze the potential benefits and drawbacks of using biotechnology in these fields. [5]
In medicine: production of insulin, growth hormone, vaccines, antibiotics and monoclonal antibodies, gene therapy, and diagnosis of diseases. In agriculture: development of transgenic (GM) crops resistant to pests, disease, herbicides an...
What is amniocentesis? Why is it done? Explain the procedure of amniocentesis. [1+1+6]
Amniocentesis is a prenatal diagnostic technique in which a sample of amniotic fluid surrounding the foetus is withdrawn and examined.
Why it is done: to detect chromosomal and genetic disorders and metabolic defects of the foetus (e.g. Down syndrome, spina bifida, sex-linked disorders) and to know the sex of the foetus for genetic counselling.
Procedure:
Due to metabolic activities, toxic substances are formed in the body. Identify these substances. Draw a labelled diagram and explain the excretory organs of human beings. [2+2+4]
Toxic (nitrogenous) waste substances formed by metabolism include urea, uric acid, ammonia, creatinine and excess salts, water and $CO2$; these must be removed to avoid poisoning. Excretory organs of humans: - Kidneys: a pair of bean-sha...
Explain the process of semi-conservative replication of DNA with necessary diagrams. How does replication contribute to the accurate transmission of genetic information from one generation to the next generation? [6+2] (Or) Discuss the different types of gene mutation and their effects on the genetic make up of an organism. Evaluate the positive and negative impacts of gene mutations and chromosomal mutations on the organisms. [4+4]
Semi-conservative replication: - The enzyme helicase unwinds the double helix at the replication fork, breaking the hydrogen bonds; single-strand binding proteins keep the strands apart. - Each parental strand acts as a template; DNA pol...
Correct option: D) Glucose. Photosynthesis fixes and water using light energy to form glucose (carbohydrate) and releases oxygen.
Correct option: A) Having two different alleles for a gene. A heterozygous genotype (e.g. ) carries two different (contrasting) alleles of the same gene.
Correct option: B) Her father and maternal grandfather were colourblind. Colour blindness is X-linked recessive, so a girl is colourblind () only when she receives from both parents. This needs the father to be colourblind...
Incomplete dominance is the phenomenon in which neither allele is completely dominant, so the heterozygote shows an intermediate (blended) phenotype.
Example - flower colour in Mirabilis jalapa (4 o'clock plant): a cross between red (RR) and white (rr) flowers gives F1 that are all pink (Rr). On selfing the pink F1:
giving 1 red : 2 pink : 1 white. Here the genotypic and phenotypic ratios are the same () because each genotype has its own distinct phenotype, unlike the ratio of complete dominance.
Toxic (nitrogenous) waste substances formed by metabolism include urea, uric acid, ammonia, creatinine and excess salts, water and ; these must be removed to avoid poisoning. Excretory organs of humans: - Kidneys: a pair of bean-sha...