NEB Class 12 · Exam intelligence
From 6 NEB Class 12 past papers: the chapters that keep coming back and their most important questions, each with a solved model answer. No guarantees; study the whole syllabus.
From the most-tested chapters first, each with a solved model answer.
Reproduction is a process of continuation of the human race. Describe the female reproductive system with a well labelled diagram of human being. How would you explain ovulation in the female human? [4+3+1] (Or) Nephrons are the structural and functional unit of the kidney. Illustrate the structure of nephron with a labelled diagram. What would happen if ADH is secreted insufficiently? [4+3+1]
Female reproductive system consists of:
Ovulation: it is the release of a mature ovum (secondary oocyte) from the Graafian follicle of the ovary, occurring about the 14th day of the menstrual cycle. A surge of luteinizing hormone (LH) from the pituitary triggers the mature follicle to rupture and release the egg into the oviduct; the empty follicle becomes the corpus luteum.
(Or) The nephron has a Malpighian body (Bowman's capsule + glomerulus) and a tubule (PCT, loop of Henle, DCT, collecting duct). If ADH is secreted insufficiently, the tubules reabsorb little water, so large volumes of dilute urine are passed (a condition called diabetes insipidus), leading to excessive thirst and dehydration.
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Amniocentesis is a prenatal diagnostic technique in which a sample of amniotic fluid surrounding the foetus is withdrawn and examined.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:
The diagram below illustrates a type of artificial vegetative propagation in an angiosperm. Answer the following: i) Identify the type of vegetative propagation and name the parts labelled P and Q. [1.5] ii) Briefly explain this type of propagation with an example. [1.5] iii) Mention any two applications of this method. [1]
i) The illustrated method is grafting. P = stock (rooted lower part) and Q = scion (the detached shoot/bud of the desired plant).
ii) In grafting, the scion of a desired variety is joined to the rooted stock so that their cambium layers unite and grow as one plant; the stock supplies water and minerals while the scion produces the shoot. Example: grafting of mango, apple, citrus and rose.
iii) Applications: (a) to multiply superior/desired varieties that do not come true from seed and combine good root (stock) with good shoot (scion) qualities; (b) to propagate seedless plants and improve disease resistance/early fruiting.
Fertilization in angiosperms.
In angiosperms double fertilization occurs. The pollen tube carries two male gametes into the embryo sac: one male gamete fuses with the egg (syngamy) to form the diploid zygote, and the other fuses with the two polar nuclei (triple fusi...
Process of male gametogenesis.
In the anther, diploid microspore mother cells undergo meiosis (microsporogenesis) to form haploid microspores (pollen grains). Each microspore nucleus then divides mitotically into a generative cell and a vegetative (tube) cell; the gen...
The role of mother in a test tube baby.
In in vitro fertilization (test-tube baby), the mother provides the ova (retrieved after hormonal stimulation) that are fertilised outside the body; she then receives the developing embryo implanted into her uterus, where it is carried t...
Development of female gametophyte.
A megaspore mother cell in the nucellus undergoes meiosis to form four haploid megaspores; three degenerate and one functional megaspore enlarges. Its nucleus divides mitotically three times to give 8 nuclei, which organise into the 7-ce...
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.
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.
Which of the following cells in an embryo sac degenerate after fertilization? A) Synergids and primary endosperm cell B) Synergids and antipodal cells C) Antipodal cells and primary endosperm cell D) Eggs and antipodal cells
Correct option: B) Synergids and antipodal cells. After fertilization the egg forms the zygote and the polar nuclei form the endosperm, while the synergids and antipodal cells degenerate as they have no further role.
Define rhizome.
A rhizome is an underground, horizontally growing modified stem with nodes, internodes and scale leaves that stores food and serves in vegetative propagation (e.g. ginger).
What does it mean by pollen grains?
Pollen grains are the microspores / immature male gametophytes of seed plants, produced in the anther and carrying the male gametes.
Mention about entomophilly.
Entomophily is pollination brought about by insects (bees, butterflies); such flowers are usually large, coloured, scented and produce nectar.
What do you mean by scion and stock?
In grafting, the scion is the short detached shoot or bud of the desired plant that is grafted onto the stock, the rooted lower portion that supplies water and minerals.
Define megasporogenesis.
Megasporogenesis is the formation of haploid megaspores from a diploid megaspore mother cell by meiosis inside the ovule.
What do you mean by chiropterophily?
Chiropterophily is pollination brought about by bats.
Define sexual reproduction.
Sexual reproduction is the mode of reproduction involving the fusion of male and female gametes (fertilization) to form a zygote, producing offspring that show genetic variation.
Elaborate about female gametophyte.
The female gametophyte of an angiosperm is the embryo sac, a typically 7-celled, 8-nucleate structure containing the egg cell, two synergids, three antipodal cells and a central cell with two polar nuclei.
Point out about anemophily.
Anemophily is pollination by wind; such flowers are usually small, inconspicuous, produce large amounts of light, dry pollen (e.g. maize, grasses).
What is sperm lysine?
Sperm lysine is an enzyme released from the acrosome of the sperm that dissolves the egg membranes (zona pellucida), enabling the sperm to penetrate the egg during fertilization.
Compare the anatomical structure of dicot and monocot leaf with neat and clean diagram. (Or) What is transpiration? Describe an experiment to show the transpiration by bell jar method.
Dicot (dorsiventral) leaf: has differentiated mesophyll into upper palisade and lower spongy parenchyma; stomata mainly on the lower surface; vascular bundles of different sizes. Monocot (isobilateral) leaf: mesophyll is not differentiat...
Describe the anatomical structure of dicot root and compare it with monocot root. (Or) Describe an experiment to demonstrate light is necessary for the process of photosynthesis with clean diagram.
T.S. of a dicot root shows: piliferous (epiblema) layer with root hairs, wide cortex of parenchyma, a single-layered endodermis with Casparian strips, pericycle, radial vascular bundles with 2-4 (di- to tetrarch) xylem groups, a small ce...
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 ...
Differentiate between simple permanent tissue and complex permanent tissue on the basis of structure, types, cell composition and functions. [4]
'Meristem is also known as Juvenile tissue'. Justify. Explain the types of meristem on the basis of position. [1+3]
Justification: Meristem is called juvenile tissue because it is made of young, thin-walled, actively dividing cells that remain permanently youthful and undifferentiated, continuously producing new cells for growth. Types on the basis of...
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