CHSE BIOLOGY PREVIOUS YEAR QUESTION PAPER

CHSE biology previous year question papers

2019

2018 to 2008

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Reproduction in Organisms

What is reproduction?need of reproduction and explain Types of reproduction

Ans.Reproduction is a biological process of continuity of a race in which the grown up individuals give rise to offsprings similar to them.
It performs the following functions:

Enables continuity of the species.

Maintains life on the earth.

Creates variations among population.

The mechanism to produce offsprings shows large variations, depending on organisms habitat, its internal physiology and several other factors.
Based on the participation of one or two organisms, reproduction can be of following two types:
(i)Asexual reproduction (ii) Sexual reproduction

Asexual reproduction A single parent is capable of producing offsprings. Thus, the offsprings are genetically and morphologically identical to one another and to their parent. These are often referred to as clone. The unit of reproduction is commonly formed from the somatic cells of the parent. Meiosis does not occur in asexual reproduction.
Asexual reproduction is common among single-celled organisms and in plants and animals with simple organisations. Cell division in itself is a mode of reproduction in protists, e.g. bacteria and monerans, e.g. Amoeba (the parent cell divide into two to give rise to new individuals).
Types of asexual reproduction are as given below:
I.Fission can be further classified as:
(i)Binary fission The body of an individual divides into two equal halves.
It can be following types:
(a)Simple binary fission When division occurs in any plane but it is always right angle to the elongated dividing nucleus, e.g.
(b)Longitudinal binary fission When division occurs along the longitudinal axis, e.g. Euglena, Vorticella.
(c)Oblique binary fission When division occurs at an angle to the transverse axis, e.g. Ceratium, Gonyaulax.
(d)Transverse binary fission When division occurs along the transverse axis of the individual, e.g. Paramecium, diatoms, bacteria,Planaria.
(ii)Multiple fission The division of the parent body into many daughter organisms, e.g. Amoeba,Plasmodium, Monocystis (all Protozoa).
II.Budding, (torulation) an outgrowth or bud develops, grows, constricts at the base and separates from the parent body, e.g. yeast and Hydra. The complex budded condition is called torala stage.
III.Sporulation occurs by tiny, single-celled, thin-walled spores that are extremely resistant to environmental extremes. The spores form new individuals. It commonly occurs in Monera, Protista, Fungi and Algae.
Spores formed can be of following main types:
(i)Pseudopodio spore (with fine pseudopodia) –   Amoeba
(ii)Zoospores (motile with flagellated)    – Chlamydomonas and Ulothrix
(iii)Conidia (non-motile) – Penicillium
(iv)Sporangiospores (non-motile) – Rhizopus
(v) Gemmules (internal buds) –   Sponges
IV.Fragmentation occurs by breaking of the parent body into two or more parts, each of which grows to form an independent individual, e.g. algae like Spirogyra and bryophytes such as Marchantia, Riccia.
V.Regeneration is a type of asexual reproduction in which the missing part of the organism is repaired by the proliferation of cells, e.g. Hydra, planaria and sponges.
VI.Vegetative propagation is the formation of a new plants from vegetative parts like root, stem, leaf, etc., naturally, e.g. water hyacinth (scourage of the water bodies or Terror of Bengal) propagates very quickly by vegetative mode and drains out dissolved 02 from water bodies. Some artificial methods of vegetative propagation are also developed by the farmers like cutting, layering, grafting, etc.
Some examples of natural method of vegetative propagation are:
The units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb all have capability to give rise to new offsprings. These structures are known as vegetative propagules.

Reproductive health

State some reproductive health awareness among people.

.The improved reproductive health of society requires following factors:
(i)Better awareness about sex-related matters.
(ii)Increased number of medically assisted deliveries and better postnatal care leading to decreased maternal and infant mortality rates.
(iii)Increased number of couples with small families.
(iv)Better detection and cure of STDs.
(v)Overall increased medical facilities for all sex-related problems.
Molecular Basis of Inheritance

Explain structure of polynucleotide chain.

Structure of Polynucleotide Chain

(i)A nucleotide has three parts, i.e. a nitrogenous base, a pentose sugar (deoxyribose in DNA and ribose in RNA) and a phosphate group.
(ii)Nitrogenous bases are purines, i.e. adenine, guanine and pyrimidines, i.e. cytosine, uracil and thymine.
(iii)Cytosine is common for both DNA and RNA and thymine is present in DNA. Uracil is present in RNA at the place of thymine.
(iv)A nitrogenous base is linked to the pentose sugar through a N-glycosidic linkage to form a nucleoside, i.e. adenosine and guanosine, etc.
(v)When a phosphate group is linked to 5′ —OH of a nucleoside through phosphodiester linkage, a corresponding nucleotide is formed.
(vi)Two nucleotides are linked through 3′ -> 5′ phosphodiester linkage to form a dinucleotide.
(vii)Several nucleotides can be joined to form a polynucleotide chain.
(viii) The backbone in a polynucleotide chain is formed due to sugar and phosphates.
(ix)The nitrogenous bases linked to sugar moiety project from the backbone.
(x)The base pairs are complementary to each other.

Evolution

1.The study of history of life forms on earth is called evolutionary biology.

2.Evolution is a process that results in heritable changes in population spread over many generations leading to diversity of organisms on earth.

3.Origin of life is considered a unique event in the history of universe.
(i)The Universe

It is very old-almost 20 billion years ago. It contains huge galaxies.

Galaxies contain stars and clouds of gas and dust.

The origin of universe is explained by Big Bang theory.

The Big Bang theory states that a huge explosion occurred, the universe expanded, temperature came down and hydrogen and helium were formed later. The galaxies were then formed due to condensation of gases under gravitation.

(ii)The earth was supposed to have been formed about 4.5 billion years back in the solar system of the milkyway galaxy.

Water vapour, methane, carbon dioxide and ammonia released from molten masses covered the surface.

UV rays from the sun broke up water molecule into hydrogen and oxygen and lighter hydrogen escaped.

Oxygen combined with ammonia and methane to form water, carbon dioxide and others.

Ozone layer formed, as it cooled, the water vapour fell as rain to fill depression and form oceans.

Life appeared 500 million (about 4 billion years back) years after the formation of earth.

what points make previous year papers worth :

Acquaints students to the board format or exam format
To know which questions where most asked and which not
Which chapter questions were asked frequently (This will help determine the weightage that each of the topics carries)
The manner in which the questions were asked (Helps prepare how to format answers)
Aids in the proper management of time. Solving as many papers as possible aids in strengthening one’s grip in the subject. This makes one well abreast with solving different questions in the least time without the worry of losing marks or leaving any question unattempted.
One can understand the scoring pattern and thereby prepare their strategy and timetable.

CHSE BIOLOGY PREVIOUS YEAR QUESTION PAPER