[2 Mark Questions]

Question 12 Marks

Draw a labelled diagram of human eye. What is the significance of the blind spot?

Answer

Labelled diagram of human eye

Blind spot is a spot on the retina present at the point of origin of the optic nerve. Photo receptor cells are absent from this region.
They are insensitive to light as both rods and cones are absent.
An image formed there is not seen by the eye.

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Question 22 Marks

i. Construct a terrestrial food chain comprising four trophic levels.
ii. What will happen if we kill all the organisms in one trophic level?
iii. Calculate the amount of energy available to the organisms at the fourth trophic level if the energy available to the
organisms at the second trophic level is 2000 J.

Answer

Gross $\longrightarrow$ Rabbit $\longrightarrow$ Wolf $\longrightarrow$ Tiger
b. If all organisms of any one trophic level are killed then its previous trophic level organisms will increase in number to such an
extent that their previous trophic level will also become extinct and the next trophic level organisms will also get extinct. For
e.g., if we remove all wolves then rabbits will increase and will eat up all the grass, at the same time tigers will also perish
because of lack of their food.
c. Energy is transferred as per 10% law : Hence, if energy available at second trophic level is 2000 J then third trophic level will
have
$\frac{10}{100} \times 2000=200 J$ and fourth trophic level will have $\frac{10}{100} \times 200=20 J$

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Question 32 Marks

What is ozone? Show the reactions of formation of ozone from oxygen in the atmosphere? Name the pollutant and its role in depletion of ozone layer.

Answer

Ozone is a triatomic molecule made of three oxygen atoms. It is present as a layer in the stratosphere. It prevents the harmful UV rays of sun from reaching the surface of earth. Ozone is formed by absorption of UV rays coming from sun $O _2 \leftrightarrow O + O + O _2 \rightarrow O _3$
UV radiations splits oxygen molecules to oxygen atoms and the oxygen atoms combine with oxygen molecule to form ozone.
CFCs are mainly responsible for ozone layer depletion. CFCs release chlorine atoms which breaks ozone to oxygen. More
amounts of CFCs thus released will cause depletion of ozone layer.

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Question 42 Marks

a. Figure shows a concave mirror with its pole at P, focus F and centre of curvature C. Draw a ray diagram to
show the formation of image of an object AB.
b. State three characteristics of the image formed.

Answer

b. Characteristics of image formed:
i. Real and inverted
ii. Smaller in size or diminished.
iii. Formed between the focus F and the centre of curvature C of the mirror

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Question 52 Marks

What is lymph?

Answer

Lymph is the plasma and formed elements that have leaked out of the capillaries into extracellular environment. It carries food and wastes to the body cells outside the circulatory system. Lymph is formed from the fluid which leaks from blood capillaries and goes to the intercellular spaces in the tissues. This fluid is collected through lymph vessels and finally returns to the blood
capillaries. Lymph also plays an important role in the immune system.

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Question 62 Marks

Why respiration is called catabolic process?

Answer

Catabolism is the degradative processes of metabolism. It concerned with the breakdown of complex food molecules to simple ones, with a concomitant release of free energy. Respiration is a catabolic process because it involves the breakdown of complex organic substances into simpler ones by oxidation.

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Question 72 Marks

List two observations on the basis of which it may be concluded that the given slide shows binary fission in Amoeba.

Answer

i. Nucleus elongates
ii. Constriction in cytoplasm/c ll membrane
These are the two observations which shows binary fission in Amoeba.

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Question 82 Marks

Name the group of derivatives of hydrocarbons that have pleasant fruity smell. Explain with the help of chemical equation how these can be prepared? Name the process involved.

Answer

Group of derivatives of hydrocarbons that have pleasent fruity smell are esters. Which is derived by alcohol and carboxylic acid.
An example of esterification reaction is given below where ethyl ethanoate is formed which is an ester of ethanoic acid and
ethanol.
$\underset{\text { Ethanoic acid }}{ CH _3 COOH }+\underset{\text { Ethanol }}{ CH _2 CH _3 OH } \xrightarrow{\text { Conc. } H _2 SO _4} CH _3 COOCH _3 CH _3+ H _2 O$
The process is called esterification.

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