CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type


In situ conservation can help endangered / threatened species. Justify the statement.

In situ conservation involves the protection of species in their natural habitats. It helps in the conservation of
threatened/endangered species via following means :
(i) Biodiversity hotspots are regions with high levels of species richness and high degree of endemism (i.e. species confined to that region are not found anywhere else). Hotspots cover less than 2% of the earth’s land area.
(a) The total number of biodiversity hotspots in the world are 34.
(b) These hotspots are regions of accelerated habitat loss.
(c) Three hotspots which cover India’s biodiversity regions are Western Ghats and Sri Lanka, Indo-Burma and Himalaya.
(d) These hotspots can reduce the ongoing mass extinctions by almost 30%.
(ii) Protected areas are ecologically unique and biodiversity rich regions. These are legally protected as biosphere reserves, national parks and sanctuaries.
(a) India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries.
(b) The first national park set up in India was Jim Corbett National Park.
(iii) Sacred groves are forest areas set aside, all the trees and wildlife within it are venerated and given total protection. These are religious and cultural places, which are protected. Some of the sacred groves in India are: Western Ghat regions of Karnataka and Maharashtra.
Khasi and Jaintia Hills in Meghalaya. Aravalli Hills of Rajasthan. Sarguja, Chanda and Bastar areas of Madhya Pradesh.


 Multiple Choice QuestionsLong Answer Type


Discuss the role of healthy ecosystem services as a prerequisite for a wide range of economic, environmental and aesthetic goods and services.

Ecosystem services are the products of ecosystem processes. Forests are the major source of ecosystem services and are
prerequisite for environmental, aesthetic goods and indirect economic values in the following ways:
1. Environmental Values
(i) Carbon-fixation Huge amount of CO2 in the atmosphere is removed naturally and fixed by plants into organic
molecules and energy through photosynthesis. All the other trophic levels, i.e. consumers depend upon this
energy produced by them.
(ii) Release of oxygen by the producers as a byproduct in the process of photosynthesis, improves the air quality
and supports life on earth.
(iii) Soil Soil formation and soil protection are the major ecosystem services accounting for nearly 50% of their total
worth. Plant cover protects the soil from drastic changes in temperature. There is little wind or water erosion as
soil particles are not exposed to them. The soil remains spongy and fertile. There are not landslides and no floods.
(iv) Nutrient cycling There is no depletion of nutrients, but the same are repeatedly circulated.
2. Economic Value
(i) Ecosystem services provide certain economical important products also. These include timber, paper, rubber,
wax, medicines, cosmetics, resins, etc.
(ii) Ecosystem also provides other benefits such as aid in pollination. Bees and other insects of natural ecosystem visit
nearby farmlands to pollinate crops.
3. Other aesthetic values Natural ecosystems are a source of spiritual, cultural and aesthetic values.


 Multiple Choice QuestionsShort Answer Type


Why do lepidopterans die when they feed on Bt cotton plant? Explain how does it happen.

Bt cotton plants are the transgenic plants that express a Bacillus thuringiensis gene called cry gene. This gene, encodes for protein crystals having insecticidal properties against insects of group Lepidoptera, Diptera and Coleoptera. Inside the bacterium, these proteins remain inactive and does not harm the bacteria. However, these inactive crystals can get activated in the alkaline pH of the gut of insects upon ingestion. After activation, these crystals can bind to the receptors present on the membranes of gut epithelial cells. Due to this binding, the membrane swells and pores are created on them. These pores lead to bursting of cell. Hence, soon the lepidopteran die due to starvation.


 Multiple Choice QuestionsLong Answer Type


State and explain the ‘law of independent assortment’ in a typical Mendelian dihybrid cross.

Law of Independent Assortment (Third law) is based on inheritance of two genes, i.e. dihybrid cross which states that when two pairs of contrasting traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters. These factors randomly rearrange in the offspring producing both parental and new combination of characters means inheritance of one character does not affect the inheritance of another character and both characters
assort independently. The Punnett square can be used to understand the independent segregation of the two pairs of genes during meiosis. Linkage is the exception of law of independent assortment.



(a) Arrange the following hormones in the sequence of their secretion in a pregnant woman.
(b) Mention their source and the function they perform.

(a) The sequence of secretion of the given hormones in a pregnant woman is:




Public all over India is very much concerned about the deteriorating air quality in large parts of North India. Alarmed by this situation the Resident’s Welfare Association of your locality organised an awareness programme entitled ‘Bury not burn’. They invited you, being a biology student to participate.
(a) How would you justify your arguments that promote burying and discourage burning?
(Give two reasons)
(b) With the help of flow charts, one for each practice, depict the chain of events that follow.

(a) Following arguments can be put forward to promote burying and discourage burning:
(i) When we burn wastes, pollutants such as carbon dioxide,NO2 , SO2 , etc. are released in the atmosphere. These
pollutants damage the environment. Due to burning, smoke is released into atmosphere which causes
problems like asthma, emphysema, etc.
(ii) Burying the waste does not have any harmful effect in fact when we bury organic wastes, the soil becomes
enriched with nutrients.
(b) The solid wastes are of two types:
Biodegradable wastes These can be degraded by the microbes, e.g. organic waster paper, etc.
Non-biodegradable wastes These cannot be degraded by the microbes and can remain as such for long periods,
e.g. plastic.
Flow charts depicting effects of burying and burning are: