Subject

biology

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsLong Answer Type

31. Explain the salient features of Hugo de Vries theory of mutation. How is Darwin theory of natural selection different from it? Explain.


Hugo de Vries based on his work on evening primrose suggested that variations occurred due to mutations. Hugo de Vries gave the name saltation (single step large mutation) to the mutations that brought about speciation. Darwin aboard the H.M.S Beagle observed that all existing living forms share similarities among themselves and also with other life forms that existed millions of years ago of which many are extinct. The evolution of life forms has been gradual and those life forms better fit in environments that leave more progeny. This is called natural selection and is a mechanism of evolution. Mutations are random and directionless while the variations that Darwin talked about were small and directional.
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32.

(a) What is El Nino effect? Explain how it accounts for biodiversity loss.

(b) Explain any three measures that you as an individual would take, to reduce environmental pollution.


(a) An El Nino event is a temporary change in the temperature, surface air pressure and currents of the Pacific Ocean in the region surrounding the equator. It affects both the ocean and atmosphere and can have major effects on the world's climate. El Nino causes global warming and the melting of polar ice cap. This leads to the submerging of coastal regions and loss of species endemic to that area. As El Nino also affects the ocean currents and causes sudden cooling or warming of the oceans, it leads to the death of marine life such as coral reefs and fishes as well. The depletion of coral reefs, in turn affects the life of other marine organisms that depend on the coral reefs for food and shelter.

(b) The measures that we as an individual can take in order to reduce environmental pollution can be

(i) Dumping of organic waste in places far from residential areas.

(ii) Using car pool so as to reduce pollution and fuel consumption.

(iii) Turning off air conditioners when not in use.

(iv) Planting more and more trees and reducing the deforestation.

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33.

(a) Name the primates that lived about 15 million years ago. List their characteristic features.

(b) (i) Where was the first man-like animal found?

(ii) Write the order in which Neanderthals, Homo habilis and Homo erectusappeared on earth.

State the brain capacity of each one of them.

(iii) When did modern Homo sapiens appear on this planet?


(a) Dryopithecus (ape-like) and Ramapithecus (man-like) were the two primates that lived 15 million years ago. These primates were hairy and their walk was similar to that of chimpanzees.

(b) (i) The first man-like animal was found in Africa.

(ii) 

Year

Evolution

Brain capacity

2 million years ago

Homo habilis (Australopithecines) lived in East Africa

650- 800 cc

1.5 million years ago

Homo erectus

900 cc

1,000 - 40,000 years ago

Neanderthal man

1400 cc


(iii) Modern Homo sapiens first appeared primarily in east Africa about 75,000 to 10,000 years ago.
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34.

(a) Explain primary productivity and the factors that influence it.

(b) Describe how do oxygen and chemical composition of detritus control decomposition?


(a) The amount of biomass produced per unit area over a time period by plants during photosynthesis is defined as the primary productivity. It is expressed as weight or energy. Productivity can be mainly divided into gross primary productivity (GPP) and net primary productivity (NPP). GPP is the rate of production of organic matter during photosynthesis.

Primary productivity is directly proportional to the amount of carbon dioxide, sunlight and water. It is inversely proportional to respiratory losses. NPP = GPP - Respiratory losses (R)

(b) Decomposition is an oxygen consuming process thus it is directly proportional to the concentration of the oxygen in the environment. It is controlled by the chemical composition of detritus and climatic conditions. The decomposition rate decreases when the detritus is rich in lignin and chitin while it is quicker if the detritus contains nitrogen and water-soluble substances such as sugars.

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35.

(a) Write the specific location and the functions of the following cells in human males:

(i) Leydig cells

(ii) Sertoli cells

(iii) Primary spermatocyte

(b) Explain the role of any two accessory glands in human male reproductive system.


(a) (i) Leydig cell are found adjacent to the seminiferous tubules in the testes. They synthesize and secrete testicular hormones called androgens (testosterone).

(ii) Sertoli cells are found in the seminiferous tubules. They act as nurse cell and provide nutrition to the male germ cells.

(iii) Primary spermatocytes are present in the testes. They are diploid cells that are derived from the spermatogonia. They undergo meiotic division to give rise to secondary spermatocyte and thereby male gamete-sperm.

(b) The male accessory glands include the seminal vesicles, prostate gland, and the bulbourethral glands whose secretions constitute the seminal plasma, which provides energy and motility to the sperms until they reach the ovum.

Prostate Gland: It stores and secretes an alkaline, milky fluid known as pre-ejaculate. The purpose of the alkalinity of the semen is to neutralize the acidity of the vaginal tract.

Bulbourethral glands: This gland secretes a viscous secretion during sexual arousal. This fluid helps to lubricate the urethra for easy passage of spermatozoa to pass through, and to help flush out any residual urine or foreign matter.

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