science pre 2

8/12/2019 Science Pre 2

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Question 13

13. (a) Name the four gases commonly present in biogas(b) List two advantages of using biogas over fossil fuels.

Sol: (a) Methane, carbon dioxide, nitrogen and hydrogen are the gases commonly present in biogas.(b) (i) Biogas is a renewable resource available in nature but fossil fuels are non-renewable.(iii) Biogas undergoes combustion completely without leaving any residue, thus causing less pollution. Fossil fuel cause

more pollution.(ii)Biogas is mainly produced from decomposing matter like cow dung, waste fodder, ever as coal, petroleum, gas etc are thefossil fuels.

Question 21

21. Write the functions of the following in the digestive process:1.Bile2.Bicarbonate secreted by the duodenal3.Pancreatic amylase.

A :1. Bile: - Bile emulsifies fats and neutralizes acids in partly digested food.

2. Bicarbonate secreted by the duodenal:- Bicarbonate secretion by the duodenal mucosa is accepted as the primary

important defence mechanism against the hydrochloric acid intermittently expelled from the stomach.

3.Pancreatic amylase: - The pancreas also makes amylase (alpha amylase) to break down dietary starch into di and

trisaccharides which are converted by other enzymes to glucose to supply the body with energy.

Question 22

22. Give reasons for the following:1. The glottis is guarded by epiglottis.2. The lung alveoli are covered with blood capillaries.3. The wall of trachea is supported by cartilage rings.

A:1. Epiglottis is thin elastic cartilaginous structure present on the roof of the tongue that folds over the glottis to prevent

food and liquid from entering the trachea during the act of swallowing.2. Exchange of gases takes place in alveoli of lungs The alveoli is permeable to molecular oxygen, carbon dioxide, and manyother gases. Blood capillaries allow sufficient oxygen diffusion.

3. The wall of trachea is supported by cartilage rings to prevent collapse of trachea C shaped cartilaginous rings arepresent.

Question23

23. Who proposed the Theory of Natural Selection? Explain this theory briefly.A. Darwin proposed the Theory of Natural Selection.

Natural selection is a process that occurs over successive generations.

If all the offspring that organisms can produce were to survive and reproduce, they would soon overrun the earth.

This unbounded population growth resembles a simple geometric series (2-4-8-16-32-64...) and quickly reaches infinity.

Organisms show variation in characters that influence their success in this struggle for existence. Individuals within a

population vary from one another in many traits.

Offspring tend to resemble parents, including in characters that influence success in the struggle to survive and reproduce.

Parents possessing certain traits that enable them to survive and reproduce will contribute disproportionately to the

offspring that make up the next generation.

To the extent that offspring resemble their parents, the population in the next generation will consist of a higher proportionof individuals that possess whatever adaptation enabled their parents to survive and reproduce.

Natural selection requires: - There must be heritable variation for some trait.

There must be differential survival and reproduction associated with the possession of that trait.

Question 24

Question 19

19.With the help of a labeled ray diagram, show the formation of image of an object by a compound microscope.

A compound microscope has an objective of focal length 0.5 cm and an eye-piece of focal length 2.5 cm. If its tube lengthis 25 cm, calculate what will be the magnifying power of the microscope.

Sol: The required labeled diagram, showing the formation of image by a compound microscope, is drawn below.


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We have magnifying power of a compound microscope

Where L = length of microscope tube, D = distance of distinct vision (=25cm),

=focal length of the objective lens and = focal length of the eyepiece.

The magnifying power of the given compound microscope is 500.

Question 21

21.State one of the evolutionary forces leading to the origin of a new species according to the synthetic theory ofevolution.Sol: Any change in gene frequency from one generation to the next leads to the origin of new species according to the

synthetic theory of evolution.

Question 22

22.Name the excretory units present in an earthworm.Sol: Nephridia are found attached to the septa, in the skin and on either sides of pharynx.

Question 23

23.A farmer floods his field everyday thinking that watering in this manner will result in a better yield of his wheat crop.

What will be the result of this action of the farmer?Sol: The farmer is watering the field to get more yield from the crop.

Question 24

24.Describe how the sex of the offspring is determined in the zygote in human beings.

Sol: All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus, thesex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome fromher father will be a girl, and one who inherits a Y chromosome from him will be a boy.

Question 25

25.State any two practices which can help in the protection of our environment.

Sol: 1. Control of pollutant release form industries into environment

2. AfforestationQuestion 26

26.Define nerve impulse. Which structure in a neuron helps to conduct anerve impulsea) towards the cell body?

b) Away from the cell body?

Sol: The nerve impulse is an electro-chemical process that travels down a neuron. This electrical signal transmitscommands from the brain to the motor nerves, and carries sensory messages from sensory nerves (skin, ears, nose, eyes, andtaste buds) to the brain. The transmission of nerve impulses from neuron to neuron is performed by neurotransmitters. Axonplays an important role in the conduction of nerve impulse.

A) Dendrites to cytonB) Cyton to axon

Question 28

28.What is potable water? State any four of i ts necessary characteristics.


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Sol: Potable water is water which is fit for consumption by humans and other animals. It is also called drinkingwater, in a

reference to its intended use.

Water that is suitable for drinking, culinary, or domestic purposes. The maximum chloride concentration is 250 mg/l.

Water that is free from disease-producing organisms, poisonous substances, chemical, biological, and radioactive

contaminants which would make it .

Physico-chemical properties of water should be maintained.

Drinking water must be away from sewage contamination.

30.With the help of a labeled diagram describe double fertilization in plants.Sol: Double fertilization in plants: Pollination is followed by fertilization in plants.After the pollen lands on a suitable stigma, it has to reach the female germ cell in the ovary.

The pollen tube grows out of the pollen grain through the style to reach the ovary.After fertilization, the zygote divides several times to form an embryo within the ovule.The ovule then develops a tough coat and gets converted into a seed.

The seed contains the future embryo which develops into seedling.The ovary develops and ripens to form a fruit.

The process of double fertilization occurs inside each embryo sac, in which two fusion, syngamy and triple fusion take place.When one male gamete fuses with the egg contained in the embryo sac of the ovule, this fusion of male and female gametesis called syngamy and its product is the zygote.The other male gamete fuses with two polar nuclei and this process is called triple fusion, where three nuclei are involved in

the fusion process, one male gamete and two polar nuclei.

Question 2323. What is the function of genes in an organism?

A: Hereditary characters are controlled by gene. It carries the complete information for making all proteins.

Question 24

24. Why is it necessary to conserve our environment?

A: To maintain the ecological balance between living organisms and nonliving organisms.

Question 25

25. Define the term 'pollution'. Describe UASB method of checking water pollution.A. Unwanted chemicals and harmful substances introduced into the environment causing pollution.UASB stands for

Upflow Anaerobic Sludge Bed.This is used for anaerobic purification o f waste water from sugar refining, beverage

industry, food and paper industry etc.

Question 26


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26. How are the following caused and what is the effect of each of them on our environment?

(i) Depletion of ozone layer (ii) Acid rain

A: i) Depletion of ozone layer by releasing catalytic destruction of ozone by Cl and Br, these two are released from

chlorofluorocarbon (CFC). It leads to a variety of biological consequences such as increases in damage to plant reduction of

plankton in oceans.

ii) Acid rains are caused by the human emission like S and N 2compounds react with atmosphere to produce acid rains. Theyshow adverse effect on forest, freshwater, killing insects, aquatic life forms and damage to buildings and having impacts on

human health.

Question 27

27. What is meant by soil erosion? Describe two practices by which soil erosion can be prevented.

A: Soil erosion is a natural process. It is one form of soil degradation along with loss of soil structure, Stalinization, nutrient

loss, soil acidity problems and compaction.1. Afforestation.2. Avoiding overgrazing and the over-use of crop lands

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