Z1xyw 1 Answer Key

[Karriem Drewery]

Question6.

Walking in a straight line and riding a bicycle are the activities which are possible due to a part of the brain. Choose the correct location and name of this part from the given table:

Question 22.

(a) List two differences between the movement of leaves of a sensitive plant and the movement of a shoot towards light.

OR

(b) What happens at synapse between two neurons? State briefly.

Answer:

Question 23.

Give the name of the enzyme present in the fluid in our mouth cavity. State the gland which produces it. What would happen to the digestion process if this gland stops secreting this enzyme?

Answer:

Salivary amylase is present in the fluid in our mouth cavity. The Salivary glands in our mouth produce saliva. If this gland stops secreting Saliva, the digestion of starch will not occur in the mouth. Also wetting of food will not occur, as a result, swallowing of food will become difficult.

(c) (i) The chemical reaction between sulphur dioxide gas and acidified potassium dichromate solution is characterised by a change in colour from orange to green.

(ii) When a piece of iron metal is placed in copper sulphate solution, then iron sulphate solution and copper metal are formed. Also the deep blue colour of copper sulphate solution fades and light green solution forms.

(d)

Question 31.

State reasons for Myopia. With the help of ray diagrams, show the

(a) image formation by a myopic eye, and

(b) correction of myopia using an appropriate lens.

Answer:

(a) Myopia is the defect of the eye vision due to which a person can see the near objects clearly, but he cannot see the far objects clearly.

Causes of myopia. Myopia is caused

. due to the elongation of the eye ball.

. due to decrease in the focal length of the eye lens. The eye lens becomes more convergent.

(b) Myopia can be corrected by using a concave lens of suitable focal length in the spectacles of such a person.

Question 32.

What is a solenoid? When does a solenoid behave as a magnet? Draw the pattern of the magnetic field produced inside it showing the directions of the magnetic field lines.

Answer:

The solenoid is a long coil containing a large number of close turns of insulated copper wire. When an electric current is passed through the solenoid, it produces a magnetic field around it. The magnetic field produced by a current-carrying solenoid is similar to the magnetic field produced by a bar magnet.

Question 33.

(a) Write the percentage of (i) solar energy captured by the autotrophs and (ii) energy transferred from autotrophs to the next level in a food chain.

(b) What are trophic levels? Why do different food chains in an ecosystem not have more than four to five trophic levels? Give reason.

Answer:

(a) (i) Autotrophs trap 1% of solar energy.

(ii) Autotrophs transfer 10% of energy to the next level in a food chain.

(b) The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. In a food chain, each step representing an organism forms a trophic level. When green plants in an ecosystem are eaten by primary consumers, a great amount of energy is lost as heat to the environment, some amount goes into digestion and in doing work and rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers.

Since very little energy is available for the next level of consumers, food chain generally consists of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

(b)

In this reaction, concentrated sulphuric acid acts as a dehydrating agent which removes water molecule from the ethanol molecule.

(ii) The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation. The process of hydrogenation takes place in the presence of nickel or palladium metal as catalyst.

The process of hydrogenation has an important industrial application. It is used to prepare vegetable ghee (or Vanaspati ghee) from vegetable oils.

Question 35.

Give reason for the following:

(a) During reproduction inheritance of different proteins will lead to altered body designs.

(b) Fertilization cannot take place in flowers if pollination does not occur.

(c) All multicellular organisms cannot give rise to new individuals through fragmentation or regeneration.

(d) Vegetative propagation is practised for growing only some type of plants.

(e) The parents and off-springs of organisms reproducing sexually have the same number of chromosomes.

Answer:

(a) The DNA in the nucleus of the cell is the information source for making proteins. If the information is changed during DNA replication, different proteins are formed leading to changes in body design.

(b) For fertilization the male gamete should combine with the female gamete. So it is necessary that first the pollen grains from the anther of stamen should be carried to the stigma of carpel. Pollination is the process of transferring of pollen grains from the anther of a stamen to the stigma of a carpel.

(d) Vegetative propagation usually involves the growth and development of one (or more) buds present on the old part of the plant to form a new plant. These buds are in dormant state (inactive state) in the old part of the plant. When provided suitable conditions these buds grow to form new plants. So only those plants which have these dormant buds in their body parts like stem, root, etc. can be grown by vegetative propagation.

(e) In sexual reproduction, the chromosomes from two gametes male and female gametes, combine together to form zygote but the number of chromosomes does not get doubled because the gametes are special type of cells which contain only half the number of chromosomes as compared to the normal body cells of an organism. For example, human sperm has 23 chromosomes and human ovum also has 23 chromosomes. Thus, after fertilization the zygote will have 23 + 23 = 46 chromosomes, which is the normal number of chromosomes of a human being.

(ii) If one bulb gets fused, the entire circuit will break in a series connection so the flow of current will stop. Thus, all the three bulbs will stop glowing in a series connection. In a parallel connection, if one bulb gets fused, the current will continue to flow into other two bulbs. Thus, in parallel connection, the other two bulbs will continue to glow.

Question 37.

On the basis of reactivity metals are grouped into three categories

(i) Metals of low reactivity

(ii) Metals of medium reactivity

(iii) Metals of high reactivity .

Therefore metals are extracted in pure form from their ores on the basis of their chemical properties.

Metals of high reactivity are extracted from their ores by electrolysis of the molten ore. Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.

(a) Name the process of reduction used for a metal that gives vigorous reaction with air and water both.

(b) Carbon cannot be used as a reducing agent to obtain aluminium from its oxide. Why?

(c) Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reactions involved in the process.

OR

(c) Differentiate between roasting and calcination giving chemical equation for each.

Answer:

(a) Electrolytic reduction. The Na (sodium) is a metal which has a very high affinity to oxygen. So reducing agent like carbon, aluminium cannot reduce oxygen from the oxide of sodium.

(b) Ahiminium (Al) has more affinity to oxygen than carbon. Therefore carbon cannot reduce , aluminium oxide to aluminium.

(c) Mercury is a less reactive metal. Its oxide is easily reduced to metal only by simply heating. Cinnabar being a sulphide ore is first roasted in air to change it into its oxide compound. Mercury oxide (HgO) on further heating in air gets reduced to give Hg metal.

OR

(c)

(b) In some animals sex is not determined genetically but it is controlled by the environ-mental factors. For example, In a turtle, high incubation temperature leads to the develop-ment of female offsprings while in the lizard, high incubation results in male offsprings.

(c) In human beings, the sex of the baby is determined by the type of sperm that fuses with the ovum. As human male produces two types of sperms in equal proportion, so there are 50% chances of a male baby and 50% chances of a female baby.

OR

(c) A female has two X chromosomes but no Y chromosomes. Therefore, all the female gametes, i.e., ova will have only X chromosomes.

Question 39.

A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distances with these mirrors as shown in the following table.

Question 5.

Given below are two columns, Column-I shows enzymes secreted by the glands in the alimentary canal of human beings and Column-II indicates the components of food on which enzymes act. Choose the options showing correct matching:

Question 31.

A reddish brown metal used in electrical wires when powdered and heated strongly turns black. When hydrogen gas is passed over this black substance, it regains its original colour. Based on this information answer the following questions:

(a) Name the metal and the black substance formed.

(b) Write balanced chemical equations for the two reactions involved in the above information.

Answer:

(a) The reddish brown metal is copper and the black substance formed is copper (II) oxide, i.e., CuO.

3a8082e126