Class X – Science Practice Paper – 6 – Answer

Ans. (d)

Graphite is a good conductor of electricity and heat. It has weak intermolecular forces between its layers. Hence it has de-localized electrons. As electrons are free to move through its structure, it conducts heat and is a good conductor of electricity.

Ans. (c)

Calcium hydroxide, when dissolved in water, is an exothermic reaction and produces an alkaline media.

Ans. (d)

Ans. (a)

Ans. (c)

Each DNA molecule consists of two twisted strands of bases that form a shape called a double helix. The two strands are held together by hydrogen bonds between pairs of bases.

Ans. (b)

Because the screen is on the same side of the object which means it is never a lens because it happens behind the lenses in such case. Moreover concave mirror forms real images i.e., image can be obtained on a screen.

Ans. (b)

Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum subspecies pallidum.

The human immunodeficiency virus (HIV) is a lentivirus (a subgroup of retrovirus) that causes HIV infection and over time acquired immunodeficiency syndrome (AIDS)

Gonorrhea is an infection caused by the bacterium Neisseria gonorrhoeae. It not only affects the reproductive tract, but can also affect the mucous membranes of the mouth, throat, eyes and rectum.

Trichomoniasis (or trich) is a very common sexually transmitted disease (STD). It is caused by infection with a protozoan parasite called Trichomonas vaginalis

Ans. (a)

In the nervous system, a synapse is a structure which serves as Junction between neuron that permits a neuron to pass an electrical or chemical signal to another neuron.

A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals that is why it is the largest cell in the human body.

Olfactory receptors are responsible for detection of odorants which give rise to the sense of smell.

Thermoreceptors are able to detect head and cold and are found throughout the skin in order to allow sensory reception throughout the body.

Ans. (b)

KOH absorbs the CO₂ gas so, in the absence of KOH, CO₂ gas turns lime water milky.

Ans. (c)

Ans. (b)

Ans. (d)

Non-metals are electronegative. They do not provide free electrons. Hence they do not replace hydrogen from acids.

Ans. (d)

Ans. (b)

Ans. (a)

The exothermic process is the one that releases an enormous amount of heat. When water reacts with water and acid reacts with water it releases an enormous amount of heat.

Ans. (d)

During electrolysis of a concentrated aqueous solution of sodium chloride. Ions get attracted to oppositely charged electrodes, sodium is produced at the anode and chlorine gas is produced at the cathode.

Ans. (a)

Ans. (c)

Digestion breaks large complex organic molecules to simple smaller ones which can be easily absorbed. However, certain molecules such as glucose, vitamin C etc. do not need any digestion before their absorption.

Ans. (a)

Ans. (a)

Ans. Scavengers feed upon discarded and dead waste. Microorganisms are called scavengers of the environment because they decompose dead bodies of plants and animals present in the soil and help in cleaning the environment by removing waste products. They lie at the top of food chain.

Ans. Glass slab: It is rectangular in shape and made up of glass. In glass slab, the direction of the incident ray and the emergent ray of light are parallel to each other.

Glass Prism: It has two triangular sides, two inclined rectangular sides, and one rectangular base. In glass prism, the direction of the incident ray and the emergent ray of light is not parallel to each other.

When a narrow beam of monochromatic light passes through:

• Glass slab: It deviates from the actual path but the direction of the incident ray and the emergent ray of light are parallel to each other.
• Glass prism: It has deviated from the actual path but the direction of the incident ray and the emergent ray of light are not parallel to each other.

When a narrow beam of white light passes through:

• Glass slab: The splitting of white light into its constituent color does not occur. And the direction of the incident ray and the emergent ray of light are parallel to each other.
• Glass prism: The splitting of white light into its constituent seven colours occurs. And the direction of the incident ray and the emergent ray of light is not parallel to each other.

1. Retina, it is a sensory membrane where image is formed.

2. Ciliary muscles, it changes the focal length of the lens.

3. Pupil, aperture through which light enters

4. Eye lens, focus light onto the retina

Ans. Power of a lens is defined as the reciprocal of its focal length f (in metres)

The SI unit of power of a lens is Diopter. The power of a converging lens is positive as f is positive.

Ans. Root hairs have thin walls. Due to this, water enters the root hairs because of osmosis. Water from root hairs continuously moves into the root xylem. To maintain the osmotic gradients, the cells of root hairs take up ions from the soil.

Ans. Denatured alcohol is ethanol made unfit for human consumption by adding one or more chemicals (denaturants) to it. Denaturing refers to removing a property from the alcohol (being able to drink it), not to chemically altering or decomposing it, so denatured alcohol contains ordinary ethyl alcohol.

Ans. If someone consumes denatured alcohol, it results in coagulation of protoplasm causing acute nausea, blindness and even death.

Ans. In aqueous solutions, strong acids ionize completely and provide hydronium (H₃O⁺) ions. On the other hand, weak acids are partially ionized and an aqueous solution of same molar concentration provides a much lesser concentration of hydronium ions.

Strong acids – Hydrochloric acid, sulphuric acid, nitric acid (Mineral acids are strong acids)

Weak acids – Citric acid, acetic acid, formic acid (Organic acids are weak acids)

Ans. The amount of waste for disposal can be reduced by:

(a) Separation of biodegradable and non-biodegradable waste at source.

(b) Decomposing the bio degradable waste & producing manure or bio-gas from it.

(c) Recycling non-biodegradable waste like plastic, metal cans etc.

Ans. It will not react with dry litmus paper.

Ans. The gas will bleach moist litmus paper

Write a balanced chemical equation for the reaction taking place.

The balanced chemical equation is

S + O₂ — > SO₂

Ans. i) If image is of same size, laterally inverted and erect, it is plane mirror.

ii) If image is bigger or smaller in size and inverted or erect, it is concave mirror.

iii) If image is smaller in size and erect as in rear view mirror, it is convex mirror

Ans. Photosynthesis is a process by which green plants having chlorophyll can synthesize simple sugar (glucose) from water and CO2 using the energy of sunlight. The light energy is used in a splitting of water molecules into hydrogen and oxygen (i.e., chemical energy)

Autotrophs: The organisms which can synthesize their own food from inorganic substances present in the environment are called autotrophs. An autotrophs or primary producer, is an organism that produces complex organic compounds, e.g. Green plants, autotrophic bacteria etc.

Ans. Chloroplasts: Chlorophyll is the green pigment capable of trapping light energy required during photosynthesis. This pigment is present in the chloroplast of leaves of all green plants.

Ans. guard cells are present in the stomata under the leaves rim. Each stomatal pore is surrounded by a pair of guard cells, that control their opening and closing by the inflow and outflow of water.

Ans. Heterotrophs: The organisms which cannot make their own food from inorganic substances and depend on other organisms for their food are called heterotrophs, e.g. all animals, yeast, most bacteria, etc.

Ans. Pepsin: It is a protein-digesting enzyme secreted from gastric glands present in the walls of the stomach, an enzyme in the stomach that begins the digestion of proteins by splitting them into peptones (see peptidase). It is produced by the action of hydrochloric acid on pepsinogen, which is secreted by the gastric glands.

Ans. DNA copies generated will be similar, but may not be identical to the original as some variation are so drastic that new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell will simply die. Therefore, there could be many other variations in the DNA copies that would not lead to such a drastic outcome. Thus, the surviving cells are similar but slightly different from each other. This tendency of variation during reproduction is the basis for evolution.

Ans. This special tissue that provides nutrition is called the placenta.

Ans. Besides providing nutrition to the embryo, placenta helps in removing waste products from embryo, it also helps in providing oxygen to the embryo and eliminating carbon dioxide from embryo.

Ans. The placenta is a disc like structure that is attached to the wall of the uterus. It is formed by two sets of a minute finger-like process called villi. One set from uterine wall and other set from the embryo. The blood flows through the fine capillaries of the placenta.

Ans. This student is unable to see far off objects. This means that the student is suffering from myopia. Doctor will prescribe a concave lens of a suitable focal length.

Ans. The conditions to obtain permanent electromagnet, if a current carrying solenoid is used, are given as follow:

i) The current through the solenoid should be direct current.

ii) The rod inside the solenoid must be made of a magnetic material.

iii) The magnetic material should be of high retentivity.

Ans. Plants also perform chemical coordination for various activities with the help of hormones. These are the chemical compounds released by stimulated cells that diffuse to various locations in plants performing different functions. These hormones produced by plants are also called as phyotohormones.

Different types of hormones produced by plants are: Auxin, Gibberellins, Cytokinins, Abscisic acid, ethylene.

The physiological effect of each plant hormone (called phytohormone) is described in following table

Ans. The brain is covered by a three layered system of membranes; called meninges, Cerebrospinal fluid is filled between the meninges. The CSF provides a cushion to the brain against mechanical shocks. The brain is located inside the skull for maximum protection. The human brain can be divided into three regions, viz. forebrain, midbrain and hindbrain.

Forebrain: It is divided into three regions:

1. Olfactory Lobes –  These lobes receive impulses from olfactory receptors of nose region.

2. Cerebrum – It is the largest part of the brain and help in speech, intellectuality, mapping, hearing, sight, taste, smell, etc.

Diencephalon – It has Hypothalamus which has control centre for hunger, thirst, sweating, emotions, etc.

Midbrain: It controls the reflex movements of head, neck and trunk in response to visual and auditory stimuli, changes in pupil size, etc.

Hindbrian: It consists of three parts:

1. Cerebellum – It maintains posture, equilibrium and muscle tone.

2. Pon Varolii – It controls some aspects of respiration

3. Medulla Oblongata – It controls heart rate, breathing movements, coughing, sneezing, vomiting, etc.

Ans. H₂SO₄ test tube i.e., A will show vigorous reaction.

Ans. It is because H₂SO₄ is strong acid than H₂CO₃

Ans. Hydrogen gas will be formed. Bring a burning splinter near the gas. It will burn with a ‘pop’ sound. It shows gas liberated is hydrogen.

Mg + H₂SO₄ — > MgSO₄ + H₂

Mg + H₂CO₃ — > MgCO₃ + H₂

Ans. Since H₂SO₄ is more acidic A will have lower pH

Ans. H₂CO₃ is a weak acid B will have lower concentration of H⁺

Ans. Some salts crystalline out from their saturated aqueous solutions with a definite number of molecules of water called water of crystallization. Such salts are called hydrated salts. These molecules of water of crystallization are in loose chemical combination with the salt. This water of crystallization is given out by heating the powdered crystals of these salts above 100°C

On heating these hydrated crystalline salts, they lose water of crystallization and (i) become amorphous (ii) Lose their colour, if coloured and become white.

Eg. CuSO₄.5H₂O – Copper sulphate pentahydrate

Na₂CO₃.10H₂O – Sodium carbonate decahydrate

Na₂SO₄.10H₂O – Sodium sulphate decahydrate

Ans. Magnetic field due to circular conductor: When a current is passed through a circular coil in clockwise direction, the magnetic field will be as shown in figure

Here the current is passing clockwise when looked from front side. At the points where the conductor passes through horizontal plane, the lines of force are almost circular, their direction being given by right hand grip rule. Near the central region, the lines are quite straight and at right angles to the plane of the coil.

Further, it is clear from the figure that all the lines enter at the nearer face and leave at the farther face. Evidently, the lines of force due to the current flowing in circular loop closely resemble those produced by a magnetized circular disc of steel of same boundary as that of the coil, so that one face of it is north and other a south pole. The polarity of any face of coil can be determined by remembering a simple rule known as clock rule. If the current round any face of the coil flows in an anticlockwise direction it behaves like a north pole and if the current is in clockwise direction, the face acts as a south pole.

Ans. 400

Since this pea plant is heterozygous for the round shape, its genotype would be Rr.

Phenotypically, the ratio will be 3:1 i.e., only rr seedlings will show wrinkled seed phenotype, rest will show round seed shape.

1200 — > Round shape (RR, Rr) 400 — > Wrinkled (rr)

Ans. Dominant and recessive phenotypes will be 50% each.

A represents the dominant gene and ‘a’ represents its recessive allele. The most likely result in the first generation offspring when Aa is crossed with aa is:

Ans. Self-pollination of homozygous tall F₂ plant (TT) will give rise to all individuals of genotype TT.

Individuals carrying two identical alleles (RR or rr) are known as homozygous