CTET Science Paper 2 MCQs with Answers Set 03

Answer: (c) The direction of field lines inside the magnet is from the North pole to the South pole

Explanation:
1. Field lines never cross, are closed curves, and are crowded near the poles where the field is strong.
2. Inside a magnet they run from the south pole to the north pole, so the statement in (c) is wrong.

Teacher's Note:
1. Outside the magnet the lines go from north to south and inside from south to north, closing the loop.
2. Closeness of lines shows field strength.

Answer: (b) Amla

Explanation:
1. Bleeding gums and weakness are signs of scurvy, caused by vitamin C deficiency.
2. Amla is very rich in vitamin C.

Teacher's Note:
1. Citrus fruits, guava and tomatoes also give vitamin C.
2. Cooking destroys much of the vitamin C.

Answer: (d) Sodium hydroxide

Explanation:
1. Sodium benzoate, sodium metabisulphite and common salt (sodium chloride) are used to preserve food.
2. Sodium hydroxide is a strong caustic base that is not a food preservative.

Teacher's Note:
1. Common salt preserves pickles, fish and meat.
2. Do not confuse caustic soda with edible chemicals.

Answer: (b) Mold

Explanation:
1. Amoeba, Euglena and Paramecium are single-celled protists.
2. Moulds are multicellular fungi made of thread-like hyphae.

Teacher's Note:
1. Yeast is the unicellular fungus.
2. Euglena has both plant and animal features but is still a single cell.

Answer: (c) (A) is true but (R) is false

Explanation:
1. Shrillness is pitch, which depends on frequency; a whistle has a higher frequency than a drum, so A is true.
2. Amplitude controls loudness, not shrillness, and a drum usually vibrates with larger amplitude, so R is false.

Teacher's Note:
1. Pitch relates to frequency and loudness to amplitude.
2. Do not mix up shrill and loud.

Answer: (d) Only D

Explanation:
1. An open-ended question has many acceptable answers.
2. D has many possible answers, while A, B and C each have a definite, limited answer.

Teacher's Note:
1. 'What if' questions are typical open-ended questions.
2. Questions with one correct answer are closed.

Answer: (a) reduce fluid drag

Explanation:
1. A streamlined shape lets water flow smoothly around the hull.
2. This reduces the resistance (drag) of the fluid.

Teacher's Note:
1. Buoyancy depends on the volume displaced, not on the shape's smoothness.
2. Fish and aircraft are streamlined for the same reason.

Answer: (b) replace one cell with a piece of metal wire

Explanation:
1. Replacing one cell with a metal wire halves the voltage, so the current and the brightness fall.
2. Chalk is an insulator and would stop the current, while removing a bulb or adding a cell makes the remaining bulb brighter.

Teacher's Note:
1. Brightness grows with current.
2. Replacing a bulb with a wire lowers resistance and increases the current.

Answer: (b) A-sand, B-clay, C-silt

Explanation:
1. Sand has large particles, so water drains fast and little is held: A is sand.
2. Clay has very fine particles, holds a lot of water, drains slowly and is rich in humus: B is clay.
3. Silt lies in between: C.

Teacher's Note:
1. Order of particle size: sand > silt > clay.
2. The finer the soil particles, the greater the water-holding capacity.

Answer: (c) The periodic tests should have both a written and an experimental component.

Explanation:
1. Current thinking favours continuous and comprehensive assessment covering both theory and practical skills.
2. Ranking and heavy weightage to annual exams go against this view, and open-book tests are accepted.

Teacher's Note:
1. Science assessment should test process skills as well as knowledge.
2. Avoid ranking children against each other.

Answer: (c) Water, Virus, Virus

Explanation:
1. Typhoid is caused by bacteria (Salmonella typhi) and spreads through contaminated water and food, so X is water.
2. Measles is a viral disease (Y = virus), and dengue is caused by the dengue virus spread by Aedes mosquitoes (Z = virus).
3. So X, Y, Z are Water, Virus, Virus.

Teacher's Note:
1. Malaria is the protozoan disease spread by a mosquito; dengue is viral.
2. Typhoid and cholera are classic water-borne diseases.

Answer: (a) Scientific concepts have to be linked to learner's local and global environment

Explanation:
1. NCF 2005 describes environmental validity as linking science to the learner's local and global environment.
2. The other options narrow it to conservation, expert assessment or separate chapters.

Teacher's Note:
1. Validity criteria in NCF: cognitive, content, process, historical, environmental and ethical.
2. Environmental validity is about relevance to the surroundings.

Answer: (b) Communicating

Explanation:
1. Students collect data and present it in a suitable pictorial form such as a bar chart or pie chart.
2. Presenting data to others in graphic form is communicating.

Teacher's Note:
1. Communicating includes drawing, graphs, tables and oral reports.
2. Prediction and hypothesis concern future outcomes or explanations.

Answer: (a) Plant growth would be a dependent variable

Explanation:
1. The factor deliberately varied (light colour) is the independent variable.
2. The outcome that is measured (plant growth) is the dependent variable.
3. Factors kept constant, such as plant type, are controlled variables.

Teacher's Note:
1. Independent = changed, dependent = measured, controlled = kept same.
2. A common mistake is to call the changed factor the dependent variable.

Answer: (c) Predict the change in current due to change in voltage

Explanation:
1. Stating, recalling and identifying are memory-level tasks.
2. Predicting the effect of changing voltage needs understanding of the relation between V and I.

Teacher's Note:
1. Application and prediction show understanding; recall does not.
2. Look for verbs like predict, explain, apply for higher-order thinking.

Answer: (d) The concept of electric charge is introduced before introducing electricity

Explanation:
1. In options a to c, observable things come first and the abstract idea later.
2. In option d, the abstract idea of charge is taught before the observable phenomenon of electricity, which reverses the order.

Teacher's Note:
1. Concrete to abstract means observed examples first, then the concept.
2. Check which option puts the abstract idea first.

Answer: (d) 9:1

Explanation:
1. Mass = density × volume, and volume ∝ r³.
2. m(A)/m(B) = (3³ × 1)/(1³ × 3) = 27/3 = 9.
3. So the ratio is 9:1.

Teacher's Note:
1. Volume depends on the cube of the radius, not the radius itself.
2. Using r instead of r³ gives the wrong 3:1.

Answer: (a) Both R1 and R2 are correct but R1 provides the correct explanation for A

Explanation:
1. A virtual image forms where rays only appear to meet, no real light reaches that point, so it cannot be caught on a screen (R1 explains A).
2. Virtual images by mirrors and lenses are always erect (R2 is true) but erectness does not explain why they cannot be projected.

Teacher's Note:
1. A real image has actual rays meeting; a virtual image does not.
2. Being erect is a property of the image, not the reason it fails to appear on a screen.

Answer: (c) Amoeba, Paramecium

Explanation:
1. Amoeba and Paramecium are unicellular and divide into two by binary fission.
2. Yeast and Hydra reproduce by budding, and the cockroach reproduces sexually.

Teacher's Note:
1. Budding: yeast, Hydra. Binary fission: Amoeba, Paramecium.
2. Yeast is a frequent trap because it is also unicellular.

Answer: (d) Ask students to vote on which of four given organs is most important and ask a few students to explain why.

Explanation:
1. A hook must draw on what students already know and also arouse interest.
2. Voting on the most important organ and explaining why uses prior ideas about organs and sets up the need to study the heart.
3. Option b only asks for a preference and uses no prior knowledge; option c needs knowledge students lack.

Teacher's Note:
1. A good hook is brief, engaging and linked to prior knowledge.
2. The source key was b, which does not use existing knowledge; changed after review, so please double-check.

Answer: (a) A is true and B is false

Explanation:
1. Chemical changes form new substances and are usually irreversible, so A is true.
2. Physical changes need not change state (e.g. stretching a rubber band, dissolving salt), so B is false.

Teacher's Note:
1. Change of state is only one kind of physical change.
2. Words like 'always' in a statement often make it false.

Answer: (a) (a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)

Explanation:
1. Algae make their own food (autotrophic); Amoeba ingests food (holozoic).
2. Cuscuta is a parasitic plant; mushroom is a saprophyte.
3. This gives (a)-(iii), (b)-(ii), (c)-(iv), (d)-(i).

Teacher's Note:
1. Saprophytes feed on dead and decaying matter.
2. Cuscuta (amarbel) is a classic parasite example.

Answer: (c) Both have same focal length

Explanation:
1. Focal length f = R/2, which depends only on the radius of curvature.
2. Both mirrors come from the same sphere, so R is the same.
3. Aperture does not change f, so the magnitudes of the focal lengths are equal.

Teacher's Note:
1. Aperture affects brightness and aberration, not focal length.
2. Signs differ (concave negative, convex positive) but the size is the same.

Answer: (d) Science is interpreted as a body of facts, laws and theories which can mainly be understood through personal experience.

Explanation:
1. Social constructivism holds that knowledge is built through discussion, argument and collaboration.
2. Treating science as a fixed body of facts understood mainly through personal experience ignores this social negotiation of meaning.

Teacher's Note:
1. Vygotsky: learning is socially mediated.
2. Science as fixed facts is the transmission view, not the constructivist one.

Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).

Explanation:
1. Synthetic fibres like polyester absorb very little water, so (R) is true.
2. Less absorbed water means less to evaporate, so they dry faster; (R) explains (A).

Teacher's Note:
1. Cotton absorbs a lot of water and holds it, so it dries slowly.
2. This is why synthetic fabrics are popular for sportswear.

Answer: (b) Liver, bile, gall bladder, fats

Explanation:
1. The liver is the largest gland, reddish brown, on the upper right abdomen.
2. It secretes bile, which is stored in the gall bladder.
3. Bile emulsifies and helps digest fats.

Teacher's Note:
1. Bile contains no enzymes; it breaks fat into small droplets.
2. Proteins are digested by pepsin, trypsin and similar enzymes.

Answer: (c) Karnal

Explanation:
1. Large seasonal swing (7.5°C minimum in January to 38.8°C maximum in May) shows a continental, northern plains climate.
2. Kochi and Chennai are coastal with small variation; Shimla is far cooler.
3. Karnal in Haryana fits, with monsoon humidity rising in July.

Teacher's Note:
1. Coastal cities have a moderate climate with high humidity all year.
2. Hill stations stay cool even in May.

Answer: (c) (A) is false but (R) is true.

Explanation:
1. White phosphorus is very reactive and catches fire in air, so (R) is true.
2. It is therefore stored under water, not kerosene (sodium and potassium are kept in kerosene), so (A) is false.

Teacher's Note:
1. Remember: phosphorus in water; sodium and potassium in kerosene.
2. Do not accept an assertion just because the reason sounds right.

Answer: (d) (B) or (C)

Explanation:
1. Zero acceleration only means the net force is zero, not that no force acts.
2. A resting object always has weight and the normal force, a balanced pair, so (A) is not valid.
3. If more forces act (e.g. friction, applied forces) they may form several balanced pairs, so (B) or (C).

Teacher's Note:
1. Rest means balanced forces, not absence of forces.
2. Gravity always acts on objects on Earth.

Answer: (d) Quick lime

Explanation:
1. Limestone, chalk and marble are all natural forms of CaCO₃.
2. Quick lime is calcium oxide (CaO), obtained by heating limestone.

Teacher's Note:
1. CaCO₃ → CaO + CO₂ on heating.
2. Slaked lime is Ca(OH)₂, a different compound again.