CBSE Class 9 Science Chapter 02 Cell The Building Block Of Life MCQs Set 02

Answer: (A) Careful observation and noticing patterns

Explanation:
The magnifying glass stands for close, attentive observation - paying attention to details that might otherwise go unnoticed. The compass, by contrast, represents direction and purpose in exploration, not observation itself.

Answer: (B) Direction and purpose, such as choosing suitable models and questions

Explanation:
A compass gives direction, and here it symbolises that scientific exploration needs purposeful choices - the right models, the right questions, and awareness of where ideas apply - rather than aimless wandering.

Answer: (C) The symbol c for the speed of light

Explanation:
Celeritas means speed in Latin, and it is the origin of the symbol c used for the speed of light, showing that scientific symbols often have historical roots rather than being convenient abbreviations.

Answer: (B) The distance travelled and the average speed

Explanation:
Just as the cricket shot example ignored the bat's brand but kept the ball's mass and speed, a useful travel-time model keeps quantities like distance and speed while dropping irrelevant details like colour or brand.

Answer: (B) It allows the basic effect of gravity to be understood clearly first

Explanation:
Ignoring air resistance is a deliberate modelling choice, not an error - it lets the core effect of gravity stand out clearly before more detail is added for accuracy.

Answer: (B) Additional details are included to improve accuracy

Explanation:
The text explains that simple models leave out fine details on purpose, and as more accuracy is needed, extra details get added back into more complex versions of the same model.

Answer: (B) It is a language that helps express and reason about relationships between quantities

Explanation:
Rather than being a hurdle for memorisation, mathematics is described as a compact way of stating relationships between quantities - a tool for reasoning clearly, not just for producing numbers.

Answer: (B) 299792458 m/s exactly

Explanation:
The text specifies the speed of light as a defined physical constant equal to exactly 299792458 m/s, unlike many other measured quantities that carry some uncertainty.

Answer: (B) The purpose is to check whether the estimate is reasonable, not precisely correct

Explanation:
The exercise is framed around sanity-checking an answer - ruling out absurd extremes like 100 g or several tonnes - rather than pinning down an exact figure, showing how rough reasoning builds useful intuition.

Answer: (A) Because nature itself has no such divisions and real problems often need several branches together

Explanation:
Problems such as climate change or new medicines rarely respect subject boundaries. The categories exist to organise human knowledge conveniently, not because nature is actually split into separate compartments.

Answer: (C) Clearly, with only one possible meaning

Explanation:
Unambiguous means having only a single, clear meaning - this is why science gives everyday words like force or cell very specific, fixed definitions so scientists everywhere understand them the same way.

Answer: (B) Focusing on the organ as a whole is more useful for understanding this particular question

Explanation:
Just as a moving car can be reduced to a single point for motion problems, the heart can be studied as one functioning pump, with the enormous detail of individual cells set aside because it is not needed to answer how the organ works.

Answer: (A) To highlight an Indian scientist whose work illustrates the value of simplified models

Explanation:
Saha's approach to studying starlight - treating a star's matter as a simple hot gas rather than tracking every particle - is used as a real example of how ignoring complexity can still lead to powerful scientific explanations.

Answer: (B) Its openness to revising theories when new evidence contradicts them

Explanation:
Science is described as reliable precisely because no theory is treated as final - when observations disagree with predictions, ideas are re-examined and corrected based on evidence, not defended out of habit.

Answer: (B) Real-world problems often require combining ideas from multiple branches of science

Explanation:
Explaining mask filtration draws on physics (particle motion), chemistry (fibre properties), biology (virus size) and mathematics (airflow modelling) together, showing that many everyday problems don't fit inside a single scientific discipline.

Answer: (B) Secondary science shifts attention to understanding how scientific knowledge itself is built, not just what is known

Explanation:
The chapter says that while middle-stage science was about curiosity and observation, secondary science adds a focus on 'how we know' — through measurement, symbols, models, and testing ideas. It is not about abandoning earlier habits but building on them with deeper methodological awareness.

Answer: (B) That all of the family's daily calorie requirement comes from rice alone

Explanation:
To make the estimate workable, the chapter assumes every calorie the family needs comes purely from rice, even though real diets include other foods. This is a deliberate simplification, similar to ignoring air resistance in a falling-object problem, just to check whether the final number is roughly sensible.

Answer: (B) Predictions are based on evidence and logical thinking, not random chance

Explanation:
Calling a prediction a 'reasoned expectation' signals that it comes from applying established laws, theories, or models to a situation — like predicting how far a football will travel using motion concepts — rather than simply hoping for an outcome.

Answer: (B) Laws, theories, and principles

Explanation:
As observations are repeated and tested through experiments, the chapter explains that scientists organise knowledge using laws (patterns), theories (explanations for patterns), and principles (broad applicable ideas), each with a distinct role.

Answer: (B) How molecules are formed

Explanation:
Atomic theory is given as an example of a theory because it goes beyond describing a pattern and instead explains why molecules come together, based on accumulated evidence about atoms.

Answer: (B) Because such failures show science is willing to revise itself based on evidence, not opinion

Explanation:
Rather than clinging to an idea out of habit or belief, the chapter stresses that scientists re-examine assumptions and models when predictions fail — this self-correcting openness, guided strictly by evidence, is presented as exactly what makes science reliable over time.

Answer: (B) That a kilogram must mean the same amount everywhere for fairness and consistency

Explanation:
• The example shows a kilogram of rice or vegetables meaning the same amount regardless of where it is sold.
• This consistency depends on internationally agreed standard units, not local objects or personal judgement.
• The chapter links this directly to fairness in everyday trade and to comparability of scientific results.

Answer: (B) Counting breaths per minute combined with balloon volume, and separately calculating a balloon-filling rate per minute

Explanation:
One method multiplied an estimated number of daily breaths by the estimated volume per breath (based on filling a balloon), giving about 10,000 litres. As a check, a second calculation used how many balloons could be filled per minute, giving a close figure of about 8,640 litres — showing estimation can be cross-verified even without exact numbers.

Answer: (C) Biology

Explanation:
The mask example splits the explanation across disciplines: physics covers particle motion and electrostatic attraction, chemistry covers polymer fibre properties, mathematics covers modelling airflow, and biology specifically deals with understanding viruses themselves.

Answer: (B) Confidence in the underlying science grows

Explanation:
Matching predictions with observed outcomes strengthens trust in the models, laws, or theories being used, though the chapter is careful to add that even trusted ideas keep being tested and can later be revised.