CBSE Class 9 Science Sample Paper 2026-27

Answer Keyincluded with every paper

1. Q1. Complex processes like every atom's movement

   The chapter notes that Saha ignored many complex processes, such as modelling every atom, every reaction, or every movement inside a star, and instead treated stellar matter as a hot gas.

2. Q2. The average speed and the distance

   To model travel time, the key variables are distance and speed. Other details like brand or colour are irrelevant, as explained in the chapter's activity about modelling.

3. Q3. Design a controlled experiment with a placebo group to compare results

   Scientific testing of predictions requires controlled, evidence-based experiments. A placebo-controlled trial eliminates bias and provides reliable data, aligning with the chapter's emphasis on testable predictions and evidence.

4. Q4. Amoeba

   Amoeba is a unicellular organism that carries out all life functions within one cell.

5. Q5. Protecting organic molecules and assisting in membrane formation

   The deposits could have shielded organic molecules from harmful radiation and helped form the first protective cell membranes.

6. Q6. Membrane fluidity and selective permeability

   Lateral movement of lipids is essential for membrane fluidity, which affects the functioning of embedded proteins and overall membrane permeability. Without it, the membrane's selective permeability and dynamic properties are compromised.

7. Q7. A group of cells similar in structure and performing a specific function

   A tissue is defined as a group of cells that are similar in structure and work together to perform a specific function. This is the basic definition from the chapter.

8. Q8. To allow continuous and rapid cell division

   Vacuoles are fluid-filled sacs that take up space and could hinder the process of cell division. Meristematic cells need to divide rapidly and continuously, so they lack large vacuoles to maintain dense cytoplasm and a prominent nucleus for efficient division.

9. Q9. Root growth requires the presence of the apical meristem at the tip

   The experiment shows that when the root tip (containing the apical meristem) is removed, growth ceases, while the intact roots continue to grow. This demonstrates that the apical meristem is essential for root elongation.

10. Q10. The distance and direction from a reference point

    To describe the position of an object, we need both the distance and the direction with respect to a chosen reference point.

11. Q11. Speed – scalar, Velocity – vector

    Speed has only magnitude (scalar), while velocity has both magnitude and direction (vector). Distance is scalar and displacement is vector.

12. Q12. Distance = 120 cm, Displacement = 40 cm

    The ball travels 80 cm up to the highest point. From there, it falls 40 cm down to reach the 40 cm height. Total distance = 80 cm + 40 cm = 120 cm. Displacement is the net change in position: final height 40 cm above start, so magnitude = 40 cm.

13. Q13. 20%

    Mass of solution = 20 g + 80 g = 100 g. Mass/mass % = (mass of solute / mass of solution) × 100 = (20/100) × 100 = 20%.

14. Q14. 0.9 g NaCl in 100 mL of solution

    % m/v indicates mass of solute (in grams) per 100 mL of the final solution, not the solvent alone.

15. Q15. Sublimation → add water and filter → evaporate the filtrate

    First, sublime camphor to separate it. Then add water to dissolve salt, filter to remove sand. Finally, evaporate water from the filtrate to recover salt.

16. Q16. Change in its colour

    A force can change speed, direction, or shape of an object, but it does not change its colour (unless through deformation causing optical changes, which is not a direct effect of force).

17. Q17. Both A and R are true and R is the correct explanation of A.

    Models simplify real systems by focusing on key features and intentionally neglecting less relevant details, which aids in understanding without being lost in complexity. Thus, R correctly explains A.

18. Q18. A is false but R is true.

    The chapter explicitly states that a scientific theory is not an untested guess but a well-substantiated explanation. Hence, A is false, while R correctly defines a theory.

19. Q19. Both A and R are true but R is not the correct explanation of A.

    Saha simplified by treating stellar matter as a hot gas to make the problem tractable, which aligns with A. R describes his focus after simplification; it is a consequence, not the reason for choosing the gas model. Thus, R does not explain A.

20. Q20. Both A and R are true and R is the correct explanation of A.

    Osmosis is defined as the movement of water across a selectively permeable membrane, and it occurs from a dilute (lower solute) to a concentrated (higher solute) solution. The reason accurately describes the direction of water movement, thereby explaining the assertion.

21. Q21. Standard units ensure consistency and avoid confusion when sharing results globally. For example, the aircraft fuel miscalculation in the chapter occurred due to mixing up pounds and kilograms.

    Using standard units like kilograms (kg) ensures that measurements mean the same everywhere, enabling accurate communication and comparison. The chapter describes an aviation incident where mixing units led to fuel shortage, highlighting the importance of a common system. (2 marks: explanation 1 mark, example/reference 1 mark)

22. Q22. A law describes a pattern observed in nature, often mathematically, like Newton's laws of motion. A theory explains why that pattern occurs, based on evidence, like atomic theory explaining molecule formation. Laws state what happens; theories explain why.

    The chapter distinguishes laws as regular patterns (e.g., Newton's laws explain the jerk when a bus stops) and theories as explanations backed by evidence (e.g., atomic theory). A law is a concise description, while a theory provides a broader explanatory framework. (2 marks: distinction 1 mark, examples 1 mark)

23. Q23. Failure of predictions leads to re-examination of assumptions and refinement of theories. This open-endedness and willingness to change based on evidence make science self-correcting and reliable, rather than rigid. It drives progress.

    Science is not about proving ideas right forever; it's about using evidence to improve understanding. When a theory's prediction fails, it reveals limitations, prompting new models and deeper exploration. This cycle ensures that scientific knowledge evolves and becomes more accurate over time, which is a fundamental strength. (2 marks: explanation of self-correcting nature 2 marks)

24. Q24. The cell membrane acts as a selectively permeable barrier that controls the movement of substances in and out of the cell, thereby maintaining the appropriate internal conditions necessary for cellular functions.

    The cell membrane's lipid bilayer and embedded proteins allow selective passage of molecules. It prevents harmful substances from entering while allowing nutrients and waste products to pass, thus preserving homeostasis.

25. Q25. The cell will lose water and shrink. The cell membrane will pull away from the cell wall, a condition known as plasmolysis. This occurs because water moves out of the cell by osmosis from a region of higher water potential (inside the cell) to a region of lower water potential (the hypertonic solution).

    In a hypertonic solution, the solute concentration outside the cell is higher than inside. By osmosis, water diffuses out of the cell to equalize concentrations. As water leaves, the vacuole shrinks, and the cell membrane detaches from the rigid cell wall, causing the cell to become flaccid and possibly plasmolyzed.

26. Q26. Standard units ensure that measurements are consistent and comparable across different places and times, avoiding confusion. For example, the aircraft fuel miscalculation occurred because pounds were used instead of kilograms, leading to underestimation of fuel and a dangerous emergency landing.

    The chapter highlights the need for standard (SI) units to allow clear communication and prevent errors. The ‘Ready to Go Beyond’ box describes how an aircraft ran out of fuel mid-flight due to mixing pounds and kilograms, illustrating the severe consequences of unit confusion.

27. Q27. Included details: distance from school to home, average cycling speed. Ignored details: colour of the bicycle, minor stops for water. Ignoring irrelevant details reduces complexity and focuses on factors that directly affect travel time, making the model easier to use without losing accuracy for the purpose.

    Activity 1.1 in the chapter asks similar questions. Including distance and speed captures the main determinants of travel time. Ignoring colour or brief stops simplifies the model because these do not significantly change the overall time, preventing unnecessary complication.

28. Q28. When a prediction fails, scientists re‑examine their models, assumptions, or measurements. This can reveal limitations or new factors previously ignored. For example, weather forecasts sometimes go wrong because tiny changes in initial conditions can lead to very different outcomes over time. Recognising this led to improvements in weather models and sparked the concept of chaos theory. Thus, failures prompt refinement and deeper understanding, strengthening science.

    The chapter states: ‘When predictions do not match observations, scientists do not reject ideas based on opinion... but only on evidence. This openness to being corrected... is what makes science reliable.’ The weather forecast example shows that failures lead to better models and an acknowledgment of limits, driving progress.

29. Q29. The fluid-mosaic model describes the cell membrane as a lipid bilayer with proteins embedded. The lipids have hydrophilic heads facing outward and hydrophobic tails inward. Key features: (1) The membrane is fluid because the lipids and proteins can move laterally. (2) It is mosaic due to the patchwork of proteins scattered within the lipid bilayer.

    The fluid-mosaic model proposes that the cell membrane consists of a double layer of phospholipid molecules, with their water-attracting heads on the outer and inner surfaces and water-repelling tails in the interior. Proteins are interspersed within this layer, some spanning the membrane and others attached to one surface. Two key features: fluidity—the molecules can move sideways, flip, or rotate; mosaic arrangement—the proteins are distributed in a mosaic pattern. This structure allows selective permeability, flexibility, and communication with the environment.

30. Q30. In a hypotonic solution, water enters the cell by osmosis, causing the cell to swell and become turgid. The rigid cell wall exerts turgor pressure, preventing further expansion. In a hypertonic solution, water leaves the cell by osmosis, causing the cytoplasm to shrink from the cell wall (plasmolysis) and the cell becomes flaccid.

    When a plant cell is in a hypotonic solution (lower solute concentration outside), water moves into the cell by osmosis, leading to an increase in internal pressure called turgor pressure. The cell wall withstands this pressure, keeping the cell turgid. In a hypertonic solution (higher solute concentration outside), water moves out of the cell. The cytoplasm shrinks and pulls away from the cell wall, a process known as plasmolysis. The cell loses turgor and becomes flaccid.

31. Q31. The bacterium likely accumulates compatible solutes (e.g., amino acids, sugars) inside its cytoplasm to increase internal solute concentration to match or exceed the external osmotic pressure. This prevents net water loss by osmosis. It could also actively pump out toxic ions. This mechanism ensures the cell remains isotonic or slightly hypertonic relative to the environment, thus maintaining cell turgor and survival.

    In a hypersaline environment, the bacterium faces water loss due to the higher external solute concentration (hypertonic medium). To counteract this, the cell can synthesize or take up osmoprotectants—small organic molecules like glycine betaine or trehalose—that raise the internal solute concentration without interfering with cellular functions. This makes the cytoplasm isotonic or slightly hypertonic to the surroundings, preventing water loss by osmosis. Alternatively, some bacteria use ion pumps to actively export salts that leak in. These adaptations maintain cellular water content and metabolic activity.

32. Q32. A scientific model is a simplified representation of a real system, focusing only on aspects relevant to the question being investigated while ignoring less significant details. Models are necessary because the natural world is complex; trying to account for every detail would make analysis impossible or too cumbersome. For a falling object, a simple model might treat the object as a point mass and consider only the force of gravity, ignoring air resistance, shape, and spin. This is justified because gravity is the dominant force, and including air resistance would complicate the model without significantly improving understanding of basic motion for many objects. If later, more precise predictions are needed, the model can be refined by adding air resistance.

    The answer should define a model, explain its purpose, and provide the falling object example with clear inclusions (gravity, mass) and exclusions (air resistance, shape) and rationale. Marking: definition (1 mark), necessity (1 mark), example with included details (1 mark), ignored details (1 mark), justification (1 mark).

33. Q33. To make it testable, the prediction must be linked to measurable conditions. I would reformulate it as: 'Rain will occur within the next 2 hours if the cloud cover exceeds 80%, humidity is above 70%, and barometric pressure is falling.' Steps: (1) Define measurable variables: cloud cover percentage, humidity level, pressure change, and actual rainfall (yes/no). (2) Collect data on multiple days with similar observations, recording these variables. (3) Compare instances when rainfall did and did not occur against the criteria. (4) If rain occurs more often when conditions meet the criteria, the prediction is supported; if not, it is not. Reliability increases with more data and statistical analysis.

    Marks: reformulated testable prediction (1 mark), identification of relevant measurable variables (1 mark), plan for data collection and comparison (2 marks), method to determine support (1 mark). Emphasize moving from casual to evidence-based reasoning.

34. Q34. Model: I would assume the disease spreads radially from an initial infection point, with a constant spread rate per day, treating the field as uniform. Assumptions: uniform plant susceptibility, constant weather conditions, no intervention, disease spreads only by contact (ignoring wind-borne spores). Key quantities: initial infected area, spread rate (area per day), distance from origin after one week. Validation: Measure actual spread after one week by mapping the infected area, and compare with predicted radius. If predictions are off, I would first check measurement accuracy, then review assumptions: maybe spread rate varies with temperature or humidity; I might include weather data, or consider a non-uniform field (e.g., patches of resistant plants). I might also incorporate spore dispersal by wind. The model would be iteratively refined, acknowledging that models are simplifications and must adapt with new evidence.

    Marks: description of model with clear assumptions (1.5 marks), list of key quantities (1 mark), validation method (1 mark), steps to improve if predictions fail (1.5 marks). Expect logical approach, mention of specific refinements, and recognition of model limitations.

35. Q35. Osmosis is the movement of water molecules through a selectively permeable membrane from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution) until equilibrium is reached. It differs from diffusion: diffusion is the net movement of any particles (solid, liquid, or gas) from higher to lower concentration, and it can occur without a membrane, while osmosis specifically involves water across a semipermeable membrane. An example: the absorption of water by plant roots from the soil.

    Step 1: Define osmosis, emphasizing the role of the selectively permeable membrane and the direction of water movement. Step 2: Define diffusion as the general movement of particles down a concentration gradient without requiring a membrane. Step 3: Highlight the key differences: osmosis is specific to water and requires a membrane, while diffusion applies to any substance and can occur without a membrane. Step 4: Provide a valid real-life example, such as water uptake by roots, to illustrate the importance of osmosis.

36. Q36. Standard units prevent mistakes and ensure reproducibility. The assistant used 500 mL, which coincidentally matches the recipe.

    Using non-standard or incorrectly assumed units can lead to errors, as shown in the aircraft fuel incident. Here, 2 × 250 mL = 500 mL, the required amount. The importance of standard units is highlighted for reliable communication.

37. Q37. It is a theory as it explains why the lid tightens. Under cold water, the lid contracts more, making it easier to open.

    A theory goes beyond stating a pattern (law) and explains the mechanism. Meera's model predicts that cooling reverses the effect: metal contracts more, reducing the grip. This can be tested and refined.

38. Q38. Use soil from both locations, grow plants under controlled water conditions. If prediction fails, revise hypothesis and test again, as science is self-correcting.

    A fair test requires isolating the variable (water) while controlling others (soil). If results contradict the prediction, the scientific method demands re-evaluation, not stubborn adherence. This iterative process builds reliable knowledge.