CBSE Class 9 Science Chapter 01 Exploration Entering The World Of Secondary Science MCQs Set 01

Answer: (A) A self-built microscope with roughly 200-300X magnification

Explanation:
Hooke built his own microscope capable of about 200 to 300 times magnification and used it to examine a thin slice of cork, where he noticed small box-like compartments he named cells. Electron microscopes came much later and were not available to him.

Answer: (A) They use a beam of electrons instead of light, allowing imaging at the nanometre scale

Explanation:
The chapter explains that electron microscopes use electron beams rather than visible light, which lets scientists see details at the nanometre scale with far greater clarity than a light microscope allows.

Answer: (B) Water moved into the piece with less solute and out of the piece with more solute, both trying to equalise concentration

Explanation:
Osmosis drives water from a dilute solution toward a concentrated one across the selectively permeable membrane until concentrations equalise. The potato in plain water gained water and swelled, while the one in salt solution lost water and shrank; the salt or sugar molecules themselves do not cross the membrane.

Answer: (C) Onion cells have a rigid cell wall that holds their outer shape even as the membrane pulls inward, but cheek cells have no such wall

Explanation:
• Plant cells like onion peel have a rigid cell wall outside the membrane.
• When water leaves by osmosis, the membrane pulls away from the wall but the wall keeps the overall shape intact.
• Animal cells such as cheek cells have no cell wall, so the whole cell shrinks visibly.

Answer: (C) Hypotonic solution

Explanation:
When the external solute concentration is lower than inside the cell, the solution is called hypotonic, and water tends to move into the cell under such conditions.

Answer: (C) Presence of a well-defined, membrane-bound nucleus and organelles

Explanation:
Both cell types have cytoplasm, a membrane, and genetic material, but only eukaryotic cells possess a true nucleus enclosed by a membrane along with other membrane-bound organelles; prokaryotic cells instead have a nucleoid region without a surrounding membrane.

Answer: (B) It creates extra room for haemoglobin, increasing oxygen-carrying capacity

Explanation:
Without a nucleus taking up space, mature RBCs have more room for haemoglobin, which boosts how much oxygen they can transport throughout the body. The trade-off is that they cannot repair or divide, giving them a short lifespan of about 120 days.

Answer: (B) Ribosomes attached to its outer surface

Explanation:
RER gets its studded, rough look from ribosomes attached along its surface, and this is where much of the cell's protein synthesis and secretion happens. Smooth ER, lacking ribosomes, appears smooth and instead handles lipid and hormone synthesis.

Answer: (B) Early microscopes could not clearly resolve the thread-like structure he observed

Explanation:
Golgi observed a thread-like network using special staining, but the microscopes of that era lacked the resolution to confirm it clearly, so many scientists remained skeptical until electron microscopes verified its existence decades later.

Answer: (B) Because this feature suggests an evolutionary link to ancient single-celled organisms like bacteria

Explanation:
The presence of their own DNA and ribosomes, allowing them to make some proteins independently, points to mitochondria and chloroplasts sharing an evolutionary history with certain bacteria, as suggested in the chapter.

Answer: (C) Starch as a food reserve

Explanation:
Leucoplasts are colourless plastids that store food materials such as starch, oils, or proteins; potato and taro cells specifically use leucoplasts to store starch.

Answer: (B) The cells would lose internal pressure, becoming less firm and causing the plant to wilt

Explanation:
The large central vacuole maintains internal pressure by holding water; when water is lost, this pressure drops, cells become less firm, and the plant shows visible wilting.

Answer: (C) Meiosis involves two rounds of division producing four daughter cells with half the chromosome number, while mitosis produces two genetically identical cells

Explanation:
• Mitosis is a single division producing two daughter cells genetically identical to the parent, used for growth and repair.
• Meiosis involves two successive divisions, producing four daughter cells each with half the chromosome number.
• Meiosis occurs only in reproductive organs and creates genetic variation, unlike mitosis.

Answer: (C) It can result in uncontrolled cell division and tumour formation

Explanation:
Faulty mitosis can disrupt the normal controlled division process, leading to abnormal chromosome numbers and uncontrolled growth that forms tumours, whereas errors in meiosis are more linked to genetic disorders and fertility issues.

Answer: (C) Rudolf Virchow

Explanation:
Schleiden showed plants are made of cells and Schwann showed the same for animals, but it was Rudolf Virchow who added the crucial idea that new cells form only from pre-existing cells, completing the classical Cell Theory.

Answer: (A) Because such extreme environments resemble early Earth conditions, and rapid mineral deposits there may have shielded organic molecules and helped form the first cell membranes

Explanation:
• Puga Valley's hot springs stay near boiling point even in a cold climate, mimicking early Earth conditions from about 3.5 billion years ago
• Scientists found calcium carbonate forming rapidly around these springs
• These deposits may have protected fragile organic molecules and contributed to the first protective membrane

Answer: (A) The smallest distance between two points at which they can still be seen as separate rather than blurring into one

Explanation:
For the unaided human eye, this limit is about 0.1 mm when viewed from the near point of 25 cm; anything closer than that appears as a single blurred point rather than two distinct ones.

Answer: (A) 200 micrometres

Explanation:
First convert 6 mm to micrometres, giving 6000 micrometres. Dividing this by the 30 cells counted along the diameter gives 6000/30 = 200 micrometres per cell.

Answer: (A) The rigid cell wall holds its outline firm while only the membrane and cytoplasm pull inward as water is lost

Explanation:
Because the cell wall is rigid, it does not collapse the way the flexible cell membrane does; as water leaves through osmosis, the membrane and cytoplasm pull away from the fixed wall, creating a visible gap while the outer shape of the cell stays intact.

Answer: (A) Nucleolus

Explanation:
The nucleolus is described as the dense round body within the nucleus where ribosomal subunits are made before they exit through nuclear pores and combine in the cytoplasm.

Answer: (A) Just before the cell is about to divide

Explanation:
In a resting, non-dividing cell the genetic material stays loosely tangled as chromatin, but as division approaches, this material condenses and organises itself into the compact, rod-like chromosomes that can be seen clearly.

Answer: (A) Diffusion is the movement of particles from a higher to a lower concentration and can occur without any membrane, whereas osmosis is specifically the movement of water across a selectively permeable membrane

Explanation:
Diffusion is a broader process describing particles spreading from where they are concentrated to where they are scarce, with or without a membrane present. Osmosis is a special case of this idea, restricted to water crossing a selectively permeable membrane, such as when root cells absorb water from soil.

Answer: (A) Different organelles each carry out a specific job, such as building materials, clearing waste, or supplying energy, and together they keep the whole cell running

Explanation:
• Organelles such as the nucleus, ER, Golgi apparatus, mitochondria and lysosomes each handle a distinct task
• These tasks range from making proteins to producing energy and clearing waste
• The factory comparison highlights how these separate jobs combine into one coordinated, functioning unit

Answer: (A) Even a fully mature, differentiated plant cell can be induced to grow into an entire new plant if given suitable nutrients and conditions

Explanation:
Haberlandt proposed that any living plant cell, not just embryonic or meristematic ones, retains the ability to develop into a complete plant under the right conditions. This property, called totipotency, became the basis for growing whole plants from single cells in laboratories.

Answer: (A) DNA governs and directs the structure and activities of a cell

Explanation:
Once the synthetic DNA was placed inside the emptied bacterial cell, the cell began growing and dividing exactly as instructed by that new genetic material, showing that DNA controls what a cell becomes and does. Notably, the rest of the cell, such as its cytoplasm and membrane, still came from an already living cell, so this was not a fully synthetic cell created from scratch.