CBSE Class 9 Science Chapter 01 Exploration Entering The World Of Secondary Science MCQs Set 03

Download CBSE MCQs for Class 9 Science: Chapter 01 Exploration Entering The World Of Secondary Science

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Chapter-wise Objective Questions: Chapter 01 Exploration Entering The World Of Secondary Science

Navigate directly to the 50 objective questions for Chapter 01 Exploration Entering The World Of Secondary Science using the digital viewer below. Each practice set includes verified answer keys, allowing students to instantly cross-check their work and identify areas requiring further revision.

Question: Which of the following best describes the primary role of the Golgi apparatus inside a cell?
A. It modifies, sorts and packages proteins and lipids into vesicles for transport or secretion
B. It synthesises ATP to power cellular activities
C. It breaks down worn-out organelles using digestive enzymes
D. It produces ribosomal subunits for protein synthesis
Show Answer & Explanation

Answer: (A) It modifies, sorts and packages proteins and lipids into vesicles for transport or secretion

Explanation:
The Golgi apparatus works like the cell's post office, receiving material from the ER and modifying, sorting, and packing it into vesicles before sending it off for secretion, transport, or lysosome formation. ATP production is the job of mitochondria, while breaking down old organelles is done by lysosomes, not the Golgi apparatus.

Question: Why do plant cells generally need a rigid cell wall while animal cells manage well without one?
A. Plants cannot move away from environmental stress, so a fixed rigid covering keeps them upright and protected
B. Animal cells contain more water and therefore never need external support
C. Plant cells lack a cell membrane, so the wall substitutes for it
D. Animals have larger cells that automatically resist wind and rain damage
Show Answer & Explanation

Answer: (A) Plants cannot move away from environmental stress, so a fixed rigid covering keeps them upright and protected

Explanation:
• Plants are usually rooted in place and cannot escape wind, rain or other physical stress.
• A rigid cell wall gives plant cells and structures like leaves and flowers the firmness needed to stay upright.
• Animals, being mobile, rely instead on a flexible cell membrane that lets cells change shape for movement.

Question: The cell membrane is often described as 'selectively permeable'. What does this term actually mean?
A. It permits some substances to cross while blocking others
B. It allows every substance to pass through without restriction
C. It completely prevents any substance from entering or leaving the cell
D. It only allows the exchange of gases like oxygen and carbon dioxide
Show Answer & Explanation

Answer: (A) It permits some substances to cross while blocking others

Explanation:
Selective permeability means the membrane acts as a gatekeeper, letting certain molecules such as water pass more freely while restricting others like larger solute particles, which is why osmosis experiments with potato pieces showed water moving in and out but not the dissolved salt or sugar.

Question: Most animal cells stop dividing once they touch neighbouring cells on all sides, a phenomenon called contact inhibition. Why do plant cells not follow this same pattern?
A. Their rigid cell walls make them grow differently, so they do not rely on contact-based signals to stop dividing
B. Plant cells never divide after the seedling stage
C. Plant cells lack cytoplasm, which is required for contact inhibition
D. Plant cells communicate only through chloroplasts, bypassing contact signals
Show Answer & Explanation

Answer: (A) Their rigid cell walls make them grow differently, so they do not rely on contact-based signals to stop dividing

Explanation:
Unlike flexible animal cells, plant cells are boxed in by a rigid wall, which changes how their growth is regulated, so they do not depend on touching neighbours to control division the way most animal cells do.

Question: In 1838, a German botanist examined various plant tissues under a microscope and made a foundational observation for the Cell Theory. What exactly did he report?
A. That all plants are composed of cells
B. That all animals are composed of cells
C. That new cells arise only from pre-existing cells
D. That cells contain a nucleus surrounded by cytoplasm
Show Answer & Explanation

Answer: (A) That all plants are composed of cells

Explanation:
This was Matthias Schleiden's contribution in 1838, focused specifically on plant tissue. The idea that animals too are made of cells came a year later from Theodor Schwann, and the notion that cells arise only from pre-existing cells was added later by Rudolf Virchow.

Question: Theodor Schwann's 1839 study extended the emerging Cell Theory by making which observation?
A. Animals, like plants, are also made up of cells
B. Plants are made up of cells
C. Cells divide to form two identical daughter cells
D. Bacteria lack a well-defined nucleus
Show Answer & Explanation

Answer: (A) Animals, like plants, are also made up of cells

Explanation:
Schwann showed that the cellular basis of life applies to animals as well, complementing Schleiden's earlier finding about plants. Together with Virchow's later addition about cell division from pre-existing cells, their combined work built the classical Cell Theory.

Question: The term 'prokaryotic' is built from two word parts. What do they signify about this type of cell?
A. A primitive or absent true nucleus, since 'pro' means primitive and 'karyon' means nucleus
B. A true, well-formed nucleus enclosed by a membrane
C. A cell that completely lacks cytoplasm
D. A cell containing many membrane-bound organelles
Show Answer & Explanation

Answer: (A) A primitive or absent true nucleus, since 'pro' means primitive and 'karyon' means nucleus

Explanation:
• 'Pro' translates to primitive.
• 'Karyon' refers to the nucleus.
• Together, the word describes cells such as bacteria, whose genetic material sits in an undefined region called the nucleoid rather than inside a proper membrane-bound nucleus.

Question: What is the function of the pores present on the double-layered nuclear membrane?
A. They allow materials to move between the nucleus and the surrounding cytoplasm
B. They store chromatin material permanently
C. They generate energy for the nucleus
D. They synthesise proteins directly inside the nucleus
Show Answer & Explanation

Answer: (A) They allow materials to move between the nucleus and the surrounding cytoplasm

Explanation:
The nuclear membrane is not a sealed barrier; its pores permit an exchange of materials, such as ribosomal subunits moving out to the cytoplasm, keeping the nucleus in communication with the rest of the cell.

Question: How does Programmed Cell Death (PCD) contribute to the normal development of a human embryo, as mentioned in the chapter?
A. It removes the cells between developing fingers so they separate instead of staying webbed
B. It causes the nucleus to shrink so cells can divide faster
C. It converts embryonic cells directly into red blood cells
D. It builds new mitochondria to supply extra energy for growth
Show Answer & Explanation

Answer: (A) It removes the cells between developing fingers so they separate instead of staying webbed

Explanation:
PCD is a controlled, genetically regulated process of eliminating specific cells when they are no longer needed. During embryo development, it clears away the tissue between the fingers, and without this process the hands would remain webbed.

Question: Looking at the diagram of a typical bacterial cell in the chapter, which structure is specifically responsible for helping the bacterium move around?
A. The appendage for locomotion
B. The nucleoid
C. The ribosome
D. The cytoplasm
Show Answer & Explanation

Answer: (A) The appendage for locomotion

Explanation:
Alongside the nucleoid holding its genetic material and ribosomes for protein synthesis, the bacterial cell diagram labels a distinct appendage used for locomotion, letting the organism move through its environment.

Question: Based on the comparison given in the chapter, how do prokaryotic and eukaryotic cells typically differ in size?
A. Prokaryotic cells are usually much smaller, around 1 to 10 micrometres, compared to 10 to 100 micrometres in eukaryotic cells
B. Prokaryotic cells are always larger than eukaryotic cells
C. Both cell types have exactly the same average diameter
D. Prokaryotic cells range from 100 to 1000 micrometres in diameter
Show Answer & Explanation

Answer: (A) Prokaryotic cells are usually much smaller, around 1 to 10 micrometres, compared to 10 to 100 micrometres in eukaryotic cells

Explanation:
The comparison table places prokaryotic cells in the 1 to 10 micrometre range, while eukaryotic cells, with their nucleus and organelles, are noticeably larger at roughly 10 to 100 micrometres.

Question: What is the stroma within a chloroplast, and what does it contain?
A. A semi-fluid substance inside the chloroplast where sugars made during photosynthesis are stored along with starch granules
B. The outer protective membrane surrounding the chloroplast
C. The green pigment that directly absorbs sunlight
D. A structure found only in animal cell mitochondria
Show Answer & Explanation

Answer: (A) A semi-fluid substance inside the chloroplast where sugars made during photosynthesis are stored along with starch granules

Explanation:
Inside the double membrane of a chloroplast lies the stroma, a jelly-like matrix that holds the disc-shaped, chlorophyll-containing structures and also stores the sugars and starch produced through photosynthesis.

Question: Lysosomes are sometimes called the cell's clean-up system. What role do they generally play?
A. They contain enzymes that break down unwanted proteins, fats, carbohydrates and damaged cell parts
B. They generate the ATP needed for most cellular processes
C. They store water, minerals and waste for long periods
D. They sort and package proteins into vesicles for secretion
Show Answer & Explanation

Answer: (A) They contain enzymes that break down unwanted proteins, fats, carbohydrates and damaged cell parts

Explanation:
Filled with digestive enzymes, lysosomes clear out cellular debris and worn-out components, releasing the breakdown products into the cytoplasm where they can be reused, keeping the cell functioning smoothly.

Question: Among the acellular infectious agents described in the chapter, what makes prions structurally different from both viruses and viroids?
A. Prions are misfolded proteins that lack any genetic material altogether
B. Prions carry genetic material but no protein coat
C. Prions have genetic material wrapped in a protein coat
D. Prions are single cells without a nucleus
Show Answer & Explanation

Answer: (A) Prions are misfolded proteins that lack any genetic material altogether

Explanation:
Viruses combine genetic material with a protein coat, and viroids carry genetic material without such a coat, but prions stand apart entirely since they consist only of misfolded protein and contain no genetic material at all.

Question: According to the chapter's description of biological organisation, what exactly is a tissue?
A. A group of similar cells working together to carry out a similar function
B. A collection of different organs performing one shared task
C. Any single cell capable of independent movement
D. A network of organelles found inside one eukaryotic cell
Show Answer & Explanation

Answer: (A) A group of similar cells working together to carry out a similar function

Explanation:
The chapter builds organisation step by step: similar cells group together to form a tissue, tissues combine into organs, and organs work together as organ systems, such as the respiratory system formed from nasal passages, trachea and lungs.

Question: The hot springs of Puga Valley are considered scientifically important mainly because the organisms living there share which trait with conditions thought to exist on early Earth?
A. They are cold-adapted algae similar to polar organisms
B. They are heat-loving unicellular bacteria called thermophiles thriving at near-boiling temperatures
C. They are multicellular fungi that grow only in acidic soil
D. They are photosynthetic plants that need constant sunlight
Show Answer & Explanation

Answer: (B) They are heat-loving unicellular bacteria called thermophiles thriving at near-boiling temperatures

Explanation:
Puga Valley's hot springs stay near the boiling point of water even in Ladakh's cold climate, and the unicellular heat-loving bacteria (thermophiles) living there resemble conditions believed to have existed on Earth about 3.5 billion years ago.

Question: How might the rapid formation of calcium carbonate around ancient hot springs have contributed to the origin of the first cells?
A. It broke down organic molecules so new ones could form faster
B. It increased radiation exposure to speed up mutations
C. It shielded early organic molecules and may have aided formation of a protective membrane
D. It dissolved early proteins to release energy for cell growth
Show Answer & Explanation

Answer: (C) It shielded early organic molecules and may have aided formation of a protective membrane

Explanation:
Researchers from the Birbal Sahni Institute suggest these mineral deposits could have guarded fragile organic molecules from radiation and harsh conditions while contributing to the very first membrane that separated a cell from its surroundings.

Question: If a student uses an eyepiece with 15X power and an objective lens with 10X power to view an onion cell that is actually 150 micrometres wide, how large will the cell appear under the microscope?
A. 15 times its real size
B. 10 times its real size
C. 150 times its real size
D. 1500 times its real size
Show Answer & Explanation

Answer: (C) 150 times its real size

Explanation:
Total magnification is the eyepiece power multiplied by the objective power, so 15 x 10 = 150X, meaning the 150 micrometre cell would appear 150 times larger than its actual size.

Question: In the lipid bilayer that forms the cell membrane, how are the fat molecules typically arranged?
A. Water-repelling tails face outward while water-attracting heads face inward
B. Water-attracting heads face outward while water-repelling tails face inward
C. Both heads and tails face outward on either side
D. Proteins replace all the fat molecules on the outer surface
Show Answer & Explanation

Answer: (B) Water-attracting heads face outward while water-repelling tails face inward

Explanation:
The fluid-mosaic model describes two layers of lipid molecules with their water-loving heads pointing outward toward the watery surroundings, and their water-fearing tails tucked inward, away from water.

Question: A gland cell that mainly produces and stores fats and hormones, rather than secreting large amounts of protein, would rely most heavily on which organelle?
A. Rough Endoplasmic Reticulum
B. Smooth Endoplasmic Reticulum
C. Golgi apparatus only
D. Nucleolus
Show Answer & Explanation

Answer: (B) Smooth Endoplasmic Reticulum

Explanation:
Smooth ER lacks the ribosomes found on rough ER, which is why it looks smooth under the microscope, and it specialises in synthesising and storing fats and hormones rather than proteins.

Question: After the Golgi apparatus finishes modifying and sorting a batch of proteins, what typically happens to them next?
A. They are sent back to the nucleus for reassembly
B. They are packaged into vesicles for transport, secretion, or lysosome formation
C. They are broken down immediately into amino acids
D. They remain permanently stored inside the Golgi stacks
Show Answer & Explanation

Answer: (B) They are packaged into vesicles for transport, secretion, or lysosome formation

Explanation:
Acting like the cell's post office, the Golgi apparatus wraps processed proteins and lipids into vesicles, which can then be moved out of the cell, released as secretions, or used to build new lysosomes.

Question: Comparing the two membranes of a mitochondrion, what distinguishes the outer membrane from the inner one?
A. The outer membrane is folded into cristae while the inner one is smooth
B. The outer membrane is smooth and porous while the inner one is folded into cristae
C. Both membranes are equally folded to maximise surface area
D. Only the inner membrane is porous, while the outer one is completely sealed
Show Answer & Explanation

Answer: (B) The outer membrane is smooth and porous while the inner one is folded into cristae

Explanation:
A mitochondrion has a smooth, porous outer covering, but its inner membrane folds inward repeatedly to form cristae, which increases the surface area available for energy-releasing reactions.

Question: During meiosis, why does a parent cell need to divide twice in succession rather than just once?
A. The first division doubles the chromosome number, and the second halves it back
B. The first division halves the chromosome number, and the second division works like mitosis to produce four cells
C. Both divisions are identical to mitosis and simply repeat the process
D. The first division forms the nucleus, and the second forms the cytoplasm
Show Answer & Explanation

Answer: (B) The first division halves the chromosome number, and the second division works like mitosis to produce four cells

Explanation:
Meiosis begins with a division that cuts the chromosome number in half, and then a second, mitosis-like division splits each of those cells again, ultimately yielding four gametes with half the original chromosome count.

Question: One of the three core ideas of the classical Cell Theory concerns the cell's role in living organisms. What does this particular idea state?
A. The cell is only a storage container with no active function
B. The cell serves as the basic unit of both structure and function in living beings
C. Cells exist only in plants and fungi, not in animals
D. Cells can arise spontaneously without any pre-existing cell
Show Answer & Explanation

Answer: (B) The cell serves as the basic unit of both structure and function in living beings

Explanation:
Beyond stating that organisms are made of cells and that cells come from pre-existing cells, the theory also holds that the cell itself is the fundamental unit responsible for both the structure and the functioning of living things.

Question: A single fertilised egg develops into a human body made of trillions of cells largely through which process?
A. Meiosis, since it produces genetically varied cells
B. Mitosis, since it repeatedly produces identical daughter cells for growth
C. Programmed cell death, which increases total cell number
D. Contact inhibition, which triggers new cell formation
Show Answer & Explanation

Answer: (B) Mitosis, since it repeatedly produces identical daughter cells for growth

Explanation:
Because mitosis generates two genetically identical daughter cells from each parent cell, repeated rounds of this division allow a single fertilised egg to multiply into the enormous number of cells that make up a fully formed body.

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