Biology MCQs

Question #761

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Mammary glands are a defining feature of which class of animals?

A. Mammalia

B. Amphibia

C. Aves

D. Reptilia

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Correct Answer: Option A

Explanation:
Mammalia is the only class of animals that possess mammary glands, which produce milk to nourish their young ones. Other defining features of mammals include the presence of hair on the skin, external pinnae (ear flaps), a four-chambered heart, and being warm-blooded (homeothermic). Examples include humans, whales, and bats.

This question belongs to: Science Biology

Question #762

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What is the correct sequence of taxonomic hierarchy from highest to lowest?

A. Kingdom, Phylum, Order, Class, Family, Genus, Species

B. Kingdom, Phylum, Class, Order, Family, Genus, Species

C. Kingdom, Class, Phylum, Order, Family, Genus, Species

D. Kingdom, Family, Class, Order, Phylum, Genus, Species

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Correct Answer: Option B

Explanation:
The correct hierarchical classification of organisms, from the broadest to the most specific category, is: Kingdom, Phylum (or Division for plants), Class, Order, Family, Genus, and Species. A helpful mnemonic to remember this is: 'King Philip Came Over For Good Spaghetti'.

This question belongs to: Science Biology

Question #763

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The edible part of a potato is a modified:

A. Flower

B. Root

C. Stem

D. Leaf

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Correct Answer: Option C

Explanation:
The potato is a modified underground stem known as a tuber. It stores food (starch) and has 'eyes' which are actually axillary buds capable of growing into new plants. This distinguishes it from modified roots like sweet potatoes, which do not possess nodes, internodes, or buds.

This question belongs to: Science Biology

Question #764

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The pitcher plant (Nepenthes) has modified leaves to trap insects primarily to obtain:

A. Water

B. Oxygen

C. Carbohydrates

D. Nitrogen

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Correct Answer: Option D

Explanation:
The pitcher plant is an insectivorous (carnivorous) plant. Its leaves are modified into pitcher-shaped structures to trap and digest insects. This adaptation is primarily to supplement the plant's nitrogen intake, as it typically grows in nitrogen-deficient soils (like bogs). The digested insects provide essential nitrogenous compounds.

This question belongs to: Science Biology

Question #765

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In sunflower, the arrangement of leaves on the stem is:

A. Opposite

B. Alternate

C. Basal rosette

D. Whorled

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Correct Answer: Option B

Explanation:
Phyllotaxy is the pattern of leaf arrangement on the stem. In sunflower (and many other plants like mustard), the phyllotaxy is alternate, meaning a single leaf arises at each node. In opposite phyllotaxy (e.g., guava), two leaves arise at a node, and in whorled (e.g., Nerium), more than two leaves arise at a node.

This question belongs to: Science Biology

Question #766

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In the light reaction of photosynthesis, which photosystem is involved in the photolysis of water?

A. Photosystem II (PSII)

B. Neither PSI nor PSII

C. Both PSI and PSII

D. Photosystem I (PSI)

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Correct Answer: Option A

Explanation:
Photosystem II (PSII), also known as P680, is the first photosystem in the non-cyclic electron transport pathway (Z-scheme). It is responsible for the photolysis of water, a process where water molecules are split into oxygen, protons (H+), and electrons. This oxygen is released as a byproduct of photosynthesis.

This question belongs to: Science Biology

Question #767

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Which enzyme catalyzes the primary carboxylation reaction in the Calvin cycle?

A. PEP carboxylase

B. Nitrogenase

C. RuBisCO

D. Carbonic anhydrase

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Correct Answer: Option C

Explanation:
RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the most abundant protein on Earth and the key enzyme in the Calvin cycle (C3 pathway). It catalyzes the fixation of CO2 by attaching it to Ribulose-1,5-bisphosphate (RuBP) to form a 6-carbon intermediate that immediately splits into two molecules of 3-PGA.

This question belongs to: Science Biology

Question #768

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Which of the following plants utilizes the C4 photosynthetic pathway?

A. Rice

B. Maize

C. Wheat

D. Soybean

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Correct Answer: Option B

Explanation:
Maize (corn), sugarcane, and sorghum are classic examples of C4 plants. They possess Kranz anatomy, where bundle sheath cells contain chloroplasts. C4 plants initially fix CO2 into a 4-carbon compound (oxaloacetate) using PEP carboxylase in mesophyll cells, which minimizes photorespiration and increases photosynthetic efficiency in hot, dry climates.

This question belongs to: Science Biology

Question #769

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CAM plants adapt to arid conditions by:

A. Keeping stomata open during the day

B. Lacking chlorophyll

C. Performing only anaerobic respiration

D. Opening stomata at night and closing them during the day

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Correct Answer: Option D

Explanation:
Crassulacean Acid Metabolism (CAM) plants, such as cacti and succulents, adapt to arid environments by opening their stomata at night to fix CO2 into organic acids (like malic acid) and storing them in vacuoles. During the day, the stomata close to prevent water loss, and the stored CO2 is released for the Calvin cycle.

This question belongs to: Science Biology

Question #770

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Which type of transpiration accounts for the maximum loss of water in plants?

A. Bark transpiration

B. Lenticular transpiration

C. Cuticular transpiration

D. Stomatal transpiration

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Correct Answer: Option D

Explanation:
Stomatal transpiration, which occurs through the stomata (pores) on the leaf epidermis, accounts for about 90% of the total water loss in plants. Cuticular transpiration occurs through the waxy cuticle and is minimal. Lenticular transpiration occurs through lenticels in woody stems and is also very small.

This question belongs to: Science Biology

Question #771

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Apical dominance in plants is primarily controlled by which hormone?

A. Gibberellin

B. Auxin

C. Ethylene

D. Cytokinin

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Correct Answer: Option B

Explanation:
Apical dominance is the phenomenon where the main central stem (apical bud) grows more strongly than the side stems (lateral buds). This is primarily controlled by auxin (specifically IAA), which is produced at the shoot apex and moves downwards, inhibiting the growth of lateral buds. Removal of the apical bud promotes lateral branching.

This question belongs to: Science Biology

Question #772

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Which plant hormone is responsible for the 'bolting' effect in rosette plants like cabbage and beet?

A. Auxin

B. Gibberellin

C. Cytokinin

D. Abscisic acid

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Correct Answer: Option B

Explanation:
Gibberellins (GAs) promote stem elongation. In rosette plants (like cabbage, beet, and radish) that have a short stem and closely packed leaves, the application of gibberellin induces sudden and rapid stem elongation just before flowering, a phenomenon known as 'bolting'. This is widely used in agriculture.

This question belongs to: Science Biology

Question #773

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Cytokinins are primarily involved in:

A. Cell division and delaying senescence

B. Fruit ripening

C. Stomatal closure

D. Root elongation

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Correct Answer: Option A

Explanation:
Cytokinins are plant hormones that primarily promote cell division (cytokinesis) in the presence of auxins. They are also crucial in delaying senescence (aging) of leaves by helping to maintain protein and nucleic acid content, a phenomenon known as the Richmond-Lang effect. They are synthesized mainly in root apices.

This question belongs to: Science Biology

Question #774

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Which hormone is commonly known as the 'fruit ripening hormone'?

A. Gibberellin

B. Auxin

C. Cytokinin

D. Ethylene

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Correct Answer: Option D

Explanation:
Ethylene is a gaseous plant hormone that is widely known for its role in promoting the ripening of fruits. It increases the respiration rate during fruit ripening (climacteric rise) and breaks down cell walls, converting starches to sugars, making the fruit softer and sweeter. It is also involved in leaf abscission and the triple response in seedlings.

This question belongs to: Science Biology

Question #775

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Abscisic acid (ABA) is often called the 'stress hormone' because it:

A. Induces stomatal closure during water stress

B. Promotes cell division

C. Accelerates fruit ripening

D. Promotes seed germination

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Correct Answer: Option A

Explanation:
Abscisic acid (ABA) is known as the stress hormone because it plays a crucial role in plant responses to environmental stresses, particularly drought. It induces the closure of stomata to reduce water loss (transpiration) and also inhibits seed germination and growth, helping the plant survive adverse conditions.

This question belongs to: Science Biology

Question #776

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Which tissue provides mechanical support and flexibility to the growing parts of a plant?

A. Collenchyma

B. Parenchyma

C. Sclerenchyma

D. Xylem

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Correct Answer: Option A

Explanation:
Collenchyma is a simple permanent tissue characterized by cells with thickened corners due to the deposition of cellulose and pectin. It provides mechanical support, tensile strength, and flexibility to the growing parts of the plant (like stems and petioles), allowing them to bend without breaking. Parenchyma is for storage, and sclerenchyma provides rigid support.

This question belongs to: Science Biology

Question #777

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Double fertilization in angiosperms involves the fusion of one male gamete with the egg and the other male gamete with:

A. Helping cells

B. Synergids

C. Antipodals

D. Central cell (secondary nucleus)

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Correct Answer: Option D

Explanation:
Double fertilization is a unique feature of angiosperms. One male gamete fuses with the egg cell to form the diploid zygote (syngamy), which develops into the embryo. The second male gamete fuses with the diploid secondary nucleus (polar nuclei) of the central cell to form the triploid Primary Endosperm Nucleus (PEN), which develops into the endosperm.

This question belongs to: Science Biology

Question #778

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What is the correct dental formula for an adult human?

A. 2123 / 2123

B. 2103 / 2103

C. 2133 / 2133

D. 2122 / 2122

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Correct Answer: Option A

Explanation:
The dental formula represents the number of each type of tooth in one half of the upper and lower jaws. For an adult human, it is 2123 / 2123. This means: 2 Incisors, 1 Canine, 2 Premolars, and 3 Molars in each quadrant (upper right, upper left, lower right, lower left), totaling 32 teeth.

This question belongs to: Science Biology

Question #779

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Which enzyme is secreted by the gastric glands of the stomach in an inactive form?

A. Trypsin

B. Amylase

C. Pepsin

D. Lipase

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Correct Answer: Option C

Explanation:
Pepsin is the main digestive enzyme in the stomach. It is secreted by the chief cells (zymogenic cells) of the gastric glands in an inactive form called pepsinogen. Pepsinogen is activated into pepsin by the acidic environment created by hydrochloric acid (HCl) secreted by parietal cells. Pepsin then digests proteins into proteoses and peptones.

This question belongs to: Science Biology

Question #780

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The inner wall of the small intestine is lined with finger-like projections called:

A. Flagella

B. Villi

C. Microvilli

D. Cilia

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Correct Answer: Option B

Explanation:
The mucosal lining of the small intestine forms numerous finger-like projections called villi, which vastly increase the surface area for absorption of nutrients. Each villus contains a network of capillaries and a central lymphatic vessel (lacteal) for absorbing amino acids, sugars, and fats, respectively. Microvilli are further projections on the epithelial cells of the villi.

This question belongs to: Science Biology

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