Free NEET Biology MCQs – Botany & Zoology Practice
Free NEET Biology MCQs- MCQAdda — Practice Questions
1. During the Calvin cycle, which molecule directly accepts CO₂ in C3 plants?
- (A) PEP (phosphoenolpyruvate)
- (B) RuBP (ribulose-1,5-bisphosphate)
- (C) G3P (glyceraldehyde-3-phosphate)
- (D) OAA (oxaloacetic acid)
Answer: (B) RuBP (ribulose-1,5-bisphosphate)
RuBP is carboxylated by the enzyme RuBisCO to fix CO₂, forming two molecules of 3-phosphoglycerate (3-PGA), the first step of the Calvin cycle.
2. A plant kept continuously in darkness for several days is suddenly exposed to light. Which process will be restored first?
- (A) Starch accumulation in leaves
- (B) ATP generation by photophosphorylation
- (C) Cell division
- (D) Protein degradation
Answer: (B) ATP generation by photophosphorylation
Light reactions begin immediately upon illumination, producing ATP and NADPH before significant carbohydrate accumulation occurs.
3. A person develops severe diarrhea leading to excessive loss of bicarbonate ions. Which acid-base imbalance is most likely?
- (A) Respiratory acidosis
- (B) Respiratory alkalosis
- (C) Metabolic acidosis
- (D) Metabolic alkalosis
Answer: (C) Metabolic acidosis
Loss of bicarbonate reduces blood buffering capacity, causing metabolic acidosis.
4. During the cardiac cycle, ventricular pressure becomes greater than atrial pressure but remains lower than aortic pressure. Which phase is occurring?
- (A) Ventricular ejection
- (B) Isovolumetric contraction
- (C) Isovolumetric relaxation
- (D) Rapid ventricular filling
Answer: (B) Isovolumetric contraction
During isovolumetric contraction, AV valves are closed while semilunar valves have not yet opened, so ventricular volume remains constant.
5. A mutation prevents formation of the synaptonemal complex. Which meiotic event will be directly affected?
- (A) DNA replication
- (B) Synapsis of homologous chromosomes
- (C) Cytokinesis
- (D) Chromatid separation
Answer: (B) Synapsis of homologous chromosomes
The synaptonemal complex is essential for pairing homologous chromosomes during zygotene of Prophase I.
6. Which tissue would be most severely affected by prolonged vitamin C deficiency?
- (A) Cartilage
- (B) Skeletal muscle
- (C) Connective tissue
- (D) Nervous tissue
Answer: (C) Connective tissue
Vitamin C is required for collagen synthesis. Deficiency weakens connective tissue, leading to scurvy.
7. A patient has normal ventilation but poor oxygen diffusion across the alveolar membrane. Which condition best explains this?
- (A) Bronchial asthma
- (B) Pulmonary fibrosis
- (C) Hyperventilation
- (D) Respiratory alkalosis
Answer: (B) Pulmonary fibrosis
Pulmonary fibrosis thickens the respiratory membrane, reducing diffusion of oxygen into the blood.
8. A mutation in the lac operon prevents binding of the repressor protein to the operator region. What will happen?
- (A) Structural genes remain permanently inactive
- (B) Structural genes are expressed continuously
- (C) RNA polymerase cannot bind promoter
- (D) Translation stops completely
Answer: (B) Structural genes are expressed continuously
Without repressor binding, RNA polymerase continuously transcribes the structural genes regardless of lactose availability.
9. In flowering plants, which structure ultimately gives rise to the seed coat?
- (A) Zygote
- (B) Endosperm
- (C) Integuments
- (D) Synergids
Answer: (C) Integuments
After fertilization, the integuments of the ovule develop into the seed coat.
10. Which adaptation contributes most directly to water conservation in CAM plants?
- (A) Bundle sheath cells
- (B) Night-time opening of stomata
- (C) Increased transpiration
- (D) Reduced chlorophyll
Answer: (B) Night-time opening of stomata
CAM plants open their stomata at night, minimizing water loss while fixing carbon dioxide.
11. A deficiency of surfactant primarily increases:
- (A) Lung compliance
- (B) Alveolar surface tension
- (C) Oxygen affinity of hemoglobin
- (D) Pulmonary blood flow
Answer: (B) Alveolar surface tension
Surfactant reduces alveolar surface tension. Its deficiency increases surface tension and may cause alveolar collapse.
12. Which blood component is primarily responsible for transporting most carbon dioxide?
- (A) Hemoglobin
- (B) Plasma bicarbonate
- (C) Dissolved CO₂
- (D) Plasma proteins
Answer: (B) Plasma bicarbonate
Approximately 70% of carbon dioxide is transported in blood as bicarbonate ions.
13. A patient receives broad-spectrum antibiotics for several weeks. Which vitamin deficiency is most likely due to reduced intestinal bacterial synthesis?
- (A) Vitamin A
- (B) Vitamin K
- (C) Vitamin C
- (D) Vitamin D
Answer: (B) Vitamin K
Intestinal bacteria synthesize vitamin K, which is essential for the synthesis of blood clotting factors.
14. A scientist inhibits crossing over without affecting chromosome pairing. Which genetic consequence is expected?
- (A) Increased mutation rate
- (B) Reduced genetic recombination
- (C) Failure of DNA replication
- (D) Polyploidy
Answer: (B) Reduced genetic recombination
Crossing over generates new allele combinations. Its inhibition reduces genetic recombination.
15. Which event occurs immediately after syngamy during double fertilization in angiosperms?
- (A) Fruit ripening
- (B) Triple fusion
- (C) Development of pollen tube
- (D) Formation of seed coat
Answer: (B) Triple fusion
After syngamy, the second male gamete fuses with the polar nuclei to form the primary endosperm nucleus through triple fusion.
16. Which plant tissue remains alive at maturity despite being part of the xylem?
- (A) Vessel
- (B) Tracheid
- (C) Sclerenchyma
- (D) Xylem parenchyma
Answer: (D) Xylem parenchyma
Xylem parenchyma is the only living component of xylem and functions in storage and lateral transport.
17. Which endocrine gland develops from Rathke's pouch during embryonic development?
- (A) Thyroid gland
- (B) Posterior pituitary
- (C) Anterior pituitary
- (D) Adrenal cortex
Answer: (C) Anterior pituitary
The anterior pituitary (adenohypophysis) develops from Rathke's pouch, an ectodermal outgrowth of the embryonic oral cavity.
18. A mutation prevents cytokinesis after mitosis in a plant cell. What will most likely be produced?
- (A) Haploid cell
- (B) Binucleate cell
- (C) Polyploid gamete
- (D) Enucleated cell
Answer: (B) Binucleate cell
Nuclear division occurs normally, but failure of cytokinesis results in a single cell containing two nuclei.
19. Which ecological interaction benefits one species while the other is neither harmed nor benefited?
- (A) Mutualism
- (B) Commensalism
- (C) Predation
- (D) Competition
Answer: (B) Commensalism
In commensalism, one organism benefits whereas the other is unaffected.
20. Which hormone is primarily responsible for milk ejection but not milk synthesis?
- (A) Prolactin
- (B) Oxytocin
- (C) Estrogen
- (D) Progesterone
Answer: (B) Oxytocin
Oxytocin causes contraction of myoepithelial cells, resulting in milk ejection. Prolactin is responsible for milk production.