NEET Biology 4 — Questions and Answers
Question 1: Which type of immunity involves memory cells that respond faster upon second exposure to an antigen?
- Innate immunity
- Active acquired immunity (Correct answer)
- Passive immunity
- Non-specific immunity
Correct answer: Active acquired immunity
Active acquired immunity involves B and T memory cells that enable a rapid, enhanced secondary immune response upon re-exposure.
Question 2: In a dihybrid cross between AaBb × AaBb, what fraction of offspring will show both dominant traits?
- 1/16
- 9/16 (Correct answer)
- 3/16
- 15/16
Correct answer: 9/16
Using the product rule, 3/4 (dominant for A) × 3/4 (dominant for B) = 9/16 show both dominant phenotypes.
Question 3: Pneumatophores are aerial roots seen in:
- Banyan tree
- Rhizophora (mangroves) (Correct answer)
- Maize
- Orchids
Correct answer: Rhizophora (mangroves)
Pneumatophores are negatively geotropic roots in mangroves like Rhizophora that project above waterlogged soil for gas exchange.
Question 4: The fluid mosaic model of cell membrane was proposed by:
- Watson and Crick
- Singer and Nicolson (Correct answer)
- Davson and Danielli
- Robertson
Correct answer: Singer and Nicolson
Singer and Nicolson proposed the fluid mosaic model in 1972, describing the membrane as a fluid phospholipid bilayer with embedded proteins.
Question 5: Which of the following is an example of mutualism?
- Tapeworm in human intestine
- Cuckoo laying eggs in another bird's nest
- Mycorrhizae with plant roots (Correct answer)
- Orchid growing on a tree branch
Correct answer: Mycorrhizae with plant roots
Mycorrhizae (fungi + plant roots) is mutualism: fungi improve nutrient uptake for the plant and receive photosynthates in return.
Question 6: During oxidative phosphorylation, ATP synthase (Complex V) is driven by:
- NADH oxidation directly
- A proton gradient across the inner mitochondrial membrane (Correct answer)
- Substrate-level phosphorylation
- Electron transfer from FADH₂
Correct answer: A proton gradient across the inner mitochondrial membrane
The proton-motive force created by H⁺ accumulation in the intermembrane space drives ATP synthesis as protons flow back through ATP synthase.
Question 7: Hardy-Weinberg equilibrium is disturbed by all of the following EXCEPT:
- Natural selection
- Genetic drift
- Random mating (Correct answer)
- Mutation
Correct answer: Random mating
Random mating is one of the conditions required to maintain Hardy-Weinberg equilibrium, not a factor that disturbs it.
NEET Biology 4
Which type of immunity involves memory cells that respond faster upon second exposure to an antigen?