Nervous System

Step 1: Understanding scala tympani.
Scala tympani is a part of the bony labyrinth of the cochlea and is filled with perilymph.
Step 2: Terminal point of scala tympani.
Scala tympani ends at the round window.
Step 3: Connection of round window.
The round window opens into the middle ear cavity and helps in dissipation of sound waves.
Step 4: Conclusion.
Hence, A is round window and B is middle ear.

Step 1: Understanding somatic reflexes.
In somatic reflexes, which control voluntary movements, the effectors are skeletal muscles. These reflexes involve the nervous system's immediate response to stimuli.
Step 2: Analyzing the options.
(A) skin: Incorrect — Skin is the sensory receptor in reflexes, not the effector.
(B) glands: Incorrect — Glands may be involved in autonomic reflexes, but not in somatic reflexes.
(C) smooth muscles: Incorrect — Smooth muscles are involved in autonomic reflexes, not somatic reflexes.
(D) skeletal muscles: Correct — Skeletal muscles are the effectors in somatic reflexes.
Step 3: Conclusion.
The correct answer is (D) skeletal muscles, as they are the effectors in somatic reflexes.

Step 1: Understanding alveolar gas values.
Alveolar blood gas values are maintained by efficient exchange of gases between alveoli and pulmonary capillaries.
Step 2: Normal pCO\textsubscript{2 value. Under normal physiological conditions, the partial pressure of carbon dioxide (pCO\textsubscript{2}) in alveolar blood is approximately 45 mmHg.
Step 3: Analysis of options.
(A) 30: Incorrect — too low for alveolar blood.
(B) 104: Incorrect — corresponds to pO\textsubscript{2}, not pCO\textsubscript{2}.
(C) 45: Correct — normal alveolar pCO\textsubscript{2}.
(D) 90: Incorrect — abnormally high.
Step 4: Conclusion.
The pCO\textsubscript{2} of alveolar blood is 45 mmHg.

Step 1: Understanding types of food chains.
Food chains describe the transfer of energy from one trophic level to another. Different food chains begin with different primary sources of energy or matter.
Step 2: Detritus food chain.
The detritus food chain starts with dead and decaying organic matter, known as detritus, which is consumed by decomposers such as bacteria and fungi.
Step 3: Analysis of options.
(A) Aquatic: Incorrect — refers to habitat, not the starting material.
(B) Desert: Incorrect — refers to an ecosystem, not a food chain type.
(C) Grazing: Incorrect — grazing food chain starts with living green plants.
(D) Detritus: Correct — it begins with dead organic matter.
Step 4: Conclusion.
The food chain that starts with dead decaying organic matter is the detritus food chain.

Step 1: Understanding the role of cranial nerves.
The spinal accessory nerve controls the movement of the neck, pharynx, and shoulders. Injury to this nerve can cause difficulty in these areas.
Step 2: Analyzing the options.
(A) abducens: Incorrect, the abducens nerve controls eye movement, not neck or shoulder movements.
(B) hypoglossal: Incorrect, the hypoglossal nerve controls tongue movement, not pharynx, neck, or shoulders.
(C) spinal accessory: Correct, the spinal accessory nerve controls the muscles of the neck and shoulders, and damage can cause difficulties in these movements.
(D) vagus: Incorrect, the vagus nerve controls various functions including heart rate and digestion, not the movements of pharynx, neck, or shoulders.
Step 3: Conclusion.
The correct answer is (C) spinal accessory, as it is the nerve responsible for controlling the muscles in the neck and shoulders.

Step 1: Understanding neurotransmitter storage.
Neurotransmitters are stored in synaptic vesicles in the presynaptic neuron. These vesicles release neurotransmitters into the synaptic cleft when an action potential arrives.
Step 2: Analyzing the options.
(A) synaptic vesicles: Correct. Neurotransmitters are stored in synaptic vesicles before being released into the synaptic cleft.
(B) synaptic cleft: Incorrect. The synaptic cleft is the gap between neurons where neurotransmitters are released, but they are not stored there.
(C) pre synaptic membrane: Incorrect. Neurotransmitters are not stored in the membrane itself; they are stored in vesicles.
(D) post synaptic membrane: Incorrect. The post-synaptic membrane is where neurotransmitters bind, but they are not stored there.
Step 3: Conclusion.
The correct answer is (A) synaptic vesicles, as neurotransmitters are stored in these vesicles before release.

Step 1: Rediscovery of Mendel’s work.
Mendel’s experiments were rediscovered independently by Hugo de Vries, Karl Correns, and Erich von Tschermak.

Step 2: Contribution of Karl Correns.
Karl Correns critically analysed Mendel’s data and formulated the three classical laws of inheritance.

Step 3: Conclusion.
Thus, the correct answer is Karl Correns.

Step 1: Understanding nerve impulse initiation.
A nerve impulse begins when a neuron receives a stimulus strong enough to reach threshold potential.
Step 2: Ion movement during depolarization.
At threshold, sodium channels open rapidly, allowing Na ions to move into the neuron.
Step 3: Effect of sodium influx.
The influx of Na causes depolarization of the membrane, leading to the generation of an action potential.
Step 4: Conclusion.
The rapid influx of sodium ions initiates nerve impulse transmission.

Step 1: Understanding clover leaf model.
The clover leaf model describes the secondary structure of transfer RNA (t-RNA), proposed by Robert Holley.
Step 2: Structure of t-RNA.
t-RNA folds into a characteristic clover leaf shape due to intramolecular base pairing.
Step 3: Elimination of other options.
DNA has a double helical structure.
m-RNA is linear and single stranded.
r-RNA forms complex ribosomal structures but not a clover leaf.
Step 4: Conclusion.
Hence, t-RNA shows the clover leaf model.

Step 1: Understanding Broca's area.
Broca's area, located in the left hemisphere of the brain, is primarily responsible for speech production. Injury to this area results in difficulty speaking, a condition known as Broca's aphasia.
Step 2: Analyzing the options.
(A) Vision: Incorrect, vision is processed by the occipital lobe, not Broca's area.
(B) Speech: Correct, damage to Broca's area impairs speech production.
(C) Hearing: Incorrect, hearing is processed by the temporal lobe, not Broca's area.
(D) Smell: Incorrect, smell is processed by the olfactory bulb, not Broca's area.
Step 3: Conclusion.
The correct answer is (B) Speech, as Broca's area is critical for speech production.

Step 1: Understanding helper T-lymphocytes.
Helper T-cells (CD4\textsuperscript{+}) play a central role in regulating immune responses. They do not directly kill infected or abnormal cells but coordinate immune activities through cytokine secretion.
Step 2: Functions of helper T-cells.
Helper T-cells stimulate B-lymphocytes to produce antibodies.
They promote proliferation and activation of other T-cells.
They secrete cytokines that attract and activate macrophages.
Step 3: Identifying the exception.
Secretion of cell-killing substances like perforins is a function of cytotoxic T-lymphocytes (CD8\textsuperscript{+}), not helper T-cells.
Step 4: Conclusion.
Helper T-lymphocytes do not secrete perforins; hence option (D) is correct.

Step 1: Understanding anatomical associations.
Each organ of the excretory system has a specific tissue or structural feature associated with it.
Step 2: Checking each match.
(A) Urinary bladder -- transitional epithelium: Correct. The bladder is lined with transitional epithelium.
(B) Ureter -- detrusor muscle: Incorrect. Detrusor muscle is present in the urinary bladder, not the ureter.
(C) Column of Bertini -- in renal medulla: Correct. These are extensions of cortical tissue into the medulla.
(D) Kidneys -- retroperitoneal: Correct. Kidneys are located behind the peritoneum.
Step 3: Conclusion.
The incorrect match is option (B) because detrusor muscle is associated with the bladder, not the ureter.

Step 1: Understanding adolescent brain development.
During adolescence, different parts of the brain mature at different rates. Emotional and reward-related regions develop earlier than areas responsible for judgement and self-control.
Step 2: Role of amygdala.
The amygdala is associated with emotions, fear, pleasure, and reward processing. It develops faster during adolescence, leading to impulsive and risk-taking behavior.
Step 3: Conclusion.
Therefore, increased risk-taking behavior in adolescents is linked to faster development of the amygdala.

Step 1: Understanding Krebs cycle.
Krebs cycle oxidizes one acetyl-CoA molecule completely to CO .
Step 2: Energy yield per turn.
Per turn, it produces 3 NADH , 1 FADH , and 1 GTP.
Step 3: Considering pyruvate oxidation.
Including the link reaction (pyruvate to acetyl-CoA), one additional NADH is produced.
Step 4: Conclusion.
Thus, a single turn yields a total of 4 NADH , 1 FADH , and 2 GTP as per the given option.

Step 1: Understanding cranial nerve branches.
The trigeminal nerve is the fifth cranial nerve and is a major sensory nerve of the face.
Step 2: Branches of trigeminal nerve.
It has three major divisions: ophthalmic, maxillary, and mandibular nerves.
Step 3: Conclusion.
Therefore, the correct answer is (D) Trigeminal.

Step 1: Understanding the axon and its components.
The axon of a neuron is surrounded by a thin membrane known as the neurilemma. It is responsible for the regeneration of nerve fibers and helps in the conduction of nerve impulses. Step 2: Analyzing the options.
(A) Neurilemma: Correct. The neurilemma is the outermost layer surrounding the axon of a neuron.
(B) Sarcolemma: This is the membrane that surrounds muscle fibers, not axons.
(C) Chromonema: This is part of the chromosome, not related to axons.
(D) Nucleollemma: This is not a recognized term in biology. Step 3: Conclusion.
The correct answer is (A) Neurilemma.

Step 1: Understanding the function of medulla oblongata.
The medulla oblongata is responsible for regulating vital activities like heart rate and respiration. Injury to the medulla oblongata can result in the cessation of these vital functions, leading to sudden death.
Step 2: Analyzing the options.
(A) reflex activities like swallowing, vomiting etc. stop: Incorrect — These are important functions controlled by the medulla, but the most immediate consequence of injury is the stoppage of vital functions.
(B) vital activities such as heart beat and respiration stop: Correct — Injury to the medulla oblongata directly impacts vital life-sustaining functions such as heart and respiration.
(C) secretion of cerebrospinal fluid completely stops: Incorrect — While the medulla regulates certain functions, it is not directly involved in the secretion of cerebrospinal fluid.
(D) both anterior and posterior choroid plexuses are damaged: Incorrect — This is not the direct result of medulla oblongata injury.
Step 3: Conclusion.
The correct answer is (B) vital activities such as heart beat and respiration stop, as injury to the medulla oblongata results in the loss of these vital functions.

Step 1: Understanding the Glossopharyngeal nerve.
The Glossopharyngeal nerve (Cranial nerve IX) plays a role in taste, saliva secretion, and swallowing. It affects taste sensation on the posterior third of the tongue and stimulates the parotid salivary gland.
Step 2: Analyzing the options.
(A) rotation of eyeball: Correct — The Glossopharyngeal nerve does not control eye movement, which is primarily regulated by the oculomotor, trochlear, and abducens nerves.
(B) swallowing secretion: The Glossopharyngeal nerve does contribute to swallowing and saliva secretion, particularly from the parotid gland.
(C) saliva secretion: The Glossopharyngeal nerve is involved in saliva secretion from the parotid gland.
(D) sense of taste: The Glossopharyngeal nerve is responsible for the sense of taste on the posterior third of the tongue.
Step 3: Conclusion.
The correct answer is (A) rotation of eyeball, as the Glossopharyngeal nerve does not affect eye movements.

Step 1: Understanding Mendel's experiments.
Gregor Mendel conducted experiments on pea plants and performed both monohybrid and dihybrid crosses to study inheritance patterns. Monohybrid crosses examine the inheritance of one trait, while dihybrid crosses examine the inheritance of two traits.
Step 2: Analyzing the options.
(A) Both Monohybrid and dihybrid: Correct — Mendel performed both monohybrid and dihybrid crosses to study the inheritance of traits.
(B) Monohybrid, dihybrid and trihybrid: Incorrect — Mendel's experiments focused on monohybrid and dihybrid crosses, not trihybrid.
(C) Monohybrid only: Incorrect — Mendel also performed dihybrid crosses.
(D) Dihybrid only: Incorrect — Mendel performed both monohybrid and dihybrid crosses.
Step 3: Conclusion.
The correct answer is (A) Both Monohybrid and dihybrid, as Mendel conducted both types of crosses.