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General ScienceEasyAsked in: NDA · NDA-I 2018, GAT

Which one of the following elements is needed in the human body to transfer electrical signals by nerve cells ?

  1. A.Lithium
  2. B.Sodium
  3. C.Rubidium
  4. D.Caesium

Correct answer

B. Sodium

Explanation

The correct answer is B, Sodium. Nerve impulses are carried by the movement of sodium and potassium ions across the membrane of the nerve cell, so sodium is essential.

A resting nerve cell keeps more sodium ions outside and more potassium ions inside, maintained by the sodium-potassium pump. When the nerve is stimulated, sodium channels open and sodium ions rush in, reversing the charge across the membrane; this is the action potential. Potassium ions then flow out to restore the resting state. The wave of charge travels along the axon as the nerve impulse. Sodium also helps control body fluids and blood pressure, and we get it mainly from common salt.

A is wrong because lithium is not needed by the body; its salts are used only as a medicine for some mental illnesses.

C is wrong because rubidium has no known essential role in human nerve signalling.

D is wrong because caesium is not an essential element, and its radioactive form is harmful.

Exam tip: nerve impulse = sodium in (depolarisation), potassium out (repolarisation); sodium-potassium pump keeps the resting potential.

Practice Questions

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Q1.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is not true for anodizing process?

  1. A.It makes aluminium corrosion resistant.
  2. B.Metals like aluminium, titanium and magnesium can be anodized.
  3. C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
  4. D.It is used in aircraft industry.
Show answer
Correct answer: C. Clean aluminium article is the anode and oxygen gas is evolved at the cathode.

In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.

Q2.General ScienceAsked in: CDS · CDS-II 2016, GKMedium

Which one of the following statements is not correct?

  1. A.The response of the ear to sound of increasing intensity is approximately logarithmic.
  2. B.The sensitivity of the human ear does not vary with the frequency of the sound.
  3. C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
  4. D.Longitudinal waves can travel in all media—solids, liquids and gases.
Show answer
Correct answer: B. The sensitivity of the human ear does not vary with the frequency of the sound.

The statement that the sensitivity of the human ear does not vary with frequency is false, because the ear is far more sensitive to some frequencies than to others.

Q3.General ScienceAsked in: CDS · CDS-I 2017, GKEasy

Kwashiorkor disease in children is caused by

  1. A.sufficient carbohydrates but less fats in diet
  2. B.sufficient carbohydrates and fats but deficient proteins in diet
  3. C.sufficient vitamins but deficient fats in diet
  4. D.sufficient fats but deficient vitamins in diet
Show answer
Correct answer: B. sufficient carbohydrates and fats but deficient proteins in diet

Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.

Q4.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is the correct order of pH for the given substances?

  1. A.Coffee < Lemon juice < Milk of magnesia < Blood
  2. B.Milk of magnesia < Blood < Coffee < Lemon juice
  3. C.Lemon juice < Blood < Coffee < Milk of magnesia
  4. D.Lemon juice < Coffee < Blood < Milk of magnesia
Show answer
Correct answer: D. Lemon juice < Coffee < Blood < Milk of magnesia

Arranged from most acidic to most basic, the four substances fall in exactly this order. Lemon juice, rich in citric acid, has a pH of about 2 to 2.5.