Biological Importance of Magnesium and Calcium - UNSOLVED PRACTICE SET

Q7. Why is magnesium called the "central atom" of chlorophyll? What would happen to plants if magnesium were deficient in the soil?

Q8. Explain the role of calcium ions (Ca²⁺) in muscle contraction. What happens when calcium levels are too low in the blood?

Q9. Your grandmother complains of frequent muscle cramps, especially at night. Her doctor suggests increasing magnesium-rich foods in her diet. Explain why magnesium deficiency can cause muscle cramps.

Q10. Why do doctors recommend calcium and vitamin D supplements together for bone health? What is the relationship between these two nutrients?

Q11. Magnesium hydroxide (Mg(OH)₂) is used as an antacid under the brand name "Milk of Magnesia." Why is it preferred over sodium bicarbonate for treating chronic acidity?

Q12. Why is calcium important for blood clotting? What happens if blood calcium levels fall below normal (hypocalcaemia)?

Q13. Describe the biological importance of magnesium in living organisms. Discuss:

(a) Its role as the central atom in chlorophyll and significance in photosynthesis

(b) Its function as a cofactor for enzymes (ATPases, DNA polymerases)

(c) Its role in nerve transmission and muscle contraction

(d) Dietary sources of magnesium and daily recommended intake

(e) Symptoms of magnesium deficiency in humans and plants

Q14. Discuss the biological importance of calcium in the human body with reference to:

(a) Structural role in bones and teeth as hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)

(b) Role in muscle contraction and relaxation

(c) Importance in blood clotting (calcium as factor IV)

(d) Role in nerve impulse transmission

(e) Regulation of calcium levels by parathyroid hormone (PTH) and calcitonin

(f) Dietary sources and recommended daily intake for Indians

Q15. India faces significant public health challenges related to calcium and magnesium nutrition. Discuss:

(a) Why calcium deficiency is widespread among Indian women, especially post-menopausal women

(b) The role of traditional Indian diets (like ragi, sesame, and dairy) in providing these minerals

(c) Why vitamin D deficiency is common in India despite abundant sunlight, and its impact on calcium absorption

(d) Government initiatives like fortification of milk and wheat flour with calcium and vitamin D

Q16. The molecular formula of chlorophyll-a is C₅₅H₇₂O₅N₄Mg. A plant leaf contains 0.5% magnesium by mass in its chlorophyll content.

(a) Calculate the molar mass of chlorophyll-a.

(b) Calculate the mass percentage of magnesium in chlorophyll-a.

(c) If a leaf contains 2 g of chlorophyll-a, calculate the mass of magnesium present in it.

[Given: Atomic masses: C = 12, H = 1, O = 16, N = 14, Mg = 24]

Q17. Hydroxyapatite, the mineral in bones, has the formula Ca₁₀(PO₄)₆(OH)₂.

(a) Calculate the molar mass of hydroxyapatite.

(b) Calculate the mass percentage of calcium in hydroxyapatite.

(c) If a 70 kg adult has about 1 kg of calcium in their body, and 99% of it is in bones, calculate the mass of hydroxyapatite in their skeleton.

[Given: Atomic masses: Ca = 40, P = 31, O = 16, H = 1]

Q18. A 25-year-old Indian woman is advised to consume 1000 mg of calcium daily. Her diet provides:

200 mL milk (contains 120 mg calcium per 100 mL)

100 g spinach (contains 99 mg calcium per 100 g)

50 g almonds (contains 269 mg calcium per 100 g)

100 g curd (contains 85 mg calcium per 100 g)

(a) Calculate the total calcium she gets from her diet.

(b) Calculate the calcium deficit she needs to cover through supplements.

(c) If a calcium supplement tablet contains 500 mg of calcium carbonate (CaCO₃), calculate how many tablets she needs to meet her daily requirement. (Note: only 40% of calcium in CaCO₃ is elemental calcium.)

[Given: Atomic masses: Ca = 40, C = 12, O = 16]