Q.(a) Describe briefly the biological importance of Calcium and Magnesium. OR

Calcium is vital for skeletal structure, blood clotting, and muscle/nerve signalling; magnesium is central to photosynthesis (as the core atom of chlorophyll) and to numerous enzyme-catalysed, energy-related reactions in cells.

Biological importance of Calcium:

1. It is a major structural component of bones and teeth, present as calcium phosphate/hydroxyapatite, giving them rigidity and strength.
2. It plays an essential role in blood clotting (coagulation), acting as one of the required clotting factors.
3. It is required for muscle contraction — calcium ions trigger the interaction between actin and myosin filaments in muscle fibres.
4. It is essential for the transmission of nerve impulses across synapses.
5. It activates several enzymes in metabolic pathways.
6. In plants, calcium (as calcium pectate) is an important component of the middle lamella of plant cell walls, providing rigidity.

Biological importance of Magnesium:

1. It is the central metal atom of chlorophyll, the green pigment essential for photosynthesis in plants — without magnesium, plants cannot photosynthesize.
2. Along with calcium, it is a structural constituent of bones and teeth. …