The S-A node (sinoatrial node) is located in the: MCQ with Answer and Explanation

Explanation:
Phosphorus is part of the phosphate backbone of DNA/RNA and the high-energy bonds of ATP. Nitrogen is in bases and amino acids, iron in hemoglobin, sulfur in some amino acids. Phosphorus is essential for energy transfer and genetic material.

Explanation:
Phloem transports organic solutes (mainly sucrose) from source (leaves) to sink (roots, fruits) in a process called translocation, using sieve tubes and companion cells. Xylem transports water and minerals from roots upwards. Collenchyma and sclerenchyma are mechanical tissues providing support. Phloem is alive at maturity, while xylem vessels are dead. Companion cells regulate sieve tube activity.

Explanation:
In plant cells, which have rigid cell walls, cytokinesis occurs by the formation of a new cell wall (cell plate) in the middle of the cell. Mitosis is equational division occurring in somatic cells for growth and repair, maintaining the same chromosome number. Meiosis is reductional division, halving the chromosome number to produce gametes. Thus, statements 1 and 3 are correct.