Assertion (A): Genetic variation is essential for evolution. Reason (R): Without variation, natural selection cannot occur because there are no differences to select from. MCQ with Answer and Explanation

Explanation:
Stomata are pores flanked by guard cells that regulate gas exchange and transpiration. Lenticels are on bark, hydathodes for guttation.

Explanation:
Testosterone, secreted by Leydig cells of the testes, is responsible for the development of male secondary sexual characteristics like facial hair, deepening of voice, and muscle growth. Estrogen and progesterone are female hormones.

Explanation:
Chlorophyll, mainly chlorophyll a and b, absorbs red and blue wavelengths and reflects green light, giving plants their characteristic color. It is the primary pigment of photosynthesis, located in the thylakoid membranes. Carotenoids reflect yellow-orange, phytochrome is a light-sensing pigment, anthocyanins are red/purple.