Consider statements about cell biology: 1. The cell membrane is selectively permeable. 2. The nucleus contains genetic material. 3. Mitochondria are the site of photosynthesis. Which are correct? MCQ with Answer and Explanation

Explanation:
Photoperiodism is the physiological reaction of organisms, particularly plants, to the length of the day or a dark period. It is the mechanism by which plants measure the relative lengths of light and dark periods to regulate developmental processes, most notably the timing of flowering. Plants are classified as short-day plants, long-day plants, or day-neutral plants based on their flowering response to photoperiod. The photoreceptor pigment phytochrome is crucial in perceiving these light/dark signals.

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.

Explanation:
Cyclic adenosine monophosphate (cAMP) is a common intracellular second messenger produced by adenylyl cyclase upon hormone receptor activation (e.g., glucagon, adrenaline). It activates protein kinase A, triggering a cascade of cellular responses. Other second messengers include IP₃, DAG, Ca²⁺.