Why are cacti green and why do they need needles

The needle-like leaves act as a self-defense mechanism that protects the plant from predators. The stem of the cactus plant is swollen and contain numerous collapsible water-storage cells that store water for a relatively long period. The stem is green and performs photosynthesis.

Explanation:

image result for how many calories of energy will 20 grams of carbohydrates provide in one gram provides 4 calories

consuming the right balance of protein, carbohydrates and fat can you maintain a healthy weight and optimize your energy levels. protein and carbohydrates both contain 4 calories per gram, while fat provides 9 calories per gram.