What is reproductive isolation required for speciation to occur

Speciation occurs when a single species becomes two or more separate species, which can no longer interbreed with one another. Reproductive isolation is required for speciation. Reproductive isolation means the groups in question cannot mate with one another, often because of physical barriers.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

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.