when mendel was working, most scientists did not know what was inside the nucleus of a cell. explain
why this made it difficult for scientists to understand how mendel's factors could cause inheritance of
characteristics.

Mendel's work and his Laws of Inheritance were not understood in his time. This is because he hypothesized that genes come in pairs and are inherited as distinct units, one from each parent. The concept of inheritance by gene was difficult to understand because they didn't know what is inside the nucleus of a plant cell.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

explanation: