The correct answer to this question is this one: they lacked oxygen. The earliest organisms were completely heterotrophic in nature because of the reason that they lacked oxygen. <span>A heterotroph is an organism that cannot fix carbon and uses organic carbon for growth. </span>
All other organs, ducts, and glands in the reproductive system are considered secondary, or accessory, reproductive organs. These structures transport and sustain the gametes and nature the developing offspring.
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Answer:
3 ways to understand the differences between compounds and mixtures are described below in explanation.
Explanation:
1. In a mixture, no new product is formed. It is a simple tacking of two molecules without any chemical reaction occurring. For example water and sand. Compound is a new substance formed by chemical reactions occurring between various molecules. For example, carbon and oxygen combine to form carbon dioxide.
2. A compound is always homogeneous whereas a mixture can be homogeneous or heterogeneous.
3. Compounds have a fixed boiling and melting temperature. Whereas, mixtures do not have a definite melting and boiling temperature.
Air, water, weather, temperature and other organisms.
