What is one of the principal chemical compounds that living things use to store energy

ATP or Adenosine triphosphate is the chief compounds which are used by the living things to store energy.

Explanation:

ATP is the compound that captures the chemical energy released through the degradation of food. It stores the captured energy and releases it at the time of need experienced by the organism.

It is made up of adenine, ribose sugar, and a phosphate group. It is produced in a cell organelle called mitochondria through a process called respiration.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.