Answer:
a fuel for cellular respiration and a starting material for making other organic molecules.
Explanation:
Plants have the ability to produce sugars by the process of photosynthesis. Plants can convert the inorganic CO2 from the air into the organic nutrients such as sugars. Plants store sugars so that they can serve as a source of ATP for the cells as and when required. The sugars enter the process of cellular respiration and are oxidized into CO2 and H2O. In addition, the energy of chemical bonds of the sugars is used to form ATP molecules.
Plants also use sugars to synthesize other organic molecules. For example, several intermediates of Kreb's cycle can serve as precursors for the synthesis of amino acids. Amino acids are joined together to form different proteins.
Direct observation is an observation you make first hand. It is something you see with your own eyes and observe yourself.
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The spines of the cactus have several functions, which are the following:
To defend them from possible predators: inside the body of the plants there is a great deal of water; if herbivores could access it, these plants would not survive.
To provide them with shade: it is true that not much, but it is enough so that the loss of water by evaporation is minimal.
Reflect sunlight: many species have white spines.
