The three-carbon molecules broken down from six-carbon molecules of glucose during the first step in the process of nutrition in all organisms is called:

pyruvate

The correct answer is option 3. pyruvate.

The three-carbon molecules broken down from six-carbon molecules of glucose during the first step in the process of nutrition in all organisms is called pyruvate.

During the initial step of the process of nutrition, which is known as glycolysis, glucose, a six-carbon molecule, is broken down into two three-carbon molecules called pyruvate. This process occurs in the cytoplasm of cells and does not require oxygen, making it anaerobic. Glycolysis involves a series of enzymatic reactions that convert glucose into pyruvate, while also producing a small amount of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide) molecules, which carry energy and electrons respectively.

Pyruvate is a key intermediate in cellular metabolism. Depending on the availability of oxygen and the metabolic needs of the cell, pyruvate can undergo further metabolic pathways. In aerobic conditions (with oxygen present), pyruvate enters the mitochondria and undergoes aerobic respiration to produce more ATP. In anaerobic conditions (without oxygen), pyruvate may be converted into lactate or ethanol through fermentation processes.

Overall, pyruvate plays a crucial role as an intermediate in the breakdown of glucose to provide energy for cellular activities in all organisms, from bacteria to plants to animals.