A cell must exchange molecules and ions with its surroundings.  This process is controlled by the selective permeability of the plasma membrane.  Passive transport requires no energy from the cell; molecules like water can diffuse into and out of the cell through the phospholipid bilayer freely by way of osmosis.  Other molecules and ions, like sodium, are actively transported across the phospholipid bilayer.  This requires ATP created by the cell.  Active transport moves solutes against their concentration gradients, which is why it requires energy. 

Tonofibrils are groups of keratin tonofilaments (intermediate filaments) most commonly found in the epithelial tissues, not endocrine tissues, and which play an important structural role in cell makeup.

Glycolysis happens in the cytosol (the fluid containing the organelles) of the cell. The next step in cellular respiration, the citric acid cycle, occurs in the mitochondria.

Fermentation oxidizes molecules of NADH to NAD⁺ so the cell can have oxidizing agents for any subsequent glycolysis reactions. It does not, however, produce any usable energy in the process.

Fermentation leads to the production of ethanol in yeast cells and lactic acid in muscle cells.

Glycolysis occurs in the cytosol of cells. Once finished, the two pyruvate products are transported into the mitochondria to go through the citric acid cycle, at a cost of 1 ATP per pyruvate. Neither the nucleus, nor the endoplasmic reticulum have any function in glycolysis or the citric acid cycle.

The conversion of glucose to two pyruvate molecules in glycolysis produces a net total of two direct ATP. When fructose-1,6-bisphosphate enters glycolysis, it bypasses the two steps involved that normally cost one ATP each, therefore, there is no required input and the net total is four produced ATP.

We have to remember that each step beyond the conversion of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate happens twice, or we would come up with two ATP created.

Glycolysis is the first step in cellular respiration, and is seen in both aerobic and anaerobic respiration. The products of glycolysis are pyruvate, NADH, ATP, and water. Oxygen is only a product of the light reactions of photosynthesis; it is consumed as a reactant in the electron transport chain.

Glycolysis, which occurs in the cytoplasm, is the first step of cellular respiration. Though it does not produce a large amount of ATP by itself, it incorporates several important steps that must take place to yield a much more significant amount of ATP later. Notable events that occur during this multi-step process include the breakdown of each glucose molecule into two 3-carbon pyruvate molecules, the production of two molecules of , and the net production of two ATP molecules.

Unlike the next two steps (the citric acid cycle and oxidative phosphorylation), glycolysis can occur in the absence of oxygen. The only step given that is not part of glycolysis is the transfer of electrons from carrier molecules to oxygen via a series of steps. This happens during oxidative phosphorylation and, unlike glycolysis, is an aerobic process.

Fermentation is the metabolic process that takes place in anaerobic environments to regenerate for glycolysis, which takes place in both aerobic and anaerobic environments. Since glycolysis is unaffected by the presence of oxygen, pyruvate concentrations will be the same in either environment. During fermentation the cell changes the pyruvate into acetaldehyde. Ethanol is also a product of fermentation. We would not expect to see more acetaldehyde or ethanol in aerobic metabolism.

Adenosine triphosphate (ATP) is the main product of cellular respiration, and the molecular energy of the cell. Aerobic metabolism results in a much higher yield of these energy carrying molecules due to the fact that it can use oxygen as a final electron acceptor in the electron transport chain.

Glycolysis takes place in the cell cytosol, and can take place under anaerobic conditions. After the completion of glycolysis, the product pyruvate is transported to the mitochondria for the citric acid cycle and electron transport chain.

The nucleus houses the cell's DNA, and the endoplasmic reticulum is involved with protein modification.