Here's how it works:

1. Glucose uptake: Pneumococcus takes up glucose from its environment.

2. Glycolysis: Glucose is broken down through glycolysis, a process that occurs in the cytoplasm. This produces pyruvate and a small amount of ATP (adenosine triphosphate), the primary energy currency of cells.

3. Fermentation: Since pneumococcus is a facultative anaerobe (meaning it can live with or without oxygen), it primarily relies on fermentation to generate energy. In the absence of oxygen, pyruvate is converted to lactic acid. This process regenerates NAD+ (nicotinamide adenine dinucleotide), which is essential for glycolysis to continue.

4. ATP production: The net gain of ATP from glycolysis and fermentation is relatively low compared to aerobic respiration, which uses oxygen. However, it's sufficient for pneumococcus's survival.

Important note: Pneumococcus can also utilize other sugars, such as lactose and maltose, for energy production through similar fermentation pathways.

Summary: Pneumococcus obtains energy through fermentation of glucose, producing lactic acid as a byproduct. This process generates a small amount of ATP, which is enough for the bacterium's survival.