Why is chirality of chemical compounds important?

First of all, chirality is the geometric property of some molecules or ions, where it is non-superimposible on its mirror image. Imagine your two hands, you cannot superimpose the two no matter how you try. The two chiral molecules are can enantiomers. Chirality is quite important in the natural world, where one enantiomer may be an important drug, while the other is toxic. An infamous example of the dangers of not understanding chirality is the drug thalidomide, which was used in the 1950s as a sleep agent for pregnant women. Unknown at the time, the enantiomer of the drug's active agent caused deformities in infants. This tragedy demonstrates the importance of understanding chirality.

Knowing that the brain only uses glucose as a source of energy, how does the body overcome the challenges of a carb-free diet? Ex. Keto-diet

The reason why the brain normally only uses glucose is because it can cross the blood-brain barrier, while fatty acids cannot and using proteins as a source of energy is inefficient. Under glucose poor conditions however, the body utilizes a chemical process called ketogenesis, where fatty acids are broken down into a compound called ketone bodies. These ketone bodies are able to cross the blood-brain barrier and then undergo additional processes before being utilized for energy by brain cells. The process is less energy efficient, hence why it is only used when conditions are less than ideal.

What is the powerhouse of the cell? :)

THE MITOCHONDRIA IS THE POWERHOUSE OF THE CELL!!!