Which one of the following nutrients is not a source of energy for the body?
a. proteins
b. carbohydrates
c. vitamins
d. lipids

The organelle pictured is found in cells of and is theorized to have once been an independent organism.

The unique structure of the neuron is dedicated to the efficient and rapid transmission of neural signals. the relationship between neurons, the spinal cord, and the brain constitutes an elaborate communication system throughout the human body. all but one of the functions listed below are a result of this interaction.

In which of the following relationships is one organism always benefited while the other organism is always harmed