Concept:The part labelled 11 is a white blood cell/lymphocyte, which defends the body against infections.
Explanation:White blood cells are important components of the immune system.
They fight disease-causing organisms and help produce antibodies.
A decrease in their number makes the body weak against pathogens.
As a result, the body loses its ability to fight infections.
This leads to a reduction in immunity.
The other options, such as urine production, energy production, or population size, are not directly affected by a fall in white blood cell count.
Answer:D. decreased immunity
