An illness caused by a bacterium
an illness caused by a virus
an illness caused by a fungus
an illness caused by a protist

Bacterium - the bacteria called streptococcus causes a sore throat infection. Infection is spread mostly through inhaling airborne droplets infected with the bacteria  released into the air when an infected person sneezes or coughs.

Virus -  the virus known as Human immunodeficiency virus (HIV) cause acquired immune deficiency syndrome (AIDS). Transmission is mostly through sexual means and use of needles, razors etc contaminated with fluid that has the virus.

fungus - the fungus called candida  causes oral thrush and also athlete's foot in man. Transmission is through skin contact with any surface that has been contaminated with the fungus, also through sharing personal items like towels and sandals.

Protist -  the protist called Entamoeba histolytica causes an infection called amoebic dysentery. Transmission is through consuming contaminated food and drink.

because the light is a great source of energy for the plants to survive. (i hope this )

i think its white blood cells

i hope this