Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.

Fact 1: a breathing mask is used for keeping harmful particles from entering the respiratory system. 
Fact 2: When mold grows in the house, it can emit particles that travel through the air.
A breathing mask can keep mold from entering the respiratory system.

Fact 1: Gametes then unite in fertilization and form a diploid zygote. 
Fact 2: Zygotes are diploid and undergo cell division to become an embryo.
Gametes then unite in fertilization and eventually become an embryo.

Fact 1: an incandescent light bulb converts electricity into light by sending electricity through a filament. 
Fact 2: Electrical energy is also energy.

a light bulb converts energy into light by sending energy through a filament.