Affect

Directions: Some words in the passage below have been highlighted. Select the best meaning for the corresponding word.

All animal life on planet earth depends on sufficient supply of oxygen for its day-to-day survival. The trees that now just sporadically dot our landscapes, but once heavily blanketed earth’s surface, still are able to provide a large portion of oxygen supply. Through a process of photosynthesis, trees take in carbon dioxide from surrounding air and in return create a sizeable amount of oxygen. Ironically, human beings, who cut down large number of trees to create land, shelter, and energy, pose the most significant threat to survival of world–wide tree population.
But humans are not the only forces that threaten the survival of these mighty members of plant kingdom. Lighting, fire, volcanoes and earthquakes not only destroy many square miles of old growth forest in a matter of hours but may prevent new trees from going. Disease causing fungi and insect pests can either eradicate certain types of trees or weaken their branches.     
Climate also determines whether particular species of tree will prosper in a given area. Amount of rainfall and range of temperature also affect distribution of tree species.