Problem: - Air goes through all the little branches in your lungs to fill up the air sacs, or alveoli - Oxygen goes through the walls of the alveoli and into the capillaries - The oxygen goes into the bloodstream - Oxygen is left and carbon dioxide is picked up - You breathe it out through your lungs - What might be the first step of the process?

A: You breathe in

Problem: - The particles remove small pieces of the rock each time they touch the rocks - The particles continue to hit, brush against, or grow against the rocks - The rock eventually is broken apart by this contact - The pieces of the rock are now small rocks - The rock pieces are worn away into smaller and smaller pieces by the same forces - What might be the first step of the process?

A: Particles in the environment interact with rocks

Problem: - Blood is carried to the kidneys through the renal arteries - The kidneys contain filters inside - The filters capture the waste products - The waste is combined with water to make urine - The urine leaves the kidney and is collected in the bladder - The cleaned blood is returned to the body. What might be the first step of the process?

A: Waste products are deposited in the blood

Problem: - Over time, more sediment piles on top - The resulting heat and pressure transforms the organic layer into a dark and waxy substance known as kerogen - Left alone, the kerogen molecules eventually crack - The molecules break up into shorter and lighter molecules composed almost solely of carbon and hydrogen atoms - It will turn into either petroleum or natural gas - What might be the first step of the process?

A:
Dead organic material accumulates on the bottom of oceans, riverbeds or swamps, mixing with mud and sand