Problem: - The oxygen travels into the lungs - The oxygen binds to hemoglobin proteins within erythrocytes (red blood cells) - The erythrocytes are pumped through the body by the heart - All cells receive the oxygen. What might be the first step of the process?

A: Oxygen enters the body through the mouth or nose

Problem: - The recyclable materials go to a recycling center - The recycling center further separates the materials - Large equipment compacts the materials into bales - The recyclable materials are shipped to other recycling centers - The other recycling centers further process the materials that center specializes in - The materials are purchased by manufacturers - The manufacturers process the recycled materials the same way they would use new materials - The recycled materials are incorporated into new products. What might be the first step of the process?

A: People separate different materials to be recycled

Problem: - Engines produce carbon dioxide - Living things produce waste - Waste decomposes - Decomposition produces methane - Water evaporates - Water vapor joins the atmosphere - Carbon dioxide, water vapor and methane are greenhouse gases - What might be the first step of the process?

A: People breathe and expel carbon dioxide

Problem: - That bacteria begins to grow and reproduce inside the cells - The dividing bacteria begin to make toxins - Those toxins damage your cells - Disease symptoms may begin. What might be the first step of the process?

A:
Someone is infected with bacteria