That the oxygen levels in the test tube increased and carbon dioxide levels decreased because plants produce oxygen using carbon dioxide
Unlike arteries, veins contain valves that ensure blood flows in only one direction. (Arteries don't require valves because pressure from the heart is so strong that blood is only able to flow in one direction.) Valves also help blood travel back to the heart against the force of gravity.
The answer might be lipid A
the correct answer is D) The photovoltaic cells absorb light energy from the sun, then the energy is stored as chemical potential energy in the battery where it can be transferred to electrical energy.
Answer:
Exposure to the disease
Explanation:
Before vaccines, the only way to develop immunity to a disease was to be exposed to the disease-causing pathogen without being harmed by it. A good example of this is smallpox, which was also the first vaccine developed. It was noticed that milk maids weren't catching and dying from small pox like everyone else, because they had been exposed to cowpox. This premise was used to create the first vaccine.
Vaccines give you immunity by injecting you with a small amount of a (usually inactive) pathogen. inside your body. This means your immune system produces antibodies against it. Similar to what happened with the milkmaids.
