The immune system.
The immune system acts as a defense system of the body. It fights against bacteria, viruses and any other disease causing pathogens. Some chemicals can weaken the immune system and make them vulnerable.
Answer: The correct answer is -
D) giraffes having increasingly longer necks over time.
Natural selection is an evolutionary mechanism that was proposed by Darwin.
According to this mechanism, organisms that are better capable of adapting to their changing environmental conditions, survive and increase their number through reproduction whereas other are eliminated from the population.
Example - Long neck of Giraffe, which is much elongated, lofty stature, that was beautifully adapted for browsing on the higher tree branches. This was an adaptation with slow and gradual change in the gene frequency as the lower vegetation was eaten by other animals. Due to this, giraffes had to search for other source (that was higher tree branches).
This is considered as a peculiar example of natural selection.
Answer:
Most humans would associate the smell of the doctor's or dentist's with something bad or painful, when on the other hand baking cookies or having a nice smell of Thanksgiving can remind us of tasty food and comfort with family or just comfort in general.
Explanation:
Above ^^
First answer is correct. Eutrophication can have serious effects, like algal blooms that block light from getting into the water and harm the plants and animals that need it. If there's enough overgrowth of algae, it can prevent oxygen from getting into the water, making it hypoxic and creating a dead zone where no organisms can survive.
Answer:
O2 contains only one type of atom.
Explanation:
