It is supposed to protect the cell from it's surroundings, or from the outside.
Answer:
The pH of an aqueous solution is the measure of how acidic or basic it is. The pH of an aqueous solution can be determined and calculated by using the concentration of hydronium ion concentration in the solution.
Explanation:
Answer: The early atmosphere
Explanation: Its early atmosphere was probably formed from the gases given out by volcanoes. It is believed that there was intense volcanic activity for the first billion years of the Earth's existence. The early atmosphere was probably mostly carbon dioxide, with little or no oxygen.
Answer:
The molarity of methylene blue is 1.5 × 10⁻⁵ M
Explanation:
When we talk about aqueous solutions, 1 ppm means 1 mg of solute per liter of solution. We need to express this concentration in molarity, which is moles of solute per liter of solution. To convert mass to moles we need the molar mass of methylene blue(MB), which is 320 g/mol.
Then,

Mixtures are a group of elements that are mixed together but not chemically combined
Elements are the fundamental materials of which all matter is composed.
Element: A substance that is made up of only one type of atom. Compound: A substance that is made up of more than one type of atom bonded together. Mixture: A combination of two or more elements or compounds which have not reacted to bond together