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Darwin made four key observations in his studies of wild populations: members of a population of the same species vary in their traits; traits can be inherited, or passed from parents to offspring; popula...

Cells are the smallest unit of life that make up every living thing. A typical animal cell is made up of a cell membrane, which maintains its structure and controls what goes in and out of the cell. Enclo...

Both these processes involve the movement of molecules from an area of high concentration to low concentration. They are also both passive processes, so happen without the use of chemical energy. However,...

Carbon dioxide is a greenhouse gas that is produced through the burning of fossil fuels such as coal, oil and gas. Increased demands for electricity, heating and cars etc. means that more fossil fuels are...

Short answer: Dead and/or inactive pathogens. Explanation (also to a further question: "How does this prevent infection later?") : Pathogens are microorganisms...