Edexcel SNAB Biology AS Exam with Guaranteed Accurate Answers

They are too large for diffusion to transport substances quickly enough (small SA:V) - correct answer Why cant complex multi cellular organisms rely on diffusion to transport substances around the body? Blood is not contained in blood vessels but circulates in large spaces - correct answer Open circulatory system A simple heart pumps blood out into the cavities surrounding the organs. The heart muscle relaxes so the pressure decreases and blood is drawn from the cavity back into the heart through open valves - correct answer How does blood circulate in an open circulatory system Blood is enclosed in tubes. - correct answer Closed circulatory system The blood is forced through fairly narrow tubes so it travels faster and under pressure. - correct answer Why is a closed circulatory system more efficient Prevent the backflow of blood - correct answer Valves The blood is pumped through the heart once for each complete circuit - correct answer Single closed circulatory system The blood is pumped through the heart twice for each complete circuit - correct answer Double closed circulatory system Substances needed can be delivered rapidly to cells as the blood is given an extra boost which decreases the time taken for the blood to circulate around the whole body. - correct answer Why is a double closed circulatory system good Carries raw material from specialised exchange organs to the body cells to remove metabolic waste - correct answer Mass transport system The process where all the particles are transported in one direction - correct answer Mass flow Oxygen is more electronegative than Hydrogen so there is a slight difference in charge between the atoms. - correct answer Why is water a polar molecule Hydrogen bonding holds water molecules together and collectively they make water very stable - correct answer Why does water remain a liquid over a wide range of temperatures the delta positive H is attracted to the delta negative O. This helps water to flow so it is good at transporting substances - correct answer Why is water cohesive Polar molecules and ionic substances dissolve in water because water is dipolar. The forces of attraction between the delta positive H and the delta negative O are stronger than the ionic bonds so the ions become hydrated and completely surrounded by water molecules - correct answer Why is water a good solvent It needs more muscle to contract so it can pump blood powerfully to the whole body. The right ventricle only pumps blood to the nearby lungs - correct answer Why is the left ventricle thicker than the right