Biology Key Points for O Level

9619 WordsDec 3, 201239 Pages
Cell structure and organization • Chloroplasts o Site of photosynthesis where light energy is absorbed o Consist of grana which are stacked up to increase surface area for absorption of light o Only present in plant cells • Cell membrane (plasma membrane) o Lipid bilayer that surrounds the cell, interspersed with protein molecule o Presence of temporary pores o Selectively permeable  Controls movement of substances o Diffusion, osmosis and active transport can therefore take place o Prevent outflowing of cytoplasm o Tonoplast  Plasma membrane surrounding the vacuole • Cell wall o Made of cellulose (a polysaccharide), and may be deposited with ligin o Maintain cell turgidity, provide mechanical support, protect from mechanical damage o…show more content…
lls of different type grouped together for the same function Organ o Different tissues working together and enabling the organ to perform its function Organ system o Different organs working together for a special purpose Movement of substances • Diffusion o The random movement of molecules of a substance from a region of higher concentration to a region of lower concentration • Osmosis o The movement of water (or solvent) molecules from a region of higher concentration to a region of lower concentration across a partially permeable membrane • Active transport o The movement of substances into or out of cells against a concentration gradient • Water potential o The measure of the free kinetic energy of water in a system, or the tendency for water to leave a system o High water potential = high tendency for water to leave the system/low tendency for water to enter a system/high concentration of water • Osmotic potential o Low osmotic potential = low tendency for water to enter a system/high tendency for water to leave the system/high water potential/high concentration of water • Hypertonic environment • • o Cell has high water potential o Cell has low osmotic potential o Water leaves the cell Hypotonic environment o Cell has low water potential o Cell has high osmotic potential o Water enters the cell Isotonic solution o Cell gains and lose water at the same rate o No net loss or gain in water Biological molecules • Importance of water o Use as a biological solvent 
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