AQA AS LEVEL BIOLOGY QUESTIONS AND VERIFIED ANSWER S SOLUTIONS LATEST UPDATE 2024 \2025 GRADED A+ "#"why does the diameter of a tree decrease during the day? ANSWER more light and higher temp increased transpiration rate so increased transpirational pull walls of xylem are pulled in bc water molecules stick to xylem wall water pulled up xylem by cohesion tension. "#"leaf structure ANSWER upper epidermis with waxy cuticle palisade cells spongy mesophyll air spaces lower epidermis guard cells and stomata "#"adaptation of palisade cells for photosynthesis? ANSWER near top so close to light large size and surface area thin cell wall so short diffusion difference for co2 many chloroplasts large vacuole pushes chloroplasts "#"structure of chloroplast ANSWER double membrane thykaloid disks stacked to make granum. contain chlorophyll surrounded by stroma "#"how does exchange in leaf occur? ANSWER when turgid, guard cells open forming stomata opening day- ps and respiration so co2 moves in and o2 moves out night - respiratio n so co2 moves out and o2 moves in "#"how does transpiration occur? ANSWER moist spongy mesophyll cell lining evaporates forming water vapour builds up in air spaces if con is high enough, water vapour diffuses out h2o molecules are polar so form hyd rogen bonds - transpiration stream "#"what are the building blocks of carbohydrates called? ANSWER monosaccharides "#"why is ATP a good source of energy? ANSWER immediate release, only need to break one bond releases small amounts of e nergy at a time, manageable "#"examples of monosaccharides ANSWER glucose, fructose, galactose "#"water properties? ANSWER dipolar partially positive hydrogen partially negative oxygen so separate water molecules form hydrogen bonds with eachother "#"difference between alpha and beta glucose? ANSWER on carbon 1, alpha glucose has an OH group on the bottom. beta glucose has it at the top. "#"how are monosaccharides joined together? ANSWER condensation reaction between 2 OH groups "#"roles of water? ANSWER -habitat, high shc so a lot of heat needs to be applied before evaporation due to hydrogen bonds. ice is less dense than wate r so floats up -solvent, dipolar so separate solutes by charge depending on partial charge. solute dissolves in water, useful for cytoplasm, diffusion and active transport ect -hydrostatic pressure, when pressurised, water provides a strong pushing force p articularly in mass flow. supports turgidity -homeostasis, sweat on skin uses blood heat to evaporate, cooling individual. sweat is made up of hydrogen bonds,stable structure, large amount of heat to evaporate. LATENT HEAT OF EVAPORATION. "#"bond in carb ohydrate? ANSWER glycosidic "#"what are inorganic ions? ANSWER salts or minerals don't contain carbon eg sodium and chloride ions "#"examples of disaccharides ANSWER sucrose, lactose (glucose + galactose), maltose (glucose + glucose) "#"kingdoms o f biology? ANSWER animal, plant, bacteria, fungi, protocista animal and plant multicellular others are microorganisms
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