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General Biology: Water, Lipids, Membranes, and Transport

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  • Why is water a polar molecule?
    Water is polar because oxygen has a higher electronegativity, pulling shared electrons closer and creating a slight negative charge on oxygen and a slight positive charge on hydrogen.
  • What are hydrogen bonds in water?
    Hydrogen bonds are weak attractions between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another.
  • How does cohesion relate to water?
    Cohesion is the tendency of water molecules to stick together due to hydrogen bonding.
  • Why can insects walk on water?
    Insects can walk on water because surface tension arises from cohesive hydrogen bonds between water molecules.
  • How do hydrogen bonds affect water's heat capacity?
    Hydrogen bonds require a lot of energy to break, so water can absorb much heat without a large temperature increase.
  • What causes evaporative cooling in water?
    When water evaporates, molecules with high energy leave, taking heat away and cooling the surface.
  • Why is ice less dense than liquid water?
    In ice, stable hydrogen bonds hold molecules farther apart, making ice less dense and able to float.
  • What is a solvent, solute, and solution?
    A solvent dissolves substances; a solute is dissolved; a solution is a uniform mixture of solvent and solute.
  • Why is water called the solvent of life?
    Water's polarity allows it to dissolve many polar and charged substances, forming aqueous solutions essential for life.
  • What ions form when water dissociates?
    Water dissociates into hydrogen ions (H+) and hydroxide ions (OH–), both highly reactive.
  • How is acidity measured and what does pH indicate?
    Acidity is measured by pH; pH less than 7 is acidic, 7 is neutral, and greater than 7 is basic.
  • What is the role of buffers in biological systems?
    Buffers resist pH changes by accepting excess H+ ions or donating H+ ions when depleted.
  • What are lipids and their main characteristics?
    Lipids are hydrophobic molecules mainly made of carbon and hydrogen, important for long-term energy storage.
  • What are the three main types of lipids?
    Fats, phospholipids, and steroids.
  • What is the structure of a fat (triglyceride)?
    A fat consists of one glycerol molecule linked to three fatty acids via dehydration reactions.
  • Difference between saturated and unsaturated fatty acids?
    Saturated fatty acids have no double bonds and maximum hydrogens; unsaturated have one or more double bonds causing kinks.
  • What are phospholipids and their role in membranes?
    Phospholipids have two fatty acids and a phosphate group; they form bilayers that make up cell membranes.
  • How do phospholipid bilayers arrange in water?
    Hydrophilic heads face water inside and outside the cell; hydrophobic tails face inward, away from water.
  • What is the function of cholesterol in membranes?
    Cholesterol stabilizes membrane fluidity by preventing tight packing at warm temperatures and maintaining fluidity at cold temperatures.
  • What is the fluid mosaic model of membranes?
    Membranes are flexible bilayers of phospholipids with embedded proteins that perform various functions.
  • What are some functions of membrane proteins?
    Membrane proteins maintain cell shape, act as receptors, enzymes, participate in cell recognition, and form intercellular junctions.
  • What is passive transport?
    Passive transport is the diffusion of molecules across membranes without energy input, moving down their concentration gradient.
  • Define osmosis.
    Osmosis is the diffusion of water across a selectively permeable membrane from low to high solute concentration.
  • What happens to animal cells in isotonic, hypotonic, and hypertonic solutions?
    Isotonic: no volume change; hypotonic: water enters, cell may burst; hypertonic: water leaves, cell shrinks.
  • What is osmoregulation?
    Osmoregulation is the control of water balance to maintain cell survival in varying environments.
  • How do plant cell walls affect water balance?
    Cell walls prevent plant cells from bursting in hypotonic solutions by exerting pressure; in hypertonic solutions, cells shrivel.