biology-exchange and transport mechanisms

• What do all organisms do with their surroundings?


  All organisms exchange substances with their surroundings.
• What do single-cell organisms that respire aerobically need to absorb and get rid of?


  They need to absorb oxygen and nutrients and get rid of carbon dioxide and waste products.
• How do single-cell organisms exchange substances?


  This happens by the process of simple diffusion.
• Why can't large multicellular organisms rely on simple diffusion?


  The distance is too great, and it would take too long.
• What is diffusion?


  Diffusion is the movement of a substance from a high concentration to a low concentration.
• What are the three requirements for effective exchange of gases, nutrients, or waste products?


  • A large surface area for exchange
  • A short diffusion distance
  • A high concentration gradient
• What does a large surface area to volume ratio indicate for organisms?


  It indicates that the surface area must be large in comparison to volume for efficient exchange.
• What do organisms require to maximize the rate of diffusion?


  Specialized exchange and transport mechanisms such as lungs, heart, and circulatory system.
• What is the lipid component of cell membranes called?


  • Phospholipid bilayer
• What are the components of phospholipids?


  Phospholipids consist of a hydrophilic head group and a hydrophobic tail.
• Why do the tails of phospholipids arrange themselves in the center of the bilayer?


  Because the tails are hydrophobic and avoid contact with water.
• What does the phospholipid bilayer act as?


  The phospholipid bilayer acts as a barrier to diffusion of many substances.
• Which substances cannot diffuse through the hydrophobic core of the bilayer?


  Polar substances such as water, glucose, amino acids, or inorganic ions cannot diffuse through.
• What do polar substances require to cross the phospholipid bilayer?


  They require specialized transport systems involving proteins and glycoproteins.
• What does the fluid mosaic model describe?


  • The structure of the plasma membrane
  • Arrangement of proteins, lipids, and carbohydrates
  • The mosaic pattern created by varying shapes, sizes, and locations
• Why can the membrane be fluid according to the fluid mosaic model?


  Due to the relatively weak forces between phospholipids, allowing movement throughout the membrane.
• What are the three mechanisms of transport across membranes?


  • Passive transport
  • Active transport
  • Co-transport mechanisms
• What are examples of passive processes?


  Simple diffusion, facilitated diffusion, and osmosis.
• What is the direction of movement in passive processes?


  Movement is always from high concentration to low concentration.
• What does the phospholipid bilayer's hydrophobic core do?


  It acts as a barrier to diffusion of polar substances, making it partially permeable.
• Which molecules can move into the phospholipid bilayer and diffuse across the membrane?

  Small non-polar molecules such as carbon dioxide, oxygen, steroid hormones, lipids, or fat-soluble vitamins.
• What is facilitated diffusion?


  Facilitated diffusion is where diffusion is assisted by proteins in the membrane.
• How do ions and small polar molecules cross the membrane?


  They are transported by channel proteins that act like pores in the membrane.
• What are gated channels?


  Gated channels are channel proteins that can open and close.
• How do larger polar molecules like glucose or amino acids cross the membrane?


  They use carrier proteins that are specific to the substance being transported.
• What happens when a substance binds to a carrier protein?


  The carrier protein changes shape, transferring the substance to the other side of the membrane.
• What is osmosis?


  Osmosis is a type of facilitated diffusion where water moves across a partially permeable membrane.
• From where to where does water move during osmosis?


  Water moves from a high concentration of water molecules to a low concentration of water molecules.
• What characterizes a dilute solution in terms of water concentration?


  A dilute solution has a high concentration of water molecules.
• What characterizes a concentrated solution in terms of water concentration?


  A concentrated solution has a low concentration of water molecules.
• What is active transport?


  Active transport is a process that uses energy to move substances against a concentration gradient.
• What do carrier proteins use as a source of energy in active transport?


  Carrier proteins use ATP as a source of energy.
• What are active proteins often called?


  These types of active proteins are often called pumps.
• What is an example of co-transport mechanisms?


  • The absorption of glucose from the gut
  • Epithelial cells lining the small intestine have carrier proteins that transport glucose with sodium ions
• How does the sodium ion pump function in epithelial cells?


  The sodium ion pump pumps sodium ions out of the epithelial cells into the blood capillaries.
• What does the sodium ion concentration gradient cause?


  The concentration gradient causes sodium ions to diffuse into epithelial cells via a co-transport protein.
• What happens to glucose once it enters the epithelial cell?


  Glucose diffuses down a concentration gradient into the blood.
• Why does glucose require a carrier protein to enter the blood?


  Because glucose is a polar molecule.