Cell Transport and Solutions

Diffusion

  • Diffusion is a type of passive transport where molecules move from an area of high concentration to an area of low concentration.

    • Example: Farts diffusing in a room, from high concentration (near the source) to low concentration (throughout the room).
    • Example: A drop of red food coloring in a glass of water. The highest concentration is where the color is the darkest red.

Solutions and Osmosis

  • Three types of solutions:

    • Hypotonic: Water moves into the cell. "Hypo the hippo" analogy: Hippos are big and fat and hang out in water, so water moves into the cell, causing it to swell.

      • If a cell has 78% water outside, it will have 22% other elements. Water moves in to balance this out, potentially causing the cell to burst if too much water enters.
      • IV solutions in hospitals are designed to replenish water in dehydrated cells.

    • Isotonic: "Iso" means same. Water moves in and out of the cell at an equal rate, so there is no net change in cell size.

    • Hypertonic: Water moves out of the cell, causing it to shrink.

Facilitated Diffusion

  • Cell membranes have tiny spaces for molecules to pass through, but larger molecules need help.

    • Facilitated diffusion uses carrier proteins or ion channels to transport large or charged molecules across the cell membrane.

  • Cell Membrane Structure:

    • Phospholipids create the basic structure.
    • Integral proteins span the membrane.
    • Peripheral proteins are on either side of the membrane.

  • Large Molecule Transport: A large molecule (e.g., glucose) can't fit between phospholipids. It binds to an integral protein (taxi) which transports it across the membrane from high to low concentration, without requiring energy.

  • Ion Transport: Ions (charged molecules) require ion channels because one side of the cell membrane is negative and the other side is positive.

    • Example: Sodium (Na+Na^+) has a positive charge and is attracted to the negative side. However, when it reaches the positive side, it's repelled. Therefore, it goes through a protein tunnel (immigrant protein) to cross the membrane.

Cell Behavior in Water

  • If a cell is placed in water, water moves into it. If the cell can't get rid of the excess water, it will explode or burst.

Experiment with Starch and Iodine

  • Starch is a large molecule that cannot pass through a cell membrane or a filter.

  • Iodine is a small molecule that can pass through a cell membrane or a filter.

  • Iodine moves from an area of high concentration to an area of low concentration.

  • Consider the location of the starch and iodine to predict the movement of iodine (into or out of a funnel) based on concentration gradients.