1. Name the organelle that performs each function: a. Creates ATP from other compounds b. Tags and packages other molecules c. Conducts photosynthesis d. Contains DNA and controls the cell 2. A cell is eukaryotic, and has a cell wall and chloroplasts. What kind of cell is it? 3. A cell is eukaryotic, but has no cell wall or chloroplasts. Does it have mitochondria?

How do cell boundaries work?

 The cell membrane provides some protection and support for the cell.  It also regulates the materials that enter and leave the cell. This is due to its composition:  The cell membrane is a lipid bilayer, meaning that it is made of two layers of lipids (fats). The individual phospholipids form a strong but flexible barrier.

 Both proteins and carbohydrates are embedded in the cell membrane.  Some of those proteins form pores, channels, pumps and carrier proteins, which serve to import and export materials.  The carbohydrates are used to function as an I.D., which enables cell-to-cell interaction.

 Cell walls are used to provide further support and protection.  Most cells have them. Animal cells are the most common cells that don’t have one.  Cell walls are often made of fibers, such as cellulose and chitin.

 As stated earlier, passive transport is the movement of molecules WITHOUT spending energy.  Diffusion is the simplest type of passive transport to understand. In any solution, particles will spread out from a high concentration to a low concentration.  Experiment: At home, place a sugar cube in a glass of water, and leave it alone. Over time, the sugar dissolves, and diffuses equally in the water.

 Diffusion is important for equally distributing molecules without spending energy.  Sometimes, membranes can interrupt diffusion, however.  If the membrane allows diffusion a substance X, it is permeable to X.  If it doesn’t, it is impermeable to X.  Most barriers – including the cell membrane – are selectively permeable, meaning that they allow only some substances to diffuse.

 Because the cell membrane is only permeable to some compounds, they CANNOT move from high to low concentrations.  The cell membrane is a good example of a semipermeable membrane. It only allows some materials to pass, but blocks many other compounds as well.

 However, the cell membrane IS permeable to water. This leads to a fascinating phenomena:  If a cell is dunked in extremely salty water, then the salt CANNOT enter the cell. However…  The water inside the cell CAN LEAVE the cell. This results in both the inside and outside of the cell having the same levels of salt.

 However, the cell membrane IS permeable to water. This leads to a fascinating phenomena:  If a cell is dunked in extremely salty water, then the salt CANNOT enter the cell. However…  The water inside the cell CAN LEAVE the cell. This results in both the inside and outside of the cell having the same levels of salt.

 As another example, we place another cell in a beaker of pure water. In this case, the salt inside the cell cannot leave the cell to make the inside and outside have the same concentration.  However, the water outside the cell CAN rush in, which does make both environments have the same concentration of salt.  This diffusion of water across a semipermeable membrane is called osmosis.

 Note the image to the left. The left side is very salty, and the right side is not.  The salt CANNOT pass through the membrane. The water can, though.  This results in both sides having the same salt content (though different volumes).

 To determine whether water will enter or leave the cell, we compare the concentration of the cell to the concentration of the solution.  If the cell is less concentrated, the solution is hypertonic.  If the cell is more concentrated, the solution is hypotonic.  If they have the same concentration, the solution is isotonic.

1. What kind of solution is the cell in? 2. In which direction(s) will water flow? 3. Predict what will happen to the cell. 4. If we added some salt to the solution, what might happen to the cell? Beaker Cell

 Facilitated diffusion is a variant of passive transport. In this case, some materials diffuse in and out of the cell through the assistance of various proteins.  Protein channels are gated pores in the cell membrane. They allow ions (charged particles) to pass.  Carrier proteins are used to transport large molecules in and out of the cell. They are specific to one type of molecule.

 Keep in mind that facilitated diffusion is still passive transport. This means:  Facilitated diffusion does NOT use energy.  Facilitated diffusion moves particles from high density to low density.  Facilitated diffusion is important because it allows materials that could not easily enter or leave the cell to do so.  For example, glucose quickly enters and leaves the cell, thanks to a carrier protein.

 Facilitated diffusion is important to the proper function of several body tissues, such as cardiac tissue and neurons.  It is also important for the uptake of various materials, most notably glucose.

 Active transport is notable because it is the only type of cellular transport that moves materials against the concentration gradient.  In other words, active transport moves molecules from low concentration to high concentration, keeping all the molecules in one area.  Since this is NOT scientifically natural, active transport REQUIRES energy.  Energy is supplied in the form of ATP.

 Active transport is usually conducted through “pumps”, specialized carrier proteins that transport molecules across the cell membrane.  A significant amount of ATP produced by the cell is used to power active transport.

 Larger molecules and materials can be imported, but this requires that the cell membrane change shape and envelope the object. We call this process endocytosis.  In endocytosis, the cell membrane folds in on itself to make a pocket or vesicle.  Often, this requires a receptor to first bind to the object that will be transported into the cell.

 In phagocytosis, the cell membrane engulfs a large object. This first forms a pocket, and then a vesicle, which can be moved around the cell.  Phagocytosis = Cell “eating”

 In pinocytosis, the cell draws liquid into small pockets, which again become vesicles. These vesicles can be moved where needed.  Pinocytosis = cell “drinking”

 Lastly, materials can be excreted, or removed from the cell. This is basically phagocytosis in reverse – a vesicle containing waste products fuses with the cell membrane, releasing waste outside the cell.

1. Identify each type of transport as passive or active: a. Osmosis b. Phagocytosis c. Simple diffusion d. Facilitated diffusion e. Exocytosis 2. Identify the transport taking place: a. A carrier protein moves glucose into the cell. b. A cell engulfs food, moving it in the cell. c. Water crosses the cell membrane, inflating the cell.