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Bell Ringer. Name the organelle that performs each function: Creates ATP from other compounds Tags and packages other molecules Conducts photosynthesis Contains DNA and controls the cell A cell is eukaryotic, and has a cell wall and chloroplasts. What kind of cell is it?
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Bell Ringer • Name the organelle that performs each function: • Creates ATP from other compounds • Tags and packages other molecules • Conducts photosynthesis • Contains DNA and controls the cell • A cell is eukaryotic, and has a cell wall and chloroplasts. What kind of cell is it? • A cell is eukaryotic, but has no cell wall or chloroplasts. Does it have mitochondria?
Cell Boundaries How do cell boundaries work?
The Cell Membrane • 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.
The Cell Membrane • 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.
The Cell Wall • 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.
Diffusion • 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 • 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.
Osmosis • 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.
Osmosis • 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.
Osmosis • 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.
Osmosis • 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.
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).
Osmosis • 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.
Bell Ringer • What kind of solution is the cell in? • In which direction(s) will water flow? • Predict what will happen to the cell. • If we added some salt to the solution, what might happen to the cell? Beaker Cell
Facilitated Diffusion • 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.
Facilitated Diffusion • 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 • 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 • 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 • 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.
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.
Active Transport • 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”
Active Transport • In pinocytosis, the cell draws liquid into small pockets, which again become vesicles. These vesicles can be moved where needed. • Pinocytosis = cell “drinking”
Active Transport • 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.
Exit Ticket • Identify each type of transport as passive or active: • Osmosis • Phagocytosis • Simple diffusion • Facilitated diffusion • Exocytosis • Identify the transport taking place: • A carrier protein moves glucose into the cell. • A cell engulfs food, moving it in the cell. • Water crosses the cell membrane, inflating the cell.