The Fluid Mosaic Membrane Modeling Membrane Structure...
Transcript of The Fluid Mosaic Membrane Modeling Membrane Structure...
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Student Objectives
• Know the different parts of the cell membrane
• Understand the role of the cell membrane in cellular transport
• Understand diffusion and osmosis
• Determine what will happen to plant and animal cell if placed in solutions of various concentrations (hypertonic, hypotonic, isotonic)
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The Cell Membrane
– Also known as the “Plasma Membrane”
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Homeostasis
• The cell membrane is an important part of maintaining Homeostasis in the cell.
• Homeostasis is when an organism or cell maintains a stable internal environment
– goldilocks
• Cells need to transport some materials inside of them, and transport other materials out
– What do cells need in?
– What do cells need out?
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Parts of the Cell Membrane - Phospholipids
• The phospolipids in the cell membrane are composed of a phosphate head region and a hydrocarbon tail region
• Phospholipids in a cell membrane are arranged in a double layer (a bilayer)
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Phospholipids and Membrane Fluidity
• The phospholipids in the membrane can move laterally (side to side) in the membrane
• This gives the membrane a fluid nature (think a layer of oil on water)
http://www.stolaf.edu/people/giannini/fla
shanimat/lipids/membrane%20fluidity.s
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Parts of the Cell Membrane - Cholesterol
• Cholesterol keeps the phospholipids in the cell membrane spread out
• This makes the membrane more fluid
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Parts of the Cell Membrane - Proteins
• 2 Types of membrane proteins – Integral Membrane
Protein • Span the entire width of the
membrane bilayer
– Peripheral proteins • Not embedded in the cell
membrane, loosely attached to the surface of the membrane
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Parts of the Cell Membrane - Proteins
• Functions of the proteins in the cell membrane
– Transporting materials in and out of the cell
– Receptors for chemicals
– Enzymes for helping chemical reactions
– Help cells to recognize each other
– Points of connection for other cells
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Parts of the Cell Membrane – Surface Carbohydrates
• Surface Carbohydrates are on the outside of the cell membrane
• They function in cell to cell recognition, cell signaling, and cell adhesion (sticking to things)
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Membrane Permeability • Cellular Membranes are
Selectively Permeable – they only allow certain substances to pass through them – What CAN pass through the
cell membrane? – Small, uncharged molecules
(Water, CO2, Oxygen)
– What CANNOT pass through the cell membrane – Large, or charged substances
(carbohydrates like starch, proteins, etc…) – Must use a transport protein
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Passive Transport
• Type of transport in cells that does NOT require an input of energy
• 3 Types of Passive transport
– Diffusion
– Facilitated Diffusion
– Osmosis
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Passive Transport – Important Vocabulary
Solute - The solid substance that is dissolved in
a solvent.
Solvent - The liquid substance in which the
solute is dissolved.
Solution - The mixture of two or more
substances (solute and solvent) in which the
molecules of the substances are evenly
distributed.
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Diffusion
• Diffusion -The passive movement of molecules from a higher concentration to a lower concentration until equilibrium is reached. • Does NOT require
energy!
• This is how oxygen gets into the blood stream from lungs!
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Facilitated Diffusion
• Facilitated Diffusion is the movement of molecules across the cell membrane with the help of special transport protein – Channel proteins
– Carrier proteins
• Still high to low concentration – So NO energy needed
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Using the cutout pieces and your notes, create a cell membrane with your table group!
Make sure to label the exterior and interior of the cell.
Raise your hand when you complete your model
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Osmosis
• Osmosis is the movement of water across a semi-permeable (or selectively permeable) membrane
– From high water concentration to low water concentration
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Important Osmosis Vocabulary
• Hypertonic Solution – A solution that has a higher relative solute concentration (and a lower water concentration)
• Hypotonic Solution – A solution that has a lower relative solute concentration
• Isotonic Solution – When two solutions have an equal concentration of solutes they are said to be isotonic
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Hypotonic Solution
Use the cell pieces
at your table to
model the diagram
above in which a cell is placed in a hypotonic environment (cell exterior)
– Q: how will water move in this situation
– Q: Which side is hypertonic, which side is hypotonic
– Fill in the information in figure 3 of your student sheet
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Hypertonic Solution
Use the cell pieces
at your table to
model the diagram
above in which a cell is placed in a hypertonic environment (cell exterior)
– Q: how will water move in this situation
– Q: Which side is hypertonic, which side is hypotonic
– Fill in the information in figure 3 of your student sheet
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Isotonic Solution
Use the cell pieces
at your table to
model the diagram
above in which a cell is placed in a Isotonic environment (cell exterior)
– Q: how will water move in this situation
– Q: Which side is hypertonic, which side is hypotonic
– Fill in the information in figure 3 of your student sheet
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Use your model to demonstrate…
• A blood cell placed in distilled water
– Hint… distilled water has NO solutes… pure H2O!
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Use your model to demonstrate…
• A blood cell placed in a 10% saline (salt) solution
– Hint… blood normally has a concentration of 0.9% salt
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What Happens to Cells in Various Solutions?
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Check for understanding…
• What prevents a plant cell from bursting when placed in a hypotonic solution?
• What happens to an animal cell if it is placed in a strong saltwater solution?
• What happens to a plant cell if it is placed in an extremely hypotonic solution?
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Active Transport
Active Transport: A movement of ions across the cellular membrane from a lower
concentration to a higher concentration
ATP-The most important molecule located within human beings
ATP…is the energy that is used in active transport.
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Examples of Active Transport
Exocytosis and Endocytosis are ways a cell can pass proteins in vesicles (membrane sacs) out or into
the cell.
Exocytosis-a process in which a vesicle moves to the cell membrane, fuses with the membrane, and
releases its contents outside the cell
Endocytosis-the cell membrane engulfs (“eats”) molecules, pinches two sides to form a circle
around the molecules, and the circle (vesicle) breaks off from the membrane now inside the cell.
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Endocytosis and Exocytosis
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Moving Substances Against Concentration Gradient
• a protein pump uses energy (ATP) to pump ions move from low concentration to high concentration
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At your table groups, create a poster for one of the following concepts:
1. Cell Membrane
2. A drink with labels for solute, solvent, solution
3. Cell in Hypotonic environment
4. Cell in Hypertonic environment
5. Cell in Isotonic environment
6. Endocytosis
7. Exocytosis
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Be sure to include: ◦Title
◦Labels
◦Movement of water (if applicable)
◦Make it colorful!
◦You have 10 minutes
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Conclusion
• Cell membranes are composed of a variety of substances (phospholipids, carbohydrates, proteins…) that perform various functions
• Cell membranes allow certain substances to pass through them, and may have proteins to allow other substances to enter or exit
• Cells can use passive transport (no energy needed) or active transport (requires energy) to move materials into and out of the cell