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)

The Cell Membrane

– Also known as the “Plasma Membrane”

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?

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)

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)

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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

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

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

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)

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

Passive Transport

• Type of transport in cells that does NOT require an input of energy

• 3 Types of Passive transport

– Diffusion

– Facilitated Diffusion

– Osmosis

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.

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!

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

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

Osmosis

• Osmosis is the movement of water across a semi-permeable (or selectively permeable) membrane

– From high water concentration to low water concentration

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

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

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

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

Use your model to demonstrate…

• A blood cell placed in distilled water

– Hint… distilled water has NO solutes… pure H2O!

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

What Happens to Cells in Various Solutions?

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?

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.

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.

Endocytosis and Exocytosis

Moving Substances Against Concentration Gradient

• a protein pump uses energy (ATP) to pump ions move from low concentration to high concentration

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

Be sure to include: ◦Title

◦Labels

◦Movement of water (if applicable)

◦Make it colorful!

◦You have 10 minutes

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