Maintaining homeostasis and providing nutrients to cells

Read Lab 7: Osmosis in an Animal
Cell
 In the background, highlight osmosis and it’s definition with your first color.
 In the background, highlight semipermeable, and solvent with your second color.
 In the background, concentration gradient in a third color.
 In a 4 th color, highlight the purpose of this lab.

 Describe osmosis and how the cell membrane is semi-permeable.
 Describe your procedures for today from the handout.
 Identify the solvent and the solute in today’s lab. (Define and write out which one is which.)

 Record the appearance or your egg.
 On data table #2, record the initial mass of your egg.
 Next carefully put your egg in the cup of vinegar, write you and your partner’s name, period and date, and put it in the box at the front of the classroom.

 Why was the vinegar solution used on the first day?
 What is the solvent in the vinegar solution?
 What is the concentration of solvent in the vinegar solution?
 What is the solute in the vinegar solution?
 What is the independent and dependent variable?

Cell Membrane Structure: Review
 What is the cell membrane made of that makes it selectively permeable?
 The lipids are arranged in a bilayer.

The bilayer is a “barrier” that is impermeable to most molecules.
 The proteins are embedded in the bilayer.
 Specific molecules can be helped across the membrane by these proteins.

What are membranes?
Membranes cover the surface of every cell, and also surround most organelles within cells. They have a number of functions, such as:
 keeping all cellular components inside the cell
 allowing selected molecules to move in and out of the cell
 isolating organelles from the rest of the cytoplasm, allowing cellular processes to occur separately.
 a site for biochemical reactions
 allowing a cell to change shape.
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The chemical properties of lipids determines the bilayer nature of the cell membrane.

 The cell membrane is described as
“selectively permeable”

 How does this feature relate to the job/function of the cell membrane?
Cell membrane acts as a “guard”
 Allows nutrients into cell
 Allows for removal of wastes and release of substances made by the cell that are needed by other cells.

Factors that affect Passive
Transport:
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1)
Whether a molecule can move through the membrane depends on : the size of the molecule
2) the type of molecule (polar or nonpolar, charged, etc.)
Molecules move by one of the following methods: diffusion, facilitated diffusion, or osmosis.
The direction of movement (in/out) depends on the concetration gradient.

Direction of movement:
Out of the blood, into the lungs
Concentration Gradient = a difference in concentration of a substance in one area compared to another.

Left Side: Below yesterday’s solutions
 What solution did you put over the egg on Monday?
 What was the solvent? The solute?
 How will you know if water moved in or out of the egg?
 If water moved out? If water moved in?

 What will we record in our data tables?
 Read over the Day 3 Tasks, You will need to answer these questions.

 Passive Transport is the movement of substances without the use of any energy
 Things go from high concentration to low concentration
 Transport continues till equilibrium is achieved (same amount inside and out)

Molecules go “down the concentration gradient”


1.
2.
3.
Passive Transport : movement of substances without any energy input by a cell.
Diffusion : molecules move straight through the membrane.
Facilitated diffusion : molecules or ions move through channel proteins embedded in the membrane.
Osmosis : water molecules move through the membrane (mostly through protein channels).
Methods of Transport

 In passive transport, the net movement is always “down the concentration gradient”.
 Molecules move from an area of higher concentration to an area of lower concentration.

It’s “passive” because it doesn’t require cellular energy.

Net Movement
Think of dye or sugar molecules in water. (Water particles NOT shown.) Dye or sugar molecules will DIFFUSE through the water.

 Draw the picture of your egg with the vinegar solution, showing where the water moved.
 Draw a picture of what you think will happen after leaving your egg over night in the sugar solution.

Lab Report Homework part 1: Due
Friday
 Using your notes and your textbook, write an introduction to the egg lab. What are we trying to see take place?
 Write a hypothesis, and state the question/purpose of this lab.
 You must have 3 sentences describing the background of osmosis.
 Then you will write the hypothesis.
 You also need a title.

What are the types of movement?
Which way does it move? Left hand page 42
 1) After taking a long bath, your fingers look like prunes.
 2) Your egg after sitting in vinegar.
 3) If there’s more carbon dioxide in your blood then in your lungs.
 4) If there’s more water outside your cell then inside your cell.

 Take your egg, and gently take off the syrup. It will break very easily, and for the lab portion, you earn a 0 if it breaks!
 Take the mass.
 Use a graduated cylinder and measure
100 ml of water.
 Which way did the water move? Answer questions to Task Day 4, and draw pictures of water movement for Day 3, and what you think will happen Day 4

 Solution:
 A mixture of solute and solvent
 Solvent:
 Something that does the dissolving (usually water)
 Solute:
 Something that gets dissolved in the solvent

 Draw 5 phospholipids, label the head, the tail, hydrophobic, hydrophilic
 Draw a channel protein
 Draw where water would cross into the cell.
 Draw where CO2 would cross into the cell

 First pour out the water into the graduated cylinder and record next to your data table number 2 the amount of water left.
 Next, mass your egg.
 Now go through your tasks for Day 5
 What other solutions could we test?
Write what you would like to investigate.

 If the membrane is permeable to both water and solutes, both will diffuse to reach equilibrium.
 Often, the membrane is NOT permeable to the solute(s). In this case osmosis occurs; water diffuses (high to low) to balance the concentration on both sides. (egg & potato labs)



Environment has a higher concentration of solute
(glucose, salt, etc) than in the cell.
Mainly water will move across the cell membrane in order to even out the concentration (%) of solutes in both the cell and the environment around the cell.

The cell will shrink as water leaves the cell to decrease the higher concentration of solute in the environment.
CELL MASS GOES DOWN



Environment has a lower concentration of solute than the cell.
Water will move from the environment into the cell in order to balance the concentration (%) of solute.


When water diffuses into the cell it will swell . Sometimes the cell may lyse or burst due to the excess water uptake.
CELL MASS GOES UP



Environment has the same concentration of solutes as the cell.
Water will diffuse in and out of the cell, but no net effect will be seen.
 Equal concentrations = equilibrium
 NO net movement of water

Equal number of molecules move in and
 out
CELL MASS DOES NOT CHANGE

From your notes or your textbook define the following, and draw a picture:
 Hypertonic
 Hypotonic
 Isotonic
 Draw a picture of each one.
 These are terms used for which type of transport?
 When was the egg hypertonic to the solution surrounding it?
 When was the solution hypertonic to the egg?

 Describe how you did the lab, step by step.
 This can be in a paragraph or bulleted points.
 Use your own words as much as possible.
 Must be accurate to earn a 4/4

 Draw a graphic to show the trends:
 This could be a bar graph or a line graph showing how water moved between the egg and the solutions.
 Write out from your tasks a summary of your interpretations:
 Example: On day 1, we added vinegar, which had a solvent of ______, and solutes of ________, on day 2 we discovered that
_______________.

 What was your hypothesis? This is your claim. Write that as your first sentence.
 Use the words
 hypotonic to the egg
 Hypertonic to the egg
To describe the solutions.

 If red blood cells are put into a hypotonic solution, explain what hypotonic is, and what happens. (Use data from your lab to describe this process)
 If red blood cells are put into a hypertonic solution, what happens.
 If red blood cells are put into an isotonic solution, explain what happens.

HIGH
LOW


 1. acting as a channel or tunnel
 2. acting as a carrier or transporter

HIGH
LOW

Diffusion through a carrier protein

 Cells move molecules from an area of
LOW concentration to an area of HIGH concentration
 Molecules move AGAINST the concentration gradient
 Requires the cell to use energy in the form of ATP
Animation

What is active transport?
Substances can move passively in and out of cells by diffusion until the concentration on both sides of the cell membrane reaches an equilibrium .
Substances can continue to move in and out of a cell using a process called active transport .
During active transport, protein carriers in the cell membrane ‘pick up’ particles and move them against the concentration gradient.
As the name suggests, active transport requires energy from the cell, which is made available by respiration (ATP).
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What is active transport?
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Active transport in plants
Plants need to absorb mineral elements such as nitrogen, phosphorus and potassium from the soil for healthy growth.
When the concentration of minerals in soil is lower than inside the plant, active transport is used to absorb the minerals against the concentration gradient.
What would happen if the plant relied on diffusion to absorb minerals?
minerals
The cells would become drained of minerals because they would travel down the concentration gradient.
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Example: Sodium-Potassium
Pump
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Three Na + ions in the cytoplasm bind to carrier protein
Shape of protein is changed, allowing the three Na + out of cell
Two K + ions outside of cell bind to protein
Shape of the protein is changed
The two K + are allowed into the cytoplasm
Similar to facilitated diffusion:
 Uses a carrier protein,
Different from facilitated diffusion:
 requires energy.
Animation 1
Animation 2
Overall: Na+ (sodium) becomes concentrated on the outside of a cell.
 Important in the proper functioning of neurons and the kidneys.

 Not all active transport moves molecules from a low concentration to a high concentration
 Active transport used in two other situations:
 Moving very large molecules through membrane
 Moving large quantities of smaller molecules through membrane

Other examples of active transport:
 Endocytosis: Process in which cells ingest fluids, macromolecules, and large particles that are outside the cell
Animation 1
Animation 2

Other examples of active transport:
 Exocytosis: how cells release large molecules (proteins) or get rid of large amounts of wastes