Movement through Cells

1. Movement through Cells Cell membrane • All organisms are made of cells • Cells are mostly liquid. • Surrounding the cells is also liquid. Inside Cell

2. Role of the Cell Membrane • The cell membrane separates the cell from the liquid it is bathed in. • a) It allows only certain particles to enters and leave the cell. Therefore the cell membrane is considered ____________________ Selectively Permeable • b) The cell membrane is made up of two parts: • ___________________________ • ____________________________ protein channels lipid bilayer

3. Role of the Cell Membrane • Large particles can only enter and exit the cell through the protein channels BUT • Small particles can enter and exit straight through the lipid bilayer!!

4. Particles of liquids • All particles of matter--atoms or molecules are constantly in motion. • In liquids, the molecules randomly move.* • A solution is made when particles of sugar, salt, or oxygen, etc. are dissolved in liquids + = solution

5. What is a solution? • Liquid mixture of 2 or more substances. • Water - solvent • The substance dissolved in the water - solute • Concentration = mass of solute/volume of solvent • Concentration is similar to density.

6. Problem: Imagine you have a beaker filled with sugar water. Imagine you add double the amount of sugar to the water. Which beaker contains a more concentrated sugar solution? Sugar

7. Concentration of Solutions • Molarity (M) = unit of concentration used in biochemistry • The greater the molarity of a solution the greater the concentration. • 0.25M sucrose solution (read as 0.25 molar) has half of the concentration of a 0.50M sucrose solution.

8. Particles in solution cross the cell membrane • Particles within an organism must continuously enter and exit the cell through the cell membrane using one of four processes: • Diffusion • Osmosis • Facilitated diffusion • Active transport

9. Diffusion • The movement of a substance (liquid or gas) from areas of high concentration to areas of low concentration. • The motion is random --eventually all particles spread out evenly throughout the solution = equilibrium.

10. Diffusion Demonstration • Food coloring (solute)+ water (solvent). • What do you think will happen over time in the solution? Discuss at table and draw on white board.

11. Diffusion • Once equilibrium is reached, the movement of particles continues, but it is equal in all directions. • Solution remains in equilibrium. • Particles remain equally spaced out.* • See molecular workbench and answer questions. (p1-6)

12. Diffusion Across a Cell Membrane • The cell membrane allows many types of particles (ions, atoms, molecules) to move in and out of the cell by diffusion. • But some types of molecules are not able to cross the membrane. • What determines whether a particle can cross the cell membrane? Complete Worksheet to find out!

13. Diffusion Across a Cell Membrane • Design an experiment to test the effect of the size of a particle on its ability to diffuse. Your materials:

14. Conclusions for Diffusion: • Small particles diffuse __________ than large particles across a cell membrane • Only substances that can permeate the cell membrane can diffuse across it. • Diffusion occurs from areas of high concentration of solute particles to areas of low concentration. • The movement of particles is always taking place. faster The cell expends NO ENERGY on the process of diffusion

15. Particles dissolved in water cross the cell membrane • Diffusion • Osmosis

16. Osmosis: A special type of diffusion • Diffusion of water through a selectively permeable membrane. Water diffuses from where there is less solute (sugar, salt, etc.) to where there is more solute. • See molecular workbench and answer questions

17. Osmosis: • Osmosis results in equilibrium when the concentration of the solutions is equal on both sides of the membrane. A solution in equilibrium is also referred to as isotonic.

18. Osmosis • When solutions on both sides of the cell membrane do not have equal concentration they are described as hypotonic or hypertonic. • Hyptonic = lower concentration of solute • Hypertonic = higher concentration of solute Overall Direction of Water flow Outside cell Inside cell

19. Osmosis in Animals At your table: Draw a picture illustrating #1 and #2 below and answer the questions! Use arrows to show the movement of water. 1. What happens if blood cells are placed in a hypertonic (more concentrated) solution? (saltwater)* 2. What happens if blood cells are placed in a hypotonic (less concentrated) solution? (distilled water)*

20. Osmosis in Animals

21. Osmosis in Animals • Under normal bodily conditions, blood is the liquid that surround the cells. • Blood has the same concentration of solutes as those inside the cell. This means that blood and cytoplasm are ______________________ to each other. isotonic

22. Osmosis in Plants 1) What happens if plant cells are placed in a hypertonic solution (example: salt water)? 2) What happens if plant cells are placed in a hypotonic solution (example: distilled water)? 3) What happens if plant cells are placed in an isotonic solution (example: water with minerals)?

23. Osmotic Pressure = Pressure created by water moving into a hypertonic cell. • A plant cell is filled with proteins, sugars, salts. • The cytoplasm of plant cells is more concentrated than fresh water •  The plant cell is hypertonic relative to freshwater • Since freshwater is used to water plants (not blood), the plant cells fill up with water.

24. Osmotic Pressure = Pressure created by water moving into a hypertonic cell. • With your table answer the following question: • Why doesn’t a plant cell burst (like a blood cell) when placed in freshwater? (Hint: What is a MAJOR difference between plant and animal cells?) Cell Wall is RIGID

25. Osmosis in one-celled organisms • In one-celled organisms the cell does not burst when in a hypotonic solution (for example pond water). • One-celled organisms have mini-pumps called contractile vacuoles. As water enters the cell, it is pumped out by this organelle.

26. Osmosis and Contractile Vacuoles *

27. Osmosis: • Because osmosis is a special type of diffusion The cell expends NO ENERGY on osmosis Now: Complete Worksheet on OSMOSIS

28. Particles cross the cell membrane • Diffusion • Osmosis • Facilitated diffusion • Active transport

29. Facilitated Diffusion • Movement of specific molecules through protein channels in the cell membrane • The protein channels are specific to a type of particle. Example: glucose moves through a protein channel that is specific to glucose.

30. Facilitated Diffusion • The movement of particles is two ways but always from areas of high concentration (hypertonic) to areas of low concentration (hypotonic). • Cells use facilitated diffusion for substances such as salt, sugars and starches*. The cell expends no energy on facilitated diffusion.

31. Particles cross the cell membrane • Diffusion • Osmosis • Facilitated diffusion • Active transport

32. Active Transport • Active Transport: Movement of material across the cell membrane in the OPPOSITE direction of diffusion.

33. Active Transport • Because the flow of solute is from an area of LESS concentration to an area of MORE concentration the solute must be pumped by the cell*. • See molecular workbench. The cell EXPENDS ENERGY (found in molecules of ATP) on Active Transport

34. Connections to Daily Life • You will be assigned an article on a topic with a group of students. Read and discuss the article with your group and present the information to the class…as a poster, as a play, as a song, etc. • Topics • Facilitated diffusion, insulin and diabetes • Diffusion of oxygen into our lungs and emphysema • Diffusion and alcohol • Pregnancy and diffusion of nutrients between mother and fetus.