Chapter 5 Homeostasis and Cell Transport

1. Chapter 5Homeostasis and Cell Transport

2. What is homeostasis? Homeostasis is the ability to maintain normal internal conditions. This means maintain a state of balance in living things. Cells must maintain homeostasis

3. What structure does a cell have to help it maintain homeostasis? • Cells are enclosed in a phospholipid bilayer called a cell (plasma) membrane that regulates their interactions with their surrounding environment. • A cell membrane has a specific structure that allows it to be semi-permeable.

4. What is the cell membrane’s structure and function? 1. Semi/Selectively permeable (controls what substances enters and leaves the cell) 2. Helps organisms maintain homeostasis

5. What is selectively permeable? • Selectively permeable means that the membrane will allow some substances to pass through and will not allow other substances to pass through.

6. What is permeable and impermeable? If a membrane allows a substance to pass through, it is said to be permeable to that substance. If a membrane does not allow a substance to pass through, it is said to be impermeable to that substance.

7. How does a cell maintain homeostasis? Through the movement of different molecules through the cell membrane by: • Passive transport or 2. Active transport

8. What is passive transport? • The movement of substances across a cell membrane without the use of energy by the cell.

9. What is diffusion? • The simplest type of passive transport. • The movement of molecules from an area of higher concentration to an area of lower concentration. • Molecules move on their own kinetic energy. Examples: When you add a sugar cube to water Microwave popcorn

11. What does it mean by kinetic energy? • Molecules are in constant motion because they have kinetic energy • Molecules move randomly in a straight line until they hit another molecule, then bounce off and move in the opposite direction. • Molecules have the tendency to move from high to low concentration.

12. What is equilibrium? • When the concentration of molecules of a substance is the same throughout a space. • Even at equilibrium there is a random movement of molecules.

13. CHECK IT: Stand Up • BRING YOUR NOTES! • Find one partner that is wearing the same color as you!

14. CHECK IT Partner #1: Explain the structure of a cell membrane and the term semi-permeable. Sentence starter: The cell membrane is made up of _____ Semi or selectively permeable means ___

15. CHECK IT Partner #2: Describe the term diffusion. Be sure to include the term “passive transport” in your answer. Sentence Starter: Diffusion is ________

16. What is a solution? • A solution is composed of a solute dissolved in a solvent. • Example: Salt water • Salt is the solute • Water is the solvent • In the case of cells, the solutes are organic and inorganic compounds, and water is the solvent.

17. What is osmosis? • Osmosis is the movement of water across a cell membrane from an area of higher concentration to an area of lower concentration. ****Because water is moving from an area of higher concentration to an area of lower concentration, osmosis does not require cells to expend energy. *****Therefore, osmosis is a type of passive transport!!!!!

18. What determines the direction of the water? • The relative concentration of water and solute on the two sides of the cell membrane.

19. Some Definitions… • Hypotonic-lower concentration of solutes • Hypertonic-higher concentration of solutes • Isotonic-even concentration of solutes

20. What happens to the cells of a freshwater fish when it is in a saltwater tank? • Fish-- Animal Cells No Cell Walls

21. What happens to the cells of a saltwater fish when it is in a freshwater tank? • Fish-- Animal Cells No Cell Walls

23. How do plant cells deal with osmosis? • Plant cells have cell wall and most live a hypotonic environment. This moves water into the cells by osmosis. • These cells swell as they fill with water until the cell membrane is pressed against the inside of the cell wall. The water exerts pressure against the cell wall called turgor pressure.

24. How do plant cells deal with osmosis? • In a hypertonic environment, water leaves the cells through osmosis. As the water leaves the central water vacuole, the cells shrink away from the cell walls, and turgor pressure is lost. • This condition is called plasmolysis, and is the reason that plants wilt if they don’t receive enough water.

26. How do unicellular organisms deal with osmosis? • Because most of them live in a isotonic environment, water is constantly entering the cells, so they must rid themselves of the excess water. • Some of them, such as the paramecia have structures called contractile vacuole which remove the excess water by pumping it out of the cell.

27. What is facilitated diffusion? • Another type of passive transport in which molecules that cannot readily diffuse across a membrane are assisted by proteins in the membrane. • Example: glucose diffusing across a cell membrane through the protein

28. Check your knowledge We have talked about three types of passive transport. Take a minute to quietly look through your notes and refresh you memory on the three types of passive transport. Circle the three types of passive transport in your notes!!!

29. Check your knowledge With your table partner discuss the following: Partner 1: Explain the term passive transport. Passive transport is the movement of molecules from and area of ______ Partner 2: Explain diffusion. What types of substances diffuse through our cells. Diffusion is the movement of ________ from an area of______

30. Check your knowledge Partner 1. Explain osmosis. What substance is moved in our cells through osmosis? Osmosis is the movement of ________ from an area of______ Partner 2. Explain facilitated diffusion. What substance is moved in our cells using facilitated diffusion. Facilitated Diffusion is the movement of ________ from an area of______

31. What is active transport? • The movement of substances, usually across a cell membrane, against (up) a concentration gradient which requires cells to use energy.

32. What does “against” a concentration gradient mean? • When cells move substances from an area of lower concentration to an area of higher concentration.

33. How are carrier proteins involved in active transport? • Carrier proteins in animal cells are involved in an active transport process called the sodium-potassium pump. In humans this process occurs in muscle cells and liver cells. Cells have to expend energy to pump Potassium (K+) ions into the cells and to pump Sodium (Na+) ions out of cells.

35. How do macromolecules that are too large to pass through the cell membrane by the other process get in and out of the cells? • 1) Endocytosis - the process by which cells ingest external fluid, macromolecules, and large particles, including other cells.

37. Endocytosis • Two types: a) Pinocytosis -involves the transport of solutes or fluids b) Phagocytosis -involves the transport of large solid particles or whole cells. Example: White blood cells engulfing bacteria.

38. 2) Exocytosis- the process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface and then fuses with the membrane to let the substance out of the cell. • Cells use exocytosis to release large molecules such as proteins, waste products, or toxins that would damage the cell if they were released within the cytosol.