Biomembranes I: Membrane Structure and Transport

NAME: ______DATE: ______

BIOMEMBRANES I: MEMBRANE STRUCTURE AND TRANSPORT WEB ACTIVITY

DIRECTIONS: 1. Log onto the internet and type the following web address into the address bar at the top of the screen. Please make sure to type the whole address in and do it accurately. http://www.phschool.com/science/biology_place/biocoach/biomembrane1/intro.html

2. Once the website it open, read the introduction. Once finished, begin the activity by clicking on the “Next Concept” button at the bottom of the screen.

Concept 1: Membrane Structure 1. Membranes consist of a ______combined with a variety of proteins in a ______arrangement.

2. The surfaces of the cell membrane are ______(water loving); the interiors are ______.

3. Hydrophilic molecules tend to interact with ______and with each other.

4. Hydrophobic molecules ______interaction with water and tend to interact with other hydrophobic molecules.

**Click the purple “Review” button in the upper right corner of the screen to proceed to the “Concept 1 Review”.

Concept 1 Review: Components and Properties of Biological Membranes 5. Biological membranes are thin, flexible surfaces separating ______and ______from their environments.

6. Different membranes have different properties, but all share a common architecture. Membranes are rich in ______, which spontaneously form ______structures in water.

7. Membrane proteins and lipids can diffuse laterally within the membrane, giving it the properties of a ______.

8. Membranes are ______; interior and exterior faces carry different proteins and have different properties.

** Click on “Close Window” to exit out of “Concept 1 Review”. Click on “NEXT CONCEPT” to proceed to Concept 2. Concept 2: Osmosis: Movement of Water Across a Membrane 9. ______(movement of water across membranes) depends on the relative concentration of ______on either side of the membrane.

10. The presence or absence of ______influences how cells respond to osmotic fluctuations in their environment.

** Click the purple “Review” button in the upper right corner of the screen to proceed to the “Concept 2 Review”.

Concept 2 Review: Isotonic, Hypotonic and Hypertonic Solutions 11. Water moves readily across cell membranes through special ______, and if the total concentration of all dissolved solutes is not equal on both sides, there will be net movement of ______molecules into or out of the cell and which direction it moves depends on whether the cell’s environment is ______, ______, or ______.

**Click on “Cells in Isotonic Solutions” below the pictures to continue!!

12. When two environments are isotonic, the total molar concentration of dissolved solutes is the ______in both of them.

13. When cells are in isotonic solution, movement of water out of the cell is ______by movement of water into the cell. A 0.9% solution of NaCl (______) is isotonic to animal cells.

**Click on “Cells in Hypotonic Solutions” below the picture to continue!!

14. Hypotonic comes from the Greek “hypo,” meaning ______and “tonos” meaning ______. In a hypotonic solution the total molar concentration of all dissolved solute particles is ______that of another solution or less than that of a cell.

15. If concentrations of dissolved solutes are less outside the cell than inside, the concentration of water outside is correspondingly ______. When a cell is exposed to such hypotonic conditions, there is net water movement ______.

16. Cells without walls will ______and may ______(lyse) if excess water is not removed from the cell.

17. Cells with walls often benefit from the ______that develops in hypotonic environments.

**Click on “A Closer Look at Plant and Animal Cells in Hypotonic Environments” below the picture to continue!! “TURGOR IN PLANTS” 18. Plants cells are surrounded by ______.

19. When plants are exposed to hypotonic environments, water rushes ______the cell and the cell ______, but is kept from breaking by the rigid cell layer.

20. The pressure of the cell pushing against the wall is called ______, and is the desired state for most plant tissues.

“LYSIS IN ANIMALS” 21. Animal cells lack rigid cell walls. When they are exposed to hypotonic environments, water rushes ______the cell and the cell ______. Eventually, if water is not removed from the cell, the pressure will exceed the tensile strength of the cell, and it will ______or ______. Many single-celled protests living in freshwater environments have ______that pump water back out of the cell in order to maintain osmotic ______and avoid lysis.

**Click “Back to review” for “Cells in Hypertonic Solutions”

22. Hypertonic comes from the Greek “hyper”, meaning ______and “tonos” meaning ______. In a hypertonic solution the total molar concentration of all dissolved solute particles is ______than that of another solution, or greater than the concentration in a cell.

23. If concentrations of dissolved solutes are greater outside the cell, the concentration of water outside is correspondingly ______. As a result, water inside the cell will flow ______to attain equilibrium, causing the cell to ______.

24. As cells lose water, they lose the ability to ______or ______.

**Now click on “A Closer Look” – “A Closer Look at Plant and Animal Cells in Hypertonic Environment”

“PLASMOLYSIS IN PLANT CELLS” 25. Plant cells are surrounded by rigid cell walls. When plants cells are exposed to hypertonic environments, water rushes ______of the cell and the cell ______from the rigid wall, resulting in ______. The plasmolyzed cells are ______and lose most or all physiological functions while in the shriveled state.

26. If cells are returned to isotonic or hypotonic environments, water ______the cell and normal functioning may be restored.

“SHRINKING IN ANIMAL CELLS” 27. Animal cells lack ______. When they are exposed to hypertonic environments, water rushes ______of the cell, and the cell ______. 28. The resulting cells are ______and lose most or all physiological ______while in the shriveled state. If cells are returned to isotonic or hypotonic environments, water ______the cell and ______may be restored.

**Click on “Close Window” to exit out of Concept 2 review. Click on “NEXT CONCEPT” to proceed to Concept 3.

Concept 3: Selective Permeability of Membranes 29. Cell membranes are ______. Some solutes cross the membranes ______, some cross with ______, and others do not cross at all.

30. A few lipophilic substances move across the cell membrane by ______. Most small molecules or ions require the assistance of ______to transport them across the membrane. ______do not cross intact cell membranes, except in certain special cases.

Concept 3 Review: Mechanisms of Movement Across Cell Membranes 31. When a membrane separates two aqueous compartments, some molecules can ______across the membrane, others cannot.

32. In living organisms, the membrane proteins play a crucial role in directing the ______across the cell membrane. Solutes fall into one of three groups:  Small ______molecules  Molecules that cross the membrane due to ______ Molecules, usually of very large size, that ______.

**Click on “Close Window” to exit out of “Concept 3 Review”. Click on “NEXT CONCEPT” to proceed to Concept 4.

Concept 4: Passive and Active Transport 33. Most biologically important solutes require ______to cross cell membranes, by a process of either ______or ______transport.

34. Active transport uses ______to move the solute “uphill” against the gradient, whereas in______, a solute moves down its concentration gradient and no energy is required. **Click the purple “Review” button in the upper right corner of the screen to proceed to the “Concept 4 Review”.

Concept 4 Review: Comparing Facilitated Diffusion and Active Transport 35. Transport of solutes across cell membranes by ______can occur in one of two ways:  The solute can move “downhill”, from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. This process is called ______or ______and does not require ______.  The solute can move “uphill”, from regions of lower to higher concentration. This process is called ______and requires some form of ______.

**Click on “Close Window” to exit out of “Concept 4 Review”. Click on “NEXT CONCEPT” to proceed to Concept 5.

Concept 5: Mechanisms of Active Transport 36. Active transport can occur as a direct result of ______(ATP pump) or by coupling of the movement of one substance with that of another (______or ______).

37. Active transport may move solutes into and out of the cell, but energy is always used to move the solute against the ______.

Concept 5 Review: Active Transport 38. In human tissues all cells have a higher concentration of ______outside the cell than inside and a higher concentration of ______inside the cell than outside. These concentration gradients of Na+ and K+ represent a form of ______.

**Click “Close Window” to exit out of “Concept 5 Review”.

**Click on the “Self-Quiz” button to test what you have learned from this activity!!