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diffusion and osmosis. help me please?

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diffusion and osmosis. help me please?

Postby lanzshade » Thu Oct 02, 2008 12:50 am

okay so i need you guys to check and answer some questions. i need to get at least and A- in this activity. sorry i'm dumb in biology but i am really trying hard to pass this class. i need help for #'s 8, 9, 11, 14, and 16. if you see some wrong answers, please tell me. thank you very much!

1. add a drop of iodine to 2 ml of starch solution in a test tub. describe the reaction.
(my answer) the starch solution turned bluish black. when iodine comes in contact with starch, it'll turn into a bluish black color.

2. add 10 drops of benedict's solution to a 5 ml of glucose solution in a test tube. place the tube in boiling water for 3 minutes. describe the reaction.
(my answer) the benedict's solution turned blue before heated and after heated it turned orange.

3. complete a chart indicating which materials have diffused and a brief supporting reason. suggest a reason for the failure of some of the molecules to diffuse through the membrane.
(my answer) the bag is semipermeable meaning it only allows some (not all) substances to pass through it.

[for the chart i made this]
a. iodine - (diffused through membrane?) yes, (experimental evidence) fluid inside the bag turned blue
b. starch - no, no color change in the fluid outside the bag (in the beaker)
c. glucose - yes, fluid from the beaker turned yellow orange after heated (positive glucose test)
d. [im not sure with this one] yes, the bag became heavier

4. examine the elodea in pond water under a microscope. sketch and label some typical cells in the space provided in this activity. describe the cell position of the chloroplasts in the cell.
(my answer) the chloroplasts are spread out in the cell. they are moving

5. observe the salt water preparation and sketch the cells. what has happened to the location of the cell membrane and chloroplasts?
(my answer) the cell membrane collapsed and it held the chloroplasts together in one place.

6. has water moved in our out of the cell?
(my answer) out

7. explain the water movement in terms of concentration difference.
(my answer) [not sure] the water moved out of the cell because it moves from area of high concentration to areas of low concentration

8. now, remove the coverslip and thoroughly rinse the elodea leaf under tap water. prepare a new slide of the same leaf using distilled water. look for changes in the cells. sketch these cells below. why did the cells change appearance?
(NO ANSWER) i need your help people! please?!

9. why do molecules diffuse?
-

10. why would molecules of a gas diffuse more rapidly than those of a liquid?
(my answer) [not sure] the molecules of a gas are spaced farther apart from each other than those in liquid, thus they have more space to move around and travel much faster than the molecules in a liquid.

11. the shrinkage of cytoplasm within a cell from diffusion is known as?
(my answer) plasmolysis
how can this process be an advantage to a cell? (no answer)
how would taking in too much water be a disadvantage to a cell? (no answer either)

12. a cell contains 3% salt and 97% water. how would this cell respond if placed in a distilled water solution? (my answer) explode? - not sure
in a 10% solution? (my answer) shrink? - not sure either

13. for the most part, plants and animals live in either a salt water environment or a fresh water environment; not both. explain this using the principles of diffusion.
(my answer) [not sure] plants and animals can't live in both environment because their environment could affect their cells. as have been mentioned, those who are living in the saltwater, when subjected to freshwater (which is hypotonic solution) can cause cell swelling which could possibly cause the cell to explode. those who are living in freshwater when subjected to salt water environment (which is a hypertonic solution), will cause cell shrinkage.

14. from evidence obtained in this experiment, list three factors that determine whether a molecule will diffuse into a cell.
(no answer)

15. a membrane that allows some molecules to pass but not others is called?
- semipermeable

16. can materials diffuse through a membrane in both directions at the same time? support your statement.
- no answer

17. in what way is the dialysis membrane like the cell membrane?
- the dialysis membrane and the cell membrane are both semipermeable. they allow substances to enter and exit the bag/cell.

18. in each case, the molecules moved from ____ concentration to ___ concentration.
- high, low

thank you to those who'll help!

sorry i know i need to brush up my english. i just came to the US a year ago.

oh yeah btw don't tell me i'm a slacker or don't do my homeworks because i am trying hard and doing my best to pass the class. see i tried answering them i just need someone to check and help me with some problems.
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Postby mith » Thu Oct 02, 2008 3:37 am

Don't double post.

Diffusion is driven by pretty much two things: entropy and brownian motion.

The assumption of entropy is that there are a number of different configurations, each equally likely. the usual example is throwing a set of dices. Each dice is independent of other dices and each outcome is equally likely i.e. The chances of throwing a 555 is the same as throwing a 123. However! The states as defined by the sum of the dices is not equally likely due to degeneracy. For example, there is only one configuration that adds up to 3:if you throw 111. However there's a number of configurations you can throw to get a sum of 9; you can throw 531, or 225 or 333, etc etc. Therefore some combinations are more likely just because there are more configurations that correspond to that state.

Brownian motion refers to random jostling of molecules just because they are at a temperature above absolute zero. Assume that all molecules are in motion and can move from their present positions. Higher temperatures correspond to faster movement.

Now combine these two concepts together. Suppose we visualize a box. On the left side of the box, we have a bunch of A molecules. On the right side of the box, we have a bunch of B molecules. In the middle we have some freespace. Given that a molecule is equally likely to go left as it is to go right(aka random walk), what do you think the distribution of the box would look like after some time. Note that a molecule at the leftmost end of the box cannot move left since it is going to bump against the box wall.

Additional: Consider the total movement of A molecules if the concentration was changed.
Additional 2: Consider the movement of A molecules if the freespace was limited i.e. consider if there was only one space open the size of a A molecule.
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