1. Water and Its Importance
Biology
Water, Diffusion, and the Cell Membrane

2. WATER!!!!!!!!!!
3 of the main properties: 1. cohesion- water molecules stick to each other

4. Due to the hydrogen bonding Water molecules are “holding hands”

5. one reason that transpiration in plants occurs

6. 2. adhesion- water molecules stick to other things

7. occurs due to hydrogen bonding
also aids in transpiration and other life processes

8. 3. surface tension- occurs at surface of a liquid that allows it to resist an external force caused by the cohesive forces of water at surface, the molecules are even more strongly attracted to each other

11. Energy and Molecules
all atoms and molecules are in constant motion –have energy * potential energy- stored energy ex: chemical energy found in food *kinetic energy- energy a moving object has energy can change from one form to another

13. in 1827, Robert Brown observed pollen grains under microscope
Brownian motion- random movement of atoms & molecules

14. what is meant by concentration?
where is there the greater concentration of sheep?

15. Where is there the greater concentration of kids?

16. Where is the greater concentration of bacteria?

17. whenever there is a difference in the concentration of substances across a space, it is called a concentration gradient
substances are going to move along the concentration gradient

18. substances are ALWAYS going to move from where there are MORE of them to where there are LESS of them
this happens until the concentration equals out

19. What’s going to happen here, then?

22. Diffusion questions

23. Diffusion
diffusion – net movement of particles from an area of greater concentration to an area of lesser concentration
occurs because of Brownian motion

24. diffusion is a SLOW process usually
rate of diffusion affected by:
concentration- the more conc, the more collisions between particles, the faster they diffuse

25. 2. temperature- an increase in temp, causes an increase in particle motion, increasing rate of diffusion

26. 3. pressure- the more pressure the particles are under, the faster they move, diffusing more quickly concentration is the primary controlling factor of diffusion

27. Results of diffusion
particles move until there is no longer a difference in conc across the space
particles continue moving, dynamic equilibrium is reached

28. Cell (plasma) Membrane

29. boundary between cell and the environment
allows steady supply of nutrients & water into cell
removes wastes & excess substances
maintains homeostasis (balance in the cell’s env) by being selectively permeable

30. composed of phospholipids (2 layers) part loves water (head)
part hates water (tail)
contains cholesterol to help stabilize membrane

31. also contains transport proteins- embedded in cell membrane- that transport particles into or out of the cell
fluid mosaic-
proteins &
phospholipids
free to move

33. water can easily go in & out of cell
selectively permeable- allows some substances to come in while keeping others out
water can easily go in & out of cell
gases (O2, CO2) are allowed to go in & out

34. cell’s survival dependent upon ability to maintain homeostasis
(selective permeability)
what must a cell receive in order to survive?
food
oxygen
water

35. some substances have limited entrance thru the cell membrane for ex: sodium and calcium ions & large molecules