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

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

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

one reason that transpiration in plants occurs

2. adhesion- water molecules stick to other things

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

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

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

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

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

Where is there the greater concentration of kids?

Where is the greater concentration of bacteria?

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

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

What’s going to happen here, then?

Diffusion questions

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

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

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

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

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

Cell (plasma) Membrane

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

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

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

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

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

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