What is a concentration
gradient?
difference in concentration of a dissolved substance across a space.
Substances tend to move from a high to low concentration.
What is Diffusion?
(net) movement
of molecules from an area
of greater concentration to
an area of lower
concentration
Does diffusion require energy?
no
What is Osmosis?
Diffusion of water (or another solvent) from area of ↑concentration
(usually in comparison to ions or large molecules) to area of ↓concentration
What is hypertonic?
Comparative term designating a solution that, if outside a cell or vesicle, results in the LOSS of water and SHRINKAGE of the membrane-bound structure. This solution has a greater solute concentration than the solution on the other side of the membrane.
What is hypotonic?
Comparative term designating a solution that, if outside a cell or vesicle, results in the uptake of water and SWELLING or even BUSTING of the membrane-bound structure. This solution has a lower solute concentration than the solution on the other side of the membrane.
What is isotonic?
Comparative term designating a solution that, if inside a cell or vesicle, results in no net uptake or loss of water and thus no effect on the volume of the membrane-bound structure. This solution has the same solute concentration as the solution on the other side of the membrane.
What kinds of molecules does a semipermeable membrane let across?
The plasma membrane is a semipermeable membrane that only easily lets
across small, non-polar molecules (and ions/molecules that have protein
channels/carriers/pumps)
*
Why does water move toward areas of higher solute (ion) concentration in cells?
ions cross the cell membrane much more slowly than water, so water moves by osmosis toward the side with higher solute (lower water) concentration.
(water moves instead of ions bc its easier for it)
imagine:
Inside the cell: lots of ions (salty)
Outside the cell: fewer ions (less salty)
The ions can’t move out easily to balance things.
So instead…
👉 Water moves toward the side with more ions
What is Facilitated diffusion?
movement of ions/molecules down their concentration gradient through a transport protein embedded in membrane
Does Facilitated diffusion require energy?
no
What is Active transport?
The movement of ions or molecules across a membrane in a single direction, often against a gradient. Requires energy (e.g., from hydrolysis of ATP) and assistance of a transport protein (e.g., pump).
Does Active Transport require energy?
Requires energy (e.g., from hydrolysis of ATP) and assistance of a transport protein (e.g., pump).
What can Facilitated diffusion be accomplished through?
- channel proteins
- carrier proteins
What is an electrochemical gradient?
high to low concentration; like to unlike charge
Why is cell size limited?
Because diffusion and the surface area-to-volume ratio limit how efficiently nutrients enter and wastes leave the cell.
How does surface area-to-volume ratio affect cells?
As a cell gets bigger, its volume increases faster than its surface area, making exchange across the plasma membrane less efficient.
What happens to nutrient and waste exchange as a cell gets larger?
Bigger cells have less surface area relative to volume, so it becomes harder to get enough nutrients in and wastes out.
Why don’t cells grow very large?
As cells grow, volume increases faster than surface area, reducing diffusion efficiency and making nutrient intake and waste removal harder.
You take a dosage of milk of magnesia, which causes a high salt concentration in the fluids of your intestinal lumen (inside of intestines, where feces are formed). If increases or decreases in water in the intestinal lumen can affect the consistency of feces, then you would expect that:
a
Milk of magnesia likely helps cure diarrhea
b
Milk of magnesia likely helps cure constipation
c
Milk of magnesia would have no effect on feces consistency
B- Milk of magnesia likely helps cure constipation
Celery stalks that are immersed in freshwater for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this, we can deduce that the freshwater:
a
and the salt solution are both hypertonic to the cells of the celery stalks
b
and the salt solution are both hypotonic to the cells of the celery stalks
c
is isotonic and the salt solution is hypertonic to the cells of the celery stalks
d
is hypertonic and the salt solution is hypotonic to the cells of the celery stalks
e
is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
e
is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
Just based on size, which do you think would lose/diffuse heat to the environment the fastest: my axolotl (<0.5 lb), my dog (~75 lbs), or me? (Think about the effects of surface area to volume ratio and size in your answer)
Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer.
a
Axolotl
b
Dog
c
Me
d
All would lose heat at the same rate
a
Axolotl
A normal cell has a low concentration of sodium on the inside and a high concentration on the outside. Yet, the net movement of sodium is out of the cell. Which of the following must be involved?
a
Osmosis
b
Facilitated diffusion
c
Active transport
d
Simple diffusion
e
Multiple of the above could be true
c
Active transport
What are two characteristics of Eukaryotes?
Includes vast majority of multicellular organisms
(e.g. plants, animals, fungi)
+ many single-celled
organisms (e.g. protists)
- Very compartmentalized -
many organelles,
including the nucleus
