Studied by 3 peoplesurface area
the amount of area of its outer surface; describes two-dimensional structure
volume
the amount of space it occupies; describes three-dimensional structure
what happens as an object gets larger (referring to surface area & volume)
Both surface area and volume increase, but volume increases faster than the surface area increases
smaller objects vs larger objects (surface area & volume)
larger objects have more surface area and volume than smaller objects overall, but b/c volume increases quicker than surface area, the larger object has less surface area to its volume than a smaller object has
Why is changing something’s size but keeping their shape not possible?
because increases/decreases in size often require changes in shape to support the new size
villi
folds of the lining of the gut; adaptations larger organisms have to increase the gut’s surface area
diffusion
the net movement of molecules from areas of higher to lower concentration of the molecules due to random motion; diffusion is fast over short distances
why are bacterial cells often small
because they rely on diffusion, and in order for molecules to diffuse efficiently the molecule needs to be small, since diffusion is fast over short distances. Also, the ratio of surface area to volume also contributes to the small size of bacteria, because more surface area and less volume allows the cell to diffuse materials needed for growth effectively
bulk flow
the movement of a fluid driven by pressure differences
phospholipids
made up of a glycerol backbone attached to a phosphate group and two fatty acids; the phosphate head is hydrophillic & the fatty acid tails or hydrophobic; amphipathic
micelle
lipids with bulky head groups and a single fatty acid tail are wedge-shaped and pack into a spherical structure
lipid bilayer
a two-layered structure of the cell membrane that has lipids with less bulky headgroups and two hydrophobic tails and are roughly rectangular; the hydrophillic heads point outward toward the aqueous environment, and hydrophobic tails pointed inward away from water
liposome
spherical structures with a lipid bilayer forming a barrier between inside and out
saturated fatty acids
do not have double bonds; have a straight structure and therefore are able to pack tightly; more stable and less fluid
unsaturated fatty acids
have one or more double bonds which form kinks; are not able to pack as tightly as saturated fatty acid tails, less stable and more fluid
cholesterol
major component of animal cell membranes; amphipathic; hydrophillic region has a hydroxyl group (-OH) and the hydrophobic region has 4 planar carbon rings; able to embed itself in the lipid bilayer affecting the fluidity of the membrane
how can cholesterol affect the fluidity of the membrane
at higher temperatures, cholesterol makes the membrane less fluid, and at low temperatures, cholesterol makes the membrane more fluid
protein function in cell membrane
some transport molecules into and out of the cell, others can pass electrons along the membrane
transport proteins
a membrane protein that moves ions and other molecules across the cell membrane
receptor proteins
a molecule that binds to a signaling molecule and triggers a response in a target cell; allows the cell to receive signals from the environment
anchor proteins
attach to other proteins and help to maintain cell structure and shape
integral membrane proteins
a protein that is permanently associated with the cell membrane and cannot be separated from the membrane experimentally without destroying the membrane itself; inside the membrane
peripheral membrane proteins
a protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions; easily separated from the membrane while leaving the structure of the membrane intact
transmembrane proteins
a protein that spans the entire lipid bilayer; most integral proteins
glycolipid
a carbohydrate that is covalently linked to a lipid
glycoprotein
a carbohydrate that is covalently linked to a protein
fluid mosaic model
a model proposing that the lipid bilayer is a dynamic structure that allows molecules to move laterally within the membrane and is a mixture of several components including lipids, proteins, and carbohydrates
concentration gradient
a difference in concentration of a substance, with regions of higher and lower concentration
dynamic equilibrium
when there is no longer a concentration gradient so net movement stops but movement of molecules in both directions continues
Passive transport
occurs when molecules move across a membrane by diffusion
simple diffusion
when molecules diffuse directly through the cell membrane; ex: oxygen and carbon dioxide move into and out of the cell using simple diffusion b/c they are small and uncharged; some hydrophobic molecules like steroids and other lipids can also use simple diffusion; no energy required since substances enter and exit the cell simply as a result of concentration differences; only works from high to low concentration
Facilitated Diffusion
diffusion across a cell membrane through a transmembrane protein, such as a channel or carrier; molecules move through a transport protein
channel protein
a transport protein with a passage that allows the movement of molecules through it; depends on a molecules’ shape and charge
carrier protein
a transport protein that facilitates movement of molecules across a cell membrane; binds to and then transports specific molecules across the cell membrane
aquaporins
a channel protein that allows water to cross the cell membrane more readily than by diffusing through the lipid bilayer
active transport
the movement of substances across a cell membrane against a concentration gradient requiring an input of energy
primary active transport
active transport that uses the energy of ATP directly; ex: sodium-potassium pump
secondary active transport
active transport that uses the energy of an electrochemical gradient to drive the movement of molecules; uses ATP indirectly
ATP in primary active transport
the energy of ATP is transferred to a transport protein which changes its shape and moves a molecule across the membrane
electrical gradient
the difference in charge
electrochemical gradient
a gradient that has both chemical and charge components
exocytosis
the process in which a vesicle fuses with the cell membrane and releases its contents to the extracellular space
endocytosis
a process where a vesicle buds off from the cell membrane, bringing material from outside the cell into that vesicle, which can then fuse with other membranes
phagocytosis
“cellular eating”; a process where a cell can ingest large particles, microorganisms, or even dead cells
solute
a dissolved molecule such as the ions, amino acids, and sugars often found in a solvent such as water
molarity
the amount of a solute in a volume of solution, expressed as moles of a solute per liter of solution; aka molar concentration
osmosis
the net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration
water potential
a parameter that combines all the physical and chemical factors that influence the movement of water, such as pressure, osmosis, and gravity; water moves from regions of higher water potential to regions of lower water potential
osmotic pressure
the pressure needed to prevent water from moving from one solution into another by osmosis; the tendency of water to move from one solution to another by osmosis
tonicity
a measure of osmotic pressure; the higher the osmotic pressure, the higher the tonicity
hypertonic solution
a solution with a higher solute concentration (lower water potential) than another solution
hypotonic solution
a solution with a lower solute concentration (higher water potential) than another solution
isotonic solution
a solution with the same solute concentration (same water potential) as another solution
pressure potential
the effect of pressure on the movement of water
solute potential
the effect of solutes on the movement of water
osmoregulation
the regulation of water and solute levels to control osmotic pressure
osmoconformers
animals that keep their internal fluids at the same osmotic pressure as the surrounding environment
osmoregulators
when animals maintain an internal solute concentration
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