methods used to transport molecules through cell membranes

what are the three kinds of passive movement?

• simple diffusion

• facilitated diffusion

• osmosis

is diffusion is a passive process? if it is , why?

• diffusion is a passive process

• as the molecules only rely on their kinetic energy and a concentration gradient for movement, they do not use energy from the cell.

what is diffusion?

• diffusion is the movement of molecules from an area of a high concentration to an area of lower concentration down a concentration gradient.

why does fat molecules such as steroids hormones can diffuse through the phospholipid membrane?

• because the bilayer consists of fatty acid tails.

why oxygen and carbon dioxide can easily fit through the spaces in the phospholipid bilayer and can be transported across phospholipid bilayers by diffusion?

• because they are small enough

large molecules such as glucose, and small charged particles such as?

• sodium ions

does this large particles such as sodium ions can able to pass through the phospholipid bilayer?

they cannot pass through

what do they need to be able to cross the membrane? And this is known as

• they need channel proteins or carrier proteins.

• facilitated diffusion.

how does channel proteins carry the molecules across the membrane?

• carrier proteins bind to the specific molecules and then change shape carrying the molecule across the membrane.

is it true or false? large or charged/polar molecules can passively diffuse though the pore of a protein channel without binding it?

• true

what is osmosis?

• is the diffusion of water molecules from a region of high water potential to a region of low water potential,

• the movement is through a partially permeable membrane (permeable to water through but not the solute)

when does the osmosis occurs?

• osmosis will occur until the concentration of water molecules is even on either side of the membrane

• meaning the water potential is the same on both sides.

what is equilibrium?

• particles move across the cell membrane in both directions all the time.

give a reason why the drug could not enter the cell by osmosis?

• because it only involves of free water molecules and not a solute.

give two reasons why this drug may have to pass through a membrane by facilitated diffusion, rather than by a simple diffusion

• because it is a big molecule which cannot pass through the membrane.

• and it is too charged

what is active transport?

• active transport and bulk transport are not passive processes.

• instead they require energy

what does active transport allows?

• active transport allows a substance to move across a cell membrane against its concentration gradient.

what does the active transport process

• a carrier protein

• energy from ATP

what is the features of carrier proteins?

• they are embedded in the lipid bilayer and span both layers.

• they change shape when they absorb energy

• which allows a substance to be moved across the membrane.

• then they return to their original shape, allowing transport to continue.

what is the function of carrier proteins in the membrane?

• can act as pumps to carry the large and charged molecules across the membrane.

which is faster — active transport or diffusion ?

• active transport

what does an ATP molecule consists of?

• adenine

• ribose

• the three phosphate groups

energy is released when?

• when the bond between the second and third phosphate group is broken in a hydrolysis reaction.

• Adenosine diphosphate (ADP) and inorganic phosphate, PI, are produced.

energy from respiration converts ADP back to?

ATP

what is the acronym of ATP

Adenosine triphosphate