bio quiz 13/14/PL3

osmosis

diffusion of water molecules

• across selective (semi-permeable) barrier

• high → low concentration

what is meant by a selective (semi-permeable) barrier

allows water molecules to pass through, but not most of molecules dissolved in water (ex. plasma membrane)

solutes

molecules dissolved in water

concentration of water is determined by

concentration of solutes in water

• adding solutes lowers water concentration

solute potential (Ψ_s)

measure of how much solutes have lowered water’s tendency to move (free energy)

• pure water has no solutes: Ψ_s = 0 (highest value)

relationship between solute concentration and Ψ_s / water concentration

as solute concentration increases, Ψ_s and water concentration decrease

where does water diffuse from and when does it stop

• diffuses from areas of higher Ψ_s to areas of lower Ψ_s

• until equal on both sides

plasma membranes and relationship with cells

selective semi-permeable barriers

• cells depend on regulated diffusion of water molecules across PM to stay alive

why is osmosis critical to cell survival (isotonic, hypotonic, hypertonic)

• if Ψ_s inside/outside cell is equal (isotonic)

  • water enters/exits cell in equal amounts

• if Ψ_s higher outside cell than inside (hypotonic)

  • water diffuses into cell, cell will swell and can burst

• if Ψ_s higher inside cell than outside (hypertonic)

  • water diffuses out of cell, cell will shrink and can dehydrate → die

brain capillaries, BECs and tight intercellular junctions

fine blood vessels that feed brain tissue

• Brain Capillary Endothelial Cells: form a tube

• tight intercellular junctions: physical connections between BECs

blood-brain-barrier (BBB)

molecules can’t pass BETWEEN BECs through intercellular junctions

• must pass THROUGH PM of BECs

clinical significance of BBB

BBB prevents most medicines from entering into brain

• can cause issues when doctors need to introduce medicines into brain

how do doctors breach the BBB

1. inject solute into blood (H2O conc. now lower in blood than inside BECs)

2. water diffuses out of BECs into blood

3. capillary walls shrink slightly / create space between cells

4. medicine can now pass between BECs into brain

role of mannitol in breaching BBB

lowers Ψ_s of blood

→ H2O diffuses out of capillary wall cells

energy

capacity to do work

kinetic energy

energy of motion

• thermal, light, mechanical, e.t.c.

potential energy

stored energy

• concentration gradients, chemical energy, e.t.c.

thermodynamics

branch of chemistry that deals with energy transformations (changes)

first law of thermodynamics

conservation law

• energy cannot be created / destroyed

• can only change from one form of energy to another

• total amount of energy in universe remains constant

second law of thermodynamics

no energy transfer is 100% efficient

• some energy always lost (usually as heat) & becomes unusable

• entropy (measure of unusable energy) in universe constantly increasing

• free energy (usable energy) in universe constantly decreasing

free energy equation

G = H - (TS)

• G = energy available to do work

• H = enthalpy (total amount of energy contained in molecule or system)

• TS = amount of unusable energy in molecule or system

• T = absolute temperature

• S = entropy

change in free energy after chemical reactions

reactants → products

• chemical reactions begin w/ reactants & end w/ products

  • reactants and products have certain amount of free energy

  • products will either have more / less free energy than reactants

exergonic reaction

-ΔG (products have less free energy than reactants)

• free energy released can be used to do work

  • can be spontaneous (rxn has potential to go forward without extra energy input)

endergonic reaction

+ΔG (products have more free energy than reactants)

• energy absorbed (input of energy needed)

  • NEVER spontaneous (rxn will not go forward without extra energy input)

endergonic graph

exergonic graph

reaction coupling in cells

exergonic & endergonic rxns coupled together in cells

• free energy released by exergonic used to drive endergonic forwards

• ATP is energy currency of cell

  • ATP hydrolysis is exergonic (releases free energy from ATP)

    • drives many endergonic in cells forwards

relationship between PFR and oxygen production rate in chlorella

as PFR increases, oxygen production rate in chlorella increases but can pleateau when totally saturated with light

• more photons reach photosystems

if “no light control” rate was negative, what was happening to oxygen in dark chlorella tube?

• oxygen gets consumed because cells carried out cell res w/o light

  • not photosynthesis since it needs light

for what do plants use oxygen

cellular respiration

• breaks down glucose to release energy in form of ATP for cellular activities

DCMU is a herbicide (blocks transfer of electrons out of PSII). how would DCMU affect production of oxygen in plants

decrease / stop oxygen production

• DCMU blocks electron transfer out of PSII, preventing normal splitting of water that releases oxygen during photosynthesis

DCMU is a herbicide (blocks transfer of electrons out of PSII). how would DCMU negatively affect production of glucose in a plant

reduce glucose production

• blocking electron transport prevents plant from making enough ATP & NADPH

  • required for Calvin cycle to convert CO2 → sugars