BIOL 260 MT1 Flashcards
How do organisms overcome the limitations of diffusion?
To overcome the limitations of diffusion organisms move fluids by bulk flow
2 examples of bulk flow in humans:
Ventilation (Respiratory system): Bulk flow moves air in and out of the lungs due to pressure differences created by the diaphragm and chest muscles.
Circulation: Blood moves from high pressure (heart and arteries) to low pressure (veins).
When referring to the diffusion of gasses why do we think in terms of partial pressure gradients?
At fixed temps and pressures, the partial pressures of a gas is proportional to its concentration.
Changing the temp or pressure will affect the partial pressures.
Henry’s Law
What does it state and how does it apply to gas exchange?
The amount of gas that dissolves in a liquid is proportional to the partial pressure of that gas above the liquid.
C = Kp — Gas concentration = Henry’s constant * partial pressure
Higher pressure = more gas dissolves
Ex:
Lung gas exchange: O2 moves into blood and CO2 moves out based on partial pressures
In a system at equilibrium what would we expect the partial pressures to be inside vs outside the liquid? Concentrations?
At eq pressure would be equal inside and outside the liquid. The concentrations would differ based on solubility.
What generates vs impedes flow?
Pressure gradients generate
Resistance impedes flow
Describe bulk flow lung ventilation in animals
Contraction of the diaphragm increases the volume of the chest cavity decreasing pressure causing air to flow into the lungs.
Relaxation of the diaphragm decreases volume increasing pressure forcing air out of the lungs.
At the end of inspiration, before any gas exchange occurs would you expect more carbon dioxide or oxygen content in the alveoli?
Lower oxygen and higher CO2.
CO2 from blood is constantly diffusing into the alveoli
O2 levels are lower due ti the leftover air in the lungs that has a lower O2 content mixing with the new air being inhaled.
How much fresh air do we get with a tidal volume of 500ml and dead space volume of 100ml?
400ml
Fresh air = Vt - Vd
Why would alveolar PO2 decrease during snorkeling?
Because the snorkel would increase the amount of dead space.
Systole and Diastole
Systole: Contraction, pressure increases
Diastole: Relaxation, pressure decreases
Which have thicker walls: ventricles or atrium?
Ventricles have thicker walls and contracts strongly.
Describe blood flow through the heart and which steps are part of the pulmonary vs systemic circuit:
Pulmonary circuit:
Blood returns to heart entering through right atrium —> Blood enters right ventricle —> Pumped from right ventricle to lungs.
Systemic:
Blood returns to left atrium ——> left ventricle —> Body
Early ventricular diastole
Ventricles begin relaxing decreasing pressure.
semilunar valves close
Ventricles are sealed until pressure drops enough
Late ventricular diastole
Ventricles fully relax
AV valves open causing blood to flow into ventricles
Cycle resets, to start again with atrial systole
Atrial systole
Atria contract increasing pressure
Blood pushed into relaxed ventricles
AV valves open
Semilunar closed
Ventricles max volume
Early ventricular systole
Ventricles start contracting, pressure increases
AV valves shut
Semilunar closed
Blood is trapped and building pressure
Late ventricular systole
Ventricles fully contract peaking pressure
Semilunar valves open sending blood to lungs and body
AV valves remain closed
In late ventricular systole what causes the valves leading to the arteries to open?
Higher pressure in the ventricle than in the blood vessels.
Which ventricle has a more muscular wall?
Left
What allows electrical signals to travel between cardiac cells?
Gap junctions at a the intercalated disk.
Pacemaker of the heart
Si notarial node
Impulse conduction steps
1) Electrical signal at SA node
2a)Electrical activity goes to AV node via internodal pathways
2b) Electrical signals spreads slowly across atria, slowing through AV node.
3)Signal moves rapidly through ventricular conducting system to apex of heart.
4) signal spreads upwards from apex
Why is the aorta a “pressure reservoir”
The aorta stores and releases pressure to maintain continuous blood flow.
During systole aortic walls stretch, storing pressure.
During diastole, aortic walls recoil continuing to push blood forward.
Why does pressure drop significantly at the arterioles?
The radius of each arteriole is small so resistance is high
What triggers increased breathing rate and depth?
(High altitude example)
Chemoreceptors in the carotid artery detect reduced oxygen levels at high altitudes.
What are some effects of Hypoxia (oxygen deprivation)?
Increased breathing rate and constrict vessels in the lungs (bad).
Increased heart rate
Dilate peripheral blood vessels in appendages.
High altitude pulmonary edema
Vasoconstriction causes increased pulmonary arterial pressure forcing fluids across capillary beds leading to it accumulating.
Causes an increase in the diffusion distance —> reduces diffusion of oxygen.
How many oxygen molecules can hemoglobin bind to?
Due to hemoglobin’s having 4 heme groups which can each bind to an oxygen molecule, one hemoglobin can bind to 4 oxygen molecules.
What role does hemoglobin play in allowing more oxygen to dissolve in plasma thus increasing the amount of oxygen that can be carried?
When O2 binds to hemoglobin it no longer contributes to the concentration dissolved in plasma or the partial pressure.
This allows more oxygen to dissolve in the plasma.
Effects of increased hemoglobin?
Blood can carry more oxygen
Total O2 per mL of blood increases.
Affinity does not change.
What is the Bohr effect?
Describes how increased CO2 and lower pH reduce hemoglobin’s affinity for oxygen, promoting it to release oxygen to tissues.
Increase in pH causes higher oxygen saturation.
What causes the Bohr Effect and why is it important?
Increased CO2, lower pH.
Helps unload oxygen from hemoglobin into active tissues (muscles) where CO2 and H+ concentrations are high.
In relation to humidity when do maximum transpiration rates occur?
Lowest humidity during the day.
Active loading of sugars into the phloem
Sugars are actively transported into the sieve tube elements from photosynthetic cells. This process requires ATP, often involving sugar transporters.
Why does water enter the phloem at the source?
The high concentration of sugars decreases its water potential, causing water to move in from the xylem by osmosis.
What creates the pressure gradient in the phloem?
The influx of water at the source increases pressure. This pressure gradient pushes the sugars towards the lower pressure area at the sink.
How is contraction limited in the xylem?
The xylem has lignified cell walls that are thick and rigid (no diddy) providing strength.
When do embolisms form in the xylem?
(Air-filled xylem)
When atmospheric pull outpaces water availability.
How does the xylem prevents embolisms?
Xylem cells are connected by pits with membranes that restrict air movement preventing the bubble from spreading.
Xylem consists of many interconnected vessels and tracheas, allowing water to bypass.
Tracheids are narrower and are not prone to embolisms.
What are the three mechanisms xylem brings water and minerals from the soil?
Positive root pressure
Capillarity
Negative pressure (transpiration)
Positive root pressure xylem loading:
The roots have a much higher mineral concentration generating a negative water potential.
Water uptake generates turf or pressure that pushes water and minerals toward the xylem and up the plant.
Hydrathodes
Specialized pressure valves that secrete water as the result of positive root pressure.
Capillarity
Capillary action causes water to move much higher in a narrow tube than in a wide tube.
Water rises up the xylem because the upwards adhesive forces outweigh the coward force (weight) of the water column.
Transpiration
The main force influencing the movement of xylem sap.
Water evaporates from leaf cells diffusing out the stomata, pulling water up due to pressure gradients.
Companion cells
Sugar loading/unloadng
Metabolically active
Steps of Phloem loading
1) Active transport moves sucrose from source into companion cells (H+ pump)
2) Once in companion cell, sucrose builds up in sieve tube member cells via diffusion.
3) High solute concentration in phloem generates negative solute potential. Water flows in from xylem increasing pressure.
Phloem unloading in metabolically active vs inactive sinks
Sucrose is rapidly being used in the sink maintaining low concentrations of sucrose. This allows sucrose to be passively transported in.
Sucrose must be actively transported into storage sinks vacuole to maintain a favourable concentration gradient.
What ancestral functions did chloroplasts maintain?
Ability to capture energy from light
Ability to incorporate inorganic CO2 into sugars.
Oxidation and reduction in photosynthesis
Water molecules are oxidized, lose electrons
Carbon dioxide molecules are reduced, gain electrons.
Two functions of glucose from photosynthesis:
Fuel to form ATP in mitochondria
Building block to creare organic biomass from inorganic CO2
Examples of icronutrients:
Copper, Zinc, Iron, Manganese
Examples of macronutrients
Magnesium, Phosphorous, nitrogen, potassium
Is most organic biomass derived from CO2 or soil nutrients?
CO2 by a landslide — 96%
What is the largest source of photosynthetic activity?
Phytoplankton — 50%
Light-dependent reaction
Water split to extract electrons
Electrons excited by light and generates ATP and NADPH (reducing power.
Light-independent reaction
ATP and NADPH created in light dependent reaction is used to fix CO2 into sugar.
Sugar stores solar energy as high-energy carbon-carbon bonds.
What captures the energy of the light?
Chloroplasts in the mesophyll cells
What controls gas exchange in leaves?
Stomata in the lower leaf epidermis.
Also regulates water balance.
Lumen, thylakoid, granum
Granum = stack
Thylakoid = individual of stack
Lumen= inside of stack
Where do light independent vs dependent reaction occur?
Dependent - Thylakoid membranes - energy absorption, generation of chemical potential
Independent - In stroma - CO2 fixation, RubisCO
What wavelengths of light do chlorophyll an and b absorb? Transmit?
Absorb red and blue light
Transmit green
What wavelengths of light do carotenoids absorb/transmit?
Absorb blue and greens
Transmit yellow, orange, red
Three possibilities of photon energy captured by pigments.
Emit heat and light in isolated pigments
Transfer of energy between adjacent antenna pigments (resonance energy transfer).
Photo chemistry - transfer of electrons to acceptor molecules. Light energy —> chemical energy in reaction center.
Antenna complex job
Capture and direct energy from photons to the reaction center.
Made up of chla, chlb, and carotenoids.
What is resonance
The excitation energy of an electron is transferred from electron to electron towards the reaction center.
Electron is not transferred.
What is the reaction center composed of?
A modified chlorophyll dimer.
What happens to the excited electrons at the reaction center?
Excited electrons are transferred to a new molecule that acts as an electron acceptor.
When the electron acceptor becomes reduced, the electromagnetic energy becomes chemical energy.
Primary electron acceptor in PSI vs PSII
PSI = Ferredoxin - modified chlorophyll A and
Fe-S cluster.
PSII = Pheophytin
Electron donors for reaction center 1 vs 2
Electron donor for reaction center 2 is water splitting.
Electron donor for reaction center 1 is a component of PSII (plastocyanin).
How do plants adjust their light harvesting capability?
Change the size of their antennas based on light intensity.
What is the core antenna made up of?
Tightly packed chlorophyll A.
What resonance scenario would have larger energy losses?
When the pigments are different
E.g. transfer from chlorophyll to carotenoid.
Things to remember about the Z scheme
of electrons in = # of electrons out
Electrons move from high to low energy
NADP reductase is the only possible EXIT for electrons
H2O is the only possible ENTRANCE for electrons.
Plastoquinone only works if it moves electrons and protons.
Where do the protons from water splitting go (PSII)?
The electrons replenish the electron lost by the reaction center during photosynthesis chemistry.
The PROTONS are released to the thylakoid lumen and contribute to the proton gradient.
What does the movement of PQ across the thylakoid membrane achieve?
Creates a H+ gradient.
After the electrons are donated to pheophytin of PSII what happens to the electrons?
They pass from the reduced pheophytin to PQ and enter an ETC.
PQ shuttles an electron AND proton from the stroma to the lumen across the thylakoid membrane. The electron then reaches the cytochrome complex.
What powers ATP synthase?
The power to synthesize ATP comes from the proton gradient between the lumen and the stroma.
What are the two components that creates the H+ gradient in the lumen?
PQ and water splitting
What happens to the electron after it reaches the cytochrome complex?
Cytochrome transfers it to plastocyanin which links PSI and PSII.
These excited electrons go down an ETC of iron and sulfur containing proteins to ferredoxin.
How is NADPH formed in the stroma?
The enzyme NADP+ reductase transfers a proton and two electrons from ferredoxin to NADP+, forming NADPH.
What functions as an electron donor in the Calvin cycle?
NADPH
Summary of electron flow in non-cyclic
Water (PSII) — Plastoquinone (PQ) — Cytochrome complex — Plastocyanin (PC) — p700 (PSI) — Ferredoxin — NADPH
When can the Calvin cycle occur
Only during the day
How many cycles to synthesize a glucose molecule?
6
Each cycle incorporates one carbon from CO2
Calvin cycle steps 1-3
Six molecules of CO2 react with 6 molecules of Ribulose 1,5 biphosphate (RuBP) (5 C each for a total of 30) to produce 12 molecules of 3- phosphoglycerate. (3-PGA) (36 carbons).
3-pga = C3 photosynthesis.
Steps 3-6 of Calvin cycle
12 molecules of 3-PGA are reduced using ATP and NADPH generating 12 molecules of glyceraldehyde 3-phosphate (G3P) (36 C).
2 molecules go to make 1 molecule of glucose
10 molecules go to regenerate the substrate,
Regeneration of the Carbon cycle
10 molecules of G3P use 6 additional molecules of ATP to regenerate 6 molecules of ribulose 1,5 biphosphate.
Cycle starts anew
What haoppens when CO2 binds to RubisCO?
Carboxylation: ATP and NADPH are used to create C-C bonds.
What happens when O2 binds RubisCO?
Photorespiration
ATP and NADPH are used to BREAK C-C bonds of phosphoglycolate generating CO2 and heat.
Waste of NADPH and ATP
Why is RubisCO such a bad catalyst?
It evolved in a CO2 rich environment when O2 was poor.
How do photosynthetic organisms cope with rubisCO’s short comings?
C3: Synthesize lots of enzyme
C4 and CAM: Concentrate CO2 around RubisCO
Why can’t C3 plants accumulate higher than atmospheric concentrations of CO2?
Because it freely diffuses across cell membranes.
What is spatial separation?
Occurs in C4
Carbon fixation and Calvin cycle occur in different cells
Mesophyll capture CO2 and convert to 4- Carbon malate which moves to bundle sheath cells.
Bundle sheath cells: malate releases CO2 for Calvin cycle
Keeps CO2 levels high near RubisCO.
What is temporal separation?
Occurs in CAM plants
Carbon fixation and Calvin happen at different times.
At night, stomata open and CO2 stored as malic acid.
Day: malic acid releases CO2 for the Calvin cycle.
Prevents water loss.
What does high temp do to CO2 solubility and rubisCO binding?
Reduces
What are the 6 essential macronutrients soil provides?
Nitrogen, Phosphorous, Potassium, Calcium, Magnesium, Sulfur
What roles do micronutrients play in plants?
Used as cofactors in enzymes and pigments.
Redox reactions
What are the 8 essential micronutrients?
Boron, Chlorine, Copper, Iron, Manganese, Molybendum, Nickel, Zinc
Topsoil made up of:
Horizon O: organic material, macronutrients.
Horizon A: Organic matter and leached minerals, source of macro and micro.
Horizon B made up of:
Miner precipitates
Source of micronutrients
How is topsoil formed?
The weathering of rocks by physical, chemical and biological processes.
What are the topsoil quality parameters?
Composition: Presence of nutrients. Organic composition and inorganic composition.
Texture: root penetration, oxygen and water availability.
Charge: Mobility and bioavailability of cationic and anionic nutrients.
Long roots - plant living conditions
Less availability to water.
Sandier soils
Organic soils and clay charge
Organic soils and clay are negatively charged which INCREASES the retention of positively charged nutrients.
REDUCES the bioavailability of positively charged nutrients.
What increases the bioavailabity of positively charged ions?
Most cations increase their availability in acidic soils.
Hydrogen ions take the place of mineral cations on soil particles, allowing these compounds to be taken up.
What increases H+ concentration in soils?
Root hairs exude H+ directly using H+ ATPases and producing H+ as a consequence of cellular respiration.
Concentration gradient in root hairs
Root hairs will use ATP to generate H+ gradients to facilitate nutrient acquisition.
Always contain higher concentration of nutrients than surrounding soils.
Specialized root structure for mineral nutrient uptake:
Lateral roots anchor the plant and enables long distance scouting of water and minerals.
Root hairs plasma membrane contain selective ion channels that filter out toxins.
Water flow through Apoplastic and symplastic route
Apoplastic: Flows through extracellular spaces and bypasses the plasma membrane (unfiltered)
Ends in Casparian strip
Symplastic: Water crosses the plasma membrane and moves cell to cell using plasmodesmata (filtered). Ends in the vasculature.
Casparian strip
Hydrophobic barrier in the cell walls of endodermal cells that stops water passage through the Apoplastic route.
Forces water to pass through cell membranes rather than around.
Which side of the membrane is more negative?
Intracellular side of the membrane is more negative than the extracellular side?
How are toxic ions eliminated from the cytosol?
Excluded from xylem by endodermal cells.
Plants store harmful ions in the central vacuole or transport them to the extracellular media.
Antiporter used to pump Na+ into vacuole alongside proton pumps.
Metallothioneins
Cysteine proteins with high affinity for metals.
Metal gets trapped and then secreted from the cell by vesicle.
What determines the spontaneous movement of nutrients?
Electrochemical potential
= chemical + electrical gradient
Channels vs Transporters
Channels regulate passive transport in favor of electrochemical potential.
Transporters regulate active transport against the electrochemical potential.
How are negative charges transported against concentration and electrical gradients? Positive charges?
Anions use the energy accumulated by H+ gradient to hitch-hike into the cell.
Proton pumps generate an electrical gradient for positive charges.
Mycorrhizae trade-off
Fungus delivers inorganic nutrients to plant, plant delivers fixed organic carbon (sugars).
N2 fixers
Fix N2 which is not directly available to plants is turned into NH4 (ammonium) which plants can readily take up.
Cause nodules on roots.
Leghemoglobin
Oxygen binding protein produced in legumes in response to infection by N2 fixing bacteria.
Buffers concentration of free oxygen to prevent the inactivation of the bacterial Nitrogenase enzyme.
Nitrogenase enzyme converts N2 to NH4 making it available for plants in exchange for sugars.
Why will a plant without N2 fixing bacteria produce less rubisCO?
Because the plant will be nitrogen deficient limiting its ability to synthesize proteins including RubisCO.
Parasitic plants
Tap into vascular tissue of their host and divert nutrients for their own growth.
Saprophytes
Parasitize fungi that digest organic matter for them.
Get food from dead matter.
