Unit 2b: Cellular Respiration and Photosynthesis Flashcards
Describe the chemical formula of glucose.
C6H12O6
How many ATPs does one glucose molecule charge?
38 (as suggested by IB)
36 (sometimes)
List the phases of aerobic respiration, where in the cell they occur and their net ATP generation per glucose molecule.
Glycolysis: cytoplasm
+2 net ATP
Link Reaction: occurs as pyruvate is being transported through outer membrane to the matrix
+0 net ATP
Citric Acid/Krebs Cycle: matrix
+2 net ATP
Oxidative Phosphorylation/ETC: inner membrane
+32 net ATP
List the components of the mitochondria.
Components relevant to this unit:
Outer membrane
Intermembrane space
Inner membrane
Matrix
Cristae
Other components:
Mitochondrial DNA
Ribosomes
What kind of reaction is glycolysis?
Redox (reduction-oxidation) reaction
State the net equation (very first reactants –> very last products) of aerobic respiration.
C6H12O6 + 6 O2 –> 6 CO2 + 6 H2O + Energy
What is OIL RIG? Explain its meaning.
Oxidation
Is
Loss (of electrons)
Reduction
Is
Gain (of electrons)
Explains the flow of electrons of a given reaction
Choose the proper answer:
Oxidation results in a…
gain/loss of electrons
gain/loss of protons (H+ ions)
gain/loss of potential energy
gain/loss of oxygen
Reduction results in a…
gain/loss of electrons
gain/loss of protons (H+ ions)
gain/loss of potential energy
gain/loss of oxygen
Oxidation:
loss of electrons (OIL RIG), potential energy, hydrogen (protons follow electrons)
gain of oxygen
Reduction:
gain of electrons, potential energy, hydrogen
loss of oxygen
Name the three phases of glycolysis, as well as the initial reactant(s) and final product(s).
Activation of Glucose
Splitting of Glucose
Oxidation of G3P to Pyruvate
Glucose –> pyruvate (via oxidation)
Describe the “activation of glucose” stage in Glycolysis.
Glucose reacts with two ATP molecules and has two phosphate groups attached to either end, forming fructose 1,6-bisphosphate (short form: F 1,6-BP) [6C]
Glucose is converted to this form because glucose is not as symmetrical as fructose
NET EQUATION: C6H12O2 + 2 ATP –> 2 F 1,6-BP + 2 ADP
Describe the “splitting of glucose” stage in Glycolysis.
Fructose 1, 6-biphosphate (F 1,6-BP) {6C} is split into two: DHAP and Glyceraldehyde 3-phosphate (aka triose phosphate/G3P) {3C}
- Because fructose is not perfectly symmetrical, the extra oxygen atom goes to the DHAP [3C]
- DHAP is identical to G3P but has an extra oxygen atom
- DHAP is converted into G3P and undergoes the same process
Every F 1,6-BP is eventually split into 2 G3Ps
NET EQUATION: 2 F 1,6-BP –> 2 G3P
Describe the oxidation of G3P to pyruvate, and provide the net ATP gain during the entire process of glycolysis.
2 hydrogen atoms are removed from each of the two G3P [3C], which then react with NAD+ and Pi, forming NADH + H+ (there are more hydrogen ions than NAD+ molecules) and attaching another Pi to each G3P
The NADH + H+ go to the ETC
The two phosphate groups from each G3P are transferred to ADP (this reaction is called substrate level phosphorylation) to form ATP
Each G3P is now a pyruvate [3C] molecule
EQUATION: 2 G3P + 2 NAD+ 2 Pi –> 4 ATP, 2 NADH + H+
Net gain of 2 ATP in glycolysis (+4 ATP in this phase, -2 ATP in the activation of glucose)
Describe the link reaction (between glycolysis and the Krebs cycle)
Two pyruvate molecules [3C] that come from the oxidation of G3P to pyruvate are transported from the cytoplasm into the mitochondrial matrix via carrier proteins on the membrane
Each pyruvate loses a carbon atom through carboxylation, which forms a carbon dioxide molecule
The new compound [2C] loses 2 hydrogen atoms to NAD+, producing NADH + H+ and forming an acetyl group
The acetyl compound combines with coenzyme A to form acetyl coenzyme A (acetyl CoA)
NET EQUATION: 2 pyruvate –> 2 CO2, 2 acetyl CoA, 2 NADH + H+
Describe the Krebs cycle, as well as all the products made per glucose molecule
.
Acetyl CoA transfers its acetyl group to oxaloacetate [4C] to make citrate [6C]
- Coenzyme A returns to the link reaction in order to bring in another acetyl molecule
The molecule [6C] reacts with 2 instances of NAD+, losing two carbons and 4 H+ ions in the process, producing 2 CO2, 2 NADH and 2 H+
ADP and an inorganic phosphate react with the energy present in the molecule [4C] to create 1 ATP via substrate level phosphorylation
The molecule [4C] loses two H+ ions to FAD, another electron carrier, to produce FADH2
The molecule [4C] then loses one H+ ion to NAD+ to produce NADH; the molecule now turns into oxaloacetate, and is able to start the cycle again by picking up another acetyl molecule
Note: because glucose produces two molecules of acetyl CoA, the Krebs cycle occurs twice per glucose molecule
Net production (per glucose molecule): 4 CO2, 2 ATP, 6 NADH + H+, 2 FADH2
What is the purpose of oxidative phosphorylation/the electron transport chain (ETC) in aerobic respiration?
To release the energy stored from the NADH and FADH2 produced by the other steps of aerobic respiration and create more ATP
Describe the process of oxidative phosphorylation/the electron transport chain (ETC), and how it is altered in the absence of oxygen.
The electron transport chain (ETC) is a long series of proteins and organic molecules found on the cristae (folds on inner membrane) of mitochondria
Hydrogen/electron carriers (NADH, FADH2) are oxidized and donate their stored electrons and protons to the ETC
As the electrons move through the ETC, they lose energy to the protein complexes located on the chain
The protein complexes use this energy to pump hydrogen ions from the matrix into the intermembrane to maintain an electrochemical gradient (aka a proton motive force); the intermembrane contains many more protons, and is thus much more positive than the matrix
Chemiosmosis is performed:
- The accumulated H+ ions pass through the transmembrane enzyme ATP synthase (due to osmosis) to move from the intermembrane space back to the matrix
- This movement is exergonic (releases energy); this provides enough energy for ATP Synthase to catalyze the phosphorylation of ADP + Pi –> ATP
At the end of the chain in the matrix, oxygen picks up the de-energized electrons in order to prevent the clogging of the chain
Two H+ ions that came into the matrix (via ATP synthase, after chemiosmosis) react with 1/2 of an O2 particle and the electron to form water
In the absence of oxygen, the electron transport chain clogs up in the 4th complex, as oxygen is unable to remove the de-energized electrons from the chain (forcing the body to undergo anaerobic respiration)
Define chemiosmosis, and provide an example.
The use of energy released from the movement of ions across a semipermeable membrane with the electrochemical gradient to catalyze a reaction
A prime example to know is the movement of H+ ions across the mitochondria’s inner membrane to catalyze ADP + Pi –> ATP
Define phosphorylation, and provide an example.
The attachment of a phosphate group to a molecule/ion.
A prime example to know is ADP + Pi –> ATP
When is anaerobic respiration used, and why is it important?
When there is a lack of sufficient oxygen
Recall that oxygen is used to “pick up” de-energized electrons at the end of the ETC; lack of oxygen means the ETC gets clogged in the 4th complex with the de-energized electrons, and hydrogen/electron carriers (NADH and FADH2) cannot drop off their electrons or protons
- Thus, chemiosmosis cannot be performed and ATP cannot be produced
Anaerobic respiration comes into clutch in an attempt to keep the organism alive by producing (significantly) smaller quantities of ATP (but at least ATP is being produced)
What is VO2 max? What happens at VO2 max?
The maximum rate that oxygen can be transported/used in the body
At this level, aerobic respiration becomes limiting; the graph of oxygen consumption vs exercise intensity plateaus
What can VO2 max measure, and what units does it use?
It is considered the best indicator for an athlete’s fitness and aerobic endurance
It is expressed either as an absolute rate (e.g. L of O2 / min) or relative rate (mm of O2/kg of body mass*min)
Describe the process of lactic acid/lactate fermentation. In what organisms does it take place?
After glycolysis and before the chain reaction, 2 pyruvate accept electrons from NADH to form 2 lactic acid and 2 NAD+ via the enzyme lactate dehydrogenase
The 2 NAD+ are reused in glycolysis; the 2 ATP produced in glycolysis are the only source of ATP
This takes place in mammal muscle and some bacteria
Describe the process of alcohol fermentation. In what organisms does it take place?
2 pyruvate molecules each lose 1 carbon to form 1 CO2 each; this is done through the enzyme pyruvate decarboxylase
- The pyruvate molecules are now acetaldehyde
The electrons from 2 NADH are donated to the acetaldehyde to produce 2 ethanol and 2 NAD+; this process is catalyzed by the enzyme alcohol dehydrogenase
The 2 NAD+ are reused in glycolysis; the 2 ATP produced in glycolysis are the only source of ATP
This takes place in yeast
How is lactic acid stored and reused?
Because they contain carbon bonds, the body can release energy by breaking said bonds
Lactic acid is stored in the liver until the exercise is finished
It is then accessed as glucose and used in cellular respiration
State the net equation (very first reactants –> very last products) of photosynthesis.
6 CO2 + 6 H2O + light energy –> C6H12O6 (glucose) + 6 O2
EXACT opposite of cellular respiration
FILL IN THE BLANKS: Red light has a ____ energy amount, ____ wavelength and ___ frequency compared to blue light, which has a ____ energy amount, ____ wavelength and ____ frequency.
RED: lower energy; longer wavelength; lower frequency
BLUE: higher energy; shorter wavelength; higher frequency
Why are plant leaves green?
Violet-blue and orange-red light both have higher action rates of photosynthesis than green-yellow light
The green light is not absorbed by the pigments in the plant leaves, resulting in it bouncing off the leaves and into our eyes
What are pigments and accessory pigments, what are their functions and what are the names of the specific types?
Pigments are substances that absorb a certain kind of light. The main pigment in plans is called chlorophyll a; chlorophyll b and the carotenoids (a group of pigments) are called accessory pigments
Accessory pigments assist in expanding the range of light colours that can be absorbed by the plant, thus increasing photosynthesis rate
Why are leaves reddish-brown in the fall?
The chlorophyll breaks down and the carotenoids are left behind, which do not absorb reddish-brown light
What about the action spectrum for photosynthesis, when compared to the chlorophyll A absorption spectrum, suggests the existence of more pigments than just chlorophyll A?
The dip in rate of the chlorophyll A absorption spectrum at about 450 nm is nearly vertical, whereas the dip for the photosynthesis action spectrum starts at ~490 um and drops more slowly. Furthermore, the sudden peak and drop of the chlorophyll A absorption spectrum occurs at 650 nm to about 670 nm, but the action spectrum for photosynthesis suggests a gradual rise from 600 and a steep dip at about 750 nm.
TL;DR: The graphs have different shapes, which suggests that there are more pigments than chlorophyll A that assist in the absorption of light.
List the components of a chloroplast.
Outer membrane
Inner membrane
Stroma
Lamellae
Thylakoid
Granum
What are the functions of the thylakoids, grana and lamellae in the chloroplast?
Thylakoids: contain pigments that allow for photosynthesis and the ETC and ATP synthase for photophosphorylation
Grana: increase SA:Vol ratio and consist of small internal volumes to quickly accumulate ions
Lamellae: connect and separate grana, allows for maximized photosynthetic efficiency (LDR); separation of grana prevents them clumping together, which would result in a lower in the SA:Vol ratio
List the stages of Light Dependent Reactions (LDR).
Photoexcitation
Electron Transport
Chemiosmosis
Halkidas only mentioned these three, but there are technically more:
Reduction of NADP+ and Photolysis of Water
Describe where LDR’s take place, as well as the components necessary for it to take place.
Occurs on the thylakoid membranes, more specifically, the ETC
ETC of thylakoid membrane contains photosystem II and photosystem I, which are proteins that contain pigments and can absorb light
ETC also consists of transport proteins and ATP synthase
Photosystems are classified according to their maximal absorption wavelengths; PS I = 700 nm, aka PS700; PS II = 680 nm, aka PS680
Describe the photoexcitation phase of LDR’s.
Photoexcitation:
Electrons released from the photolysis of water enter photosystem II
Photons from sunlight are absorbed through the pigment of photosystem II
Electrons present in the photosystem are excited - charged with energy
Describe the electron transport phase of LDR’s.
Electrons are passed through the ETC
As they pass through the chain they transfer energy to transport proteins, which pump H+ ions into the thylakoid
Describe the chemiosmosis phase of LDR’s.
Chemiosmosis:
- The accumulation of protons within the thylakoid creates an electrochemical gradient/proton motive force
- The H+ ions return to the stroma along the proton gradient via the enzyme ATP synthase
- The energy of H+ ions passing through the ATP synthase is used to catalyse the synthesis of ADP + Pi –> ATP
- This process is called photophosphorylation (rather than just phosphorylation), as it relies on light as the initial energy source
Describe what happens to de-energized electrons in LDR’s.
After the de-energization of electrons from the electron transport phase, the electrons are taken up by photosystem I (P700)
They are then either recycled back to the chain or taken up by an enzyme/carrier molecule and used to reduce NADP+ + H+ –> NADPH
- The NADPH, along with ATP, are necessary for LIR’s
Describe the photolysis of water in LDR’s.
Photolysis of water:
Light energy splits water molecules into 1/2 O2, 2 H+, and 2 e-
The electrons lost from photosystem II (P680) are replaced by electrons released from the water
The oxygen eventually gets released back to the atmosphere, and the hydrogen is used for the electrochemical gradient
What are the three stages of the Calvin Cycle/Light Independent Reactions?
Carbon fixation/carboxylation
Reduction
Regeneration
Describe the carbon fixation/carboxylation phase of the Calvin Cycle.
The Calvin Cycle begins with ribulose bisphosphate (RuBP) [5C]
An enzyme, RuBP carboxylase (aka rubisco), catalyzes the attachment of a CO2 molecule to RuBP
The resulting compound [6C] is unstable, and breaks down into two instances of 3-phosphoglyceric acid (3-PGA) [3C]
A single cycle involves three molecules of RuBP combining with three molecules of CO2 to make six molecules of 3-PGA
Net equation: 3 RuBP + 3 CO2 –> 6 3-PGA
Describe the reduction phase of the Calvin Cycle.
3-PGA reacts with ATP to form ADP, Pi (inorganic phosphate) and
1,3-Bisphosphoglyceric acid (1,3-BPG) [3C]
1,3-BPG is then reduced with NADPH –> glyceraldehyde 3-phosphate (G3P) [3C] + NADP+
These steps are repeated 6 times simultaneously
Net equation:
6 3-PGA + 6 ATP –> 6 ADP + 6 Pi + 6 1,3-BPG
6 1,3-BPG + 6 NADPH –> 6 NADP+ + 6 G3P
Describe the regeneration phase of the Calvin Cycle.
Previously, in the reduction phase, 6 instances of G3P were produced
Only one G3P turns into a triosephosphate - half a sugar molecule
Thus, two cycles are required to produce a single glucose monomer, and even more are required to product more complex polysaccharides, such as starch
The remaining 5 G3P [3C] are recombined to regenerate RuBP
The energy from 3 ATP is used for this regeneration
Net equation:
5 G3P + 3 ATP –> 3 RuBP [5C] + 3 ADP
Why do seeds need to store energy, and what form is it stored in?
They need energy in preparation for growth when they are in the right condition. it is stored in the form of starch
What conditions are required to be ideal for a seed to grow?
Water, temperature, oxygen
Sunlight is not necessarily needed yet; the seed is growing, not performing photosynthesis
How does a respirometer work? How is the rate of respiration measured?
Small organisms are placed on a shelf on a sealed container
They are placed over soda lime; a substance that CO2
The one entrance of the tube goes towards a piece of coloured liquid in front of a scale
When the organisms undergo respiration, oxygen in the container is consumed and CO2 is produced, but the CO2 is absorbed by the soda lime
When oxygen is consumed, the net amount of gas in the container decreases, and the rate of cellular respiration can be measured by how far the coloured liquid moves on the scale
List the three basic steps of Calvin’s photosynthesis experiments.
Radioactive labelling
2D/Double way Paper Chromatography
Autoradiography
Describe the process of Beta Decay.
A neutron turns into a proton and releases a high-energy electron in the process (as well as an antineutrino, but not mandatory to know that)
In autoradiography, this emitted electron is used to create an image on a piece of X-ray film
Briefly Calvin’s experiment using relevant terminology.
A radioactive isotope, carbon-14, is added to algae in a spherical container
Light is shone in the container to allow photosynthesis to occur
After varying periods of time (the experiment is repeated several times), the algae is killed by running it into a solution of heated alcohol located underneath the algae sphere - this stops photosynthesis from happening
The dead algae samples are analyzed using 2D chromatography, which separates the varying carbon compounds
Radioactive carbon compounds present on the chromatogram are identified via exposure to X-ray film
By comparing the different results from the experiments with varying time periods, the order by which carbon compounds are generated was determined
Calvin used this information to propose the sequence of events now known as the Calvin cycle, or light independent reactions
Describe the radioactive labelling phase of Calvin’s experiments.
Radioactive carbon-14 isotope is added to a “lollipop”-like apparatus into green algae (chlorella)
Light is shone on the apparatus to allow the algae to perform photosynthesis
- In doing this, the carbon-14 isotope will be incorporated into the organic products
Describe the process of 2D chromatography in Calvin’s experiments.
The algae samples killed by the heated alcohol are analyzed using 2D chromatography, which separates the varying carbon compounds
- Paper with substance is dipped into and kept in a solvent - the substance is not in the solvent!
- After some time, the substance develops upwards linearly
- The paper is turned 90 degrees clockwise, dipped into and kept in a different solvent
- The chromatogram now has a scatter plot-like array of dots, which is used in autoradioagraphy
Describe the process of autoradiography in Calvin’s experiments.
Any radioactive carbon compounds present on the chromatogram produced after 2D chromatography are identified via exposure/contact to X-ray film
Describe the shapes of the graphs of photosynthesis vs each of light intensity, CO2 concentration and temperature.
Photosynthesis vs.
- Light intensity, CO2 concentration: linear-like rise followed by a plateau
- An excess of either of these two factors do not harm the rate of photosynthesis
- Temperature: quadratic-like rise, peak, followed by a somewhat steep decrease
- The temperature at which the peak occurs is called the optimum temperature
- Temperature that’s too high results in the denaturation of enzymes, resulting in a decline
State three factors that affect the rate of photosynthesis.
Light intensity
CO2 concentration
Temperature
Wavelength/light colour
Amount of water
+ many more
Describe the atmosphere of primordial Earth.
Had a reducing atmosphere
- Low levels of oxygen gas (2%) and other oxidizing gases
- Consisted mostly of non-oxidizing gases + reducing gases, e.g. hydrogen, carbon monoxide, hydrogen sulfide
What caused the rise of oxygen levels since primordial Earth? What caused and stopped the plateau of oxygen levels?
Cyanobacteria containing chlorophyll first performed photosynthesis ~2.5 billion years ago
Because oxygen is a byproduct of photosynthesis (during the photolysis of water), oxygen levels rose and plateaued at 2% until 750 million years ago
Oxygen is very reactive; the plateau was a result of oxygen reacting with things in the environment as fast as it was produced
The plateau ended when there were no more things to react with
How did the oxygen production during primordial Earth affect the atmosphere?
Oxygen generation reacted with the methane in atmosphere, creating carbon dioxide and water
CO2 and H2O are unable to insulate the Earth in the same manner that methane could, which resulted in the Earth’s inability to trap heat, leading to the first Ice Age
However, afterwards, the generation of oxygen allowed the formation of an ozone (O3) layer, which shields the Earth from damaging levels of UV radiation and allowed for the evolution of a wide range of organisms
How did the oxygen production during primordial Earth affect its oceans and rock deposits?
Soluble iron compounds that were found in oceans were oxidized into insoluble iron oxides that precipitated onto the seabed
When the iron in the ocean was completely consumed, oxygen gas started accumulating in the atmosphere
Additionally, rocks with layers rich in iron ore called banded iron formations (BIF) were formed on land due to the rise of O2 levels in the atmosphere
How did the oxygen production during primordial Earth affect life on Earth at that time?
Life on earth was anaerobic; the increase of O2 in the atmosphere nearly wiped all life on the planet
Eventually, however, life adapted to be aerobic and was able to survive in the new environment
