SBI4U · Unit 2 test review

Metabolic Processes: Test Review

Everything for the Unit 2 test on one page: the key facts from all 4 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

Energy, Thermodynamics and ATP

First law: energy is transformed, never created or destroyed. Second law: every transformation increases the entropy of the universe; some energy is lost as heat.
$Δ G = Δ H - T Δ S$ ; $Δ G < 0$ is exergonic (spontaneous), $Δ G > 0$ is endergonic (needs energy input).
$ATP + H_{2} O \to ADP + P_{i}$ , $Δ G^{\circ'} = - 30.5 kJ/mol$ .
Energy coupling: $Δ G_{total} = Δ G_{endergonic} + Δ G_{ATP hydrolysis};$ the coupled process runs if the sum is negative.
OIL RIG: oxidation is loss (of electrons, often as H atoms); reduction is gain.
Energy carriers: $NADH$ and $FADH_{2}$ in catabolism; $NADPH$ in anabolism (photosynthesis).

Aerobic Cellular Respiration

$C_{6} H_{12} O_{6} + 6 O_{2} \to 6 CO_{2} + 6 H_{2} O,$ $Δ G \approx - 2870 kJ/mol$ .
Glycolysis (cytosol): net 2 ATP, 2 NADH, 2 pyruvate. Pyruvate oxidation (matrix): 2 acetyl-CoA, 2 $CO_{2}$ , 2 NADH.
Krebs cycle (matrix), per glucose: 2 ATP, 6 NADH, 2 $FADH_{2}$ , 4 $CO_{2}$ (per turn: 1 ATP, 3 NADH, 1 $FADH_{2}$ , 2 $CO_{2}$ ).
ETC pumps $H^{+}$ into the intermembrane space; $H^{+}$ returns through ATP synthase (chemiosmosis); $O_{2}$ is the final electron acceptor, forming $H_{2} O$ .
Yield: about 2.5 ATP per NADH and 1.5 per $FADH_{2}$ , so about 30–32 ATP per glucose (older value 36–38).
Efficiency $\approx \frac{32 \times 30.5}{2870} \approx 34%$ .

Fermentation, Other Fuels and Metabolism in Society

Fermentation = glycolysis + regeneration of $NAD^{+}$ ; net 2 ATP per glucose (about 2% efficient).
Alcoholic: pyruvate $\to$ acetaldehyde $+ CO_{2}$ , then acetaldehyde $+$ NADH $\to$ ethanol $+ NAD^{+}$ .
Lactic acid: pyruvate $+$ NADH $\to$ lactate $+ NAD^{+}$ (no $CO_{2}$ ).
Fats: glycerol $\to$ glycolysis; fatty acids $\to$ acetyl-CoA by beta-oxidation. Proteins: deamination $\to$ urea; carbon skeletons enter glycolysis or the Krebs cycle.
PFK is the main control point: inhibited by ATP and citrate, activated by AMP/ADP (allosteric feedback).
Cyanide blocks cytochrome c oxidase (ETC stops); DNP uncouples (ETC runs, energy lost as heat, little ATP).

Photosynthesis

$6 CO_{2} + 6 H_{2} O + light \to C_{6} H_{12} O_{6} + 6 O_{2}$ (endergonic, $Δ G \approx + 2870 kJ/mol$ ).
Light reactions (thylakoids): PSII (P680) then PSI (P700); photolysis $2 H_{2} O \to 4 H^{+} + 4 e^{-} + O_{2}$ ; products ATP, NADPH, $O_{2}$ .
Calvin cycle (stroma): rubisco fixes $CO_{2}$ + RuBP $\to$ 2 PGA; PGA reduced to G3P; RuBP regenerated.
Per G3P: 3 $CO_{2}$ , 9 ATP, 6 NADPH. Per glucose: 6 $CO_{2}$ , 18 ATP, 12 NADPH.
Noncyclic flow: ATP + NADPH + $O_{2}$ . Cyclic flow (PSI only): ATP only.
Photorespiration: rubisco fixes $O_{2}$ when hot and dry. C4 separates fixation in space; CAM separates it in time.

Where marks get lost

Saying energy is "used up" or "destroyed" in a food chain. The first law forbids that; energy is transformed, mostly into heat that cannot do cellular work. (Energy, Thermodynamics and ATP)
Claiming that breaking the phosphate bond of ATP releases energy. Breaking any bond requires energy; the energy comes from the whole hydrolysis reaction because ADP and $P_{i}$ are more stable than ATP. (Energy, Thermodynamics and ATP)
Thinking a spontaneous (negative $Δ G$ ) reaction must be fast. $Δ G$ says nothing about rate; activation energy and enzymes control the rate. (Energy, Thermodynamics and ATP)
Mixing up the carriers: NADPH is the anabolic carrier used in photosynthesis, while NADH and $FADH_{2}$ carry electrons in respiration. (Energy, Thermodynamics and ATP)
Reversing OIL RIG when hydrogen is involved. A molecule that loses H atoms (like glucose) is oxidized; the one that gains them (like oxygen becoming water) is reduced. (Energy, Thermodynamics and ATP)
Thinking glycolysis happens in the mitochondrion. It happens in the cytosol and needs no oxygen; only pyruvate oxidation, the Krebs cycle and the ETC are mitochondrial. (Aerobic Cellular Respiration)
Forgetting to double the Krebs cycle numbers. Each glucose makes two acetyl-CoA, so the cycle turns twice: 6 NADH, 2 $FADH_{2}$ , 2 ATP and 4 $CO_{2}$ per glucose. (Aerobic Cellular Respiration)
Saying the ETC makes ATP directly. The chain only pumps protons; ATP synthase makes ATP as the protons flow back (chemiosmosis). (Aerobic Cellular Respiration)
Saying the oxygen we breathe ends up in the $CO_{2}$ we exhale. Oxygen is the final electron acceptor and ends up in water; the oxygen atoms in exhaled $CO_{2}$ come from glucose and water used in the Krebs cycle. (Aerobic Cellular Respiration)
Giving 36–38 ATP as the definite answer. Those numbers assume whole-number yields per carrier; modern measurements give about 30–32. State your assumptions (for example, 2.5 per NADH and 1.5 per $FADH_{2}$ ). (Aerobic Cellular Respiration)
Saying fermentation's purpose is to make ATP. The fermentation steps after glycolysis make no ATP; they regenerate $NAD^{+}$ so that glycolysis can continue making its 2 ATP. (Fermentation, Other Fuels and Metabolism in Society)
Writing that human muscle makes ethanol or $CO_{2}$ during fermentation. Animal cells make lactate only; ethanol and $CO_{2}$ come from alcoholic fermentation in yeast and some bacteria. (Fermentation, Other Fuels and Metabolism in Society)
Thinking anaerobic means "no respiration at all". Glycolysis runs in both; the difference is what accepts the electrons from NADH. (Fermentation, Other Fuels and Metabolism in Society)
Believing cyanide and DNP act the same way because both are deadly. Cyanide stops electron flow; DNP lets electrons flow freely but wastes the gradient as heat. (Fermentation, Other Fuels and Metabolism in Society)
Assuming fats can only enter respiration as glycerol. Most of a fat's energy is in the fatty acids, which enter the Krebs cycle as acetyl-CoA after beta-oxidation. (Fermentation, Other Fuels and Metabolism in Society)
Saying the $O_{2}$ released comes from $CO_{2}$ . It comes entirely from the photolysis of water in photosystem II. (Photosynthesis)
Thinking the Calvin cycle happens at night. "Light-independent" means it does not use light directly; it needs ATP and NADPH from the light reactions, so it runs in the day. (Photosynthesis)
Mixing up locations: light reactions are on the thylakoid membranes; the Calvin cycle is in the stroma. Protons are pumped into the thylakoid lumen, and ATP is made on the stroma side. (Photosynthesis)
Forgetting that plants also respire. Plant cells have mitochondria and carry out cellular respiration day and night; photosynthesis only exceeds it in the light. (Photosynthesis)
Using the per-G3P numbers for glucose. Glucose needs two G3P, so double them: 6 $CO_{2}$ , 18 ATP and 12 NADPH. (Photosynthesis)

Practice test

24 questions from across the unit. Each one shows the lesson it comes from.

Energy, Thermodynamics and ATP
1
Which statement best expresses the second law of thermodynamics as it applies to cells?
Energy, Thermodynamics and ATP
2
A biosynthetic reaction has $Δ G = + 21.0 kJ/mol$ . It is coupled to the hydrolysis of one ATP ( $Δ G = - 30.5 kJ/mol$ ). What is the overall $Δ G$ in kJ/mol, to one decimal place?
kJ/mol
Energy, Thermodynamics and ATP
3
Why does the hydrolysis of ATP release free energy?
Energy, Thermodynamics and ATP
4
Name the five-carbon sugar found in ATP.
Energy, Thermodynamics and ATP
5
Match each energy carrier (reduced form) to its main role.
NADH
FADH₂
NADPH
ATP
Energy, Thermodynamics and ATP
6
What general term describes a metabolic pathway that builds complex molecules from simpler ones and consumes energy?
Aerobic Cellular Respiration
7
Where in a eukaryotic cell does the Krebs cycle take place?
Aerobic Cellular Respiration
8
What is the net number of ATP produced by glycolysis per molecule of glucose?
ATP
Aerobic Cellular Respiration
9
A muscle cell makes 30 ATP per glucose. Using $30.5 kJ/mol$ per ATP and $2870 kJ/mol$ per glucose, what is the efficiency of respiration as a percentage, to 3 significant figures?
%
Aerobic Cellular Respiration
10
Match each structure or process to its location.
Glycolysis
Krebs cycle
Electron transport chain
High H⁺ concentration
Aerobic Cellular Respiration
11
What is the name for the process in which the energy of an H⁺ gradient across a membrane is used to make ATP?
Aerobic Cellular Respiration
12
A student bubbles exhaled air through bromothymol blue solution. What should the student observe, and why?
Fermentation, Other Fuels and Metabolism in Society
13
What is the essential function of the reactions that follow glycolysis in fermentation?
Fermentation, Other Fuels and Metabolism in Society
14
Yeast ferments 45.0 g of glucose ( $M = 180.16 g/mol$ ) completely. What mass of ethanol ( $M = 46.07 g/mol$ ) is produced, in grams to 3 significant figures?
g
Fermentation, Other Fuels and Metabolism in Society
15
Name the allosteric enzyme of glycolysis that is the main control point of cellular respiration.
Fermentation, Other Fuels and Metabolism in Society
16
Put these steps in order to show how the carbon of a dietary protein ends up as exhaled $CO_{2}$ .
1. 1The amino group is removed by deamination
2. 2The carbons are oxidized in the Krebs cycle and released as CO₂
3. 3The carbon skeleton is converted into pyruvate, acetyl-CoA or a Krebs cycle intermediate
4. 4Protein is digested into amino acids
Fermentation, Other Fuels and Metabolism in Society
17
What term describes an organism, such as baker's yeast, that respires aerobically when oxygen is present but switches to fermentation when it is absent?
Fermentation, Other Fuels and Metabolism in Society
18
What happens to most of the lactate produced by muscles during intense exercise?
Photosynthesis
19
The oxygen gas released by photosynthesis comes from which molecule?
Photosynthesis
20
How many ATP molecules does the Calvin cycle use to produce one molecule of glucose?
ATP
Photosynthesis
21
Put these in order to show the path of electrons in noncyclic electron flow.
1. 1Ferredoxin
2. 2Photosystem I (P700)
3. 3NADP⁺, forming NADPH
4. 4Water
5. 5Photosystem II (P680)
6. 6Electron transport chain (plastoquinone, cytochrome complex, plastocyanin)
Photosynthesis
22
What term is used for the light-driven splitting of water molecules at photosystem II?
Photosynthesis
23
Which products are made by cyclic electron flow?
Photosynthesis
24
Which statement correctly compares photosynthesis and aerobic respiration?

Endless drill

Fresh numbers every time, for the calculation questions in this unit.

Endless drillnew numbers every time

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