⚡ Strand B: Metabolic Processes

Course: SBI4U — Biology, Grade 12
Focus: Cellular respiration and photosynthesis — how cells transform energy

1. Cellular Respiration Overview

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~36-38 ATP
Cellular respiration is the process by which cells break down glucose to release energy stored in ATP. It occurs in three main stages: glycolysis, the Krebs cycle, and the electron transport chain.
GLYCOLYSIS Location: Cytoplasm Input: 1 Glucose Output: 2 Pyruvate 2 NADH NET: 2 ATP (No O₂ required) KREBS CYCLE Location: Mitochondrial Matrix Input: 2 Acetyl-CoA Output: 6 NADH, 2 FADH₂ 4 CO₂ 2 ATP ELECTRON TRANSPORT CHAIN Location: Inner Mitochondrial Membrane Uses: NADH + FADH₂ Produces: H₂O 32-34 ATP TOTAL: ~36-38 ATP per glucose Efficiency: ~34% (rest = heat)

2. Photosynthesis Overview

6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂
Photosynthesis occurs in chloroplasts and has two stages: light-dependent reactions (thylakoid membrane) and the Calvin cycle (stroma). It converts light energy into chemical energy stored in glucose.

Comparison: Respiration vs Photosynthesis

FeatureCellular RespirationPhotosynthesis
LocationMitochondriaChloroplasts
ReactantsGlucose + O₂CO₂ + H₂O + Light
ProductsCO₂ + H₂O + ATPGlucose + O₂
EnergyReleases (exergonic)Absorbs (endergonic)
OrganismsAll living cellsPlants, algae, some bacteria
TimeContinuousOnly in light

📝 Worksheet — Strand B: Metabolic Processes

1. [K/U — 3 marks] Fill in the blanks for the three stages of cellular respiration:

StageLocationInputATP Produced
Glycolysis
1 Glucose
Krebs Cycle
2
ETC
NADH + FADH₂

2. [Thinking — 4 marks] During intense exercise, muscle cells switch from aerobic to anaerobic respiration.

a) Why does this switch happen?

b) What is the product of anaerobic respiration in muscle cells?

c) Why is anaerobic respiration less efficient? Compare ATP yield.

3. [Communication — 3 marks] Explain why cellular respiration and photosynthesis are considered complementary processes. Use a diagram or cycle to support your explanation.

4. [Application — 4 marks] Cyanide is a poison that blocks Complex IV in the electron transport chain.

a) Explain which stage of cellular respiration would be directly affected.

b) Would glycolysis still function? Explain why or why not.

c) Predict the overall effect on ATP production and explain why cyanide is lethal.

5. [Thinking — 3 marks] A plant is placed in a sealed container with a CO₂ sensor. Predict and sketch what happens to CO₂ levels over a 24-hour period (12h light, 12h dark). Explain your graph.

SBI4U — Biology, Grade 12 | Strand B: Metabolic Processes | Ontario Curriculum 2008