A comprehensive high school biology unit investigating carbon cycling in living organisms and Earth systems. Students trace matter and energy through photosynthesis, model biochemical compounds, analyze cellular respiration pathways, and evaluate biotechnological applications in wastewater treatment.
Photosynthesis takes place inside specialized plant cell organelles called chloroplasts. Inside the chloroplast are flattened membrane discs called thylakoids, arranged in tall stacks like stacks of coins called grana. Thylakoid membranes are packed with green pigment molecules known as chlorophyll. Chlorophyll absorbs high-energy blue and red wavelengths of visible sunlight, while reflecting green light back to our eyes (which is why healthy plant leaves appear vibrant green). Surrounding the thylakoid stacks is a thick, enzyme-rich liquid matrix called the stroma.
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A Two-Stage Relay: Light Reactions & The Calvin Cycle
Photosynthesis functions as a two-stage relay race. In Stage 1 (Light-Dependent Reactions), sunlight striking the thylakoid energizes chlorophyll, which splits water molecules (\( \text{H}_2\text{O} \)). The hydrogen atoms are stripped of electrons to charge up two molecular batteries: ATP and NADPH. Oxygen atoms are paired up and released into the air as \( \text{O}_2 \). Next, in Stage 2 (The Calvin Cycle) in the stroma, the plant uses the chemical energy from ATP and NADPH to "fix" inorganic carbon dioxide gas into stable, energy-dense 6-carbon rings of glucose.
Stage 1: Thylakoid Membrane
What goes in: Sunlight + Water (\( \text{H}_2\text{O} \))
What comes out: Oxygen gas (\( \text{O}_2 \))
Energy carriers produced: ATP & NADPH
Stage 2: Stroma Fluid
What goes in: Carbon Dioxide (\( \text{CO}_2 \)) + ATP + NADPH
What comes out: Glucose Sugar (\( \text{C}_6\text{H}_{12}\text{O}_6 \))
Uses enzyme RuBisCO to build carbon chains
Reading Comprehension & Language Development
1. According to Paragraph 4, where does the oxygen gas that we breathe actually come from?
✏️ Sentence Frame:According to the text, oxygen gas is produced in the thylakoid when solar energy splits molecules of _______...
2. Explain how ATP and NADPH act like rechargeable batteries between Stage 1 and Stage 2.
✏️ Sentence Frame:In Stage 1, ATP and NADPH are charged with energy from _______. Then, they travel to the stroma to power the assembly of _______ in Stage 2.
Section 2.1 Informative Science Text • Solar Power Page 2 of 2
✏️ Sentence Starter:Light energy from the Sun is transformed into chemical potential energy stored in the bonds of the product molecule...
Unit 2: Carbon in the Earth System • Section 2.1 (ELD Scaffolded) Page 1 of 2
Unit 2 • Section 2.1
Transforming Light Energy & Evaluation
ELD Supported
Exploration 3
Chloroplast Organelle & Two-Stage System
Chloroplast / Cloroplasto
Photosynthesis occurs inside the chloroplast in two linked steps:
Stage 1: Light-Dependent Needs Sun ☀️
• Location: Thylakoid membranes (stacks called grana)
• Input: Sunlight + Water (\( \text{H}_2\text{O} \))
• Output: Oxygen gas (\( \text{O}_2 \)) + ATP + NADPH
• Water is split; oxygen is released as a byproduct.
• Enzyme RuBisCO "fixes" carbon into organic sugar.
3. Refute the myth: A student says plants can keep making sugar in the dark forever because the Calvin Cycle is "light-independent." Why is this false?
✏️ Sentence Starter:This is false because the Calvin Cycle requires _______ and _______ that are made during the light-dependent reactions. Without light...
💬 Structured Partner Talk (Turn & Talk): Share with your partner: "In Stage 1, light energy splits _______ to make oxygen, and in Stage 2, carbon from _______ is fixed into glucose."
Evaluate
Mastery Checkpoint
4. If a plant receives carbon dioxide with labeled heavy oxygen (\( \text{C}^{18}\text{O}_2 \)), where will that heavy oxygen appear?
[ ] A. Released oxygen gas (\( \text{O}_2 \))
[ ] B. In synthesized glucose (\( \text{C}_6\text{H}_{12}\text{O}_6 \))
[ ] C. Split water in thylakoid
[ ] D. ATP enzyme synthase
5. How does deforestation (cutting down forests) change the amount of carbon in the atmosphere?
✏️ Sentence Frame:When large forests are removed, atmospheric \( \text{CO}_2 \) levels [increase / decrease] because trees normally absorb \( \text{CO}_2 \) during...
Unit 2: Carbon in the Earth System • Section 2.1 (ELD Scaffolded) Page 2 of 2
Product B: 6 Oxygen Molecules (\( 6\text{O}_2 \))
Pair the remaining 12 oxygen atoms into 6 diatomic molecules (\( \text{O=O} \)) using double covalent bonds. These represent the oxygen released into the atmosphere as a byproduct.
Teacher Lab Verification: Confirm all 6 C, 12 H, and 18 O are accounted for with zero leftovers.
Teacher Initials
Part 3 Polymerization: From Monomer to Macromolecule
Plants do not keep all glucose as simple monomeric sugars. Through dehydration synthesis, hundreds of glucose rings are linked together into long-chain polysaccharides:
Starch: Coiled chains used by plants for long-term energy storage in roots and seeds.
Cellulose: Rigid, interlocking fibers that constitute tough cell walls in stems and wood.
Synthesis Questions
2. Did any atoms enter or leave the system during this chemical rearrangement? How does this physical model prove the Law of Conservation of Mass?
3. Compare the bond energy of the reactants (\( \text{CO}_2 \) and \( \text{H}_2\text{O} \)) to the synthesized glucose molecule. Why is glucose considered an energy-rich organic molecule?
Biosynthesis of polymers like proteins, DNA, and membranes.
2. Transport Work
Active transport pumping ions against concentration gradients.
3. Mechanical Work
Muscle contraction, vesicle transport, and cilia movement.
Every living human cell recycles its own weight in ATP every single day!
Exploration 4: Bioengineering
Microbial Respiration in Wastewater Treatment
Aerobic Digestion
Pumps air/oxygen into sewage basins. Aerobic bacteria rapidly consume organic waste molecules (carbon compounds), converting them to \( \text{CO}_2 \) and harmless sludge.
Cleans water before environmental release
Anaerobic Digestion & Biogas
In sealed oxygen-free digesters, specialized anaerobic methanogens break down concentrated sludge into methane gas (\( \text{CH}_4 \)).
Captured methane generates renewable electricity!
Biotech closes the carbon loop: Turning human waste into green renewable energy. HS-LS2-3 Application
Language Arts Connection & Unit Synthesis
Food and Energy: Tracing Carbon Footprints
Trophic Carbon Efficiency
Only about 10% of the chemical energy in one trophic level is incorporated into biomass at the next level.
The remaining 90% is released as heat during cellular respiration or passed as undigested organic matter.
Critical Scientific Analysis
Compare the carbon footprint of eating primary producers (plants) versus secondary consumers (meat):
Plant diet = Direct solar carbon capture
Animal diet = Multi-step respiration losses
Proceed to your Respiration Systems Packet for analysis activities. Unit 2 • Section 2.2
Section 2.2 Informative Science Text • Energy Harvest Page 1 of 2
Unit 2 • Section 2.2 Informative Science Text
Coupled Cycles & Environmental Bioengineering
Part 2: Earth Systems & Technology
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The Great Biosphere Loop: Photosynthesis & Respiration
Notice the beautiful symmetry in the living world: the chemical waste products of cellular respiration (\( \text{CO}_2 \) and \( \text{H}_2\text{O} \)) are the exact raw ingredients required by autotrophs to conduct photosynthesis! Conversely, the products of photosynthesis (glucose and \( \text{O}_2 \)) are the vital reactants required for respiration. In this reciprocal global loop, matter is endlessly recycled between the atmosphere, oceans, and living biomass, while radiant energy from the Sun flows continuously through living organisms and eventually radiates into space as low-grade heat.
Humans use this natural microbial respiration to solve massive urban challenges. In modern wastewater treatment plants, cities pump oxygen into giant tanks where aerobic bacteria rapidly respire dissolved human sewage, turning dirty liquid into clean water. Next, concentrated organic sludge is pumped into sealed, oxygen-free tanks called anaerobic digesters. In the dark without oxygen, specialized microbes called methanogens perform anaerobic respiration and fermentation, converting sewage into biogas (60% methane, \( \text{CH}_4 \)). Cities capture this clean-burning methane to spin electrical generators and power municipal vehicles, closing the carbon loop!
Aerobic Water Treatment
• Environment: Oxygen pumped continuously
• Microbes: Aerobic bacteria consume sewage
• Outcome: Clean water safe for rivers
Anaerobic Biogas Capture
• Environment: Sealed tank with ZERO oxygen
• Microbes: Methanogens ferment thick sludge
• Outcome: Renewable methane gas electricity
Reading Comprehension & Language Development
1. According to Paragraph 3, how are the chemical equations for photosynthesis and respiration connected?
✏️ Sentence Frame:The two equations are reciprocal because the products of photosynthesis (glucose and oxygen) serve as the exact _______ of cellular respiration...
2. In Paragraph 4, how does capturing methane gas from anaerobic digesters help protect Earth's climate?
✏️ Sentence Frame:Capturing biogas helps the climate because communities can burn this renewable fuel for electricity instead of relying on...
Section 2.2 Informative Science Text • Energy Harvest Page 2 of 2
Unit 2: Carbon in the Earth System • Section 2.2 (ELD Scaffolded) Page 1 of 2
Unit 2 • Section 2.2
Biotechnology & Energy in Food Systems
ELD Supported
Exploration 4
Applications in Wastewater Treatment
Biogas / Biogás
Treatment plants use bacteria and cellular respiration to clean wastewater and capture fuel:
Aerobic Basins (With Oxygen):
Air is pumped into wastewater. Aerobic microbes consume organic matter, releasing \( \text{CO}_2 \) and purifying the water.
Anaerobic Digesters (No Oxygen):
Methanogens ferment organic sludge without oxygen, producing methane biogas (\( \text{CH}_4 \)) used for electricity.
2. How does capturing methane from anaerobic digesters help human communities save energy?
✏️ Sentence Starter:By capturing methane gas produced by anaerobic microbes, treatment facilities can burn it to generate _______ instead of relying on...
Language Arts
Food and Energy: Scientific CER Writing
10% Trophic Rule
"Only about 10% of energy in food is stored as biomass in the consumer. The other 90% is burned during cellular respiration for movement and body heat. Eating plants directly requires 10 times less farm energy than feeding grain to animals for meat."
Construct your CER argument: Use the sentence starters below
Claim (Your answer to the question): "A plant-based food system uses..."
Evidence (Data or facts from the passage): "The text states that roughly 90% of energy is..."
Reasoning (Explain how the science connects them): "Because respiration burns most energy as heat..."
Peer Collaboration: Read your Claim and Evidence aloud to your partner. Check: Did they include the 10% rule?
Unit 2: Carbon in the Earth System • Section 2.2 (ELD Scaffolded) Page 2 of 2
Atmospheric \( \text{CO}_2 \) levels systematically decrease by ~6 ppm across the hemisphere.
October to April (Northern Hemisphere Winter):
Atmospheric \( \text{CO}_2 \) levels systematically rebound and rise by ~6 ppm.
5. Why does atmospheric \( \text{CO}_2 \) decline sharply during the Northern Hemisphere summer? Cite the specific biological mechanism in autotrophs responsible.
6. During winter, why do atmospheric \( \text{CO}_2 \) levels rise even when deciduous trees have lost their leaves? Cite cellular respiration by decomposers and soil microbes.
Part 4: Extended Systems Synthesis (8 pts) NGSS HS-LS2-3 Capstone
Prompt:
Synthesize how photosynthesis and cellular respiration maintain the global equilibrium of matter and energy. In your response: (1) Trace the movement of carbon atoms and energy between both processes, and (2) Explain how human activities (such as fossil fuel combustion and modern wastewater methane capture) modify this Earth system balance.
Unit 2: Carbon in the Earth System • Unit Assessment Page 2 of 2
