Photosynthesis and Cellular Respiration: A Cycling of Matter
Assessment · Grade 8 · Science (Biology)
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Grade
8
Method
five_e
Phases
Name: Engage
Minutes: 10
Purpose: Surface students' prior knowledge and spark curiosity about how plants and animals are chemically connected, creating a need-to-know that motivates the Explore activity on matter cycling between photosynthesis and cellular respiration.
Materials
Device and projector to display time-lapse video of seedling growth
Small potted plant (physical specimen)
Whiteboard or chart paper for recording 'Our Current Thinking' responses
Student science notebooks and pencils
Student Action: Watch the time-lapse video, then discuss with a partner where the plant's added mass comes from. Share initial ideas with the class; record personal hypothesis in science notebook under the prompt: 'I think the plant's new matter comes from ___ because ___.'
Teacher Action: Display a 60-second time-lapse video of a seedling sprouting and growing visibly larger, then hold up a small potted plant and ask: 'This plant has gotten bigger — where did all that extra matter come from? Turn and talk with your partner for 90 seconds, then we'll hear a few ideas.' Circulate and listen for misconceptions (e.g., 'from the soil' or 'from water') without correcting them yet. Capture 3–4 student responses on the board under the heading 'Our Current Thinking' to revisit at the end of the unit arc.
Name: Explore
Minutes: 35
Purpose: Students investigate the inputs and outputs of photosynthesis and cellular respiration through hands-on data collection and modeling, building their own understanding of how matter cycles between the two processes before any formal vocabulary or explanation is introduced.
Materials
Molecule Sorting Cards (H₂O, CO₂, O₂, glucose, sunlight, ATP — one set per group)
Two-column sorting mat ('Green Plant Cell' / 'Animal/Fungal Cell') — one per group
Pre-printed plant cell and animal cell outline diagram — one per group
Colored pencils (at minimum green and red)
Sticky notes
Markers for annotating diagrams
Driving-question anchor chart posted at front of room
Student Action: In groups of 3-4, students sort the Molecule Sorting Cards onto the two-column mat, debating placement and justifying choices to each other. They then transfer their thinking onto the cell-outline diagram using colored arrows (e.g., green for inputs, red for outputs) and annotate with their own descriptive language — avoiding textbook terms if they do not yet know them. During the gallery walk, students leave sticky-note agreements or questions on other groups' diagrams, noting patterns they notice across all posters.
Teacher Action: Distribute 'Molecule Sorting Cards' (sets of cards labeled H₂O, CO₂, O₂, glucose, sunlight, ATP) and a blank two-column mat labeled 'Green Plant Cell' and 'Animal/Fungal Cell.' Pose the driving question posted on the board: 'Where do the molecules go — and where do they come from?' Circulate and probe with questions such as 'What do you think the plant is releasing?' and 'Where might that gas end up?' without confirming or correcting answers. After 15 minutes of card sorting, direct groups to use colored pencils and a pre-printed outline of a plant cell and an animal cell to draw arrows showing molecule movement, then write one sentence per process describing what is being 'used up' and what is being 'made.' Reconvene for a 5-minute gallery walk so groups can compare arrow diagrams before the Explain phase.
Subject
Science (Biology)
Standards
MS-LS1-6
MS-LS1-7
Objectives
SWBAT explain how the products of photosynthesis become the reactants of cellular respiration and vice versa, using a labeled cycle diagram.
Method Note
This lesson covers the Engage and Explore phases and represents Day 1 of a 3-day arc. Day 1 (this lesson): Engage — students encounter a phenomenon and surface prior ideas; Explore — students investigate the inputs and outputs of photosynthesis and cellular respiration through a guided inquiry activity. Day 2: Explain — students construct formal explanations and are introduced to vocabulary after sense-making. Day 3: Elaborate and Evaluate — students apply the cycling concept to a new ecological context and complete a summative assessment.
Method Label
5E Instructional Model (NGSS)
Teacher Notes
This is Day 1 of a 3-day 5E arc. Resist the urge to correct student misconceptions or introduce formal vocabulary during Engage and Explore — the goal today is productive struggle and surfacing of ideas. During the Explore card sort, circulate and ask probing questions ('Why did you place that card there?' 'What would happen to this process if that molecule disappeared?') rather than confirming or denying student placements. Collect exit tickets at the door to inform Day 2 Explain instruction. If the phenomenon video is unavailable, a sealed plastic bag containing a sprig of Elodea in water placed under a lamp the previous day (showing visible oxygen bubbles) makes an equally compelling live anchor. Ensure molecule card sets are laminated or printed on cardstock for reuse across class periods.
Differentiation
Ell
Provide a bilingual molecule reference card listing photosynthesis and cellular respiration reactants and products with visual icons during the Explore phase
Pre-teach the terms 'reactant' and 'product' with a simple visual analogy (e.g., ingredients vs. baked goods) before the Explore activity begins
Allow students to label their cycle diagram in their home language first, then add English terms
Iep
Provide a partially completed molecule card sort with some arrows pre-drawn during the Explore phase to reduce cognitive load
Offer a sentence frame for the exit ticket: 'Photosynthesis makes ___ and ___, which are used by cellular respiration. Cellular respiration makes ___ and ___, which are used by photosynthesis.'
Allow verbal explanation of the diagram in lieu of written sentence during exit ticket if written expression is a documented barrier
Extension
During the Explore phase, challenge students to calculate the molar ratios of molecules exchanged between the two processes using the balanced chemical equations
Ask extension students to predict what would happen to the cycle if one process were removed (e.g., no photosynthesis in a sealed terrarium) and sketch a modified diagram showing the disruption
Prompt students to research how the carbon cycle connects to these two processes and annotate their diagram with a third layer showing atmospheric carbon
Duration Minutes
45
Materials Summary
Short video clip or photograph showing a sealed terrarium with a plant and a small animal thriving over time (phenomenon anchor)
Q1. Draw a simple diagram showing photosynthesis and cellular respiration as two connected processes. Label at least two molecules that move between them and use arrows to show the direction of flow. In one sentence, explain why these two processes depend on each other.
Check For Understanding
When: Engage
Method: cold call
Look Fors
Students can name at least one thing a plant needs to survive
Students articulate a question or observation about where a plant's mass comes from
Students surface the idea that air or light might be involved in plant growth
When: Explore
Method: circulate and probe
Look Fors
Students correctly identify oxygen and glucose as outputs of photosynthesis
Students correctly identify carbon dioxide and water as outputs of cellular respiration
Students begin to notice that one process's outputs match the other's inputs
When: Explore
Method: exit slip
Look Fors
Students draw arrows connecting at least two molecules between photosynthesis and cellular respiration
Students use evidence from the activity (molecule cards or data) to justify their arrow placement
Students articulate in writing that the two processes are linked, even if vocabulary is informal