Why Can Cattle Live on Grass, but Humans Cannot?

In this task, students will develop and use systems models and construct scientific explanations to illustrate how matter and energy flow through interconnected biological processes, including photosynthesis, digestion, microbial fermentation, cellular respiration, and protein synthesis. By tracing the flow of matter and energy, students demonstrate systems thinking and explain how organisms break down food molecules, transform energy, and reorganize matter to support their cellular functions.

This task is designed as a multi-day, phenomenon-driven science investigation that integrates modeling, explanation, and systems thinking rather than a single-sitting assessment. While it can be used formatively, its structure is best suited for instructional use within a unit on matter and energy in organisms, biological systems, digestion, or carbon cycling.

The task is intentionally scaffolded across multiple prompts that progressively build student understanding. Early prompts focus on comparative digestion and microbial fermentation. Middle prompts emphasize matter and energy transformations within biological systems. Later prompts require students to synthesize through systems modeling, carbon tracing, and biosynthesis explanations. 

For this reason, the task should be implemented as a series of connected learning experiences rather than administered all at once.

Teachers may use this task in several ways:

• As a multi-day performance task embedded within a biology unit
• As a phenomenon-based anchoring investigation for LS1.C (Organization for Matter and Energy Flow in Organisms)
• As a modeling-focused assessment aligned to Science and Engineering Practices
• As a capstone synthesis task, after instruction on digestion, cellular respiration, and photosynthesis
• As a transfer task connecting organismal biology to Earth system processes

Because the task requires iterative model revision and increasingly complex explanations, it is particularly effective when students are given opportunities to discuss, revise, and refine their models over time. Student models should be treated as evolving representations rather than final products, using prompts as checkpoints for sensemaking and conceptual development.

This task should not be treated as a timed test. Instead, it is most effective when students engage in cycles of:

• Reading background information
• Constructing or revising models
• Writing evidence-based explanations
• Reflecting on how new information changes their understanding

Suggested pacing is 2–3 instructional days, depending on class schedule and depth of discussion. Prompts may be assigned sequentially across lessons, with short whole-class synthesis discussions between sections to reinforce systems connections.

Teachers may also choose to:

• Facilitate small-group model construction before individual explanations
• Use the comparison table and background information as guided sensemaking tools
• Pause after major prompts (2, 3, and 4) for model revision checkpoints
• Provide sentence starters for explanation prompts if needed for differentiation

Students should have prior experience developing and interpreting scientific models that represent systems and processes, including inputs, outputs, and transformations of matter and energy. They should also understand that models can be used to explain biological phenomena and to trace processes across multiple scales, from cellular to organismal systems.

Students are expected to have foundational knowledge of:

• Cellular respiration as the process by which cells produce ATP, the primary usable form of energy.
• Photosynthesis as the process by which plants convert light energy into chemical energy stored in glucose
• Digestion as the process of breaking down large food molecules into smaller, absorbable molecules
• The principle that matter and energy are conserved and transformed within biological systems

Students do not need advanced biochemistry knowledge of metabolic pathways; however, they should be able to reason about how molecules are transformed and used within living organisms. Familiarity with carbohydrates, including the distinction between structural and storage carbohydrates (e.g., cellulose and starch), can support deeper sensemaking but is not required for initial engagement.

It is also assumed that students can:

• Trace the movement of matter (especially carbon) through biological systems
• Interpret comparative diagrams or tables of biological structures and functions
• Use evidence from readings, models, and background information to construct scientific explanations
• Revise models over multiple prompts as new scientific information is introduced

Because this is a multi-day modeling task, students should be comfortable engaging in iterative sensemaking rather than producing a single final answer. Understanding is designed to develop progressively across prompts, with earlier scaffolds supporting later systems-level explanations about digestion, energy transformation, biosynthesis, and biological outputs.

Facilitators should maintain a scientific, systems-focused framing throughout the task, emphasizing how organisms transform matter and energy to support survival, growth, and biological production rather than focusing on policy, debate, or value-based discussions.