How Cells Stay Alive

Overview

In this fourth lesson of the “Cells: The Units of Life” unit, students use simplified models and scenarios to explain how cells obtain usable energy, remove waste, and reproduce. They connect these processes to the central idea that cells are the basic functional units of all living things.

Learning intentions

Students will be able to:

• Explain how cells release usable energy from food.
• Identify common inputs and outputs of cellular respiration.
• Describe how cells remove wastes and reproduce.
• Follow a multistep procedure to complete a cell-process model.
• Write an accurate, organized explanation based on a science text and model.

Success criteria

• I can use a model to show how glucose and oxygen help a cell obtain energy.
• I can identify carbon dioxide and water as products of cellular respiration.
• I can explain why waste removal and cell reproduction help cells stay alive.
• I can summarize the cell processes using evidence from the text and model.

Curriculum links

• Reading technical texts: follow a multistep procedure when completing a scientific model.
• Reading technical texts: determine central ideas and write an accurate summary.
• Writing in science: introduce and organize information into categories such as energy, waste, and reproduction.
• Reading technical information: connect words, symbols, and diagrams in a model.

Lesson structure (45 minutes)

1. 0–5 min · Hook and connection. Display the opening question in the cell survival introduction slides: “What would happen if a cell could get food but could not remove its waste?” Students make a prediction, then briefly share with a partner. Teacher connects responses to the previous lesson’s cell structures and explains that today they will investigate what cells must do to remain alive.

2. 5–13 min · Read and teach. Use the cell-process teaching slides to introduce three linked processes: cellular respiration releases usable energy from glucose; cells move wastes such as carbon dioxide and excess water out; and cell division produces new cells for growth, repair, and reproduction. Emphasize that cellular respiration is not the same as breathing: breathing brings oxygen into an organism, while cellular respiration is a chemical process inside cells. Students annotate the cell survival notes and model worksheet by recording the purpose, inputs, and outputs of each process.

3. 13–25 min · Guided model procedure. Distribute the worksheet and provide each pair with the matching materials from the respiration inputs and outputs matching cards. Model the first step, then direct students to follow the written procedure: identify the cell’s needs, match respiration inputs to outputs, place arrows to show movement, and label where waste leaves the cell. Students read each step aloud with a partner, construct the model, and check each stage against the instructions. Teacher circulates, asking, “Which part of your model shows energy becoming available to the cell?”

4. 25–34 min · Scenario application. Present scenarios from the cell scenarios and discussion slides, such as an active muscle cell needing more energy, a cell surrounded by excess waste, and a cut needing new cells for repair. Pairs select or receive one scenario and complete the corresponding section of the worksheet. They explain which process is most important, identify relevant inputs or outputs, and use a labeled arrow or short sequence to show what happens. Invite two pairs to share; classmates identify accurate evidence and ask one clarifying question.

5. 34–41 min · Written explanation. Students independently write a short response on the worksheet: “How do cells stay alive?” Require a clear introduction and three organized categories—energy, waste removal, and reproduction. Students include at least two accurate scientific details and refer to their model. Provide the sentence frame, “Cells stay alive by ____. First, ____. In addition, ____. Finally, ____.” Students may use the completed model but should not copy a partner’s response.

6. 41–45 min · Plenary and exit check. Return to the opening question using the review and exit prompt slide. Students complete the worksheet exit ticket: “Explain one way a cell obtains energy and one way it stays healthy by removing waste or making new cells.” Collect responses and ask students to hold up one finger for energy, two for waste removal, or three for reproduction as they name the process they can explain most confidently.

Resources

• the cell survival introduction slides
• the cell survival notes and model worksheet
• the respiration inputs and outputs matching cards
• Projector or interactive display
• Pencils or colored pencils
• One set of matching cards per pair
• Timer
• Board space for the three process categories

Assessment

• During the model, check whether students follow each procedure step in order and correctly connect glucose and oxygen with cellular respiration outputs.
• Review pair scenario explanations for accurate use of energy, waste removal, and reproduction concepts.
• Use the written explanation and exit ticket to assess central idea, scientific accuracy, organization, and the student’s ability to summarize information without relying on unsupported opinions.

Differentiation

• Provide a partially completed model, word bank, visual arrows, and sentence frames for students who need reading or writing support.
• Pair students strategically and assign roles such as reader, card manager, checker, and recorder so all students participate.
• For multilingual learners, preview terms with simple definitions and visuals: glucose, oxygen, energy, waste, respiration, and reproduction. Allow students to discuss ideas before writing.
• Challenge students to explain why a cell cannot survive if any one of the three processes stops, using a cause-and-effect statement and evidence from the model.