MYP6 Unit 3 - Cells
Content
Scheme of work
Unit introduction
In this unit students move from the idea of living things to the microscopic structures that make life possible. They begin by deciding what living things have in common, then learn how microscopes allow scientists to observe cells directly.
The unit links observation, practical skill and scientific explanation. Students compare plant and animal cells, explore specialised cells, and learn that cells are organised into tissues, organs and organ systems.
6u3.1 - What does it mean to be alive?
Students begin the unit by thinking carefully about the difference between living, once-living and non-living things. This lesson introduces the idea that living things share common features, even when they look very different from each other.
Alive or not alive?
Students classify a range of objects or images into groups such as alive, once alive and never alive. The purpose is not only to get the correct answer, but to justify the decision using evidence.
Activity - Classification of objects
Materials
- Images or physical examples of living, non-living and once-living things.
- Examples may include a plant, shell, feather, stone, candle, apple, seed, wooden ruler, insect, toy animal and piece of paper.
Procedure
- Students sort the examples into groups.
- Each group must explain the reason for at least three difficult decisions.
- The class discusses examples that are not obvious, such as seeds, fruit, wood and dead insects.
Evidence for life
A seed may not appear to be active, but it can grow when conditions are suitable. This means that a seed is living, even though some life processes are very slow or paused.
Summary
- Living things share common features.
- Some examples are difficult to classify and need careful reasoning.
- Scientists use evidence to support their decisions.
Check your understanding
- Why is a seed considered living?
- Give one example of something that was once living but is not alive now.
- Why is classification sometimes difficult?
Teacher notes & learning objectives
- LO1 — Differentiate between living, once-living and non-living things.
- LO2 — Use evidence to justify a classification.
- LO3 — Recognise that some living processes may be slow or hidden.
This lesson sets up the later discussion of single-celled organisms and cells as the basic unit of life.
6u3.2 - Life processes
Students are introduced to the seven characteristics of living things. These life processes provide a checklist for deciding whether something is alive.
MRS GREN
The seven life processes are often remembered using the abbreviation MRS GREN: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.
Marty the Martian
Students consider a fictional organism and decide whether it is alive. The debate should focus on evidence for life processes rather than appearance.
Activity - Life processes discussion
- Introduce MRS GREN using a story, diagram or short reading.
- Students apply the seven life processes to familiar organisms.
- Students then apply the same checklist to unusual examples, such as fire, viruses, seeds or fictional organisms.
Single-celled life
The life processes will be reinforced later when students observe single-celled organisms. A living thing does not need to be large or made of many parts to carry out life processes.
Summary
- Living things carry out life processes.
- MRS GREN is a useful way to remember the seven life processes.
- Even single-celled organisms can carry out the processes needed for life.
Check your understanding
- What does each letter in MRS GREN stand for?
- Which life process involves releasing waste products?
- Why is movement alone not enough to prove that something is alive?
Teacher notes & learning objectives
- LO1 — Recall the seven characteristics of living things.
- LO2 — Apply the life-process checklist to examples.
- LO3 — Understand that evidence, not appearance, is used to judge whether something is living.
6u3.3 - Using microscopes
Students are introduced to the parts of the light microscope and learn how microscopes are used to observe objects that are too small to see clearly with the naked eye.
Parts and functions of the microscope
Students should learn the names and functions of the main parts of the microscope, including the eyepiece lens, objective lenses, stage, clips, light source, coarse focus and fine focus.
Activity - Microscope introduction
Skills focus
- Carry the microscope safely using two hands.
- Start with the lowest power objective lens.
- Place the slide on the stage and secure it with clips.
- Use coarse focus first, then fine focus.
- Do not allow the objective lens to crash into the slide.
Edge of slide practice
- Students focus on the edge of a slide to practise finding a clear image.
- They then observe assorted inanimate objects such as sand, salt, thread, paper fibres or hair.
Summary
- Microscopes magnify small objects.
- Each part of the microscope has a specific function.
- Good microscope technique protects both the slide and the microscope.
Check your understanding
- Why should you begin with the lowest power objective lens?
- What is the function of the fine focus knob?
- Why should microscopes be carried with two hands?
Teacher notes & learning objectives
- LO1 — Identify the main parts of a light microscope.
- LO2 — Use a microscope safely and correctly.
- LO3 — Practise focusing on non-living objects before observing cells.
Students should gain confidence with focusing before attempting wet mounts or stained slides.
6u3.4 - Looking at cells
Students now use microscopes to observe living or once-living material. They prepare or view simple slides and begin to recognise that living things are made from cells.
Wet mount slide
An onion epidermis slide is a good first example because plant cells are often clearly visible. The cell wall gives each cell a box-like shape.
Activity - Onion cell wet mount
Apparatus
- Microscope, microscope slide, coverslip, onion epidermis, forceps, dropper and water.
- Iodine stain may be used if appropriate.
Procedure
- Place a thin layer of onion epidermis on a slide.
- Add a drop of water or stain.
- Lower the coverslip carefully to reduce air bubbles.
- Observe using low power first, then higher magnification if appropriate.
- Draw a labelled diagram of several cells.
Amazing cells
Short videos may be used to show students that cells can have very different appearances and functions, even though they share some basic features.
Summary
- Cells are the basic building blocks of living things.
- Plant cells often have a clear cell wall and regular shape.
- Microscope drawings should be clear, simple and labelled.
Check your understanding
- Why are onion cells useful for early microscope work?
- What is the purpose of a coverslip?
- Why should microscope drawings avoid shading?
Teacher notes & learning objectives
- LO1 — Prepare and observe a simple wet mount slide.
- LO2 — Identify visible plant cell structures.
- LO3 — Produce a clear biological drawing.
This lesson introduces cells visually before formal cell theory and cell part functions are developed.
6u3.5 - Seed investigation
Students plan and begin an investigation into a factor affecting seed growth. This provides an opportunity to apply experimental design skills while continuing to explore life processes.
Planning the investigation
Students decide which factor they will change and how they will measure seed growth. The investigation should include a clear independent variable, dependent variable and controlled variables.
Activity - Factor affecting seed growth
Possible independent variables
- Amount of water.
- Light or darkness.
- Temperature.
- Type of liquid used for watering.
- Amount of salt in the water.
Procedure outline
- Choose one independent variable to change.
- Keep other important variables the same.
- Set up seeds on day 0.
- Observe and record changes for at least one calendar week.
- Record day 1, day 2, day 3 and day 4 observations carefully.
Experimental variables
If the investigation is about the effect of water volume on seed growth, the volume of water is the independent variable. The height of the seedling or number of germinated seeds could be the dependent variable. The type of seed, number of seeds, container and location should be controlled.
Summary
- Seed growth is a useful context for investigating life processes.
- A fair test changes one main variable at a time.
- Repeated observations over several days provide better evidence.
Check your understanding
- What is the independent variable in your seed investigation?
- What will you measure or observe as your dependent variable?
- Name two variables that should be controlled.
Teacher notes & learning objectives
- LO1 — Plan a simple biological investigation.
- LO2 — Identify independent, dependent and controlled variables.
- LO3 — Record observations over time.
This may be used as a combined Criterion B and Criterion C formative task.
6u3.6 - Cell theory and microscope history
Students connect their microscope observations to the development of cell theory. They learn that scientific knowledge changes as new tools and evidence become available.
Basic cell theory
Students should know three basic ideas: living things are made of cells, cells are the basic unit of life, and cells come from pre-existing cells. This also introduces the idea that cells divide and pass on genetic information.
Science and technology
The development of microscopes changed biology because scientists could directly observe structures that had previously been invisible. Better instruments allowed better evidence.
Activity - Microscope history assignment
Task
- Students research an important scientist or development in the history of microscopy.
- They identify what new evidence became possible because of the microscope.
- They explain how this changed scientific understanding of living things.
This assignment may be used as a formative Criterion D task.
Further microscope work
Students may observe cheek cells stained with methylene blue and pond water samples. This reinforces the difference between plant cells, animal cells and single-celled organisms.
Summary
- Cell theory is based on evidence from microscopy.
- Scientific ideas can change when new technology provides new evidence.
- Plant cells, animal cells and single-celled organisms can look very different.
Check your understanding
- State one idea from cell theory.
- How did microscopes help scientists understand living things?
- Why is pond water useful for observing microscopic life?
Teacher notes & learning objectives
- LO1 — Recall the basic ideas of cell theory.
- LO2 — Connect microscope development to changes in scientific understanding.
- LO3 — Observe different types of cells and microscopic organisms.
Cheek cell work requires appropriate hygiene and disposal procedures. Methylene blue stains skin and clothing.
6u3.7 - Plant and animal cells
Students compare plant and animal cells and learn the basic functions of important cell parts. They use drawings and comparison tools to organise similarities and differences.
Main cell structures
Students should recognise the nucleus, cytoplasm and cell membrane in animal cells. In plant cells they should also recognise the cell wall, vacuole and chloroplasts when visible.
Plant cells and support
Plant cells often have large water-filled vacuoles. These help give plant cells structural strength. The cell wall also helps explain why many plant cells have a rigid, box-like appearance.
Activity - Drawing and comparing cells
- Observe a prepared plant cell slide or onion cell slide.
- Draw the visible structures carefully.
- Create a Venn diagram comparing plant and animal cells.
- Match cell parts to their functions.
Summary
- Plant and animal cells share some structures.
- Plant cells usually have a cell wall and large vacuole.
- Chloroplasts are found in many plant cells that carry out photosynthesis.
Check your understanding
- Name two structures found in both plant and animal cells.
- Name two structures usually found in plant cells but not animal cells.
- Why do onion cells often appear box-shaped?
Teacher notes & learning objectives
- LO1 — Identify the main cell structures in plant and animal cells.
- LO2 — Compare plant and animal cells using a Venn diagram.
- LO3 — Link basic cell structures to their functions.
Keep organelle detail age-appropriate. Focus on structures students can reasonably understand or observe.
6u3.8 - Specialised cells
Students learn that multicellular organisms contain different types of cells. These specialised cells have structures that help them carry out particular functions.
Form and function
The structure of a specialised cell is related to its function. For example, a red blood cell has features that help it transport oxygen, while a root hair cell has features that help it absorb water and minerals.
Activity - Specialised cell assignment
Task
- Each student is assigned one specific specialised cell type.
- Students research where the cell is found, what it does and how its structure helps its function.
- Students prepare a short presentation or visual explanation.
Possible cell types
- Red blood cell.
- Nerve cell.
- Muscle cell.
- Sperm cell.
- Egg cell.
- Root hair cell.
- Palisade cell.
- Guard cell.
Summary
- Specialised cells have particular jobs.
- The shape and structure of a cell help it carry out its function.
- Multicellular organisms are made of many different types of cells.
Check your understanding
- What is a specialised cell?
- Give one example of a specialised animal cell.
- Explain how one cell structure helps a cell carry out its function.
Teacher notes & learning objectives
- LO1 — Explain that different cells have different functions.
- LO2 — Describe the relationship between form and function in specialised cells.
- LO3 — Prepare a short researched presentation.
6u3.9 - Cell presentations
Students complete and present their specialised cell work. Non-presenting students use a guide sheet to record key information from each presentation.
Activity - Specialised cell presentations
Presentation expectations
- Name the specialised cell.
- State where it is found.
- Describe its function.
- Explain at least one structure that helps it do its job.
- Use a clear labelled diagram or image.
Audience task
- Record the name and function of each cell presented.
- Write one form-function link for each example.
- Ask one scientific question if something is unclear.
Microscope review
If time allows, students review microscope function using moss leaf exploration and drawings. This gives further practice with biological observation and drawing.
Summary
- Presentations help students learn a wider range of cell examples.
- Good scientific communication is clear, accurate and supported by diagrams.
- Specialised cells show the link between structure and function.
Check your understanding
- Which specialised cell example did you find most interesting?
- What structure helped that cell carry out its function?
- Why do multicellular organisms need specialised cells?
Teacher notes & learning objectives
- LO1 — Communicate scientific information clearly.
- LO2 — Listen actively and record information from peers.
- LO3 — Consolidate the idea of structure and function.
Lessons 17-19 may be used for finishing work and individual presentations.
6u3.10 - Levels of organisation
Students finish the unit by learning how cells are organised in multicellular organisms. Cells form tissues, tissues form organs, organs form organ systems, and organ systems work together in an organism.
From cells to organisms
A single specialised cell can carry out a particular job, but in large organisms cells work together. Groups of similar cells form tissues. Different tissues work together to form organs.
Animal example
A muscle cell is part of muscle tissue. Muscle tissue can form part of an organ such as the heart. The heart is part of the circulatory system.
Plant example
A palisade cell is part of a leaf tissue. The leaf is an organ that helps the plant make food by photosynthesis.
Activity - Levels of organisation examples
- Students arrange examples into the order cell, tissue, organ, organ system and organism.
- Students create one animal example and one plant example.
- Students revise plant and animal cell basics, specialised cells and microscope use.
Summary
- Cells are the basic unit of life.
- Specialised cells work together in tissues and organs.
- Multicellular organisms are organised into levels of increasing complexity.
Check your understanding
- Put these in order from smallest to largest: organ, cell, tissue, organism, organ system.
- Give one example of an organ in an animal.
- Give one example of an organ in a plant.
Teacher notes & learning objectives
- LO1 — Describe the levels of organisation in multicellular organisms.
- LO2 — Give plant and animal examples of cells, tissues and organs.
- LO3 — Review core ideas from the unit.
Useful revision areas include animal and plant cell basics, specialised animal cells, specialised plant cells, levels of organisation and microscope use.