Year 7 Cells Checklist — Comprehensive Revision Notes

MRS GREN characteristics

  • MRS GREN is a mnemonic used to remember the life processes of living organisms:

    • Movement: organisms move or parts of them move.

    • Respiration: chemical reactions to release energy from food.

    • Sensitivity (response to stimuli): organisms detect and respond to changes in their environment.

    • Growth: increase in size and/or number of cells.

    • Reproduction: producing offspring (not essential for individual survival, but for the species).

    • Excretion: removal of waste products from metabolism and other processes.

    • Nutrition: taking in food or nutrients for energy and growth.

The Cell Theory

  • Three key statements (the three requirements) of the Cell Theory:

    • All living things are composed of cells.

    • Cells are the basic unit of life and carry out the essential processes of life.

    • All cells arise from pre-existing cells (cell division).

  • Cells are the smallest units of living things; a microscope is needed to view them.

  • Organisms can be unicellular (comprising a single cell) or multicellular (comprising many cells).

Levels of organisation in organisms

  • Hierarchy from smallest to largest:

    • CELLS → Tissues → ORGANS → Body Systems → ORGANISMS

  • Explanation:

    • Cells are the building blocks.

    • Tissues are groups of similar cells performing a function.

    • Organs are structures composed of tissues working together.

    • Body systems are groups of organs performing major functions (e.g., digestive system).

    • An organism is an individual living thing composed of all its organ systems.

Organelles in animal and plant cells; labeling and function

  • Common organelles to label in both cell types:

    • Nucleus: stores genetic material; controls activities of the cell.

    • Cytosol (cytoplasm): jelly-like fluid where organelles are; site of many reactions.

    • Cell membrane: semipermeable layer that surrounds the cell; controls entry/exit of substances.

    • Mitochondria: powerhouse; produces energy via cellular respiration, the process of taking nutrients such as sugar and using oxygen to break it down to release energy for all tasks.

    • Vacuoles: vesicles (small bubble-like sacs used for storing or moving substances around cells) ; plant cells have a large central vacuole.

  • Plant cell-specific organelles:

    • Cell wall: rigid layer outside the cell membrane; provides support and shape; made of cellulose.

    • Chloroplasts: site of photosynthesis; contain chlorophyll.

  • For each organelle, describe its function (role) in both animal and plant cells where relevant.

Differences between animal and plant cells

  • Plant cells have additional structures not typically found in animal cells:

    • Cell wall (rigid support).

    • Chloroplasts (photosynthesis).

    • Large central vacuole (storage and turgor pressure).

  • Plant cells generally have a larger vacuole; animal cells usually have smaller vacuoles or multiple vesicles.

  • Overall shape differences due to these structures; plant cells tend to be more rectangular, animal cells more irregular/rounded, depending on tissue.

Types of cells and how shape supports function

  • Different cell types exist to perform specialized roles.

  • How shape supports function (examples, not exhaustive):

    • Guard cells/epidermal cells in leaves: shapes that regulate gas exchange and water loss, as the stomata help let gas come out and transpire.

  • Cells’ physical characteristics are adapted to help carry out their tasks most effectively

Microscope safety and handling

  • Safe handling of a light microscope includes:

    • Carry microscope with one hand on the arm and another supporting the base

    • Place microscope on a stable, flat surface

    • Carry slides and specimens carefully to avoid breakage.

    • Clean the lens with lens paper to avoid scratches

    • After use, turn off the light, wrap cables and return safely to original position.

Parts of the light microscope (labeling)

Common components to label and their purpose:

  • Eyepiece (ocular lens): The lens you look through to view the specimen; it magnifies the image produced by the objective lens.

  • Nosepiece (turret) with objective lenses: A rotating part that holds the objective lenses, allowing easy selection of different magnifications.

  • Objective lenses (e.g., 4x, 10x, 40x): Lenses with different magnifications that are positioned closest to the specimen and produce the initial magnified image.

  • Stage and stage clips: The flat platform where the microscope slide is placed, and clips to hold the slide securely in position.

  • Light source (mirror or lamp): Provides illumination (light) that passes through the specimen.

  • Diaphragm (condenser) and adjustable light intensity: Controls the amount of light that passes through the specimen, affecting contrast and brightness.

  • Coarse and fine focus adjustment knobs: Knobs used to move the stage (or objective lenses) up or down to bring the specimen into sharp focus; the coarse knob for large adjustments and the fine knob for small, precise adjustments.

  • Arm and base: The arm connects the head to the base and is used to carry the microscope. The base is the bottom support of the microscope.

Main steps for using a light microscope to view a specimen

  • Step-by-step approach:

    • Place the slide on the stage and attach with stage clips.

    • Turn the turret to 4x objective lenses, and try to get the specimen into focus.

    • Use the coarse adjustment knob to bring the stage with the slide up.

    • Use the fine adjustment knob to fine focus the specimen to create a clearer image.

    • Do the same with the 10x and 40x objective lenses.

    • Refocus the specimen by moving it into place if it gets moved while turning the objective lenses.

Preparing a specimen and making a wet mount

  • water or stain on slide, specimen, hold coverslip,

  • Wet mount preparation steps:

    • Place a small drop of water or stain on the slide.

    • Add a small amount of the specimen to the drop.

    • Hold a coverslip at an angle and slowly lower it to avoid air bubbles.

    • If staining (optional), apply a stain to enhance contrast and rinse as needed.

  • Wet mounts improve visibility of cell details by increasing contrast and maintaining hydration.

Rules for drawing cells viewed under the microscope

  • Drawings should be accurate and proportional:

    • Use a sharp pencil; avoid shading to pretend depth; keep to scale.

    • Include a clear title with the object and magnification.

    • Draw only what is visible; avoid adding features not seen.

    • Label key features clearly.

    • Include a scale bar if instructed.

    • Show multiple cells when possible to illustrate variability.

Writing headings and labeling diagrams of cells viewed under the microscope

  • arrows, labels,

  • When labeling diagrams:

    • Use a sharp pencil.

    • Make sure arrows are pointing horrizonatly to the right of the diagram

    • Make sure to not sketch or colour in anything

    • Label key features clearly

    • Take a sample of what is visible and shown, not all cells.

    • Include a clear title, and total magnification

Why stains are useful in wet mounts

  • Stains increase contrast and visibility of otherwise transparent organelles.

  • They help differentiate structures (e.g., nucleus vs cytoplasm).

  • Stains can highlight specific components (e.g., cell walls, chloroplasts) depending on dye properties.

Magnification calculations

  • Formula for total magnification

  • Magnification formula: objective lens magnification multiplied by eyepiece lens magnification (Total Magnification = Objective Magnification x Eyepiece Magnification).

  • Example:

    • If the objective lens has a magnification of 40x, then as the eyepiece lens magnification is 10x, then the total magnification would be 400x

  • Practical notes:

    • Higher magnification reveals more detail but reduces the field of view and may reduce image brightness.

How changing total magnification affects the image

  • Increasing total magnification:

    • Increases the size of the image but narrows the field of view.

    • May require more precise focusing and brighter illumination.

  • Decreasing total magnification:

    • Wider field of view and brighter image, but less detail.

How moving the slide on the stage affects the image

  • Moving the slide translates to moving the image in the opposite direction on the viewing screen.

  • Use stage controls to locate and center the area of interest when observing under higher magnification.

  • Practice careful, small movements to avoid losing your place when scanning the slide.

Note: The page includes a space for a name: Name: . Use this to write your own details when completing the activity.

Here is a short answer test based on your notes:

  1. What does the acronym MRS GREN stand for, and name two of the characteristics it represents?

MRS GREN stands for Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. Movement ( organisms move or parts of them move) and Respiration ( chemical reactions to provide energy from food such as photosynthesis.)

  1. List the three key statements of the Cell Theory.

All cells come from pre-existing cells. Every living thing is made out of cells. Cells are basic units of life, and carry out all essential processes of life.

  1. Describe the hierarchical levels of organization in organisms, starting from cells up to organisms.

Cells-Tissues-Organs-Body Systems- Organisms

  1. Name two organelles common to both animal and plant cells and state their functions.

    Nucleus (control center of the cell, stores genetic material and controls the cell’s activities.) and Mitochondria (breaks down nutrients such as sugar into energy for the cell)

  1. What are two structures found in plant cells that are typically absent in animal cells?

    A cell wall ( holds structure and support for the plant cell, rigid layer) and a chloroplast, which creates nutrients for the cell through photosynthesis.

  2. Explain how the shape of a guard cell supports its function in a leaf.

    Guard cells are shaped in a way to allow them to regulate gas exchange and water loss. They control the opening and closing of stomata, which are pores on the surface of the leaf.

  3. When carrying a light microscope, what is the correct handling procedure?

Have one hand on the arm, and another hand supporting the base, and always make sure to use two hands with it.

  1. What is the purpose of the objective lenses on a light microscope?

To magnify the specimen at different strengths (4x, 10x, 40x), increasing the clarity of specimens.

  1. Outline the first three steps you would take to view a specimen using a light microscope, starting from placing the slide.’

  • Place the slide on the stage and place the stage clips

  • Turn the turret to the lowest power objective

  • Turn the coarse focus adjustment to make the objective lense as close to the slide as possible without touching the slide.

  1. Why is a coverslip used when preparing a wet mount, and what should you try to avoid?

A coverslip is used to hold the specimen in place, and also so that the objective lense does not come into contact with the specimen and liquid on the slide. When putting on the coverslip, you should try to avoid air bubbles in order to see the specimen more clearly.

  1. When drawing cells viewed under a microscope, what are two important rules to follow regarding accuracy and detail?

  • Use a sharp pencil

  • Avoid shading or color

  • Take a sample of what cells are shown instead of all cells shown

  1. Explain why stains are useful when examining cells in a wet mount.

  1. State the formula for calculating total magnification of a microscope.

  2. How does increasing the total magnification affect the field of view and the amount of detail seen in the image?

  3. If you move a microscope slide to the right on the stage, in which direction will the image appear to move through the eyepiece?