4. Seeing Cells

Summary
The invisibly small world of the cell comes to life as students look at plant and animal cells through a microscope. Students create wet-mount slides of onion skin, elodea leaf, and human cheek cells. They learn some of the gross differences between plant and animal cells (cell walls are present in plant but not in animal cells), and even some of the differences between different plant cells (chloroplasts are found in the leaves but not in the roots). It is suggested that this lesson take place after students learn the parts of a cell and their functions. Resources for good cell diagrams are provided in the Sources section. This lesson may be used in conjunction with the Pond Water activity for students to get a sense of the diversity of microscopic life, both single celled and multi-celled.

Objectives
Can name and describe the function of certain plant and animal cell organelles.
Can identify whether a cell viewed through a microscope if plant or animal.
Can draw and label a picture of plant and animal cells.
Can recognize that all living things are made of cells.
Can begin to recognize the huge variations in cell size, shape, structure, and function.
Can operate a compound light microscope.
Can make simple wet-mount slides.

Vocabulary
Cell
Organelle
Cell membrane
Cell wall
Cytoplasm or cytosol
Nucleus
Chloroplast
Microscope
Objective lens
Eyepiece
Focus
Stage
Elodea
Methylene blue

AttachmentSize
4seeing_cells.doc57.5 KB
cell_images.doc1.64 MB
cells_lab_handout.doc41.5 KB
cell_quiz.doc316.5 KB

4. Seeing Cells - Logistics

Time
45-75 min introduce the parts of a cell and their functions
Optional: 10-15 min discuss microscope parts and usage
5-10 min demonstrate proper procedures for making slides
45-90 min make slides, look at cells, create diagrams, and answer questions
10-15 min discussion and review

Grouping
Teams of 2.

Materials

  • A copy of plant and animal cell coloring diagrams (see Sources for several ways to obtain cell coloring diagrams)
  • A copy of the Seeing Cells lab handout for each student
  • Transparency or photocopies of the Cell Images page for the final discussion
  • Overhead projector
  • Assortment of colorful transparency markers
  • Colored pencils
  • 1 compound light microsope for every 2 students
  • 3 glass or plastic slides for every 2 students
  • 3 glass or plastic cover slips for every 2 students
  • Iodine
  • Methylene blue (0.25% solution, available from aquarium stores for the treatment of fungal infections in fish or at science supply companies such as Carolina Biological catalog # 87-5911, $9 for 25 ml).
  • Tap water
  • Eye droppers
  • Half of a red onion chopped into 1 cm x 1 cm or smaller pieces
  • Several Elodea plants (available from aquarium stores)
  • Flat toothpicks
  • Optional: images of other kinds of cells (For best collection of images of cells, see the Cells Alive website and particularly the cells image gallery)

Setting
Classroom

4. Seeing Cells - Background

Animal cell: Image created by Mariana Ruiz VillarrealAnimal cell: Image created by Mariana Ruiz Villarreal Plant cell: Image created by Mariana Ruiz VillarrealPlant cell: Image created by Mariana Ruiz Villarreal Bacterial cell: Image created by Mariana Ruiz VillarrealBacterial cell: Image created by Mariana Ruiz Villarreal

Teacher Background
Students often have difficulty conceptualizing that cells are the basic building block of all living things. Thus, it is essential for them to have experience making slides of familiar living things – onions, plants and their own cheek cells – and viewing them under a microscope to see that cells really do make up all living things.

Multicellular creatures such as plants and animals have different levels of organization, from organic molecules to organelles to cells to tissues to organs to organ systems to a whole organism. Cells are the smallest unit that can fulfill all the necessary characteristics of life – it can metabolize, grow, reproduce, maintain homeostasis, evolve, respond to its environment and so on. Its organelles (parts of a cell, each has a specific job similar to the organs in the human body) participate in fulfilling these various functions.

Important organelles in eukaryotes such as plants and animals (prokaryotes such as bacteria have much simpler cells):

  • Cell membrane – the cell’s skin that protects the cell from changing environmental conditions and from invaders as well as letting selected molecules in and out of the cell
  • Cell wall – a feature of plants cells that functions like stiff lattice-like wall which helps plant cells maintain their structure and shape
  • Nucleus – the cell’s control center that contains the DNA
  • Cytoplasm – a jelly-like liquid that fills the interior of a cell and surrounds and supports all the organelles
  • Chloroplast – a feature of plant cells that allows plants to do photosynthesis and make their own glucose from sunlight, water and carbon dioxide
  • Mitochondria – the cell’s power plant that turns glucose into energy that the cell can use to run its organelles
  • Ribosome – tiny organelles that function as little protein factories (see Protein Factory activity)
  • Golgi complex – a complex series of interconnected membranes that functions like a post office - it processes, sorts, and labels proteins, making the proteins more effective at their various jobs and helping them to end up in the right place
  • Endoplasmic reticulum – a system of membrane-enclosed canals and passageways used to quickly transport proteins within the cell
  • Vacuole – a prominent feature of certain plant cells, though animal cells also have vacuoles as well, that is used as a storage container for nutrients or other materials
  • Lysosome – a cell’s garbage and recycling center for digesting wastes and recycling the building blocks for other purposes
  • Centriole – a feature of animal cells important for coordinating cell division

Using a light microscope only the largest features of a cell can be observed (the first 5 organelles on the list above). Greater magnification is required to visualize other cell parts. Still students can discover how all living things are similar in that they are made of cells but also discover the great diversity in cells themselves.

Student Prerequisites

Experience with light microscopes is helpful. A basic understanding of the parts of a cell is essential to the completion of this activity.

4. Seeing Cells - Getting Ready

Getting Ready

  1. Make copies of cell coloring diagrams. Make one copy on a transparency so that you have one to color in along with your students.
  2. Make copies of Seeing Cells Lab handouts.
  3. Make transparency of the Cell Images and any other images of cells you found.
  4. Set up microscopes.
  5. Set out stations for students to make slides. Each station should include glass slides, cover slips, iodine, methylene blue, tap water, eye droppers, several pieces of red onion, one Elodea stem, and clean toothpicks.

4. Seeing Cells - Lesson Plan

Lesson Plan

  1. Ask students to free associate what comes to mind when you write the word “cell”. In addition to biological cells, they may come up with prison cells, cell phones, a terrorist cell and more. In all these uses, a “cell” is a single functioning unit or compartment that is part of a larger whole. That too is what a cell is in biological terms, the building block upon which all living things are built.
  2. Show students pictures of cells. Have students tell you what they see and notice. Emphasize both the diversity of different cell shapes and sizes and also how all cells share certain features.
  3. Give students the cell coloring diagrams. Lead your students in coloring the diagrams and describe the job of each cell part as you go. You may want to have students write the job of each part of the cell beside the name of the part.
  4. Now that students have learned a little bit about cells, they will now get a chance to look at some real cells through a microscope. If students have not used a microscope before, go over the parts of a microscope and how to properly use it.
  5. Demonstrate how to make each type of slide (see the directions on the Seeing Cells student handout, one of the attachments at the bottom of the main summary page).
  6. Answer any questions then let students begin work on the lab in groups of two. By the end of the activity, students should have 2 labeled drawings of each type of cell, one at 40x and one at 400x.
  7. Assist students with making slides, using the microscopes, and bringing cells into focus. The human cheek cells are often difficult to find and get into focus since they are much smaller and more disperse than the onion and Elodea cells. Many will need help locating these cells on the slide.
  8. When all student have completed the drawings, review what they saw using the Cell Images transparency.
  9. Point out the cell parts that can be seen through a light microscope (cell membrane, cell wall, cytoplasm, nucleus, and chloroplasts).
  10. Discuss why it is that other cell parts could not be readily observed (they are too small or need special dyes to be able to see them).
  11. Discuss the differences between plant and animal cells (plants have cell walls and chloroplasts) as well as the difference between the elodea and onion skin cells (only leaf cells have chloroplasts).

4. Seeing Cells - Assessment

Assessment

  1. Have students turn in their labeled diagrams and conclusion questions.
  2. Provide an unlabelled cell diagram for them to correctly label and describe the function of each part.
  3. Assign a cell quiz. Use the one attached to this lesson, use the one at Shannan Muskopf’s Biology Corner website, or create your own.

Going Further

  1. Build a model of a cell in any of a hundred different ways. Use the Slimy Cells activity. Make shoebox cells. Turn your classroom into a cell. Be creative.
  2. Ask students to draw an analogy between cells and a city, a factory, a school, a fantasy kingdom or science fiction evil empire. Show your students Shannan Muskopf’s analogy of a city that makes widgets then invite your students to come up with their own analogy.
  3. Observe microscopic organisms found in pond water in the Pond Water activity. Some of the creatures you find, like diatoms, are single celled creatures. Of the multicellular creatures, you can observe single cells at work in many of them, particularly the algae.

4. Seeing Cells - Sources

Sources
Blank cell coloring diagrams can be found at:

The best resource for this lesson is the fabulous Biology Corner website of Shannan Muskopf. In Biology 1 and 1A, Chapter 3, she provides:

  • a fantastic overview of how to use a microscope including a lab, worksheet and quiz
  • a cheek cell lab
  • plant and animal cell coloring diagrams
  • a “cell city” extension activity
  • a webquest using the Cells Alive website
  • a cell crossword puzzle
  • a cell quiz

Thank you thank you thank you! Check out all the other fantastic labs, projects, field trips and assessments at Biology Corner.

Standards
Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
a. Students know cells function similarly in all living organisms.
b. Students know the characteristics that distinguish plant cells from animal cells, including chloroplasts and cell walls.
c. Students know the nucleus is the repository for genetic information in plant and animal cells.
d. Students know that mitochondria liberate energy for the work that cells do and that chloroplasts capture sunlight energy for photosynthesis.
e. Students know cells divide to increase their numbers through a process of mitosis, which results in two daughter cells with identical sets of chromosomes.
f. Students know that as multicellular organisms develop, their cells differentiate.

Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.

Grades 9-12 Biology
Cell Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
c. Students know how prokaryotic cells, eukaryotic cells (including those from plants and animals), and viruses differ in complexity and general structure.
e. Students know the role of the endoplasmic reticulum and Golgi apparatus in the secretion of proteins.
f. Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.
g. Students know the role of the mitochondria in making stored chemical-bond energy available to cells by completing the breakdown of glucose to carbon dioxide.
j. * Students know how eukaryotic cells are given shape and internal organization by a cytoskeleton or cell wall or both.