Grade 4 Science

Core Unit: Cells and Systems

Unit overview:

In this unit students learn some general aspects of cell theory. They then study the skin in detail, considering its various components, and how the skin functions as an organ.

Related units:

The grade 4 Optional Unit on Nutrition and Digestion extends students' understanding of cells and cell theory.

The Optional Unit in grade 5 called Human Circulation and Breathing, and the grade 6 Optional Unit Human Body Control Systems are also related.

This Core Unit forms the base for what will be learned later, through the Middle and Secondary Levels and beyond.

Suggested themes:

cells, living things, skin, the body

Factors of scientific literacy which should be emphasized:

Common Essential Learnings foundational objectives which should be emphasized:

To develop an understanding of how knowledge is created, evaluated, refined and changed within science. (CCT)
To develop students' appreciation of the value and limitations of technology within society. (TL)

Science foundational and learning objectives:

Explain some aspects of cell theory.
1. Describe the basic structure of cells.
2. Identify cells as the smallest components of organisms.
3. Recognize the relationships between cells, tissues, and organs.
4. Recognize the characteristics of cells, tissues, and organs.
Explain the function of the skin as an organ.
1. Examine the skin on the hands and arms.
2. Describe the skin on the hands and arms.
3. Identify the location of the hair follicles and oil glands.
4. Compare the sweat glands with the oil glands.
5. Describe the origin and growth of fingernails.
6. Examine fingerprints.
7. Study the skin in detail.

Suggested Activities:

Because cells are usually depicted in two dimensions, students may get an incorrect impression of them. Have groups of students build and label three dimensional models of typical cells, or of a cross-sectional layer of skin. A two dimensional illustration in a reference book may be used by students to design their three dimensional model. One way is to fill a plastic bag with salt water and place a small floating object into the bag to represent the nucleus. Another way is to use an egg to represent a cell. The yolk represents the nucleus.
Factors: A1, C2, C3, C4, E3, E4, G1
Objectives: 1.1, 2.2, 2.3, 2.4
Assessment Techniques: 3, 4, 5, 8, 9
Common Essential Learnings: Communication. The three dimensional models allow students to share what they have learned with others. It also allows them to identify the names of components of cells, and to gain an understanding of the characteristics of those components.
Sprout grass or cereal grain seeds. When the sprouts are two to three centimetres high, use a fine tip pen with permanent ink to mark from the tip of the shoot every 2 mm interval back to the base of the shoot. Handle the sprouts with care; they are delicate. Observe the relative spacings of the marks for the next several days as the plants grow. What inferences can be drawn from the results? (You should notice that growth occurs primarily near the tip of the sprout. One infers from this that cell differentiation has occurred.)
Extend this activity by developing a growth chart for students in the class. Let them search for similarities and differences between the rate at which they are growing and the rate at which plants grow.
Factors: B1, B4, C3, C4, C9, F2, G1, G3
Objectives: 1.3, 1.4
Assessment Techniques: 1, 3, 5, 8, 9
Common Essential Learnings: Critical and Creative Thinking. Growth occurs near the tips. Why this occurs is a fascinating subject in itself. The mechanism responsible for this is complex, and is based on the production of hormones by the cells. Research is being conducted to determine how genes influence cell growth and differentiation.
The activity is designed to provoke the students' curiosity about an interesting problem. Some may revisit this topic at a more advanced level.
Examine cells, using a microscope. Compare different plant cells from the same plant, from different plants, and from a variety of plants and animals. The thin membranes on the inside of onions works well. The thin membrane on the bottom side of a geranium leaf also works. Samples of hair, fish scales, sand, thread, paper fibres, newspaper cartoons, and nylon are also interesting to examine, though some are not related to cells. The availability of microscopes in your school will determine how this activity can be performed. If enough microscopes are available in your school, or can be borrowed from another school, students could work in pairs, with one microscope per pair.
Whenever students work in groups, ensure that all students have an opportunity to participate actively. To ensure equal participation, rotate the various tasks within the group.
Instructions have to be given on the proper use and care of microscopes, and on the preparation of specimens for viewing. (These instructions would likely be at least one full lesson.)
If only one microscope is available, then set it up beforehand with the specimen to be viewed at an activity station, complete with related exercises and activities. Student-grade microscopes are available from scientific supply companies.
Students should attempt to illustrate and label, as neatly and accurately as possible, what they have viewed through the microscope. Developing this skill is important.
If no microscope is available, less desirable alternatives are preferable to no visual experience of cells at all. Cell diagrams on posters and overhead transparencies, or slides of micrographs can be used. This may even be an advantage, because of the better quality of the image. Specimens carefully prepared by professionals often reveal detail which can not be seen with a student microscope.
Even if microscopes are available, it is useful to display microphotographs in some way, to assist in pointing out some important cell characteristics.
A 35 mm slide viewer and an assortment of colour microphotographic slides (available from scientific supply companies or possibly from local hospitals) can be set up at a learning activity centre.
Factors: A1, B1, B4, C2, C3, C4, D1, E1, E3, E4, G1, G3
Objectives: 1.1, 1.4, 2.1
Assessment Techniques: 1, 3, 5, 8, 9
Common Essential Learnings: Technological Literacy. Learning how to use a microscope helps to provide students with an understanding of the value and limitations of technology in society. By being able to examine microscopic details, knowledge has been extended. That knowledge has been put to good use. An understanding of certain types of diseases, for instance, resulted from the knowledge about bacteria that microscopes provided. Knowledge can also be put to undesirable use, as in the development of bacteriological warfare.
Using microscopes shows students that things exist that cannot be seen with the naked eye.
Microscopes have limitations. A light microscope can not resolve detail smaller than the wavelength of light. Other technologies have been developed to view smaller things, such as some kinds of viruses.
An interesting project that some gifted students might undertake is to photograph objects through a microscope. This is a rather specialized field of photography, requiring high resolution film, and a special microscope adapter to fit a 35 mm camera. The slides or prints obtained can be used to enhance science fair projects, or kept from one year to the next to build a collection of specimens. Reference material dealing with photomicrography is available for those who are interested. Good camera stores either have these references in stock or could order them. Check as well with your teacher-librarian to help you locate information.
Twin with Secondary Level students on this project. Have some of those older students serve as assistants and advisors. They can develop black and white film and make prints of the photographs. Some more advanced senior students could develop colour transparencies and produce colour prints from the slides.
Factors: A1, B2, B4, C2, C3, C4, D1, E1, E3, E4, F2, G1, G3
Objectives: 1.1, 1.3, 1.4, 2.1, 2.2
Assessment Techniques: 1, 2, 3, 4, 5, 9
Common Essential Learnings: Technological Literacy. Photography provides an accurate record of objects or events. Before photography was invented, people had to rely on artistic sketches to illustrate observations. The camera made it possible to gain more detailed knowledge and insight.
Make pencil smudges on a piece of paper, using the flat side of a pencil. Have students rub each finger on the pencil smudges and press the sticky side of some transparent tape on the finger. (This procedure is much better than using ink to produce the fingerprints.) Tape the fingerprints on the activity cards below. Examine each of the fingerprint samples with a hand magnifier. Look for patterns that are similar.
Examine a mystery fingerprint made by someone in the class. Compare the mystery fingerprint with the fingerprints on the activity cards. See if students can find out who made the mystery fingerprint.
Examine the fingerprint classification patterns shown below. Using the fingerprint activity cards, see which pattern is closest to each of the fingerprints on the activity cards. Record all observations. If any students in the class are related, have them compare fingerprints to see if any similarities exist. A comparison of the fingerprints of siblings or identical twins is an interesting extension activity.
The fingerprint impression on the transparent tape can be attached to a clear acetate sheet and projected using an overhead projector. (Use the shiny, transparent type of tape. The translucent, matte-finish type projects as a black strip when viewed on the overhead.) Alternatively, the fingerprint can be transferred to a sheet of white paper, then photoenlarged several times. An acetate transparency of the enlargement will provide a bigger pattern when viewed on the overhead projector.
For an interesting diversion, make two identical fingerprint transparencies. Superimpose them on the overhead. Move one slightly to create a moiré pattern.
Fingerprints are used in forensic science for identification. Have some students research this topic and make a presentation to class.
Invite a police officer to class to explain how fingerprinting is used in police work.
Activity 5: Making Fingerprints
Factors: A1, C3, C4, E1, E4, F2, G1, G3
Objectives: 1.3, 1.4, 2.1, 2.2, 2.6
Assessment Techniques: 2, 3, 4, 5, 8, 9
Common Essential Learnings: Critical and Creative Thinking. Students make careful observations in this activity. They compare those observations with others. They also strengthen their perceptual abilities through concrete experiences. Good public relations between the police and the public are also developed through activities such as these.
Independent Learning. The follow-up activity which provides some students with an opportunity to make a presentation to the class about forensic science, is a useful extension. It enables the teacher to adapt the activity to meet the needs of those students who are able to pursue learning with greater independence.
With extreme care, use a straight pin to make horizontal scratches just above the cuticle on several students' fingernails and toenails. Apply a small dab of nail polish to the scratch to mark it, and remove any excess nail polish with tissue paper. Every week measure the height that the scratch has moved above the cuticle. Reapply polish on the scratch whenever it is necessary to do so. Continue until the scratch marks have moved all the way up to the end of the fingernail.
Relate the activity to Health, by discussing the proper ways to care for fingernails. Related topics dealing with such things as ingrown toenails can also be developed. This might also be an appropriate time to discuss nail biting, suggesting some strategies to break the habit.
Factors: A1, B1, C2, C3, C4, F2, G1
Objectives: 2.5
Assessment Techniques: 1, 3, 5
Common Essential Learnings: Numeracy. The data collected during the activity enables students to pose a variety of interesting questions. Why do fingernails grow at a different rate on the hands than on the toes? Why do some people's fingernails grow faster than others? Why can fingernails which have been broken off at the cuticle regenerate themselves?
Tabulate and graph the results. Compare the rate of growth for different fingers on the same person; between fingers and toes for the same person; from one person to the next.
Bring in some potatoes, potato peelers, and small jars to class. Have several boys and girls each peel a potato, without washing their hands. (Caution students about the sharp edges on the potato peelers.) Place those peeled potatoes into jars and label them with the student's name as the ones peeled with unwashed hands. Make sure that all of the jars and lids have been thoroughly cleaned beforehand.
Have the same students wash their hands thoroughly. Wash the potato peelers as well. Give the same students another potato to peel. Place these potatoes in different jars, labelling them with the student's name as the ones peeled with clean hands and clean peelers. Put lids on all the jars. Observe and record the changes in the potatoes every few days for several weeks.
Some of the potatoes peeled with unwashed hands may begin to develop mold after a few days. Some peeled with washed hands may not develop mold, but a few others may, depending on whether or not any mold made contact with those potatoes while they were being peeled. Cleanliness during the second peeling with washed hands is important in obtaining reasonably good results. Compare the results.
Repeat the activity several times. On the second trial, place a few of the potatoes peeled with dirty hands on some carpeting, to simulate what might happen if foods are dropped while being prepared. Try having students put dust on their hands before peeling the potatoes. Of course, these modifications could be included into the activity initially.
Discuss some of the health implications when preparing food. The activity will give students a very good understanding of why it is important to wash their hands before preparing food and before eating. They might also establish that even though hands do not appear dirty several hours after washing, various microscopic spores and bacteria may settle on the surface of the skin. If left there for long enough, they may begin to produce some rather unpleasant odours. This may help to inform students to pay careful attention to personal hygeine. Excellent cross-subject integration with Health exists with this activity.
Fingerprints may also be put on agar and incubated. This could form an interesting research project. Consult with a Secondary Level Biology teacher for information on how to prepare the agar.
Another extension of the activity is to measure the mass of the potatoes before peeling. After peeling, measure the mass of the peeled potato and the skins. Confirm that mass is conserved, i.e. that the mass of the peeled potato plus the mass of the peels equals (or at least is very close to) the mass of the potato before peeling. Draw a pie graph to show how much of the mass of the original potato has been lost in peeling. Explain that some of the best nutrients in the potato, located in or near the peel, have been lost through "processing" it in this way. Use this to illustrate how food processing can rob foods of their essential nutrients. If the potato has been peeled, the peels create waste. If the peels have to be removed, they should be composted to produce compost for a garden or a flower bed.
Factors: A1, B1, B2, B4, C2, C3, C4, C9, E3, F2, G1, G3
Objectives: 2.2, 2.7
Assessment Techniques: 3, 4, 5, 8, 9
Common Essential Learnings: Critical and Creative Thinking. Students draw inferences from the implications of what they learned. By relating the activity to preparing and eating foods, and to personal hygeine, students make connections between the activity and things of importance in their lives.
Ask students to think about how a cell is like a city. Have them discuss this with partners, then brainstorm as a whole class. Have students "become the city" and say how they feel. They can share in small groups and participate in a large group discussion. In small groups, students are asked to think about all the ways that cells and cities are different. Afterwards, continue with large group sharing.
Have students develop their own analogy for a cell and give reasons why it would be a good analogy. Have them share their ideas in small groups.
Students could simulate in small groups how components of a cell would interact and then how the individual cells would interact with each other. A skit or mime could be developed to illustrate their concept.
Factors: A1, B2, B4, C2, C4, F2, G1, G3
Objectives: 1.1, 1.4
Assessment Techniques: 1, 3, 5
Common Essential Learnings: Critical and Creative Thinking, Communication. The combination of small and large group work, and the way in which the activity has been structured, develops these two Common Essential Learnings particularly well. Consider using this or other synectics activities.