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Discovering Natural Fibres: Practical Lesson Ideas for Teachers

Essential Content
Students learn about:
4.11 natural resources b) give examples of resources from living things and resources extracted from the air, Earth and oceans

(in this case, starch and cellulose).
Activities
Examining plant cells 1-2 lessons
Non-newtonian fluids 1-2 lessons
Starch in cells 1-2 lessons
Student Research Invetsigations 1-2 lessons
Locating Plant Cellulose in stems Short intervals over 2 days
Extracting fibres from plant material Short intervals over 2 days

Guidelines for Laboratory Drawings

Equipment necessary:

  • sharp HB pencil
  • ruler
  • rubber
  • blank paper

Guidleines for Biological Drawings - from University of Tasmania

Biological Drawing Guidelines - from Saskatchewan Schools and School Districts

Rules for Biological Drawings - from Chehalis School District(pdf 48.6kB)

Assessment Template for Biological Drawings - from Faculty of Education, AlbertaUniversity

Biological Diagram - rubric from Virtual Library, Ontario (word doc 33.3kB)

Skills developed

1. Examining plant cells

Preparation

Collect filamentous algae. Aquarium shops sell plants for fish tanks or a student may have a fishpond at home.

Use a small fish tank or large wide-mouthed jar. A delicatessen may donate a large pickle jar. Keep in a large wide mouthed glass container or small fish tank in a well lit area, but not in direct sunlight. Do not overcrowd. Facing south is best. Use a piece of glass from an old picture frame or perspex as a cover to keep out dust and fumes.

The following are part of a Series of Fact Sheets to help you, from teh Royal Botanical Gardens, Sydney

Collecting freshwater algae

Examining freshwater algae

Preserving freshwater algae - from Royal Botanic Gardens, Sydney

ALGPIC - pictorial gallery of the freshwater algal genera

Equipment
  • Microscopes (Check that the lenses are clean. Use lens paper if necessary.)
  • Microscope slides
  • cover slips
  • water droppers
  • small beakers for water
Alternatives to algae
  1. Cut an onion vertically into segments and pull off pieces of the thin inside membrane of the leaf bases with blunt forceps and mount in water on a slide. No chloroplasts will be seen.
  2. Use a Chinese cabbage leaf (bok choy). Slit the leaf stem with a sharp knife then quickly pull it apart using two hands. The torn edge will probably have a single layer of cells which can be viewed by cutting small pieces off, lifting with a small wet paintbrush and mounting in water. Keep the torn edge moist.
Teacher Demonstration
Show students the technique of lowering the coverslip from one side at an angle to avoid air bubbles.

PREPARING MICROSCOPE SLIDES - from Microbus

Microscope Slide Preparation - from Utah State Office of Education

Student Activity
  1. Collect a microscope slide and coverslip
  2. Mount a piece of torn leaf into a water drop on the slide, with blunt forceps or take a strand of alga and mount in a water drop on a slide under a coverslip.
  3. Students focus and view under Low Power first, and then change to High Power. They should see the box-like cell walls made of cellulose and the green chloroplasts (not in onion) where simple sugars are made. The nucleus may be visible as yellowish oval body.
  4. Make labelled drawings, including a descriptive heading.
Images

Introduction: Plants - from Microscope Imaging Station, The Exploratorium

Cell Unit - Lesson Plan - includes images ocf cells from slides prepared by students, as well as full lesson plan adn weekly outlines

Unbranched filaments - various algae, from Royal Botanic Gardens, Sydney

Sample worksheet

Exploring Plant Animal Cells - worksheet in MS Word, from Memorial University, Canada (word doc 755kB)

Extension
Students examine other examples of plant leaf cells.
  • Are the cells all the same shape?
  • Do the chloroplasts look the same?
2. Starch in plant cells
The Test for Starch - Teacher demonstration

Preparation

Equipment for demonstration
  • Overhead projector
  • Labelled Petri dishes
  • 2% solutions of glucose, sucrose and starch
  • paper
  • Dropper bottle of iodine solution
Materials
Iodine solution
In a 500 ml stoppered bottle, make a saturated aqueous solution of potassium iodide), then use a spatula to add a few crystals of the element iodine (some crystals may not dissolve, do not worry). Insert the stopper and shake. This makes a concentrated stock solution. Pour off a little of the dark solution into a beaker and dilute with water until it is translucent. Top up with water, shake and store. This will provide iodine solution for quite a few years. Provide the dilute solution in dropper bottles. If not using for a while decant the solution and wash the bottles or the rubber tops will deteriorate. Refill when required.
Starch Solution
If this is needed, mix a teaspoonful of flour or cornflour with water to make a creamy slurry, pour in about 100ml boiling water and stir vigorously. It does not need to be very concentrated, if is the colour will be almost black instead of an obvious blue. Test a little and dilute if necessary. The starch solution will not keep more than a week in the refrigerator.
Method

Use the OHP to demonstrate the effect of placing dilute iodine solution on samples of glucose solution, sucrose solution, starch (use a little diluted paste if in a hurry) and paper towel or tissue (cellulose). Clean up immediately to avoid heat drying out the dishes.

Students discuss the results and write notes to describe how to test for the presence of starch.

Students test plant cells for starch
Preparation
  • Small paint brushes, the cheapest quality is OK
  • Glass pipette
  • Single edge razor blades or scalpel with a wide new blade
  • Small pieces of potato and onion on watch glasses or small petri dishes
  • Starch suspension - make a very thin suspension of powdered starch in water in a conical flask, insert he glass pipette
  • Dropper bottles of iodine solution
  • Microscope slides and cover slips
  • Small trays for students to carry materials to microscopes
  • Scrap paper to place on bench under slides
  • Water droppers
Clean up
  • Labelled beakers or containers of water for students to return slides and cover slips, add a little detergent to each
  • Wipe down the microscope stages with paper towel
  • Return microscopes to storage boxes
Method

Students put one drop of very dilute aqueous iodine solution and one drop of water onto each of three glass slides. They collect cover slips for each slide.

  • Slide 1: add a drop of starch suspension and add a cover slip
  • Slide 2: use a scalpel to scrape a little raw potato juice into the drops and add a cover slip
  • Slide 3: Pick up a piece of onion membrane with a wet paintbrush, place on slide and add a cover slip

Students learn to focus and view under Low Power (4X or 10X) first, and then change to High Power (40X). This avoids damage to lenses.

Outcomes
  • Students should detect the presence of starch grains by their blue colour
  • Students make labelled drawings of what they see on the three slides, including a descriptive heading for each
  • Students design and complete a table to present their observations
  • Students write conclusions based on their data
Discussion
  • Why do plants have starch grains? (Food reserves)
  • What do cell walls do for the plant? (Support, stiffening; unlike us they do not have skeletons)
  • Of what are plant cells walls composed?
3. Plant Cellulose

Locating the fibrous xylem vessels in a stem, using a dye solution

Materials
  • Plant material, stems of Bizzie Lizzie (Impatiens), young geranium or celery stalks with leaves (petioles)
  • Dropper bottles of methylene blue or eosin solution
  • Jam jars (Students could provide these, plastic containers tip over too easily)
  • Small Petri dishes
  • Microscope slides and cover slips
  • Paste stick or paste
  • Grease pencils or pasted labels to label containers. (Sticky labels are too hard to remove.)
  • Waste polystyrene foam
  • Sharp knife or strong scissors to cut stems
  • Single edge razor blade or scalpel with new wide blade for teacher use
Method

Student groups put a couple of drops of methylene blue or eosin solution into a small container of water. They use a sharp knife to cut the bases of stems of Bizzie Lizzie (Impatiens), young geranium stems or fresh celery under the water to stop air from entering the xylem, and leave to stand in the solution.

Label with group names and date. Leave where other classes cannot interfere.

(An alternative is to split a celery stalk vertically up about one third from the base and put one side in a container of water and the other in a container of the dye solution. Have students discuss the point of this.)

Examine the plant material next lesson. After looking at the whole stems, teacher cuts cross sections by making a hole with a pencil the same size as the stem in a piece of polystyrene foam cut allowing 2-3 mm around the stem. Insert the stem into the hole. Wet a single edged razor blade; hold it parallel to the surface to cut very thin cross (transverse) section slices off the stem, dropping them into a small Petri dish of water.

Students collect a microscope slide and cover slip and use the paint brushes to pick up the cross sections and place them on the slides.

Add a drop of water and a cover slip and examine under low power to see where xylem vessels strengthened with cellulose are located in the stems. Xylem carries water and salts up the stem from the roots to the leaves.

Pulling out the strings of the celery and examining under the microscope will show the cellulose stiffened plant xylem fibres. These are the tubes used to carry water and salts from the ground up to the leaves

Make labelled drawings, including a descriptive heading.

Extensions
  • Try using variegated grass and other plants
  • Try soaking pieces of crepe paper in water to extract dyes and see if they are effective. White carnations are often coloured by florists using this technique.
4. Extracting fibres from plant material

This is the original ancient method called “water retting”. Bacteria do the smelly work of separating the fibres from the rest of the plant material.

Materials
  • Sources of cellulose: Any clean leaves of fibrous plants such as Mat Rush (Lomandra), Flax Lily (Dianella), sugar cane mulch, banana stem pieces about 20 cm long, or split NZ flax leaves
  • Plastic garbage bin or large plastic lidded box as used for clothes storage
  • Thick Plastic sheet
  • Clean bricks or cement blocks Sodium hydrogen carbonate (Bicarb or baking soda)
  • Kitchen strainer
  • Metal dog comb
  • Scissors
Method
  1. Soak the plant material in the container overnight to soften it
  2. In the playground drain off the water onto a garden
  3. Spread the material on the plastic sheet; have class members trample it to break down the material
  4. Put into the container and cover with water.
  5. Add 10g sodium bicarbonate because the bacteria like alkaline conditions
  6. Place some clean bricks in to keep the fibres under water
  7. Leave the material about three days for bacteria to break down the unwanted material between the fibres (There may be some odour so find a location which is not going to cause problems, erect a sign( Class, Teacher, Date, Request)
  8. Take a small sample of a few drops before each lesson and set up slides on microscopes so students can examine the material under HP with the microscope. A drop of methylene blue or diluted gentian violet may stain the bacteria. The bacteria will probably be small rods.
  9. After three days or less in warm weather put on disposable gloves and strain the fluid off into the garden, where it will do some good.
  10. Rinse the fibres in water, drain, cover again and add about 10g of sodium bicarbonate (alkaline) to the water to help with the washing, rinse, spread out on the plastic sheet and beat the fibres again using a wooden mallet or a rolling pin
  11. Rinse
  12. Use a metal dog comb to organise the fibres into bundles.
  13. Tie loosely with plastic string.
  14. Hang to dry.
Internet images

Pictures for the Lab#1 - from Department of Biology, University of North Carolina at Charlotte
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/labpics/lab1pics.htm

For discussion

Students should not touch the liquid. Why not?

Clean up

Drop the slides into a beaker of water and microwave about 2 minutes before rinsing and washing. This will kill the bacteria.

Alternatively

Use a good computer USB microscope if available and make a series of short videos to show students instead. Some students may be happy to edit the short videos together into a movie. Use Windows Movie Maker or Mac iMovie.

Students
  • Snip off small samples and examine them under the microscope
  • Wrap a few fibres with Glad Wrap and tape into notebooks
  • Write a description of how the fibres were prepared
  • Students are looking at natural cellulose extracted from plants

Why were improved mechanical and chemical methods of fibre extraction developed in many countries in the past?

Extension

Use a cold water cellulose dye (Procion) to dye a small bundle of the fibres. Instructions are on the packet.

Internet

Procion Dyes - from Zart Art

About Fiber Reactive Dyes - from All About Hand Dyeing
(Note: Soda ash is sodium carbonate or washing soda)

Preparing Solutions Directions for preparing some os the standard solutions needed forthe above activities


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