Experiment 7 - Parenchyma and Sclerenchyma tissues in plants

Learning Objective:

To identify Parenchyma and Sclerenchyma tissues in plants, striped muscle fibres and nerve cells in animals, from prepared slides and draw their labelled diagrams.

Materials Required:

Safety Precautions:

1. HANDLE MICROSCOPE WITH CARE

2. HANDLE RAZOR BLADE UNDER SUPERVISION, DO NOT CUT YOUR BODY

Experimental Accuracy:

1. Ensure that the microscope is clean

2. Ensure that the most promising region of the slide is in the centre of the stage

3. Ensure that low power is used first, before higher power

4. Ensure an appropriately herbaceous/not too woody stem is selected

5. Ensure that cross sections of the plant are kept in water

6. Add a drop of water to the slide to prevent air bubble formation, and promote better light dispersion

7. Do not confuse the xylem with the sclerenchyma tissue

Note: The slides will be prepared and the methodology is optional

Methodology (Optional):

1. Cut the stem into smaller pieces and place them in water

2. Use a wet razorblade to obtain cross sections of the stem, and place these cross sections in water. Repeat this process to get multiple cross sections

3. Choose a thin, transparent section, out of all the other produced sections

4. Add a drop of water to the slide, before transferring the cross section to it. Add 3 drops of Safranin solution and wait for five minutes.

5. Use blotting paper to remove any excess stains, and add 3 drops of dilute glycerine to the stained regions

6. Gently place a coverslip

7. Focus the microscope on low power, before choosing the appropriate power

8. Observe the image of the cells and make a clean sketch in your notebook/note your observations

Experiment in Context:

Plants contain two types of tissues: Meristematic and Permanent. Meristematic tissues are those where cell division can occur, and hence allow the tissue to grow/develop. Permanent tissues on the other hand do not have this ability, but instead are more differentiated. Permanent tissues are further divided into the sub divisions of simple and complex tissues.

Simple tissues are those that contain cells that are both structurally and functionally similar. There are three types of simple tissues” parenchyma, collenchyma and sclerenchyma.

Parenchyma: this tissue constitutes the Pith(packaging tissue in the centre of the stem) and the ground tissue. Parenchyma consists of thin-walled living cells which in turn have: a large central vacuole, intercellular spaces and often plays the role of storage(of air, water and food). There are different subdivisions of parenchyma depending on its specialized function in the plant(such as aerenchyma, which gives rise to buoyancy).

Sclerenchyma: this tissue provides strength and support to the plant. It contains elongated lignified, tightly packed , non-living cells. Due to its hard/thick cell wall, it is mainly considered to be a waterproof mechanical tissue. It is found under the epidermis and around vascular bundles.

Collenchyma: this tissue comprises of elongated cells with minute intercellular gaps, containing uneven cell walls made of pectin and hemi-cellulose. These offer mechanical support and flexibility, mostly in young plants.