Aim Of The Experiment
To study the different tissues and diversity in sizes and shapes of animal and plant cells such as guard cells, palisade cells, parenchyma, sclerenchyma, collenchyma, phloem, xylem, squamous epithelium, mammalian blood smear and muscle fibres through the preparation of permanent/temporary slides.
Theory
What is a tissue?
A tissue is a cluster of cells that perform a shared function that is similar in size and shape. Tissues can be grouped as follows:
- Simple tissue – They contain one type of cells only. Furthermore, they can be classified into:
- Parenchyma
- Collenchyma
- Sclerenchyma
- Complex tissue – They possess more than one cell type
- Meristematic tissue
- Permanent tissue
Cells of various types of tissues vary in their size, structure, shape, wall composition and function.
Related Link: The Plant Tissue System
Requirements
A. Permanent Slides of:
- T.S of Nerium Leaf, T.S of Lotus leaf, T.S of Lotus stem/petiole
- V.S of root apex and shoot apex
- T.S of Mentha/Cucurbita stem
- Macerated material of Tridax, Vitis/Bougainvillea
B. Requirements for Maceration Technique
- Tiny twigs of locally accessible plants
- Safranin
- Glycerine
- Beaker(100ml)/Boiling test tube
- Cotton blue
- Slides
- Glass rod
- Needles
- Tripod stand
- Burner
- Wire gauge
- Microscope
- Knife (sharp-edged)
- Thread
- Cheese/muslin cloth
Maceration Fluid
- Chromic acid should be dissolved with an equal quantity of 10% nitric acid
- Preparation of chromic acid is done by adding 100ml of concentrated H2SO4 gradually in 10ml of water
- Now add K2Cr2O7 (potassium dichromate) – 50gm
- The stock solution is ready. 10ml of this solution is diluted up to 100ml for the preparation of the working solution of the maceration liquid.
Procedure
- Pick some fresh green younger branches from a locally accessible woody plant—thickness – that of a toothpick.
- Snip the twigs into smaller bits of 0.5 cm long
- Shift the pieces to a beaker holding water. Boil it for 10-15minutes until the sample settles at the base
- This way the air inside the sample is removed
- Shift the material into a beaker holding the maceration fluid. Bring it to a boil until it turns pulpy and soft for close to 10-15 minutes.
- The muslin cloths to the beaker’s mouth. With tap water, rinse the material continuously to eliminate the traces from the maceration fluid.
- Add some drops of safranin to the material to stain the xylem or for phloem – cotton blue.
- Onto a glass slide, place the stained material in a drop of glycerine.
- Split the cells using two needles
- Plant a cover slip onto the slide and observe under a microscope
- Sketch your observation. Compare with the diagram given
Analyse the following slides:
- For spongy and palisade tissue – T.S of Nerium Leaf
- For Aerenchyma – T.S of Lotus petiole. Lotus leaf
- For meristem – V.S of root and shoot apex
- For simple tissues – T.S of Mentha stem or Cucurbita
Observations
- Chlorenchyma is parenchyma cells comprising chloroplasts. They may have spongy or loosely arranged cells or palisade – columnar cells compactly aligned.
- It is aerenchyma if there is a presence of large intercellular spaces into the cells.
- The protective tissue or the epidermis is the parenchyma tissue forming the outer covering of leaves, stem or root.
Differences between different types of simple tissues:
| Properties | Parenchyma | Schlerenchyma | Collenchyma |
| Cell wall | Thin, presence of primary wall only. | Thick | At the corners, thick primary wall |
| Cell arrangement | Arranged loosely | Compactly arranged | Compactly arranged |
| Nature of cells | Living. Presence of nucleus | Cells are dead. Absence of cellular contents | Living. Nucleus observed |
| Shape | Oval, polygonal, spherical, rod-shaped or rectangular | Elongated | Variable shape |
| Intercellular Space | Many | Absent | Absent |
| Vacuoles | Vacuolated cells | Absent | Absent |
- Section of the leaf needs to be observed.
- Mesophyll of the leaf is covered by lower and upper epidermis.
- Lower epidermis exhibits small pores known as stomata. In some plants, both the lower and upper epidermis of the leaf show stomata.
- Tissues are observed for their characteristics, position in the different parts of the material of the plant.
- Sketch diagrams to display the tissue type and their locations.
Viva Questions
Q.1. Why does aerenchyma have large air spaces?
A.1. It is because they promote gas circulation through large air spaces and render buoyancy.
Q.2. Name a plant type where aerenchyma cells are found.
A.2. In aquatic plants. Example: Hydrilla.
Q.3. Write about the constituency of the sclerenchyma cell wall.
A.3. They have thick cell walls containing lignin with high levels of cellulose content.
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See Also