Stomata: An Introduction
Stomata are the elliptical openings on leaves, guarded by two cells, which when swollen with water allow stomata to open and when flaccid allow stomata to close. The guard cells of the stomata possess large vacuoles, chloroplast, and nucleus. Stomata help the plant to take in carbon dioxide needed for photosynthesis. They look like tiny mouths opening and closing as they help in transpiration.
The bigger/wider the leaf, the greater the rate of transpiration as more surface means more stomata will be present. Plants possessing smaller stomata have lower levels of evaporation and survive harsh conditions better. All green plants are termed as producers as they produce their own food from solar energy, and carry out the vital processes of photosynthesis and respiration where gaseous exchange between the tissue of plants and the atmosphere is an essential component of the whole ecosystem. This is carried out through the tiny openings known as stomata.
Types of Stomata
A plant survives better with faster growth if it possesses a higher number of stomata and a wet climate. The lower the number of stomata, the lower the rate of photosynthesis, and a drier climate is not ideal for plant growth.
There are four types of stomata:
Moss Type: These are found in certain mosses.
Gymnospermous: These are naked seed plants deeply sunken to reduce water loss during transpiration.
Coniferous: Sunken stomata and the guard cells are elliptical.
Gramineous: These are found in grade families, two guard cells and two subsidiary cells are present too.
On the basis of arrangement, the types of stomata are:
Anomocytic Stomata - This type of stomata is embedded in the epidermal cells having fixed shape and size where there is no fixed number of cells surrounding the stomata.
Anisocytic Stomata - In this arrangement, three subsidiary unequal cells are surrounding the stomata.
Paracytic Stomata - Here the stomatal pore and guard cells surround the stomata.
Diacytic Stomata - It is surrounded by subsidiary cells lying perpendicular to the guard cells.
Gramineous Stomata - Stomata has two dumbbell shaped guard cells and subsidiary cells which lie parallel to guard cells.
Coniferous Stomata - It is found on the surface of the leaves of gymnosperm plants and is found below the leaf surface.
Experimental Setup
Materials Required:
To prepare a temporary mount of a leaf peel to show stomata, we need to follow the correct method of arrangement. We need some essential equipment such as needles, forceps, watch glass, dropper, slides, coverslip, blotting paper, safranin, glycerine, and a compound microscope.
Procedure:
First and foremost, fold a leaf to pull apart and take the peel off the leaf from the lower surface. Peeling the leaf with a blade requires patience and dexterity. We must immediately dip the transparent peel off the leaf in water kept in watch glass to avoid shrinkage and crumpling. Let it remain in the water for a while and in the watch glass, add a few drops of glycerine so that the peel remains hydrated.
Let it rest, then add a few drops of safranin which are red in colour through a dropper. Now we take out the peel with the help of forceps and put it gently on the glass slide. We blot away the excess glycerin and safranin with blotting paper. On examination, under a compound microscope, we clearly observe the epidermal cells containing stomata on the lower surface of the leaf.
Experimental Observations
The epidermal cells are seen in an irregular manner with no intracellular space between them. Stomata and guard cells both are observed clearly on the surface. Guard cells possess a nucleus and chloroplasts too. They possess a thin outer and thick inner cover. The number of stomata is less compared to those found on the lower surface of the leaf. The reason behind this is to prevent excessive loss of water through evaporation which happens because of exposure to direct sunlight.
Leaf Observed Under Microscope
Interesting Fact
An interesting fact is that the stomata are studied during research if a plant has undergone any kind of stress due to excessive heat, drought, or any kind of harsh conditions.
Important Questions
1. What are light induced stomatal responses?
Ans: Light induced stomatal responses were first reported by Darwin (1989). Stomata open up in response to light that includes blue and red light. Red light makes it possible for stomata to open by photosynthesis in the guard cell chloroplasts. Blue light brings about stomatal opening. Phototropins in the guard cell act as receptors for blue light and opening of stomata.
2. Which hormone is responsible for stomatal colour?
Ans: The hormone which is responsible for the colour of stomata is abscisic acid. It is a plant hormone largely involved in the growth and development of the plant.
Key Features of Preparing a Temporary Mount of a Leaf Peel to Show Stomata
The peel should be cut to a proper size and kept hydrated with glycerine
A few drops of safranin help in magnifying the stomata and guard cells with ease.
A coverslip should be placed in such a manner as to avoid air bubbles.
Stomata are better seen on the lower surface of a dicot leaf
FAQs on Preparing a Temporary Mount of a Leaf Peel to Show Stomata
1. What is the first step in preparing a temporary mount of a leaf peel?
The first and most crucial step is to obtain a thin, transparent layer, known as the epidermis or leaf peel. This is usually done by folding a fresh leaf and gently tearing it. A thin, colourless membrane can then be carefully pulled off from the torn edge using forceps.
2. Why is glycerine used when mounting a leaf peel on a slide?
A drop of glycerine is added to the slide for two main reasons. First, it prevents the delicate leaf peel from drying out and shrivelling under the microscope's light. Second, it is a hydrating agent that helps in getting a clearer and more focused view of the cells.
3. What kind of leaf is best for observing stomata in this experiment?
For a clear observation of stomata, it's best to use a fresh, healthy leaf that has a thin epidermis which is easy to peel. Leaves from plants like lily or tradescantia are excellent choices. Generally, the lower surface of a dicot leaf (like a sunflower leaf) will show a higher number of stomata.
4. What do stomata and the surrounding cells look like under a microscope?
Under a microscope, you will see a layer of flat, irregularly shaped cells called epidermal cells. Scattered among them are tiny pores, which are the stomata. Each stoma is enclosed by two bean-shaped cells known as guard cells, which regulate its opening and closing.
5. Why is a stain like safranin often used when preparing the leaf peel?
Plant cells are mostly transparent, which makes them hard to see distinctly under a microscope. A stain like safranin is used to add colour to different parts of the cells. This makes the cell nucleus and cell walls more visible, causing the guard cells and stomata to stand out clearly.
6. What happens if the leaf peel used for the slide is too thick?
If the leaf peel is too thick, light from the microscope cannot pass through it effectively. This results in a dark and blurry image where you cannot distinguish individual cells. For a successful observation, it's essential to have a single, transparent layer of epidermal cells.
7. What is the main purpose of observing stomata through this experiment?
The main purpose is to visually understand the structure and importance of stomata. Seeing them firsthand helps connect theory to practice. This experiment demonstrates how plants are adapted for essential life processes, such as:
- Regulating gas exchange for photosynthesis.
- Controlling water loss through transpiration.
8. What are some common mistakes to avoid while preparing the slide?
Besides letting the peel dry out, other common mistakes to avoid for a clear view include:
- Air bubbles: These get trapped when the coverslip is placed flat. Lower the coverslip gently at an angle with a needle to prevent them.
- Folded peel: Ensure the leaf peel is laid flat in the drop of glycerine, not folded over itself.
- Excess stain: Using too much stain can make the entire view too dark to see any details.
