The aim of my particular experiment was to investigate into the possible existence of distribution of stomata within different leaf types.

Authors Avatar

Aim

The aim of my particular experiment was to investigate into the possible existence of distribution of stomata within different leaf types. My investigation also requires me to research into the rate of transpiration into the different leaf types and if this has an effect of the distribution of stomata on the leaves surface.

Prediction

I predict that the environment of which I found my particular leaf type had an effect on the stomata distribution in my particular leaf type. From the background knowledge I predict that those plants grown in a dryer environment and thus must adapt to such climate and within this situation they will have less stomata on there leaves thus giving less transpiration from the leaves. The leaves that I obtained from a dryer environment may have up to less than 150 stomata per 2mm of leave surface where those in a moist living area have more than 500 stomata per 2 mm.
         My prediction also includes that most of the stomata will be found on the lower epidermis of a leaf. I have based this prediction on the function of stomata; to let gases in and out of the leaf i.e. to allow exchange of CO2 and O2 between the inside of the leaf and the surrounding atmosphere and to allow the escape of water vapour from the leaf.
To reduce water loss the leaf has a waxy cuticle on the upper epidermis, which is waterproof, so the leaf uses the lower epidermis for gas exchange. With such a prediction I would need to carry out the background research on each particular leaf type chosen to research.

Background Knowledge

Dermal tissue is a kind of complex tissue consisting both of flattened cells covering the upper and lower surfaces of the leaf and of specialized cells calledGuard cells regulate gas exchange between the environment and the interior of the leaf by controlling the size of the stomata, openings through which gas exchange takes place. The upper and lower layers of dermal tissues are respectively called the upper and lower epidermis. The epidermises serve both to protect the plant and for water conservation as the outer surface of the epidermal cells are covered with a waxy waterproof cuticle.

Guard cells within any plant cell:

The guard cells are specialized dermal cells that regulate the size of the openings or stomata in the epidermis of the leaf. Each stoma is surrounded by two guard cells that either take up or release water to the surround cells. Picture:

When the guard cells release water to the surrounding epidermal cells, the guard cells become flaccid which causes the two cells to close off the stoma. This prevents water loss from the leaf. Conversely, when the guard cells take up water from the surrounding cells, the guard cells swell (become turgid) which causes then to bow out, opening the stoma. This allows gas exchange and an increase in water loss from the leaf, transpiration.

Water is not directly pumped into or out of the guard cells. Instead, the guard cells actively transport potassium ions and the water follows by osmosis.

Guard cells can emit water into three different directions; outwards, into the neighboring subsidiary cell, and into the respiratory cavity that is a part of the intercellular system lying beneath the guard cells.

An equilibrium between the water vapour of the atmosphere and the respiratory cavity results when the stomata are opened. Plants form an intermediate distributor, since a large difference in water potential between the moist soil and the normally dry atmosphere is very common. They close when too much water is lost, or when not enough supply exists. The osmotic pressure of the stomata is far larger in the guard cells than in the subsidiary cells. This ratio shifts in favor of the subsidiary cells when the stomata are closed.

When the guard cells close their stomata, this conserves water, something which is important when water is in short supply, but this also means that carbon dioxide cannot be taken up by the leaf for photosynthesis and excess oxygen produced by photosynthesis removed.

If the plant is to obtain sufficient carbon dioxide for photosynthesis it is necessary that the stomata are open, however, in being open, water can be lost through these same stomata by evaporation. It is this evaporation, known as transpiration, which is the driving force for pulling water through a plant. In most broad leaved plants, a greater number of stomata are found on the cooler, lower surface. This ensures that sufficient carbon dioxide can enter while at the same time cutting down the amount of water lost by transpiration.

In this scenario water-uptake can also be preceded by an uptake of potassium ions. These potassium ions are  (by a potassium pump) from the subsidiary cells into the vacuoles of the guard cells. At the same time, anions (chloride, malate) accumulate within the vacuoles. Protons are given off to the subsidiary cells. The ion flows are quantitatively enough to explain a rise of the turgor that is large enough for the guard cell movements.

A fungal toxin can activate the potassium pump. If consequently the toxin is applied to the stomata, then the loss of water becomes higher than its supply resulting in withering.

Water movement through a plant

As transpiration takes place, water diffusing into the air spaces from the spongy mesophyll cells takes its place. This is turn sets up a concentration gradient across which water moves by osmosis out of the xylem cells and across the leaf. A similar concentration gradient occurs between the xylem and palisade layer so that water will also move by osmosis to the palisade cells in order that it can be used by these cells in the food manufacturing process of photosynthesis.

Join now!

In most plants about 98% of the water taken in by the roots is transpired from the leaves' surfaces. To give some idea of the magnitude of water movement, it has been calculated that during the day a 15 meter high Silver Maple (Acer saccharinum) can lose up to 220 liters of water per hour through transpiration.

Carbon Dioxide & Light:

Plants contain specialized structures within the epidermis of their leaves which allow for the uptake of carbon dioxide (used as the carbon source for photosynthesis) and the release of water. These structures are composed of openings, known as stomata’s, and guard ...

This is a preview of the whole essay