What is the mechanism for opening and closing stomata?
The opening and closing of stomata in leaves occurs due to turgor events in guard cells. The movement of water from the epidermal cells into the guard cells causes turgor to increase in the guard cells and causes elastic stracking on the guard cell walls. With the development of these two guard cells, this results in the closing of the stomata. However, if the turgor pressure is low, the stomata will open again. This means that the opening and closing of the stomata is determined by the turgor that occurs in the guard cell.
Photosynthetic light in mesophyl cells, reduced CO2 in the intercellular space, raises the pH in the guard cells, enzymatic changes to sugars, raises sugar levels, raises the osmotic pressure of cell sap, increases stomatal turgor, opens (Pandey and Sinha, 1983). Affecting Transpiration.
Explain the factors that affect the movement of stomata in plant metabolism?
As discussed earlier, light causes the stoma to open and darkness causes the stoma to close, so a lot of light also increases transpiration. Since these rays also contain heat (especially infrared rays), more light also adds heat, thereby increasing the temperature. An increase in temperature to a certain extent causes the stoma to widen and thus increases transpiration
We formulate that the temperature of the leaf and its surroundings is the same. In fact, leaves exposed to direct sunlight have a temperature several degrees higher than the surrounding air, and therefore light affects transpiration not only through controlling the opening and closing of stomata but also through a secondary effect on leaf temperature.
Tjitrosomo (1990) formulated that light affects the rate of transpiration in two ways as follows:
a. A leaf exposed to direct sunlight will absorb radiant energy. Only a small part of this energy is used in photosynthesis. Such heating increases transpiration, as leaf temperature is usually the most important factor influencing the rate of this process. The fact that leaves exposed to sunlight have a higher temperature than air temperature allows for fast transpiration rates, even in saturated air.
b. Light does not always have to be in the form of direct light, it can also affect transpiration through its effect on the opening and closing of stomata.
It is the most important environmental factor that affects the transpiration of leaves that are in a state of turgor. The temperature of the leaves in the shade is approximately the same as the air temperature, but the leaves exposed to the sun have a temperature of 10 -20o F higher than the air temperature.
The effect of temperature on leaf transpiration can also be viewed from another angle, namely in relation to the water vapor pressure inside the leaf and the water vapor pressure outside the leaf. The increase in temperature increases the vapor pressure inside the leaf. The increase in temperature of course also increases the vapor pressure outside the leaf, but since the air outside the leaf is not in a confined space, the vapor pressure will not be as high as the vapor pressure confined inside the leaf. As a result of this pressure difference, water vapor will easily diffuse from inside the leaves into the free air
3. Air humidity (Air humidity)
On a sunny day the air does not contain much water vapor. In such a state, the vapor pressure inside the leaf is much higher than the vapor pressure outside the leaf, or in other words, the space inside the leaf is more filled with water vapor than the air outside the leaf, so the water molecules diffuses from a high concentration (inside the leaf) to a low concentration (outside the leaf. The conclusion is, wet air inhibits transpiration, while dry air promotes transpiration
Under natural conditions, air always contains water vapor, usually in concentrations between 1 and 3 percent. Some of these water molecules move into the leaf through the stomata by the reverse process of transpiration. The rate of movement of the entry of water vapor molecules is proportional to the concentration of water vapor in the air, namely humidity. The movement of water vapor from the air into the leaves reduces the net rate of water loss. Thus, if the other factors are the same, transpiration will decrease with increasing air humidity
In general, the wind is moderate, increasing the activity of transpiration. Because the wind moves the water vapor that accumulates near the stoma. Thus, the steam that is still in the leaf then gets a chance to diffuse outward
Wind has a dual effect that tends to contradict each other on the rate of transpiration. In short it can be concluded that wind tends to increase the rate of transpiration, either in shade or light, through the sweep of water vapor. However, in sunlight, the effect of wind on lowering leaf temperature, and thus lowering transpiration rate, tends to be more important than its effect on moisture removal.
In very still air a thin layer of saturated air forms around the leaf surface which is more actively transpiration. If the air as a whole is not saturated, then there will be a gradation of the concentration of water vapor from the saturated air layer to the air which is getting further and more unsaturated. Under such conditions transpiration stops because the saturated air layer acts as a barrier to the diffusion of water vapor into the air around the leaf surface. Therefore, in still air there are two resistances that water vapor must overcome in order to diffuse from the intercellular spaces into the outside air. The first is the resistance that must be passed in the stomata holes, and the second is the resistance that exists in the saturated air layer adjacent to the leaf surface. Therefore, in moving air, the size of the stomatal opening has a greater influence on transpiration than in still air. However, the effect of wind is actually more complex than described above because its tendency to increase the rate of transpiration to some extent is confused by the tendency to cool the leaves thereby reducing the rate of transpiration. But the overall effect of the wind is always to increase transpiration
5. The state of water in the soil
Water in the soil is the only essential source, from which plant roots get the water they need. Absorption of water through other parts above the soil such as stems and leaves is also present, but the absorption of water through these parts is nothing compared to the absorption of water through the roots.
The availability of water in the soil is another environmental factor that affects the rate of transpiration. When groundwater conditions are such that the supply of water to the mesophyll cells is inhibited, a decrease in the rate of transpiration will immediately appear
Transpiration rate can be influenced by soil water content and the rate of water absorption from roots. During the day, water is usually transpired at a faster rate than it is absorbed from the soil. This causes a water deficit in the leaves. At night the opposite condition will occur, because the air temperature and leaf temperature are lower. If the water content of the soil decreases, as a result of absorption by the roots, the movement of water through the soil into the roots becomes slower
Name the parts of stomata and give a brief explanation?
Stomata Sections and their explanations
Stomata are small oval-shaped holes surrounded by two special epidermal cells called guard cells, where the guard cells are epidermal cells that have undergone changes in shape and function to shape the size of the holes between them.
Stomata are generally found on the green parts of plants, especially the leaves of plants. In plants that live below the surface of the water there are tools that are similar in structure to stomata, even though these tools are not stomata. In green leaves, stomata are present on only one surface.
Stomata can be divided into several parts, including:
Guard cell part
The part that is the neighboring cell
Inner air chamber
The guard cells consist of a pair of cells that look symmetrical, generally kidney-shaped, there are upper and lower cell walls, ladges are visible, sometimes the ledge is only found on the upper cell wall.
The function of the banister is as a barrier to the front cavity above the porus. While the rear room divider (Basic Cavity) is located between the pores and the air space below. The uniqueness of guard cells is that the fine cellulose microfibrils in their cell walls are arranged around the guard cells, this arrangement pattern is known as radial micellation.
Because these cellulose fibers are relatively inelastic, if the guard cells absorb water, these cells cannot increase in diameter but lengthen. As a result of the attachment of the guard cells to each other at both ends, they will bend outward. This event causes the stomata to open.
The process of stomata in absorbing Carbon Dioxide and releasing Oxygen into the air by means of the stoma taking CO2 from the air to be used as photosynthetic material, releasing O2 as a result of photosynthesis. The stoma (plural: stomata) is like the human nose where the stoma takes CO2 from the air and releases O2, while the nose takes in O2 and expels CO2. The stoma is located in the lower epidermis. In addition to the stoma, certain plants also breathe through lenticels located on their stems.
The end products of photosynthesis are simple sugars. These compounds need to be converted into other more complex sugars (eg sucrose) before being transported because they are easy to react. Through the phloem, sucrose is transported to non-photosynthesizing leaf cells to stem cells and root cells for the purposes of the plant itself. The remaining sucrose is converted into sugars, proteins and lipids as food reserves. Food reserves are mainly stored in roots and stems, but some are stored in leaves.
Another result of photosynthesis is oxygen which is released into the environment through stomata which is used by other living things to breathe.
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