what are the functions of guard cells in the leaves

Guard cells help in the regulation of the opening and closing of stomata for exchange of gases and loss of water from the surface of the leaves.

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The function of the guard cells are that they help to regulate the rate of transpiration by opening and closing the stomata, thus preventing excessive water loss. 

Another function of guard cells is that they help to regulate the rate of transpiration by opening and closing the stomata. The guard cell opens when there is too much water. It is also adapted for gaseous exchange between plants and the environment. 
For example, it opens during rainy days and closes when the weather is too dry or windy. 
They also control the size of the pore.

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The job of guard cells is to open and close the stomata.
Stomata are the pores found on the leaves of plants. Their function is to allow carbon dioxide to enter the leaf (for photosunthesis) and oxygen (made by photosynthesis) to leave the leaf.
Usually stomata open during the day and close at night. This is to save water, since water vapour can escape as long as the stomata are open.
The guard cells control the size of the stomatal pore by changing their shape. When they are curved, a gap opens up between them. When they straighten (lose their curved shape) the gap is closed.
The change in shape is caused by water either entering the guard cells (to open the stomata) or leaving the guard cells (to close the stomata).

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  Guard cells are specialized cells located in the leaf epidermis of plants. Pairs of guard cells surround tiny stomatal airway pores (Figure 1). These tiny holes in the surface of leaves are necessary for gas exchange into and out of the plant; carbon dioxide (CO2) enters the plant allowing the carbon fixation reactions of photosynthesis to occur. Oxygen (O2) exits the plant as a byproduct of photosynthesis. The opening and closing of the stomatal gas exchange holes is regulated by swelling and shrinking of the two surrounding guard cells (Figure 1). Due to the presence of the stomatal pores on plant leaf surfaces, water evaporates through the stomatal openings causing plants to lose water. Over 95% of water loss from plants can occur by evaporation (transpiration) through the stomatal pores. Therefore, it is important for plants to be able to balance the amount of CO2 being brought into the plant with the amount of water escaping as a result of the open stomatal pores. Hence, the guard cells are the gate keepers of the plants ability to take in CO2 from the atmosphere for photosynthesis – while regulating how much water plants lose to the atmosphere.[1][2][3][4]Opening and closure of the stomatal pore (Figure 1) is mediated by changes in the turgor pressure of the two guard cells. The turgor pressure of guard cells is controlled by movements of large quantities of ions and sugars into and out of the guard cells. When guard cells take up these solutes, the water potential (Ψ) inside the cells decreases, causing osmotic water flow into the guard cells. This leads to a turgor pressure increase causing swelling of the guard cells and the stomatal pores open (Figure 2). The ions that are taken up by guard cells are mainly potassium (K+) ions[5][6][7] and chloride (Cl-) ions.[8] In addition guard cells take up sugars that also contribute to opening of the stomatal pores. diagram of signals affecting stomatal aperture

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The job of guard cells is to open and close the stomata. Guard cells are specialized cells located in the leaf epidermis of plants.

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very good yarath . where are u from

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 Leaves have tiny pores on their surface called stomata.The opening and closing of the stomata are controlled by guard cells.Leaves take in carbon dioxide through them.

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Guard cells are specialized cells located in the leaf epidermis of plants. Pairs of guard cells surround tiny stomatal airway pores (Figure 1). These tiny holes in the surface of leaves are necessary for gas exchange into and out of the plant; carbon dioxide (CO2) enters the plant allowing the carbon fixation reactions of photosynthesis to occur. Oxygen (O2) exits the plant as a byproduct of photosynthesis. The opening and closing of the stomatal gas exchange holes is regulated by swelling and shrinking of the two surrounding guard cells (Figure 1). Due to the presence of the stomatal pores on plant leaf surfaces, water evaporates through the stomatal openings causing plants to lose water. Over 95% of water loss from plants can occur by evaporation (transpiration) through the stomatal pores. Therefore, it is important for plants to be able to balance the amount of CO2 being brought into the plant with the amount of water escaping as a result of the open stomatal pores. Hence, the guard cells are the gate keepers of the plants ability to take in CO2 from the atmosphere for photosynthesis – while regulating how much water plants lose to the atmosphere.[1][2][3][4] Opening and closure of the stomatal pore (Figure 1) is mediated by changes in the turgor pressure of the two guard cells. The turgor pressure of guard cells is controlled by movements of large quantities of ions and sugars into and out of the guard cells. When guard cells take up these solutes, the water potential (Ψ) inside the cells decreases, causing osmotic water flow into the guard cells. This leads to a turgor pressure increase causing swelling of the guard cells and the stomatal pores open (Figure 2). The ions that are taken up by guard cells are mainly potassium (K+) ions[5][6][7] and chloride (Cl-) ions.[8] In addition guard cells take up sugars that also contribute to opening of the stomatal pores.  diagram of signals affecting stomatal aperture

Figure 1. A stomatal p pore in the surface (epidermis) of a leaf as viewed through a microscope. The central stomatal pore is formed by a pair of guard cells. The stomatal pore can either open (left) or close (right) depending on the environmental conditions.

Ion uptake and release

diagram of ion channels controlling stomatal aperture
Figure 2. Ion channels and pumps regulating stomatal opening and closure.

Ion uptake into guard cells causes stomatal opening: The opening of gas exchange pores requires the uptake of potassium ions into guard cells. Potassium channels and pumps have been identified and shown to function in the uptake of ions and opening of stomatal apertures (Figure 2).[7][9][10][11][12][13][14][15] Ion release from guard cells causes stomatal pore closing: Other ion channels have been identified that mediate release of ions from guard cells, which results in osmotic water efflux from guard cells due to osmosis, shrinking of the guard cells, and closing of stomatal pores (Figures 1 and 2). Specialized potassium efflux channels participate in mediating release of potassium from guard cells.[11][16][17][18][19] Anion channels were identified as important controllers of stomatal closing.[20][21][22][23][24][25][26] Anion channels have several major functions in controlling stomatal closing:[21] (a) They allow release of anions, such as chloride and malate from guard cells, which is needed for stomatal closing. (b) Anion channels are activated by signals that cause stomatal closing, for example by intracellular calcium and ABA.[21][24][27] The resulting release of negatively charged anions from guard cells results in an electrical shift of the membrane to more positive voltages (depolarization) at the intracellular surface of the guard cell plasma membrane. This electrical depolarization of guard cells leads to activation of the outward potassium channels and the release of potassium through these channels (Figure 2). At least two major types of anion channels have been characterized in the plasma membrane: S-type anion channels and R-type anion channels.[20][21][23][28]

[edit] Vacuolar ion transport

Vacuoles are large intracellular storage organelles in plants cells. In addition to the ion channels in the plasma membrane, vacuolar ion channels have important functions in regulation of stomatal opening and closure because vacuoles can occupy up to 90% of guard cell’s volume. Therefore, a majority of ions are released from vacuoles when stomata are closed.[29] Vacuolar K+ (VK) channels and fast vacuolar channels can mediate K+ release from vacuoles.[30][31][32] Vacuolar K+ (VK) channels are activated by elevation in the intracellular calcium concentration.[30] Another type of calcium-activated channel, is the slow vacuolar (SV) channel.[33] SV channels have been shown to function as cation channels that are permeable to Ca2+ ions,[30] but their exact functions are not yet known in plants.[34]

[edit] Signal transduction

Guard cells perceive and process environmental and endogenous stimuli such as light, humidity, CO2, temperature, drought, and plant hormones to trigger cellular responses resulting in stomatal opening or closure. These signal transduction pathways determine for example how quickly a plant will lose water during a drought period. Guard cells have become a model for single cell signaling. Using Arabidopsis thaliana, the investigation of signal processing in single guard cells has become open to the power of genetics.[24] Cytosolic and nuclear proteins and chemical messengers that function in stomatal movements have been identified that mediate the transduction of environmental signals thus controlling CO2 intake into plants and plant water loss.[1][2][3][4] Research on guard cell signal transduction mechanisms is producing an understanding of how plants can improve their response to drought stress by reducing plant water loss.[1][35][36] Guard cells also provide an excellent model for basic studies on how a cell integrates numerous kinds of input signals to produce a response (stomatal opening or closing). These responses require coordination of numerous cell biological processes in guard cells, including signal reception, ion channel and pump regulation, membrane trafficking, transcription, cytoskeletal rearrangements and more. A challenge for future research is to assign the functions of some of the identified proteins to these diverse cell biological processes.

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 guard cells are present around every single cell in the leaf. They regulate the opening and closing of the stomata, according to its need.

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the function of the guard cells is to control the opening and closing of the cells.

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the function of guard cells is to protect the leaves by guards

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they will protect the stomatal openings

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They control opening and closing of the stomata.   up please...

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They control opening and closing of the stomata.   up please.

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guard cells regulate the closing and opening of stomata.......when over or extra water flows into the stomata,the guard cell closes and does not lets the water go into it... it is like a ring around the stomata...

hope it helps u!!!!!keep smiling

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 The function of the guard cells are that they help to regulate the rate of transpiration by opening and closing the stomata, thus preventing excessive water loss.

Another function of guard cells is that they help to regulate the rate of transpiration by opening and closing the stomata. The guard cell opens when there is too much water. It is also adapted for gaseous exchange between plants and the environment.
For example, it opens during rainy days and closes when the weather is too dry or windy.
They also control the size of the pore.

please thumbs up.

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