What two conditions does the closing of the stomata help to prevent?

What two conditions does the closing of the stomata help to prevent?

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I was given the following question:

What two conditions does the closing of the stomata help to prevent?

I know that one of them is transpiration, but multiple searches on google could not yield another result…

This paper gives 3 reasons stomata close:

  1. Prevent Desiccation
  2. Prevent Infection
  3. Response to Cold Stress

If I had to guess, I think your question is asking about the #1 and #2. They are the more well known examples and are much easier to explain. In addition, #1 and #3 serve the same purpose; regulating transpiration.

Stomata also open and close based on available sunlight. However, different plants have opposite responses to sunlight. This is also another aspect of how stomata regulate transpiration.

I think your question, as the the homework you were assigned and not your post, is worded a little strangely. Stomata close primarily as a preventative measure, so describing it as being caused by a condition is a little awkward. I doubt your teacher will grade you too harshly if your answer does not reference the current condition of the plant.

Figure 5.7 On a hot, dry day, plants close their stomata to conserve Water. What impact will this have on photosynthesis?

Figure 5.7 On a hot, dry day, plants close their stomata to conserve Water. What impact will this have on photosynthesis?

Description of the impact of the closing of stomata on photosynthesis during hot dry condition.


Stomata are the small opening that exists in the membranes of the plants through which exchange of gas and water takes place. Stomata play an important role in the intake and transpiration of the CO2 which is significant for the process of photosynthesis.

Explanation of Solution

During hot dry conditions, the stomata close its opening to conserve water. The humidity around the leaves is affected by the temperature of the air around it. If the temperature of the air is higher, the water from the leaves will diffuse more into the air. But it is noted that the leaf has a waxy cuticle blocking the water loss whereas carbon dioxide and oxygen exchange with the environment is required for photosynthesis.

There are specialized epidermal cells around the stomata known as guard cells. These guard cells swell up when there is enough water in the cells opening the stomata. But in case the water is less, these guard cells don't swell and hence the stomata remain closed so that the plant does not lose water. If the stomata are closed, then there is no photosynthesis and the plant will starve.

During the hot dry season, as there is not enough water in the cells, the guard cells do not swell keeping the stomata closed. As result, photosynthesis does not take place and eventually cause starvation of the plant.

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Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata. Light is the main trigger for the opening or closing. Each guard cell has a relatively thick cuticle on the pore-side and a thin one opposite it. As water enters the cell, the thin side bulges outward like a balloon and draws the thick side along with it, forming a crescent the combined crescents form the opening of the pore.

Guard cells contain phototropin proteins which are serine and threonine kinases with blue-light photoreceptor activity. Phototrophins contain two light, oxygen, and voltage sensor (LOV) domains, and are part of the PAS domain superfamily. [5] The phototropins trigger many responses such as phototropism, chloroplast movement and leaf expansion as well as stomatal opening. [5] Not much was known about how these photoreceptors worked prior to around 1998. The mechanism by which phototropins work was elucidated through experiments with broad bean (Vicia faba). Immunodetection and far-western blotting showed blue light excites phototropin 1 and phototropin 2, causing protein phosphatase 1 to begin a phosphorylation cascade, which activates H + -ATPase, a pump responsible for pumping H + ions out of the cell. [6] The phosphorylated H + -ATPase allows the binding of a 14-3-3 protein to an autoinhibitory domain of the H + -ATPase at the C terminus. [7] Serine and threonine are then phosphorylated within the protein, which induces H + -ATPase activity. [5] The same experiment also found that upon phosphorylation, a 14-3-3 protein was bound to the phototropins before the H + -ATPase had been phosphorylated. [5] In a similar experiment they concluded that the binding of 14-3-3 protein to the phosphorylation site is essential for the activation of plasma membrane H + -ATPase activity. [7] This was done by adding phosphopeptides such as P-950, which inhibits the binding of 14-3-3 protein, to phosphorylated H + -ATPase and observing the amino acid sequence. As protons are being pumped out, a negative electrical potential was formed across the plasma membrane. This hyperpolarization of the membrane allowed the accumulation of charged potassium (K + ) ions and chloride (Cl − ) ions, which in turn, increases the solute concentration causing the water potential to decrease. The negative water potential allows for osmosis to occur in the guard cell, so that water entered, allowing the cell to become turgid.

Opening and closure of the stomatal pore 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. Guard cells have cell walls of varying thickness(its inner region, adjacent to the stomatal pore is thicker and highly cutinized [8] ) and differently oriented cellulose microfibers, causing them to bend outward when they are turgid, which in turn, causes stomata to open. Stomata close when there is an osmotic loss of water, occurring from the loss of K + to neighboring cells, mainly potassium (K + ) ions [9] [10] [11]

Water stress (drought and salt stress) is one of the major environmental problems causing severe losses in agriculture and in nature. Drought tolerance of plants is mediated by several mechanisms that work together, including stabilizing and protecting the plant from damage caused by desiccation and also controlling how much water plants lose through the stomatal pores during drought. A plant hormone, abscisic acid (ABA), is produced in response to drought. A major type of ABA receptor has been identified. [12] [13] The plant hormone ABA causes the stomatal pores to close in response to drought, which reduces plant water loss via transpiration to the atmosphere and allows plants to avoid or slow down water loss during droughts. The use of drought-tolerant crop plants would lead to a reduction in crop losses during droughts. [ citation needed ] Since guard cells control water loss of plants, the investigation on how stomatal opening and closure is regulated could lead to the development of plants with improved avoidance or slowing of desiccation and better water use efficiency. [1] Research done Jean-Pierre Rona shows that ABA is the trigger for the closure of the stomatal opening. To trigger this it activates the release of anions and potassium ions. This influx in anions causes a depolarization of the plasma membrane. This depolarization triggers potassium plus ions in the cell to leave the cell due to the unbalance in the membrane potential. This sudden change in ion concentrations causes the guard cell to shrink which causes the stomata to close which in turn decreases the amount of water lost. All this is a chain reaction according to his research. The increase in ABA causes there to be an increase in calcium ion concentration. Although at first, they thought it was a coincidence they later discovered that this calcium increase is important. They found Ca2+ ions are involved in anion channel activation, which allows for anions to flow into the guard cell. They also are involved in prohibiting proton ATPase from correcting and stopping the membrane from being depolarized. To support their hypothesis that calcium was responsible for all these changes in the cell they did an experiment where they used proteins that inhibited the calcium ions for being produced. If their assumption that calcium is important in these processes they'd see that with the inhibitors they'd see less of the following things. Their assumption was correct and when the inhibitors were used they saw that the proton ATPase worked better to balance the depolarization. They also found that the flow of anions into the guard cells were not as strong. This is important for getting ions to flow into the guard cell. These two things are crucial in causing the stomatal opening to close preventing water loss for the plant. [14]

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. [11] [15] [16] [17] [18] [19] [20] [21] 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. [17] [22] [23] [24] [25] Anion channels were identified as important controllers of stomatal closing. [26] [27] [28] [29] [30] [31] [32] Anion channels have several major functions in controlling stomatal closing: [27] (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. [27] [30] [33] 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. At least two major types of anion channels have been characterized in the plasma membrane: S-type anion channels and R-type anion channels. [26] [27] [29] [34]

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. [35] Vascuolar K + (VK) channels and fast vacuolar channels can mediate K + release from vacuoles. [36] [37] [38] Vacuolar K + (VK) channels are activated by elevation in the intracellular calcium concentration. [36] Another type of calcium-activated channel, is the slow vacuolar (SV) channel. [39] SV channels have been shown to function as cation channels that are permeable to Ca 2+ ions, [36] but their exact functions are not yet known in plants. [40]

Guard cells control gas exchange and ion exchange through opening and closing. K+ is one ion that flows both into and out of the cell, causing a positive charge to develop. Malate is one of the main anions used to counteract this positive charge, and it is moved through the AtALMT6 ion channel. [41] AtALMT6 is an aluminum-activated malate transporter that is found in guard cells, specifically in the vacuoles. This transport channel was found to cause either an influx or efflux of malate depending on the concentrations of calcium. [41] In a study by Meyer et al, patch-clamp experiments were conducted on mesophyll vacuoles from arabidopsis rdr6-11 (WT) and arabidopsis that were overexpressing AtALMT6-GFP. [41] It was found from these experiments that in the WT there were only small currents when calcium ions were introduced, while in the AtALMT6-GFP mutant a huge inward rectifying current was observed. [41] When the transporter is knocked out from guard cell vacuoles there is a significant reduction in malate flow current. The current goes from a huge inward current to not much different than the WT, and Meyer et al hypothesized that this is due to residual malate concentrations in the vacuole. [41] There is also a similar response in the knockout mutants to drought as in the WT. There was no phenotypic difference observed between the knockout mutants, the wild type, or the AtALMT6-GFP mutants, and the exact cause for this is not fully known. [41]

Guard cells perceive and process environmental and endogenous stimuli such as light, humidity, CO2 concentration, 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. [30] 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] [42] [43] 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.

During the development of plant leaves, the specialized guard cells differentiate from “guard mother cells”. [44] [45] The density of the stomatal pores in leaves is regulated by environmental signals, including increasing atmospheric CO2 concentration, which reduces the density of stomatal pores in the surface of leaves in many plant species by presently unknown mechanisms. The genetics of stomatal development can be directly studied by imaging of the leaf epidermis using a microscope. Several major control proteins that function in a pathway mediating the development of guard cells and the stomatal pores have been identified. [44] [45]

What two conditions does the closing of the stomata help to prevent? - Biology

Background Information:

Leaf stomata are the principal means of gas exchange in vascular plants. Stomata are small pores, typically on the undersides of leaves, that are opened or closed under the control of a pair of banana-shaped cells called guard cells. When open, stomata allow CO2 to enter the leaf, and allow for water and oxygen to escape. In addition to opening and closing the stomata, plants may exert control over their gas exchange rates by varying stomata density in new leaves when they are produced (such as in the spring or summer). The more stomata per unit area is the stomata density.

Why might it be adaptive for a plant to control its rates of water loss and CO2 uptake? One answer can be found in the sun. Increases in heat could denature proteins of membranes of chloroplasts. When overheated, plants may open the stomata to evaporate water to lower the temperature. Based on this, you could hypothesize that leaves in the sun would have a higher stomata density than leaves in the shade.

On the other hand, if water is not available, such as under drought conditions, excessive evaporation might lead to desiccation (drying out.) Plants in hot areas may benefit from fewer stomata so that they can conserve water.

The discussion illustrates an important concept in experimental biology, that there are often alternative hypotheses to explain variation in nature. In this case, the stomata density may increase or decrease in response to environmental variation in sunlight and water availability.

Prelab Questions

1. What role do stomata play in homeostasis?

2. Two hypothesis for stomata density are described. How could you test them?

3. Plant species might have variation in the number of stomata present on their leaves. Why?

4. Plants move waters from the roots of the plant to the leaves through transpiration. As water evaporates from the leaf, cohesion pulls water up from the roots. Suggest a relationship between transpiration and stomata density.

Procedure for Counting Stomata

1. Obtain a leaf. Trace the outline of the leaf on a piece of graph paper. Estimate the surface area by counting how many squares fit inside the outline of the leaf. If you have partial squares, try to add them up to equal whole squares. Record the surface area in the table below.
2. Paint a thin strip of clear fingernail polish a section of the leaf (paint between parallel veins). Allow the fingernail polish to completely dry.
3. Place a piece of clear tape over the dried nail polish. Gently but firmly press the tape onto the leaf.
4. Peel the tape from the leaf and place the tape sticky side down onto a microscope slide. Examine the tape, which now contains an impression of the leaf cells. Try to use both scanning and low power.
5. Count the number of stomata in the field of view. Move the slide so you can see other areas. It may be best to take an average of several areas on the leaf.
6. Find the density of stomata can be measured by dividing the number of stomata by the surface area of the leaf.

Choose a question to investigate:

1) How does the density of stomata vary amongst different types of plants?

2) How does the density of stomata vary amongst leaf surfaces (upper versus lower surface of leaf)?

3) How does the density of stomata vary among leaves found on the same plant (leaves at the top very leaves at the bottom)?

Experimental Design - the procedure for counting stomata and calculating density is described above. Consider the question you chose to investigate, collect data and create a data table to organize your observations. You may want to take photos to include with your final report.

Make a Claim that summarizes the answer to your experimental question.

Using data from this experiment, provide Evidence that supports the claim.

Using background knowledge and data from this lab, provide Reasoning that uses the evidence to justify the claim. For this section you may need to do research outside the class on the type of plant you investigated.

Your group will share your data, claim, evidence and reasoning with the class as either a poster, powerpoint slides, or a digital infographic.

/>This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

What are stomata give two functions of stomata Class 7

Click to rate this post! [Total: 1 Average: 5]Solution: The small pores in the leaves of the plant are known as stomata. The functions of the stomata are: (a) Exchange of gases like oxygen and carbon dioxide. (b) Removal of excess of water through the process of transpiration The main functions of stomata are: Gaseous exchange- Stomatal opening and closure help in the gaseous exchange between the plant and surrounding. It helps in transpiration and removal of excess water in the form of water vapour. Stomatal closure at night prevents water from escaping through pores Functions of stomata: 1. It helps in the transpiration of water, i.e., the loss of excess water from the plant. 2 Let us do the question of what has to matter give two functions of stomata. So the numerous Force Under the surface of the leaf are called stomata and their functions are transportation that is taking water to every part of the tree and the exchange of gases. So let us write down They are pores surrounded by specialized parenchymatic cells, called guard cells. Stomata have two main functions, namely they allow for gas exchange acting as an entryway for carbon dioxide (CO2) and releasing the Oxygen (O2) that we breath. The other main function is regulating water movement through transpiration

6. What are stomata? Give two functions of stomata ..

  1. Stomata are tiny pores present on the surface of a leaf. Functions of stomata: (a) Stomata help in the exchange of gases. (b) Evaporation of water from the leaf surface occurs through stomata. Functions of stomata
  2. NCERT Solutions for Class 7 Science Chapter 11 - Transportation in Animals and Plants Give two functions of stomata. Answer : Stomata are tiny pores present on the surface of a leaf. Functions of stomata: (a) Stomata help in the exchange of gases. (b) Evaporation of water from the leaf surface occurs through stomata
  3. What are stomata? Give two functions of stomata. Answer: The numerous pores under the surface of leaf are called stomata. Functions of stomata-Transpiration(loss of water in the form of water vapours) and exchange of gases (carbon dioxide and oxygen) are the main functions of stomata. Question 7: Does transpiration serve any useful function in.
  4. Small pores in leaves of plants are called stomata. Functions of stomata are : absorption of oxygen from air. removal of excess water by transpiration
  5. Functions of the stomata They allow the exchange of gases (CO 2 and O 2) with the atmosphere. Evaporation of water from the leaf surface occurs through the stomata. Thus, the stomata help in the process of transpiration
  6. Stomata are tiny pores present on the surface of a leaf. Functions of stomata: Stomata help in the exchange of gases. Evaporation of water from the leaf surface occurs through stomata

. (ii) Stomata help in evaporation of water from the leaf surface during the process of transpiration. Q 7 Functions of stomata: (i) Evaporation of water in plants in the form of vapour takes place through stomata during transpiration. (ii) Exchange of gases (oxygen and carbon dioxide) also takes place..

Two Main Functions of Stomata . The two main functions of stomata are to allow for the uptake of carbon dioxide and to limit the loss of water due to evaporation. In many plants, stomata remain open during the day and closed at night. Stomata are open during the day because this is when photosynthesis typically occurs Q6. What are stomata? Give two function of stomata. Answer: The small pores present on the under-surface plant leaves whose opening are surrounded with guard cells is known as stomata. Functions: (i) It helps in the exchange of gases. (ii) It helps in transpiration of water. (iii) It helps in evaporation of water through the leave Answer 6 The small opening at the surface of leaves are called as stomata. The function of stomata are: 1) It helps in the exchange of gases. 2) It helps in loss of excess of water (Transpiration

Stomata- Structure, Functions, Types & Mechanism of Stomat

  • What is stomata ?Give two functions of stomata. Ask questions, doubts, problems and we will help you
  • Stomata are tiny pores present on the surface of a leaf. Functions of stomata: (a) Stomata help in respiration. (b) Evaporation of water
  • What are stomata? Give two functions of stomata. Solution: Stomata are tiny pores or openings present on the surface of a leaf. Functions of stomata: (a) Stomata help in the exchange of gases. (b) Evaporation of water from the leaf surface occurs through stomata
  • Stomata are enclosed by two kidney-shaped cells called guard cells. The main function of stomata are : They are necessary for exchanging gases like Co2 or O2 with the atmosphere. Photosynthesis is not possible without them
  • ute pores which are usually, found in leaf for the exchange of gas and transpiration are known as stomata (singular stoma). Stomata are found on the leaves of plants. They can either be present on either the sides or just on one side of the leaf. They are essential for a plant's life functions because they allocate carbon-containing carbon dioxide gas to enter the plant's.
  • Stomata are tiny pores present on the surface of a leaf. Functions of stomata: 1) Stomata help in the exchange of gases. 2) Evaporation of water from the leaf surface occurs through stomata
  • Give two functions of stomata. Solution: Tiny pores present on the leaf surface are known as stomata. Explain. Solution: Transpiration serves following function in plants . NCERT Solution for class 7 Science Chapter 11 Transportation in Animals and Plants It helps in lowering temperature of plants, thus preventing heat injury of plants

Q.6.What are stomata? Give two junctions of stomata. Ans.There are small openings on the lower surface of the leaves. These pores are called stomata. These openings are surrounded with guard cells. Functions of stomata: 1. It helps in the transpiration of water, i.e., the loss of excess water from the plant. 2 Definition of Stomata 2. Types of Stomata 3. Top function of Stomata. Definition of Stomata: The stomata are minute pores which occur in the epidermis of the plants. Each stoma remains surrounded by two kidneys or bean shaped epidermal cells the guard cells. The stomata may occur on any part of a plant except the roots

Stomata are the tiny pores present on the surface of the leaves. These are surrounded by two bean shaped cells called guard cells. Functions of stomata : (i) The exchange of gases in plants occurs through stomata. (ii) The excess water in plants evaporates through stomata by a process called transpiration. Question 7 The two main functions of stomata are to allow for the uptake of carbon dioxide and to limit the loss of water due to evaporation. In many plants, stomata remain open during the day and closed at night. Stomata are open during the day because this is when photosynthesis typically occurs

Q6 What are stomata Give two functions of stomata LID

  1. ute pores which are usually, found in leaf for the exchange of gas and transpiration are known as stomata (singular stoma). 11. Stomata facilitates exchange of gases and transpiration. Stomate, any of the microscopic openings or pores in the epidermis of leaves and young stems. 5. Abscissic acid (ABA) functions in the presence of carbon dioxide
  2. NCERT Solutions for Class 7 Science Chapter 11 Transportation in Animals and Plants in English Medium or अध्याय 11 जंतुओं और पादप में परिवहन in हिंदी मीडियम free to download in PDF file for offline use or view it online for 2020-21. Give two functions of stomata.
  3. Definition :-Stomata are tiny openings or pores in plant tissue that allow for gas exchange. It's functions are :- 1) It helps in the gaseous exchange . 2) It helps in temperature regulation . 3) It helps in ascent of sap 4) It helps in transpiration. Additional information :
  4. Give two functions of stomata. Answer: The numerous pores under the surface of leaf are called stomata. Transpiration and exchange of gases (carbon dioxide and oxygen) are the main functions of stomata. Result for Stomata. NCERT Science Class-7 Exercise Solutions
  5. What are stomata? Give two functions of stomata. Solution: The tiny pores or openings present under the leaves of the plants is called stomata. Two functions of stomata: (i) It helps in breathing of the plants. (ii) It helps in exchange of gases which takes place inside the plant cells

What are two functions of stomata

  1. Class 7, Science, Chapter 11, Transportation in Animals and Plants, NCERTSolutions, Solved Questions and Answers for NCERT Text Book. Give two functions of stomata. Answer 6 The small opening at the surface of leaves are called as stomata. The function of stomata are: 1) It helps in the exchange of gases..
  2. Givetwofunctionsofstomata. There are small openings on the lower surface of the leaves. These pores are called stomata. These open
  3. Q.State any two functions of the cells found surrounding the stomata? Ans. The cells surrounding the stomata are guard cells. They perform following functions: (i) Protect the inner tissues from external factors, pathogenic attacks etc. (ii) They regulate the opening and closing of stomatal cells
  4. Functions of Stomata: The main function of stomata is to open and close the pores in the leaves for an exchange of gases. It allows the plant to take in carbon dioxide and give out oxygen for photosynthesis. Additionally, what are the two main functions of stomata? The two main functions of stomata are as follows: Stomata help in exchange of.
  5. Q No 5: What are the functions of the stomata? Ans: Functions of the stomata: The exchange of gases (CO 2 and O 2) with the atmosphere. The loss of excess water in the form of water vapour. This process is known as transpiration
  6. 3. What are stomata? Give two functions of stomata. 4. Does transpiration serve any useful function in the plants? Explain. 5. What are the components of blood? 6. Why is blood needed by all the parts of a body? 7. What makes the blood look red? 8. Describe the function of the heart. 9. Why is it necessary to excrete waste products? 10

Structure and function of stomata. The stomata. control gas exchange in the leaf. Each stoma can be open or closed, depending on how turgid. its guard cells. are. The stomata can open and close to Stomata are the tiny pores found on the surface of leaves of plants. The opening and closing of the stomata controls the passage of gases and water vapour into and out of the leaf. (1) Carbon dioxide gas enters in and oxygen gas 'goes out' through stomata during photosynthesis. (2) Water vapour passes out through stomata during transpiration

(a) Diagram of stomata : Functions of stomata: (i) Exchange of gases (ii) Transpiration (b) The conditions in which photosynthesis takes place are: carbon dioxide, water, chlorophyll and sunlight. Chemical equation for photosynthesis : 6CO 2 +6H 2 O C 6 H 12 O 6 +6O Find detailed video answer solutions to NCERT Solutions Science , Class 7 Transportation in Animals and Plants Exercise questions taught by expert teachers. Access free tutor videos and make learning fun on LIDO learning

NCERT Solutions for Class 7 Science Chapter 11

Q.11. What is stomata? Draw its structure and write its functions. Ans. Stomata are the tiny pores present on the surface of leaves. These pores are surrounded by 'guard cells'. One pore is called 'Stoma'. Functions of stomata are: It helps in exchange of gases. It helps in process of transpiration Class 7 - Biology - Nutrition in Plants. Download PDF. Question 1: Why do organisms need to take food? Give a brief description of the process of synthesis of food in green plants. The pores through which leaves exchange gases - Stomata . Question 8: Tick the correct answer: (a) Amarbel is an example of: (i) autotroph (ii) parasite. Science NCERT Grade 7, Chapter 11, Transportation in Animals and Plants lays emphasis on the two systems of the human body: The circulatory system. The excretory system The first part of the chapter, Transportation in Animals and Plants deals with the circulatory system and its related concepts

CBSE NCERT Solution for Class 7 - Biology - Transportation

  • Follow us at: us out at
  • erals from soil to leaves
  • Stomata: Definition. Take a deep breath in and then let it out. Breathing to you is a very natural function that you usually do without even thinking about it
  • Give two reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue (2) 1. distribution may not be uniform OR so it is a representative sampl
  • Stomata is plural of stoma=== mouth, it is a pore that occurs on the surface of leaves, young branches , sepals , sometimes on young fruits etc. Through these pores gaseous exchange between plant and outer air occurs.Many variations occur regardin..

Name and describe two protective tissues of plants.Give their another function as well. Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day. Kindly Sign up for a personalised experienc Stomata can be distributed in the following ways on the two sides of a leaf: • An amphistomatous leaf has stomata on both surfaces. Most plants have such a distribution. • A hypostomatous leaf has stomata only on the lower surface. Many tree species are characterized by having hypostomatous leaves, such as horse chestnut (Aesculus hippocastanum) and basswood (Tilia europaea) (Meidner and. Mature stomata each consist of two bean-shaped guard cells subtended by an air-filled cavity (Figs. 1-3). In cross section, guard cells are larger than epidermal cells and they each contain a large starchfilled chloroplast (Figs. 1, 2)

What are stomata? Draw a labelled diagram of stomata. Write two functions of stomata. [Foreign 2008] Answer: Stomata are small pores present on the leaves underside. Two functions of stomata: Allows the exchange of gases, O 2 and CO 2. It helps in losing extra water by transpiration and creates suction pull which helps the water to rise in xylem (b) Two functions of stomata are: (i) Exchange of gases between the plant and the atmosphere takes place through stomata. (ii)Transpiration in plants takes place through stomata. (c) Opening and Closing of Stomatal Pore: The opening and closing of the pore is a function of the guard cells Stomata, the small pores on the surfaces of leaves and stalks, regulate the flow of gases in and out of leaves and thus plants as a whole. They adapt to local and global changes on all timescales.

What are the functions of stomata? - BYJU'S Q&

Each stoma (the tiny pore or hole) is flanked by two guard cells which expand and contract, closing and opening the stoma. Two controls on the opening and closing of the stomata are the plant's water balance and the carbon dioxide concentration. When the plant becomes dehydrated and wilts, the closing of a plant's stomata will retain water Notice whether you can identify the organelles inside of the two cells that make up the stomata. These two stomata cells are called guard cells because they guard the opening. (Your textbook discusses the details of the chemical processes by which the stomata are opened and closed.) Look at the skin cells around the stomata Get detailed answer of Q.1 Match structures given in Column I with functions given in Column II. Column- I (i) Stomata (ii) Xylem (iii) Root hairs (iv) Phloem Column-II (a) Absorption of water (b) Transpiration (c) Transport of food (d) Transport of water (e) Synthesis of carbohydrate

What are stomata? Give two functions of stomata

  1. Stomata open and close to allow the intake of carbon dioxide and the release of oxygen. Furthermore, what are the 3 function of Stomates? Stomata (1 of 3) Function. Image caption: Carbon dioxide enters, while water and oxygen exit, through a leaf's stomata
  2. Tiny pores called stomata are seen in the epidermal cells. Each stoma consists of two kidney-shaped guard cells. Each guard cell has a nucleus and many chloroplasts. RESULT Minute apertures called stomata are seen in the temporary mount of leaf peel. Each stoma is enclosed by two kidney-shaped guard cells
  3. Stomata : Stomata (the word stomata means mouth) are small pores found in the leaves of the plant that helps in gaseous exchange during photosynthesis and.
  4. In botany, a stoma (from Greek στόμα, mouth, plural stomata), also called a stomate (plural stomates) is a pore, found in the upper epidermis of leaves, stems, and other organs, that controls the rate of gas exchange.The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the stomatal opening
  5. (b) (i) Name the class to which the plant organ was obtained. (ii) Give a reason for your answer in (b) (i) above. (c) Name the part labeled X 17. The number of stomata on the lower and upper surfaces of two leaves from plant species X and Y were counted under the field of view of a light microscope. The results were as shown in the table.
  6. Write two functions of flower relating to reproduction. Answer Two functions of flowers related to reproduction are as follows: To produce male and female gametes, after developing male and female gametophytes in reproductive organs, respectively. To accomplish the fusion of male and female gametes or fertilisation. Question 27

NCERT Solutions for Class 7 Science: Chapter 11

What does stomata mean? Stomata are very small openings in membranes, particularly in plants, through which water and gas pass. (noun) An exampl.. Guard cell function. Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata. Light is the main trigger for the opening or closing. Each guard cell has a relatively thick cuticle on the pore-side and a thin one opposite it 11. Write about the functions of - (a) Epidermis (b) cork (c) stomata. Ans. Epidermis - its main function is protection. It forms waterproof coating, which reduces loss of water. Stomata - These are the small opening which helps in exchange of gases Cork - It is protective in function Learn stomata biology with free interactive flashcards. Choose from 179 different sets of stomata biology flashcards on Quizlet

What is the Function of Plant Stomata? - ThoughtC

What are the functions of the stomata? Answer: Stomata are necessary for exchanging gases with the atmosphere, transportation (loss of water in the form of water vapour) also takes place through stomata. Question 6. Diagrammatically show the difference between the three types of muscle fibres. Answer: Question 7 7. Examine the preparation under low and then high power of the microscope. Draw and label the leaf section in your data table. 8. Note the location and spacing of the stomata. Count the number of stomata that are open. Data and Observations Water Mount No. of stomata open (sample) 16 out of 17 Salt Solution Mount No. of stomata open 13 out of.

Science Class 7- Chapter 11- Transportation in Animals and

Transpiration Definition. Transpiration is the evaporation of water from plants. Most of the water absorbed by the roots of a plant—as much as 99.5 percent—is not used for growth or metabolism it is excess water, and it leaves the plant through transpiration. Transpiration is very important for maintaining moisture conditions in the environment Guard cells become flaccid on losing water and stomata close. when the guard cells become fully turgid on water and stomata open. 7. Abscisic: Abscisic acid accumulates in the leaves when the plants experience water stress or water deficit. It has been observed that ABA stimulates closure of stomata under these condition. 3/29/2018 16 17

Chapter 11 Transportation in Animals and Plants Class 7

  1. Stomatal Closure. When water is low, roots synthesize abscisic acid (ABA), which is transported through the xylem to the leaves. There, abscisic acid causes calcium channels to open. Calcium (Ca 2 +) opens anion channels, and malate, chloride, and nitrate exit the cell.The membrane potential decreases (the difference in charge across the membrane becomes less pronounced) as anions leave the cell
  2. Loss-of-function mute plants produce meristemoids but have no stomata mute meristemoids undergo excessive asymmetric 'amplification' divisions, and become surrounded by a 'rosette' of sister cells, but they cannot progress further through the stomatal lineage to differentiate into guard mother cells (Figure 1B)
  3. Stomata are pores that regulate the gas and water exchange between the environment and aboveground plant tissues, including hypocotyls, leaves, and stems. Here, we show that mutants of Arabidopsis thaliana LLM-domain B-GATA genes are defective in stomata formation in hypocotyls. Conversely, stomata formation is strongly promoted by overexpression of various LLM-domain B-class GATA genes, most.
  4. The main function of the meristematic tissue or meristem is to divide and produce new cells. It is responsible for growth in length (primary growth) in plants. Question 3. Give any two main functions of stomata. Answer: Small pores present in the epidermis of the leaf are called stomata. Stomata are enclosed by two kidney-shaped cells called.
  5. The intricate and interconnecting reactions of C 3 photosynthesis are often limited by one of two fundamental processes: the conversion of solar energy into chemical energy, or the diffusion of CO 2 from the atmosphere through the stomata, and ultimately into the chloroplast. In this review, we explore how the contributions of stomatal morphology and distribution can affect photosynthesis.
  6. Q5 : What are the functions of the stomata? Answer : Functions of the stomata: (i) They allow the exchange of gases (CO2 and O2) with the atmosphere. (ii) Evaporation of water from the leaf surface occurs through the stomata. Thus, the stomata help in the process of transpiration
  7. If you count the stomata under the whole grid at 400X total magnification multiply by 16 for the final number of stomata in 1mm 2. If, at 400X, you count only 20 small squares of the grid you need to multiply by 5 and by 16 for the number of stomata per mm 2. Calculate the number of stomata per mm 2 for both the lower and the upper leaf surface

What is stomata ?Give two functions Homework Help

Stomata - breathing pores that enable photosynthesis, and sense and drive climate change. Stomata - cellular breathing pores on plant leaves that balance photosynthetic carbon dioxide (CO 2) uptake and evaporative water loss - have fascinated scholars and botanists for several centuries.Alexander von Humboldt, famous geographer, naturalist and explorer, wrote a botanical manuscript about. 1. Match structures given in Column I with functions given in Column II. Column I Column II (i) Stomata (a) Absorption of water (ii) Xylem (b) Transpiration (iii) Root hairs (c) Transport of food (iv) Phloem (d) Transport of water (e) Synthesis of carbohydrate Carbon dioxide enters the leaf and oxygen and water vapour leave the plant through the stomata. Leaves are adapted in several ways to help them perform their functions. Features of leave function. A group of cells that carries out a specific function is called a tissue. Different functions are performed by different tissues, which is known as division of labor. Hence, multi-cellular organisms can show the division of labor and can perform complex body functions The stomata control gas exchange in the leaf. Give examples of two Insectivorous plants, and explain their adaptations for capturing insects. And lenticels is that stomata are open, and explain what is the role of stomata in photosynthesis class 4 adaptations for capturing insects placed the. To know about stomata function in detail the.

Q.6 What are stomata? Give two functions of stomata

Stomata are small pores, typically on the undersides of leaves, that are opened or closed under the control of a pair of banana-shaped cells called guard cells (see figure above). When open, stomata allow CO 2 to enter the leaf for synthesis of glucose, and also allow for water, H 2 O, and free oxygen, O 2, to escape. In addition to opening and. Guard Cells Definition, Function, Structure of Stomata on Plants Definition: What is a Guard Cell? Essentially, guard cells are two bean-shaped cells that surround a stoma. As epidermal cells, they play an important role in gaseous exchange in and out of plant leaves by regulating the opening and closing of pores known as a stoma There are many stomata on each leaf - up to one million per square centimeter, and they have two main functions: to regulate gas exchange and to help prevent water loss what is stomata class 9. Valora esta carrera: Plan de estudios Perfiles Campo profesional Sedes Titulación Puntajes mínimos.

What are the functions of the stomata? CBSE MASTER

Stomata was discovered by Pfeffer & name 'stomata' was given by Malphigii. Stomata cover 1-2% of leaf area. It is minute pore present in soft aerial parts of the plant. Algae, fungi and submerged plants do not possess stomata. (a) Stomata are minute pores of eliptical shape, consists of two specialized epidermal cell called guard cells Stomata resemble doughnuts — a circular pore with a hole in the middle for gas to enter or leave the plant. The pore consists of two cells — each known as a guard cell. They can swell or shrink to open or close the pore, which is critical for regulating gas exchange for photosynthesis, as well as moisture levels in tissues Plants and trees hold an entire level of the ecosystem pyramid. They give us air to breathe, food to eat, and many other things too. One of the most important parts of plants is the stomata. Its singular form is called stoma, and it means 'mouth'. Stomata function is to regulate the process of photosynthesis, transpiration, respiration, etc Structure of Stomata. Each stomata consists of a minute pore called stoma surrounded by two guard cells. The stoma acts as a turgor-operated valve, which closes and opens according to the turgidity of guard cells. The guard cells have unevenly thickened walls. The cell wall around stoma is tough and flexible and the one away from stoma is thinner

1. Name & describe two structural features of the leaf that are designed to reduce a plant's water-loss: 2. What is the function of a terrestrial plant's roots? 3. What is the function of plant's xylem? 4. When a leaf is in the light, and its stomata are open, in which direction are the following moving through the stomata: H 2 O, CO 2, O. Stomata -- the plant pores that give us life -- arise thanks to a gene called MUTE Date: May 7, 2018 Source: University of Washington Summary: New research in plants shows that a gene called MUTE. Patchy stomata are a common and characteristic phenomenon in plants. Understanding and studying the regulation mechanism of patchy stomata are of great significance to further supplement and improve the stomatal theory. Currently, the common methods for stomatal behavior observation are based on static images, which makes it difficult to reflect dynamic changes of stomata

Plant Transpiration Basics

Plant Transpiration is a term that describes what occurs in all living trees, grass and plants. Transpiration in plants is the upward internal movement of water that begins in the roots and ends when water is released into the air, via the stomata, as water vapor.

(The term “Translocation” refers the downward movement through the phloem of sugars produced in the leaf by photosynthesis.) Transpiration in plants occurs in all living species with few exceptions, so whether you own an orchard or are growing a lawn, transpiration is an essential active process.

In fact, almost 100 percent of water taken in by plants is eventually released into the atmosphere. Water traveling through channels within the plant is used to transport essential nutrients, ensure proper plant function, and necessary for survival.

Large trees can absorb many gallons of water each day. The water entering through the roots slowly moves toward the leaves where it is released through the stomata. The stomata are tiny openings on the leaf surface through which gas exchanges take place. Here is what happens.

In trees, for example, water enters the plants though millions of tiny root hairs. One of the function of roots is to filter out particles and bubbles that could hinder water movement. Any bubbles that escape is later captured in other places in the plant. After a time, the water starts to move upward through channels in the xylem.

How Does Water Move Upward in Plants?

You may be wondering how water moves upward against gravity. For effective plant transpiration to occur, water molecules bond together in a process called cohesion, known as the “Cohesion-Theory”.

This cohesion, sometimes referred to as surface tension, is what allows some insects, small rodents such as shrews, and certain lizards to actually walk across the surface of water. Inside the plant, water molecules bond to each other forming a continuous strand within the xylem.

Molecules at the leaf’s surface escape through the open stomata. The cohesion of water molecules actually pulls the remaining water upward as it takes the place of the evaporated water molecules.

Why is this Large Intake and Water Loss Necessary?

It is all wrapped up in photosynthesis. The absorption of carbon dioxide is necessary for photosynthesis and plants absorb a tremendous amount of CO₂. Plant photosynthesis produces all of the food the plant uses to live on.

However, carbon dioxide cannot enter a cell in a gas form. It must be diffused first and water is necessary for diffusion. Plant transpiration and photosynthesis are closely tied together and one cannot exist for long without the other.

The Stomata’s Role in Plant Transpiration

Large plants will have literally thousands of stomata. The stomata (singular is Stoma) are tiny openings on the leaf’s surface that opens and closes and is responsible for the release and absorption of gases.

Plant transpiration may be controlled by several factors, but nothing happens unless the stomata are open. The major factors controlling stomata are air temperature, humidity, availability of soil water, and light intensity.

Guard cells around the stomata are responsible for its opening and closing. During the day carbon dioxide is absorbed through the stomata, while oxygen and water vapor is released.

Carbon dioxide is necessary for carbon fixation, which is an essential element of photosynthesis. In the evening the opposite occurs where oxygen is absorbed and carbon dioxide is released.

Gas exchange cannot take place when the stoma is closed, therefore no transpiration in plants occurs in winter on deciduous plants after the leaves have fallen.

Drought Conditions and the Stomata

During drought when water is scarce, the stomata will close to prevent water from escaping and causing the tree to weaken or die. We can apply chemicals to close the stomata to prevent the tree from being damaged. See information below on antitranspirants.

Note: Dormant season can be pruning season for a lot of trees. However, some trees should never be pruned during the dormant season. Trees, such as maples, elms, etc. have positive pressure inside the tree when no leaves are present and when plant transpiration is not occurring. If a branch is cut in the winter or if no leaves are on the tree, the tree will often bleed sap for weeks.

The term “bleeding” describes how water and plant juices ooze from a wound or cut on a tree and may continue for days. Sometimes it develops a bad smell. It's called "wetwood", when this happens because bacteria enter the wound creating not only dark patches on the bark, but the bacteria is also responsible for the bad odor.

Many gallons of fluids can ooze from wounds of larger trees, even pooling on the ground, creating an unsightly mess. Once the bud breaks in spring and leaves are forming, transpiration in plants resume again. Plant transpiration equalizes the pressure and no bleeding will occur when the tree is pruned.

Using Antitranspirants to Slow Transpiration

Antitranspirants are chemicals that are sprayed on plants to protect them from drying out too quickly. They come in two types: metabolic antitranspirants and film-forming antitranspirants.

Metabolic types work by influencing the closing of stomata. Film-forming types work by coating the leaf surface and blocking the stomata opening. Both types are designed to prevent water loss through plant transpiration, but the film-forming types generally have a greater longevity.

Antitranspirants are used on Christmas tree farms, on cut flowers, and are sprayed on trees during drought conditions and are used on newly transplanted plants.

Common Disagreements about Antitranspirant Research

While antitranspirants are widely used in many parts of the green industry, no all groups agree with the popular research, especially concerning live plants. For example, many manufacturers of antitranspirants state that gas exchange is not hindered, yet is very effective in slowing water vapor loss.

However, other researchers say that blocking of the stomata does prohibit essential gas exchange. Since plants need to absorb carbon dioxide for photosynthesis to take place, blocking or preventing the opening of the stomata only harms the plant. The concern is not really a problem for cut plants and flowers.

For best results on living plants, use antitranspirants as directed and only when needed. Plant transpiration is a necessary function of living plants, but preventing water loss under certain conditions may outweigh the concerns.

The Biology of Grass Seed Germination
Understanding the basic biology of grass seed germination will reinforce your knowledge of planting a lawn and help answer the “Why is it done this way?” line of questions.

Soil Nutrients and the Nutrient Cycle
Nutrient cycles are the circle of life from a soil nutrients perspective. This page explains the cycle process and how it applies to your lawn.

History and Discovery of CAM plants

The discovery of CAM plants was begun in a rather unusual manner when Roman people discovered that some plant leaves used in their diets tasted bitter if harvested in the morning, but were not so bitter if harvested later in the day. A scientist named Benjamin Heyne noticed the same thing in 1815 while tasting Bryophyllum calycinum, a plant in the Crassulaceae family (hence, the name "Crassulacean acid metabolism" for this process). Why he was eating the plant is unclear, since it can be poisonous, but he apparently survived and stimulated research as to why this was happening.

A few years before, however, a Swiss scientist named Nicholas-Theodore de Saussure wrote a book called Recherches Chimiques sur la Vegetation (Chemical Research of Plants). He is considered as the first scientist to document the presence of CAM, as he wrote in 1804 that the physiology of gas exchange in plants such as the cactus differed from that in thin-leaved plants.

Why cereal is better

Whether barley, wheat, maize or rice: The grass family includes all the major cereals. They are vital for feeding the world's population. Farmers produce 80 percent of all plant-based foods from grass crops. This success is due in part to the plants' ability to adjust more quickly to dry conditions and sustain lack of water better than other plants.

But why are grasses more tolerant to water scarcity? Can other food crops be bred for this property, too, to assure or boost agricultural yields in the future? This could be important in the face of a growing world population and climate change that will entail more periods of dry and hot weather.

The plant researchers Professor Rainer Hedrich, Professor Dietmar Geiger and Dr. Peter Ache from Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, are looking into these questions. They studied brewing barley to determine why grasses are more stress-tolerant and are therefore "better" crop plants than potatoes and the likes.

Two amino acids make the difference

The scientists discovered that this difference can be attributed to the protein SLAC1 of the guard cells. Just two amino acids, the building blocks that make up proteins, are responsible for the plant's drought tolerance. "We now want to find out whether this small difference can be harnessed to make potatoes, tomatoes or rapeseed more tolerant to stress as well," says Rainer Hedrich.

The new insights have been published in the prestigious journal Current Biology where Hedrich, Geiger and Ache describe how they pinpointed the tiny difference between grasses and other plants.

Ion transport is a key process

The JMU researchers began scrutinising microscopically small leaf pores called stomata. These openings admit carbon dioxide for photosynthesis into the plant. But they also serve as outlets for water. To prevent losing too much water through evaporation, land plants have learned during evolution to actively open and close their stomata using special guard cells. Membrane proteins such as SLAC1 play a key role in this regulatory process: acting like channels, they guide ions into and out of the cells.

Hedrich is convinced that a basic understanding of the molecular goings-on during ion transport through the plasma membrane of the guard cells is the key to improving the drought tolerance and yields of agricultural crop plants.

Ion shuttles make leaf pores more efficient

The stomata of grasses have a special feature: The pore is bordered by two pairs of cells where other plants only have a single cell pair. Grass cereals boast two dumbbell-shaped guard cells that form and regulate the pore. Additionally, they are flanked by two subsidiary cells.

The JMU researchers have demonstrated that the subsidiary cells absorb and store the potassium and chloride from the guard cells when the pore closes. When the stoma opens, they pass the ions back to the guard cells. "Our cereals use the subsidiary cells as a dynamic reservoir for osmotically active ions. This ion shuttle service between guard cell and subsidiary cell allows the plant to regulate the pores particularly efficiently and quickly," Dietmar Geiger explains.

Two measuring systems for more drought resistance

There is a second mechanism that makes grasses more tolerant to dry conditions. When water is scarce, plants produce the stress hormone ABA (abscisic acid). Inside the guard cells, it activates the ion channels of the SLAC1 family, thereby initiating the closing of the stomata to prevent the plant from withering within a matter of minutes.

"Interestingly, we found that nitrate must be present in brewing barley and other grass cereals in addition to ABA to enable the pore to close," Peter Ache says. The nitrate concentration allows the barley to measure the shape the photosynthesis is in. If it works smoothly, nitrate levels are low.

Barley hence relies on two measuring systems: It uses ABA to register water availability and nitrate to assess photosynthesis performance. "By combining the two, the barley is better able than other plants to negotiate between the extremes of 'dying of hunger' and 'dying of thirst' when facing water scarcity," Rainer Hedrich explains

Testing the nitrate sensor in other plants

Which mechanism is responsible for the difference in stoma regulation at the molecular level? To answer this, the researchers analysed SLAC1 channels of various herbaceous plants compared to grasses. This allowed them to identify the "nitrate sensor" of the grasses: It is comprised of a motif of two amino acids which first occurred in moss during evolution and was subsequently further optimised to give the guard cells their unique properties.

In a next step, the team of researchers wants to establish whether herbaceous agricultural crops also benefit from having a nitrate sensor. To achieve this, the scientists want to fit arabidopsis plants that lack the SLAC1 channel with the SLAC1 channel of barley. "If this step increases their stress tolerance, we can consider breeding optimised potatoes, tomatoes or rapeseed," Hedrich says.

Financed in the BayKlimaFit programme

The research activities were undertaken within the scope of the Bavarian BayKlimaFit consortium. Its goal is to find strategies to make food crops fit for climate change. The consortium receives funding from the Bavarian State Ministry of the Environment and Consumer Protection.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

Explain the mechanism of opening and closing of stomata.

Stomata are small pores present in the epidermal cells of leaves in plants. Stomata are open during the day and close during night.Stomata take in carbon dioxide required for the photosynthetic activity during the day. They give out excess water released in the process of respiration during night along with carbon dioxide. Opening and closing of stomata is controlled by concentration of solutes in the guard cell.

Mechanism of opening and closing of stomata
Opening of stomata: Solutes from neighbouring epidermal and mesophyll cells enter the guard cells lowering its osmotic potential and water potential. This lowered water potential and osmotic potential will allow movement of water into guard cells from neighbouring cells. Guard cells become turgid due to water accumulation in them which results in the opening of the guard cells.
Closing of stomata: As the somata open the solute concentration is reduced. This makes the water from the guard cells to move away into neighbouring cells. Now, guard cells becom flaccid with no water. They collapse against each other and result in the closing of stomata.

Mechanism of opening and closing of stomata
Opening of stomata: Solutes from neighbouring epidermal and mesophyll cells enter the guard cells lowering its osmotic potential and water potential. This lowered water potential and osmotic potential will allow movement of water into guard cells from neighbouring cells. Guard cells become turgid due to water accumulation in them which results in the opening of the guard cells.
Closing of stomata: As the somata open the solute concentration is reduced. This makes the water from the guard cells to move away into neighbouring cells. Now, guard cells becom flaccid with no water. They collapse against each other and result in the closing of stomata.

C4 plants

Although Rubisco is responsible for the vast bulk of organic carbon on the surface of the Earth, its oxygenase activity can severely reduce photosynthetic efficiency. Some plants have evolved a way to minimize the oxygenase activity of Rubisco.

Learning Objectives

  • Identify the conditions that increase oxygenase activity of Rubisco
  • Describe how the oxygenase activity of Rubisco reduces photosynthetic efficiency
  • Distinguish C3 and C4 schemes for carbon fixation
  • Weigh the advantages and disadvantages of C3 versus C4
  • Compare and contrast photosynthesis and respiration, and their relationship in the global carbon and oxygen cycles.

Rubisco’s oxygenase activity impairs photosynthetic efficiency
Rubisco has oxygenase activity as well as carboxylase activity it sometimes fixes O2 to RuBP instead of CO2. The oxygenase activity occurs at low CO2, high O2 conditions, and becomes pronounced at high temperatures. As a result, organic carbon is oxidized, the opposite of photosynthesis, which reduces inorganic carbon to make organic carbon.

For the curious: oxygenase activity of Rubisco, from Wikipedia. RuBP (1) interconverts to an enol isomer (2) that combines with oxygen to form the unstable intermediate (3) that hydrolyzes into phosphoglycolate (4) and 3PG (5)

The oxygenation of RuBP produces 2-phosphoglycolate, a 2-carbon toxic compound which undergoes a series of reactions in the peroxisome and mitochondria, releasing CO2 and resulting in loss of organic carbon and energy production. This process is called photorespiration – an awfully misleading name for students, because it has nothing to do with respiration and yields no ATP. All Biol 1510 students need to remember about photorespiration is that it reduces photosynthetic efficiency, and that it occurs when Rubisco oxygenates RuBP instead of carboxylating RuBP.

Rubisco evolved even before oxygenic photosynthesis, when there was no oxygen in the atmosphere or in the ocean waters, so there was no selection against oxygenase activity. Nevertheless, in over 2 billion years, neither nature nor human genetic engineering has been able to eliminate or even significantly reduce the oxygenase activity of Rubisco without also affecting the carboxylase activity.

C4 plants have evolved a mechanism to deliver CO2 to Rubisco

In order for plants to take in CO2, they have to open structures called stomata on their leaves, which are pores that allow gas exchange. Plants also lose water vapor through their stomata, which means that they can die from dehydration in dry conditions as they keep their stomata open for photosynthesis. In response, plants close their stomata to prevent dehydration. The immediate* consequences of closed stomata in the short term are reduced CO2 concentration (CO2 levels decrease as it is utilized for photosynthesis) and increased O2 concentration (O2 levels increase as it is produced by photosynthesis). The rising O2 levels increase the rate of photorespiration (reaction of rubisco with oxygen instead of carbon dioxide), when then drastically reduces the efficiency of rubisco, which is already a very slow-working enzyme. So this means plants in dry conditions are at risk of dehydration if they open their stomata to promote gas exchange, or inability to produce sugar if they keep their stomata closed to minimize dehydration. (*the long-term consequence of permanently-closed stomata is death by suffocation as the mitochondria run out of oxygen to carry out respiration.)

Many plants which live in hot and/or dry conditions have evolved an alternative carbon fixation pathway to enhance the efficiency of rubisco so that they don’t have to keep their stomata open as much, and thus they reduce the risk of dying from dehydration. These plants are called C4 plants, because the first product of carbon fixation is a 4-carbon compound (instead of a 3-carbon compound as in C3 or “normal” plants). C4 plants use this 4-carbon compound to effectively “concentrate” CO2 around rubisco, so that rubisco is less likely re react with O2.

There are two important adaptations that allow C4 plants to do this:

  • First, C4 plants use an alternate enzyme for the first step of carbon fixation. This enzyme is called phosphoenolpyruvate (PEP) carboxylase, and it has no oxygenase activity and has a much higher affinity for CO2 than rubisco. As the name “PEP carboxylase” suggests, the enzyme attaches CO2 to a compound called phosphoenolpyruvate (PEP).
  • Second, C4 plants have specialized leaf anatomy with two different types of photosynthetic cells: mesophyll cells (on the exterior of the leaf, near stomata) and bundle sheath cells (in the interior of the leaf, far away from stomata). Rubisco is located in bundle sheath cells, but not in mesophyll cells.

PEP carboxylase is located in the mesophyll cells, on the leaf exterior near the stomata. There is no rubisco in the mesophyll cells. CO2 entering the stomata is rapidly fixed by PEP carboxylase into a 4-carbon compound, called malate, by attaching the CO2 to PEP. The malate is then transported deeper into the leaf tissue to the bundle sheath cells, which are both far away from the stomata (and thus far away from oxygen) and contain rubisco. Once inside the bundle sheath cells, malate is decarboxylated to release pyruvate and CO2 the CO2 is then fixed by rubisco as part of the Calvin cycle, just like in C3 plants. Pyruvate then returns to the mesophyll cells, where a phosphate from ATP is used to regenerate PEP. Thus in C4 plants, C4 carbon fixation has a net added cost of 1 ATP for every CO2 delivered to rubisco however, C4 plants are less likely to die of dehydration compared to C3 plants in dry conditions.

The image below illustrates the pathway we just described:

C4 carbon fixation overview, from Wikimedia

What Biol 1510 students need to remember about C4 is that these plants have added a CO2 concentration mechanism to feed rubisco and the Calvin cycle the mechanism uses PEP carboxylase to initially make a 4-carbon compound, that then releases CO2 to rubisco in leaf cells that are exposed to little oxygen. While this mechanism reduces the oxygenase activity of rubisco, it has an extra energy cost in the form of another ATP per mole CO2 fixed.

The (cropped) video below provides a great overview comparison of C3 vs C4 photosynthesis, but be aware of the following issues with this video: the video makes it sound as though RuBP catalyzes its own reaction with CO2 to form to 2 molecules of 3-carbon 3PG, instead of being one of the reactants in this reaction. This enzymatic reaction is catalyzed by rubisco, and it is rubisco that has oxygnase activity, not RuBP! The video also makes it sounds like PEP catalyzes its own reaction with CO2 to form 4-carbon malate, when in reality this reaction is catalyzed by PEP carboxylase.

If you want to know more, the video below gives a more thorough (albeit somewhat slow) illustration of this process:

Advantages and disadvantages of C4 and C3 carbon fixation

  • C4 plants grow better than C3 plants under hot, dry conditions when plants must close their stomata to conserve water – with stomata closed, CO2 levels in the interior of the leaf fall, and O2 levels rise.
  • C3 plants grow better than C4 plants under cool, moist conditions when plants can open their stomata, because C3 plants do not incur the additional cost of ATP of C4 carbon fixation.

Photosynthesis and Respiration: mirror images
The chemical equations for oxygenic photosynthesis and aerobic respiration are exactly the reverse of each other.

A balance between the global rates of photosynthesis (primary production) and global rates of respiration is needed to maintain stable atmospheric concentrations of CO2 and O2.

In eukaryotes, both photosynthesis and respiration occur in organelles with double membranes and their own circular genomes, that originated as prokaryotic endosymbionts.

Both processes have electron transport chains, chemiosmosis and ATP synthase powered by proton motive force.

The powerpoint slides used in the video screencasts are in the Carbon fixation slide set.

Watch the video: Regulation of Stomatal Closing and Opening (February 2023).