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    in the given transverse section of the leaf identify the layer of cells where maximum photosynthesis occurs.


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    Leaf Structures Involved in Photosynthesis

    Leaves, and the structures they contain, play key roles in photosynthesis.

    Leaf Structures Involved in Photosynthesis

    Leaf Structures Involved in Photosynthesis Dicot leaf

    Leaves, and the structures they contain, play key roles in photosynthesis.

    When it comes to photosynthesis, the most important parts of the plant are the leaves. Their cells and structures are specialized to take in light and allow for gas exchange with the air around them. They also contain vascular structures that transport water from the roots into the cells that carry out photosynthesis.

    1. The plant’s vascular tissues—xylem and phloem—transport water to the leaves and carry glucose away from the leaves.

    Anyone who cares for plants could probably tell you that pouring water directly onto the leaves isn’t the best idea. Plants absorb water from the soil, using their roots.

    As you probably already know, water is necessary for photosynthesis, which primarily occurs in the plant’s leaves. You might wonder how the water gets from the roots into the leaves, and the answer is through the plant’s vascular system! Just like the veins and arteries that circulate blood throughout our bodies, the plant’s vascular tissues move water, nutrients, and the products of photosynthesis throughout the plant.

    When a plant’s roots absorb water and nutrients from the soil, these materials move up the stem and into the leaves through the xylem. Capillary action—which relies on liquid’s properties of cohesion, surface tension, and adhesion—is what allows water to “defy gravity” as it travels through the xylem and into the leaves.

    Once photosynthesis has occurred, the produced sugars move through the phloem to other parts of the plant to be used in cellular respiration or stored for later.

    2. Stomata, regulated by guard cells, allow gases to pass in and out of the leaf.

    We may not be able to see them with the naked eye, but the leaves of plants contain tons of tiny holes, or pores, called stomata (sing. stoma). They play a central role in photosynthesis, allowing carbon dioxide to enter the leaf and oxygen to exit the leaf. The stomata also facilitate transpiration, the process by which water vapor is released through a plant’s leaves.

    The stomata can be opened and closed, depending on the turgor pressure—the pressure of a cell’s contents against the cell wall—in the two guard cells that border each stoma. High turgor pressure causes these cells to bend outward, opening the stomatal pore. Low turgor pressure, due to loss of water, keeps the stomatal pores closed.

    3. Cells in the mesophyll of the leaf have numerous chloroplasts.

    In leaves, cells in the mesophyll (the tissue between the upper and lower epidermis) are uniquely suited to carry out photosynthesis on a large scale. This is due to their high concentration of chloroplasts, which are the sites of photosynthesis. More chloroplasts means more photosynthetic capability.

    Certain types of plants (dicots and some net-veined monocots) have two different types of mesophyll tissue. Palisade mesophyll cells are densely packed together, whereas spongy mesophyll cells are arranged more loosely to allow gases to pass through them. Palisade mesophyll cells also have more chloroplasts than spongy mesophyll cells.

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    External Sources

    A fun and easy activity from Scientific American that allows you to observe capillary action.

    An OSU page explaining turgor pressure inside plant cells.

    An article on transpiration and the water cycle from the USGS.

    स्रोत : www.visiblebody.com

    8.2: Overview of Photosynthesis

    In multicellular autotrophs, the main cellular structures that allow photosynthesis to take place include chloroplasts, thylakoids, and chlorophyll.

    8.2: Overview of Photosynthesis - Main Structures and Summary of Photosynthesis

    Last updated Jun 9, 2022

    8.1: Overview of Photosynthesis - The Purpose and Process of Photosynthesis

    8.3: Overview of Photosynthesis - The Two Parts of Photosynthesis

    Boundless Boundless Learning Objectives

    Describe the main structures involved in photosynthesis and recall the chemical equation that summarizes the process of photosynthesis

    Overview of Photosynthesis

    Photosynthesis is a multi-step process that requires sunlight, carbon dioxide, and water as substrates. It produces oxygen and glyceraldehyde-3-phosphate (G3P or GA3P), simple carbohydrate molecules that are high in energy and can subsequently be converted into glucose, sucrose, or other sugar molecules. These sugar molecules contain covalent bonds that store energy. Organisms break down these molecules to release energy for use in cellular work.

    Figure 8.2.1 8.2.1

    : Photosynthesis: Photosynthesis uses solar energy, carbon dioxide, and water to produce energy-storing carbohydrates. Oxygen is generated as a waste product of photosynthesis.

    The energy from sunlight drives the reaction of carbon dioxide and water molecules to produce sugar and oxygen, as seen in the chemical equation for photosynthesis. Though the equation looks simple, it is carried out through many complex steps. Before learning the details of how photoautotrophs convert light energy into chemical energy, it is important to become familiar with the structures involved.

    Figure 8.2.1 8.2.1

    : Chemical equation for photosynthesis: The basic equation for photosynthesis is deceptively simple. In reality, the process includes many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3P molecules.

    Photosynthesis and the Leaf

    In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll. The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma ), which also play a role in the plant’s regulation of water balance. The stomata are typically located on the underside of the leaf, which minimizes water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes.

    Figure 8.2.1 8.2.1

    : Structure of a leaf (cross-section): Photosynthesis takes place in the mesophyll. The palisade layer contains most of the chloroplast and principal region in which photosynthesis is carried out. The airy spongy layer is the region of storage and gas exchange. The stomata regulate carbon dioxide and water balance.

    Photosynthesis within the Chloroplast

    In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope composed of an outer membrane and an inner membrane. Within the double membrane are stacked, disc-shaped structures called thylakoids.

    Embedded in the thylakoid membrane is chlorophyll, a pigment that absorbs certain portions of the visible spectrum and captures energy from sunlight. Chlorophyll gives plants their green color and is responsible for the initial interaction between light and plant material, as well as numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen. A stack of thylakoids is called a granum, and the liquid-filled space surrounding the granum is the stroma or “bed.”

    Figure 8.2.1 8.2.1

    : Structure of the Chloroplast: Photosynthesis takes place in chloroplasts, which have an outer membrane and an inner membrane. Stacks of thylakoids called grana form a third membrane layer.

    Key Points

    The chemical equation for photosynthesis is 6CO2+6H2O→C6H12O6+6O2.6CO2+6H2O→C6H12O6+6O2.

    In plants, the process of photosynthesis takes place in the mesophyll of the leaves, inside the chloroplasts.

    Chloroplasts contain disc-shaped structures called thylakoids, which contain the pigment chlorophyll.

    Chlorophyll absorbs certain portions of the visible spectrum and captures energy from sunlight.

    Key Terms

    chloroplast: An organelle found in the cells of green plants and photosynthetic algae where photosynthesis takes place.mesophyll: A layer of cells that comprises most of the interior of the leaf between the upper and lower layers of epidermis.stoma: A pore in the leaf and stem epidermis that is used for gaseous exchange.

    स्रोत : bio.libretexts.org


    =CROSS SECTION OF A LEAF= [image:http://i.imgur.com/xmFDQxM.png?1] '''Cuticle''': A waxy layer th



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    Cuticle: A waxy layer that prevent water loss by evaporation. The cuticle is transparent and very thin to allow maximum light penetration.Upper Epidermis: A protective layer of cells that produces the cuticle. The epidermis is is also transparent and very thin to allow maximum light penetration.Palisade Mesophyll: Rod shaped cells that contain large numbers of chloroplasts for photosynthesis. These cells are located close to the leaf surface to maximise light absorption. They are upright, elongated and tightly packed together in order to increase the surface area for light absorption. Chloroplasts are found near the palisade cell surface to maximise light absorption and to reduce the distance that carbon dioxide and oxygen have to diffuse (to / from the chloroplast stoma)Spongy Mesophyll: These cells are smaller than those of the palisade mesophyll and are found in the lower part of the leaf. They also contain chloroplasts, but not quite as many. These cells have large air spaces between them that allow carbon dioxide and oxygen to diffuse between them. The air spaces also gives these cells a large surface area to maximise the diffusion of carbon dioxide into the cell and oxygen out of the cell.Vein: Plant veins consists of xylem (vessels that carry water) and phloem (vessels that carry dissolved nutrients such as sugar). These vessels play an essential role in transporting water to the chloroplasts in the mesophyll tissues for photosynthesis. They also transport the sugar produced by photosynthesis away from these cells to the rest of the plant tissues to be used as an energy source or stored.Lower Epidermis: A protective layer of cells. The lower epidermis produces a waxy cuticle too in some plant species. The lower epidermis contains pores called stomata that allow carbon dioxide and oxygen to move in and out of the plant respectively.Stomata: Tiny pores (small holes) surrounded by a pair of sausage shaped guard cells. These cells can change shape in order to close the pore. In very hot conditions water inside the leaf evaporates and the water vapour can escape through the stomata. Closing them prevent reduces water loss, but also limits the diffusion of carbon dioxide and oxygen in and out of the leaf.

    Credit: Ben Himme

    स्रोत : www.pathwayz.org

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