Adaptations to maximise light absorption: Each leaf is not in the shade of another. Transparent waxy cuticle — a protective layer that allows light to enter the leaf.
It is waterproof in order to prevent water loss by evaporation. Epidermis — transparent, physical defence layer that does not contain chloroplasts. It allows light into the leaf. Palisade mesophyll layer — regularly shaped allowing many to pack together closely at the top of the leaf. These cells also have many chloroplasts in order to trap as much light as possible. Above Image: Diagram showing the special types of cells present in leaves Without leaves, there would not be life on Earth.
Leaf Structure Leaves are complex organs consisting of many different cell types see Figure 1 including the epidermis, palisade mesophyll layer, spongy mesophyll layer, and vascular bundles. Leaves have an upper epidermis that is located on the upper part of the leaf. A cuticle can also sometimes be present on the outside of the epidermis.
This waxy layer helps prevent water loss, especially in dry regions. The palisade mesophyll layer is made up of closely-packed, elongated cells located just below the upper epidermis. They contain chloroplasts and carry out most of the photosynthesis. Vascular bundles are made up of xylem and phloem cells. These are the cells that carry water and nutrients throughout the plant and are visible as the veins in leaves.
The spongy mesophyll layer is located directly below the palisade mesophyll layer. It consists of irregularly-shaped cells that are loosely packed with air spaces in between. Cells in the spongy layer usually contain few chloroplasts especially in dicot plants and are the storage place for the products of photosynthesis. The air spaces are all interconnected and lead to the outside of the leaf through stomata. The lower epidermis is located on the underside of leaves. Stomata are usually present on the lower epidermis.
In order to minimize transpiration that occurs with gas exchange, most dicot plants have their stomata on the lower epidermis. On the other hand, monocot plants such as corn can have their stomata on both the top and bottom sides of leaves. This is because corn leaves grow upright rather than parallel to the ground and therefore both upper and lower surfaces of leaves experience transpiration.
Chloroplasts and Photosynthesis Inside chloroplasts, there are membrane bound structures called thylakoids that are surrounded by the stroma see Figure 2. Stomata and Gas Exchange Stomata or pores in the leaf surface are surrounded by specialized leaf cells called guard cells see Figure 3.
How is the opening and closing of stomata regulated? Glossary Air spaces: Spaces between spongy mesophyll cells where gas exchange takes place.
Carbon dioxide: A gas used by plants for photosynthesis; a gas produced as waste by animals during cellular respiration. Chlorophyll: A class of pigments produced in plants that give plants their green colour.
Chloroplast: An organelle found in plants and some algae where photosynthesis takes place. Cuticle: A waxy layer usually present on the outside of the epidermis in plants. Dicot: A group of flowering plants. The seeds in this group of plants contain two seed leaves. Epidermis: A single layer of cells that covers all parts of a plant.
Grana singular granum : A stack of thylakoid discs that resembles a stack of coins or pancakes. Guard cells: Specialized cells surrounding stomata that also control stomatal opening and closing. Lamellae: Connect grana stacks together. Monocot: A group of flowering plants. The seeds in this group of plants contain one seed leaf. Osmosis: The movement of molecules through a semi-permeable membrane from a region of higher concentration to lower in order to equalize the concentration on both sides of the membrane.
Oxygen: A gas used by animals during respiration; a gas produced by plants during photosynthesis. Palisade mesophyll layer: Tightly packed layer of elongated cells located directly below the upper epidermis. Phloem: Specialized cells within vascular bundles that transport nutrients throughout the plant. Using an electron microscope , it's possible to not only clearly observe mesophyll cells, but also the architecture of the thylakoid membrane.
However, for the purposes of observing mesophyll cells, a light microscope is sufficient. With various samples, a vibratome is used for cutting in order to obtain thin sections that can be viewed under the microscope. However, with some samples, such as very thin leaves, alternative approaches may be used to cut in order to obtain the thinnest needed.
Here, a young, thin cassava stem is first cleaned and dried under the sun or in the oven. A small leaf sample 1cm sq is then cut out and inserted between the sliced cassava cork so that the sample is held between the sliced cork - Here, it's important to ensure that the cassava cork can fit in the hole of the mini microtome.
When viewed under the microscope, well prepared slices will display preserved mesophyll cells. Here, the epidermis will appear thin and darker while spongy cells will appear scattered below well organized palisade cells.
Return to Plant Biology overview. Return to Leaf Structure under the Microscope. See also info on Meristem cells of plants and Transgenic Plants. Return to learning about Guard Cells. Return to Organelles - Animal and Plant. Return from Mesophyll Cells page to MicroscopeMaster home. David S. Shatelet, et al. Chicago Journals. An alternative simple method for preparing and preserving cross-section of leaves and roots in herbaceous plants: Case study in Orchidaceae.
Eiji Gotoh, et al. Palisade cell shape afects the lightinduced chloroplast movements and leaf photosynthesis. Scientific Reports. Robbertse and N. The taxonomic value of leaf anatomy in the genus Ficus. Keith Roberts. Handbook of Plant Science, Volume 1. Nobuo Chonan. Faculty of Agriculture, Ibaraki University.
Methanobacteria is a class of the phylum Euryarchaeota within the domain Archaea. Read more here. The Islets of Langerhans is an endocrine tissue located within the pancreas. It consists of a variety of cells capable of producing different hormones. Hydrogen-oxidizing Bacteria are species that can use gaseous hydrogen as the electron donor to oxidize hydrogen. The material on this page is not medical advice and is not to be used for diagnosis or treatment.
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