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| Photosynthetic Apparatus |
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| The photosynthetic pigments chlorophylls are present in the leaves because of which the leaves are green in colour and are called the photosynthetic organs. The leaves have the following structure: |
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| Histological Details of a Leaf in Cross Section |
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| As shown in the diagram, the mesophyll region of the leaves has cells made of Palisada tissue which contain the pigments. Inside the cell the pigments are present in organelles called chloroplasts which are also known as the photosynthetic organelles. |
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| Chloroplasts can be seen easily under a light microscope (4 6 micrometer in diameter). A continuous double membrane surrounds the chloroplast. In the chloroplast of higher plants, stacks of lamellar structures, called grana (singular granum) are present. Its inner membrane lines the lumen of the chloroplast and it is called matrix or stroma. In the cross-section of the grana, lamellae form sac like structures called thylakoids. A thylakoid of one granum is connected to other granum with the help of a membrane. It is called stroma lamellae. |
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| Section of Chloroplast as seen under electron microscope |
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| The lower epidermal layer of the leaves have specialised cells which guard the openings called the stomata. It is through the stomata that the carbon dioxide enters and the oxygen produced leaves the plant body. Water is made available by the vascular bundles of the midrib and the veins in the leaves. From the vascular bundles, the water moves by osmosis into the photosynthetic cells. |
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| In higher plants, the leaves along with the chloroplasts are considered the photosynthetic apparatus of the plant. Certain young regions may, however, contain chlorophyll. However, in the lower plants like algae, the entire plant body contains the pigments. The exchange of gases and uptake of water takes place through the general surface of the plant body. |
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