Organs and tissues
An organ is a collection of tissues joined in structural unit to serve a common function. Functionally related organs often cooperate to form whole organ systems. Organs exist in all higher biological organisms, they are not restricted to animals, but can also be identified in plants, e.g. the leaf is an organ in a plant as is the root, stem, flowers and fruits.
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Cabbage by Christian Guthier
Leaf Structure
The leaf is the main photosynthesising organ of a plant. The Leaf is an organ because it contains a number of tissues including epidermis, xylem, phloem and parenchyma working together to make food for the plant in photosynthesis.
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Diagram of a section through a leaf
- Upper epidermis
- Palisade layer
- Air space
- Mesophyll
- Xylem
- Phloem
- Stoma
Leaf Adaptations
The upper epidermis is transparent to allow light to pass through to the chlorophyll-containing cells deeper in the leaf.
The palisade cells are tightly packed just underneath the upper epidermis. They are full of chloroplasts for photosynthesis.
Intercellular spaces allow for diffusion and gaseous exchange.
Spongy mesophyll contains chloroplasts for photosynthesis and air spaces to aid diffusion of gases.
Xylem transports water to the cells, as water is a requirement of photosynthesis.
Phloem transports the products of photosynthesis (starch etc.) away from the leaves.
Stomata (controlled by guard cells) allow carbon dioxide to enter and oxygen to leave by diffusion for photosynthesis.
Video – (free, to be embedded) Plant Structure: http://www.neok12.com/php/watch.php?v=zX64544265547901594f5567&t=Plants
Video – (free, to be embedded) Photosynthesis http://www.neok12.com/php/watch.php?v=zX4b7a504d047d5b6e660173&t=Plants
Assignment 3 - Structure of a dicot leaf
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A Label parts 1-7 (7)
B Write down the function and one adaptation of each part. (14)
