Learn about Leaves

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Leaves are the plants food factory.

A leaf is a flat, thin plant organ that uses the sun to make its own food. In general leaves are green and use the chemical called chlorophyll to trap energy from the sun. This process is known as Photosynthesis. The energy is used to combine water from the soil and carbon dioxide gas from the air to make sugar. Oxygen is released during this process a process called Respiration. The leaf acts almost like a solar panel for attracting energy from the sun. Leaves are prominent in the human diet as leaf vegetables like lettuce.You may not realize it but we eat some form of leaf almost every day…well I know I do!

What are the types of leaves?

Most leaves are flat to increase absorption from the sun although this is not always the case. The main flat area is called the blade or lamina. Not all leaves are flat but most are. A simple leaf has an undivided blade. A compound leaf has a fully subdivided blade with is separated by a main or secondary vein.

What is a plant?

A living thing that usually can produce its own food, reproduces, and rarely is able to move by itself. Many (although not all) plants are green and are part of our ecosystem. A plant is what the leave is attached to.

What are the parts of a plant?

The plant is made up of three parts:

The Leaves – are basically a food making machine.

The Stems – The stems are the plant’s support system. Stems hold up leaves to the light and keep fruits and flowers attached. They grow straight up, trail along the ground, climb fences and trees or stay underground.

The Roots – the roots are the plants anchor and hold the plant firmly in the ground. Roots are also absorbers of water and minerals from the soil. They also store minerals.

What are the parts of a leaf?

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There is awesome variety in leaf structure and some may have all or few of the following parts. The main flat area is called the blade or lamina. Small processes located to either side of the base of the petiole are called the stipule. In some leaves there is no stipule for example. Nearly every leaf has a leaf stalk. The leaf stalk is called the petiole. The petiole attaches to the stem at a point called the leaf axil. Leaves can store food, water and minerals and these are transported through the veins and stem.

What are the layers of a leave?

A leaf is made up of three layers:

Epidermis – This is the outer layer of cells covering the leaf. It is usually transparent and is waxy to prevent water loss.

Mesophyll – This is the interior of the leaf between upper and lower epidermis. This is where most of the photosynthesis occurs. The Mesophyll is divided into two layers a) The upper palisade layer which is tightly packed. Beneath the palisade layer is the b) spongy layer which is, you’ve guessed it…spongy!

Veins – The blackish lines in the leaf blade are called veins. The largest black line is the leaf’s single “midvein,” running from the petiole to the leaf tip, the smaller blackish lines branching off the midvein are “secondary veins”.Veins lend support to the leaf tissue, helping it keep its shape, just like the ribs in an umbrella. Veins also move substances within the leaf, rather like the veins in our own bodies move blood.

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Why do leaves change color?

Chlorophyll is the chemical in leaves that make them green in color. In spring and summer, when there is lots of sunlight, this chemical absorbs energy from the sun and turns it into carbon dioxide and water into sugar and starch.

However, during the fall and winter when there isn’t much sunlight the leaves stop making food and the chlorophyll breaks down making the green color disappear. The other color of the leaves begin to show such as red, orange, yellow and gold. As the leaf is changing colors, the stem is also changing.

Where it is attached at the tree (leaf axil) the cells supporting the leaf are cut. When the wind blows or if the stem is dry, the leaf falls to the ground. That’s why the trees become bare in autumn! Trees that lose there leaves after changing color are called deciduous trees for example oak, maple, birch and elm.

Interesting Facts

  • Leaves alone account for 75% of our solid waste in the fall
  • The oils in some leaves are said to have healing properties. Used in aromatherapy to alleviate headaches and repel insects.



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