What is a Leaf?
Leaves are one of the three organs of a plant. The most important job of a leaf is to make food for the plant. Leaves are the main (but not only) organ responsible for turning sunlight into food. Leaves have different sizes, shapes, and textures, depending on what is most useful in their habitat. The green pigment found in most leaves absorbs sunlight, which is one of the important ingredients in the food-making process.
Leaves contain many parts. Let's explore these leaf parts!
Leaves are composed of a petiole and leaf blade. The leaf blade is made up of many smaller parts. Use this interactive image to learn more about the petiole and the parts that make up the leaf blade.
Petiole. The petiole attaches the leaf to the stem. Sometimes the petiole can look like a stem, but it is actually part of the leaf. Petioles can be long or short, wide or narrow!
Lamina. The lamina is the surface part of the leaf. It has the most area of any leaf part.
Midrib. The midrib supports the leaf from the middle. It is important for helping the leaf keep its shape!
Vein. Every leaf has a system of veins, and this system can look very different among leaves from different plants. Leaf veins have different patterns, but all leaf veins do the same job. Leaf veins are responsible for moving the nutrients and water that come up from the stem around the leaf. Leaf veins are also responsible for moving the sugars (created by the leaf during photosynthesis) to the stem.
Cuticle. The cuticle is a waxy layer that covers the outside of the leaf, and cloaks it in a protective layer. This protective layer acts as a sort of armor for the leaf.
Leaves are the main (but not only) organ responsible for turning sunlight into food. The green pigment found in most leaves absorbs sunlight, which is one of the important ingredients in the food-making process. This process is called photosynthesis.
During photosynthesis, chlorophyll captures the energy of sunlight. The plant combines energy from sunlight, carbon dioxide from air, and water and nutrients absorbed by the roots to make glucose (sugar). Oxygen is produced during photosynthesis and is used by most living things (including people).
Leaves have a very important part that is too small for us to see with our eyes. Stomas! To see stomas on a leaf, we need to use a microscope.
Stomas are small holes on the surface of the leaf that allow gasses into and out of the plant. Each stoma contains two guard cells. Like guards of a castle, the guard cells protect the stoma, opening the stoma when it is time to exchange gasses with the air, and closing the stoma when the plant needs to conserve resources. Without stomas, plants could not get the gasses they use in photosynthesis to make their own food.
When we get thirsty, we try to find water. Sometimes we get our water from our water bottle or a drinking fountain. The water we drink helps us survive and grow.
Plants don’t have water bottles and drinking fountains! They need another way to store water for later. Many desert plants store water in their leaves. Leaves that store water are called succulent leaves.