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Spongy Layer of a Leaf: Function & Concept

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  • 0:00 What is the Spongy…
  • 0:47 Functions of the Leaf Layers
  • 2:41 Lesson Summary
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Lesson Transcript
Instructor: Terry Dunn

Terry has a master's degree in environmental communications and has taught in a variety of settings.

The spongy layer of a leaf may sound odd, but it has an important role in how the leaf functions. Here, you will learn what the spongy layer is, where it is, and what it does.

What is the Spongy Layer of a Leaf?

Chances are, you are near a leaf right now. Perhaps it's on a tree outside your window, or maybe it's part of a nearby houseplant. You may even be sitting near thousands of leaves at the moment. But, how often have you thought about what's inside that leaf or how it's spending its time? It turns out, that leaf is probably more complex and busier than you've ever thought.

The spongy layer of a leaf is the squishy middle layer inside the leaf, kind of like the creamy center of a sandwich cookie. It's made up of parenchyma cells, loosely arranged cells that come in all shapes and sizes. Some of them have chloroplasts, which handle photosynthesis for the leaf. However, it's another layer of the leaf that's the real photosynthesis workhorse.

Functions of the Leaf Layers

Imagine you are on the end of a pin being inserted into a leaf from the upper surface to the bottom surface. First, you would pass through the leaf's cuticle, which is the waxy surface that protects the leaf from water loss. Then you would quickly enter the single-celled layer of the epidermis, which is clear so the sun can reach other cells below.

After that, you would enter the mesophyll, which is made up of two different types of parenchyma cells; the cells in the palisade mesophyll layer and the cells in the spongy mesophyll layer. This is where the work of the leaf is done.

The cells in the palisade layer are shaped like long pills and are arranged vertically when compared to the leaf surface. There are anywhere from one to three layers of palisade cells, and they are absolutely packed with chloroplasts. The task of the palisade layer is photosynthesis.

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