Parts of a Leaf

What are the different cells found in a leaf?


A leaf is made up of many different kinds of cells that work together in a system. This system’s main goal is to undergo photosynthesis to provide food and energy to the plant so the plant can perform the basic life functions. In this lesson, we will focus on the cells specialized for photosynthesis and we will look at cells with other specialized functions in the next lessons.



A10.5 Leaf structure



A10.6 Onion Dermal tissue cells
The dermal tissue or epidermis covers the upper and lower surfaces of the leaf. Just like our skin, it helps to protect the leaf from disease and microorganisms. These cells also produce a substance called cuticle that creates a waxy coating on the leaves. This helps prevent water from escaping through the epidermis. Water is needed for photosynthesis, so the plant must conserve it as much as possible.

The main function of these cells is not photosynthesis, so they do not contain chloroplasts; however, they are relatively see-through to allow sunlight to pass through them to the cells below.

A10.7 Stomata and guard cells
Stomata are small holes in the lower surface of the leaf that allow for carbon dioxide to enter the leaf and oxygen to leave the leaf. Carbon dioxide is needed for the process of photosynthesis, so it is important this gas is allowed into the leaf. Oxygen is also produced by photosynthesis, so plants must have a way of releasing the excess oxygen produced. Excess water is also allowed out of the leaf through these openings.

Guard cells surround the stomata, controlling the size of the hole. In this way, the plant can control how much carbon dioxide, oxygen, and water is being allowed into and out of the leaf. If it is very hot, the guard cells will close the stomata to stop water from evaporating out of the leaf.

We will study the stomata and their guard cells in more detail when we look at gas exchange and water transportation in plants.

A10.8 Palisade cells contain chloroplasts
These cells are the ones that undergo the most photosynthesis, as they are packed with chloroplasts. They form a layer right below the dermal tissue cells on the upper side of the leaf and are the top layer of the ground tissue. This gives them the best access to the sunlight. They are rectangular in shape, and they form a dense layer. This makes sure they can catch as much of the sunlight that enters the cell as possible. Their structure and organization is designed with photosynthesis in mind.

©Berkshire Community College via Flickr
A10.9 Spongy tissue cells
These cells make up the remainder of the ground tissue. They are loosely packed to allow for the movement of the carbon dioxide needed for photosynthesis and the oxygen produced by photosynthesis. These cells also contain chloroplasts, though not nearly as many as the palisade tissue cells. This is to allow the spongy tissue cells to catch any sunlight that makes it through the palisade layer.

A10.10 Phloem tissue cells
These cells carry the glucose made by photosynthesis in the leaves to the rest of the plant. This is how the rest of the plant gets energy to perform their life functions. Remember, energy is needed for active transport, to create proteins and lipids in the endoplasmic reticulum, to package the proteins in the Golgi apparatus, and for other cell functions.

  Digging Deeper


A10.11 Aphids on a stem

Aphids eat by piercing a single phloem tissue cell. Their mouthpiece, called a stylet, is so small it only damages the one cell. The pressure in the phloem force feeds the aphid by pushing the phloem sap into the aphid’s food canal. Go to the following link for more information on how aphids eat. https://en.wikipedia.org/wiki/Aphid#Diet

Learn More

A10.12 Xylem Tissue Cells
These cells carry water and minerals needed for photosynthesis from the roots up to the leaves. Both the xylem and the phloem are visible in the leaf as the veins of the leaf. Both types of cells are found within those veins, just like you can sometimes see the veins in your hand or feet.

  Read This

Please read pages 303 and 311 under “Ground Tissue” and 313 under “Vascular Tissue” in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the process of photosynthesis and the role the ground tissue plays in that process. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. Using the specialized cells you have learned about, explain the process of photosynthesis.
Your answer should include the following steps:

  • Carbon dioxide enters the cell through the stomata, which are opened by the guard cells.
  • Water is brought up from the roots to the leaf through the xylem and is prevented from escaping by the epidermis cells.
  • The palisade tissue cells capture the sunlight and undergo photosynthesis in their chloroplasts.
  • The spongy tissue cells also capture a bit of light for their chloroplasts.
  • The oxygen produced is able to diffuse around the leaf through the spongy tissue cells, and the excess oxygen is released through the stomata.
  • The glucose produced is transported to the rest of the plant for use or storage through the xylem tissue cells.
  1. How are the epidermis cells and the palisade tissue cells designed with photosynthesis in mind?
Your answer should include the following:

  • Epidermis cells are transparent to allow the sunlight to reach past their layer.
    • They also control the entry and exit of carbon dioxide, oxygen, and water, which are all needed or produced by photosynthesis.
  • The palisade tissue cells are full of chloroplasts to catch as much of the sunlight as they can.
    • They are also rectangular in shape, so they can be as closely packed as possible. This also helps them catch as much sunlight as possible as sunlight is needed for photosynthesis.