Leaf & Chloroplast Anatomy - Online Tutor, Practice Problems & Exam Prep

The mesophyll is the leaf's interior tissue, rich in chloroplasts, where photosynthesis occurs. Stomata, tiny pores on the leaf surface, regulate gas exchange, allowing carbon dioxide and oxygen to enter and exit. Chloroplasts, the photosynthesis sites, consist of an outer and inner membrane, thylakoids (stacked as grana), and stroma. Photosynthesis is powered by absorbing electromagnetic wavelengths of light, essential for plant energy conversion. Understanding these structures is crucial for grasping plant biology and the photosynthetic process.

Leaf & Chloroplast Anatomy

In this video, we're going to talk a little bit about leaf and chloroplast anatomy. We're going to start off by defining the mesophyll. The mesophyll refers to the interior leaf tissue consisting of, of course, lots of mesophyll cells. These cells are characterized by having many chloroplast organelles, and recall that the chloroplasts serve as the site of photosynthesis. Because these mesophyll cells have many chloroplasts, and these cells make up the mesophyll tissue, the mesophyll tissue of a leaf is responsible for performing photosynthesis for the plant. Within the word "mesophyll," you can see the roots: "Meso" is a root that means "middle" and "phil" is a root that means "leaf." So, "mesophyll" refers to the middle leaf or the interior leaf tissue.

If we look at our image below on the left-hand side, notice we are showing you a leaf that you might be able to walk outside and see in a tree or find on the ground somewhere. If you zoom into this leaf, you'll notice that it has tissue consisting of mesophyll cells. Notice how these mesophyll cells are found right here in this interior middle region of the leaf. Side by side here, each of these cells contains many chloroplasts. The chloroplasts are these tiny green circles that you see within each mesophyll cell. If we were to zoom into one of these chloroplasts, it would look like this.

It's important to note that the leaf also has very important structures referred to as stomata. The stomata are not to be confused with the stroma, which is a region within the chloroplast itself. Stomata differ from the stroma, so you don't want to confuse these two terms. What are these stomata? The stomata are tiny holes or pores in the leaf itself. These holes or pores can open and close. They control gas exchange between the leaf and the environment, responsible for the gas exchange of carbon dioxide, oxygen, and even water as water vapor, all components of photosynthesis. When the stomata are open, they allow for this gas exchange and enable photosynthesis to proceed as normal.

Later in our course, when we talk about different types of photosynthesis, comparing C₃, C₄, and CAM photosynthesis, we'll be able to discuss the stomata in greater detail. For now, know that the stomata are tiny holes in the leaf that allow for gas exchange with the atmosphere. In addition, we need to recall the anatomy of the chloroplast itself, which is the organelle that acts as the site of photosynthesis. Chloroplasts have two membranes: an outer membrane that surrounds the entire organelle and an inner membrane embedded within.

Within the inner membrane, you will notice stacks of structures that look like green pancakes. These are not actually pancakes but are called thylakoids. Each individual green pancake is called a thylakoid, whereas an entire stack of thylakoids is referred to as a granum or grana for plural. Just outside of the thylakoids but still within the chloroplast, this region is referred to as the stroma - different from the stomata, which are the openings in the leaf allowing gas exchange. The stroma is this fluid-filled space within the chloroplast.

Chloroplasts are the site of photosynthesis, powered by absorbing electromagnetic wavelengths of light. We will discuss more about these electromagnetic waves of light as we move forward in our course. For now, note that electromagnetic waves of light provide the power to drive photosynthesis, and chloroplasts are able to obtain that power by absorbing these electromagnetic waves of light. This concludes our brief introduction to leaf and chloroplast anatomy, defining the mesophyll, the stomata, and reviewing chloroplast anatomy. As we move forward in our course, we'll continue to talk more and more about photosynthesis. I'll see you all in our next video.

A gelatinous matrix inside the chloroplast containing ribosomes, DNA and enzymes is the:

a) Granum.

b) Chlorophyll.

c) Thylakoid.

d) Stroma.

e) Mitochondria.

• A. Granum
• B. Chlorophyll.
• C. Thylakoid.
• D. Stroma.
• E. Mitochondria.

Which plant structure is responsible for a plant's gas exchange with the atmosphere?

a) Chloroplast.

b) Stomata.

c) Mesophyll.

d) Stroma.

• A. Chloroplast.
• B. Stomata.
• C. Mesophyll.
• D. Stroma.

Here’s what students ask on this topic:

What is the function of mesophyll in a leaf?

The mesophyll is the interior tissue of a leaf, primarily responsible for photosynthesis. It consists of mesophyll cells, which are rich in chloroplasts, the organelles where photosynthesis occurs. The mesophyll can be divided into two layers: the palisade mesophyll, which is densely packed and located just below the leaf's upper epidermis, and the spongy mesophyll, which has a looser arrangement and is found below the palisade layer. The palisade mesophyll is the main site for light absorption, while the spongy mesophyll facilitates gas exchange due to its air spaces. Together, these layers enable the leaf to efficiently capture light energy and convert it into chemical energy through photosynthesis.

What are stomata and what role do they play in photosynthesis?

Stomata are tiny pores located on the surface of leaves, primarily on the underside. They play a crucial role in photosynthesis by regulating gas exchange between the leaf and the environment. When stomata are open, they allow carbon dioxide (CO₂) to enter the leaf, which is essential for the photosynthetic process. Simultaneously, oxygen (O₂), a byproduct of photosynthesis, is released through these pores. Stomata also facilitate the release of water vapor in a process known as transpiration. The opening and closing of stomata are controlled by guard cells, which respond to environmental conditions to optimize gas exchange and minimize water loss.

What is the structure and function of chloroplasts in plant cells?

Chloroplasts are specialized organelles in plant cells that serve as the site of photosynthesis. They have a double membrane structure, consisting of an outer membrane and an inner membrane. Inside the chloroplast, there are stacks of membrane-bound structures called thylakoids, which resemble green pancakes. These thylakoids are organized into stacks known as grana (singular: granum). The space surrounding the thylakoids is called the stroma. Chloroplasts capture light energy through pigments like chlorophyll, which are embedded in the thylakoid membranes. This light energy is then used to convert carbon dioxide and water into glucose and oxygen, providing energy for the plant.

How do electromagnetic wavelengths of light power photosynthesis?

Photosynthesis is powered by electromagnetic wavelengths of light, primarily in the visible spectrum. Chloroplasts contain pigments such as chlorophyll that absorb light energy. When these pigments absorb light, they become excited and transfer this energy to the photosynthetic reaction centers. This energy is then used to split water molecules (H₂O) into oxygen (O₂), protons (H⁺), and electrons. The electrons move through the electron transport chain, creating a proton gradient that drives the synthesis of ATP and NADPH. These molecules are then used in the Calvin cycle to convert carbon dioxide (CO₂) into glucose, a form of chemical energy that the plant can use.

What is the difference between stomata and stroma in plant cells?

Stomata and stroma are distinct structures in plant cells with different functions. Stomata are tiny pores located on the surface of leaves, primarily involved in gas exchange. They allow carbon dioxide (CO₂) to enter the leaf and oxygen (O₂) and water vapor to exit, facilitating photosynthesis and transpiration. Stroma, on the other hand, is the fluid-filled space inside chloroplasts, surrounding the thylakoids. It contains enzymes, DNA, and ribosomes necessary for the Calvin cycle, where carbon dioxide is converted into glucose. While stomata are external structures on the leaf surface, stroma is an internal component of chloroplasts.