The Ultimate Guide To Mesophyll Cells

Mesophyll cells play a significant role in the plant as they are vital during the photosynthesis process. However, what they are and what role they play are often overlooked.

The Ultimate Guide To Mesophyll Cells

In order to truly understand photosynthesis and how it works, you need to understand what mesophyll cells are. 

Mesophyll cells are an integral part of the plant’s structure and an essential part, especially during photosynthesis. This means that in order to understand how photosynthesis works, you need to know about mesophyll cells. 

In this guide, we’ll be taking you through everything you need to know about mesophyll cells from what they are as well as other relevant information such as their structure and function within the plant. 

What Are Mesophyll Cells?

Before we delve into how mesophyll cells function, it’s essential to understand what they actually are as this will give you a basic understanding.

Mesophyll cells are defined as differentiated cells that are found in the mesophyll layer within plant leaves alongside palisade cells. 

The mesophyll cells are defined by their spongy texture and contain a few chloroplasts, allowing some light to be absorbed as well as providing a pathway for carbon dioxide to pass through during the photosynthesis process. 

Mesophyll cells have a wide range of characteristics and defining features. Here are the main characteristics you need to know:

  • Mesophyll cells can be found just above the lower epidermis and just beneath the palisade cells which, in turn, are beneath the upper epidermis. 
  • They can vary in shape but tend to be cylindrical which allows for easier pathways for carbon dioxide to pass through. 
  • Mesophyll cells and palisade cells make up the majority of internal tissue within leaves.
  • Together, these cells create a variation of ground tissue.

Historically, the word mesophyll has its origins in the Greek language as it is formed from the words “mesos” which means middle, and “phyllo” which means leaf.

This makes sense as the mesophyll cells and mesophyll layer are found in the middle of the leaf. 

There are two layers of cells found in the mesophyll tissue which are the spongy mesophyll cells and the palisade cells, which we will be discussing in detail later in the guide.

However, there are exceptions to this as mesophyll tissue in monocots consists of isodiametric cells. These isodiametric cells are polyhedral compared to the cylindrical shape of the mesophyll cells and palisade cells. 

Where Can The Mesophyll Cells Be Found?

Mesophyll cells cannot be seen with the naked eye. This is because they are located in the middle of the leaf.

Leaves may not seem like they contain a lot, but they contain a complex cellular structure that is made up of a variety of different cells that help the plant through the photosynthesis process. 

Leaves tend to be made up of a variety of tissues that include the mesophyll layer that is surrounded by the upper and lower epidermis as well as vascular tissue. 

The upper and lower epidermis make up the surface of the leaf, while the vascular tissue and mesophyll layer is found between these epidermis layers.

The upper and lower surface of the leaf is known as the adaxial and abaxial, respectively. The upper and lower epidermis protect the layers in the middle, allowing the photosynthesis process to take place. 

The mesophyll layer can be found between the upper and lower epidermis and is made up of two main types of cells: the spongy mesophyll cells and the palisade cells.

The palisade cells are located just beneath the upper epidermis and sit on top of the spongy mesophyll cells while the spongy mesophyll cells are located between the palisade cells and sit on top of the lower epidermis.

When it comes to the location of the vascular tissue, this is also found within the mesophyll layer and is evident when there is a material movement within the cells.

The vascular tissue travels through the spongy mesophyll cells and is specifically known as xylem and phloem.

The spongy mesophyll cells and palisade cells may both be found within the mesophyll layer of a leaf, but they both serve very different functions in order to achieve an efficient system when photosynthesis is taking place. 

Structure Of The Mesophyll Layer

The structure of the mesophyll layer is an essential part of understanding the mesophyll cell’s function as it is made up of two different types of cells that provide a significant role during the photosynthesis process. 

Here are the two types of cells that can be found in the mesophyll layer:

Mesophyll Cells

The first type of cell found in the mesophyll layer is the mesophyll cells. These are located beneath the palisade cells and above the lower epidermis.

The mesophyll cells are defined by their spongy texture and spherical shape. They are sporadically spaced within the leaves, meaning that there are large spaces between the cells. 

When mesophyll cells are observed under a microscope, there tend to be between four and six layers of mesophyll cells that can be found beneath the palisade cells.

The mesophyll cells contain a nucleus, cell membrane, chloroplasts, and a vacuole. 

Compared to palisade cells, mesophyll cells contain fewer chloroplasts because the function of the mesophyll cells is to allow carbon dioxide to pass through, meaning that they don’t require as much light.

An interesting part of the mesophyll cells’ vacuoles has crystal inclusions which is something that is a lot smaller and shorter than the crystals that are found in other cells within the leaf. 

The mesophyll cells are made from spongy parenchyma that can be up to two times thicker than palisade cells. 

There are three different types of spongy parenchyma that can be found within the mesophyll layer depending on what kind of plant the leaf is part of. Here are the variations that you should know about:

  • Aerenchymatous spongy cells
  • Palisade-like spongy cells
  • Typical spongy parenchyma cells

The reason that mesophyll cells don’t contain as many chloroplasts as palisade cells is that the combination of mesophyll and palisade cells allows carbon dioxide to pass through and convert thanks to the light that has been absorbed by the palisade cells. 

Palisade Cells 

The second type of cell that is found in the mesophyll layer is the palisade cells, which we have briefly discussed in the section above.

The palisade cells are located on top of the mesophyll cells and just under the upper epidermis. They are cylindrical and are formed into columns. 

Palisade cells are made up of a large vacuole, chloroplasts, a cell membrane, and a nucleus. There are small spaces in between each cell that allow light and other materials to pass through and are arranged vertically beneath the upper epidermis. 

Palisade cells, like mesophyll cells, have a significant function when it comes to photosynthesis.

This is because they contain 70% of all chloroplasts in the leaf, which is the main source of light absorption, which is then passed through and converted into carbon dioxide and eventually released as oxygen.

The cylindrical shape of the palisade cells means that they can hold more chloroplasts. 

The upper epidermis is one of the thinnest layers of the mesophyll layer, which means that the palisade cells are able to absorb more light.

The more light the palisade cells can absorb, the better the photosynthesis process will be, and the plant will be able to thrive. 

Understanding the benefits of palisade cells will help you to understand how they help the mesophyll cells and how the two work together to efficiently perform the photosynthesis process. Here are the major benefits that the palisade cells provide: 

Chloroplast Movement

The first benefit that palisade cells boast is that they promote chloroplast movement, which is an essential part of the photosynthesis process.

The palisade cells contain the majority of chloroplasts in the plant, which means that it is important that as much light as possible can be absorbed by the cells. 

If the leaf is located in an area where natural light is limited, this can cause an issue and delay in the photosynthesis process.

Therefore, to boost the chances of light absorption, the chloroplasts will move within the palisade cells so that they are in a position where they are able to absorb the light that is available. 

If there is too much light, the chloroplasts will move to areas within the palisade cells where they can hide away from the light to prevent overexposure.

The elongated cylindrical shape of the palisade cells allows the chloroplasts to move around accordingly and adjust their position to prevent any issues in the light absorption stage of photosynthesis. 

Large Vacuole

The second benefit that palisade cells have is their large vacuole which ensures that the chloroplasts stay in place beside the cell membrane.

This means that the palisade cell can absorb as much light as possible as the chloroplasts can be reached easily to ensure that photosynthesis takes place. 

The Function Of The Mesophyll Layer During Photosynthesis

The Function Of The Mesophyll Layer During Photosynthesis

Now that you know about the structure of the mesophyll layer, it’s essential that you understand the function of the layer during the photosynthesis process.

This is because it plays a crucial role during photosynthesis, which, in turn, ensures that the plant thrives.

Here are the functions of the spongy mesophyll cells and palisade cells during photosynthesis:

Spongy Mesophyll Cells

Firstly, spongy mesophyll cells do not receive as much light as the palisade cells because they are located beneath the palisade cell layer, thus meaning that they are not exposed to as much light. Therefore, they contain fewer chloroplasts than palisade cells.

The real function of the spongy mesophyll cells is that they contain a clear pathway for carbon dioxide to travel through which can then be converted into oxygen.

However, in order to allow the carbon dioxide to travel through, the cells need to contain some energy. This is done via a gaseous exchange which is done with the lower epidermis as the large space between them is ideal for this to take place.

The lower epidermis has small openings which allow carbon dioxide and other gases to reach the mesophyll cell which triggers the photosynthetic process and helps in the production of oxygen. 

Oxygen is eventually released as the carbon dioxide is exchanged within the mesophyll cells and then used during the photosynthesis process. The photosynthesis process will occur when the plant is exposed to an appropriate level of light. 

Palisade Cells

When it comes to the palisade cells, have a different function than mesophyll cells, but are equally important when it comes to the photosynthesis process.

The palisade cells contain many chloroplasts, which absorb light and help begin photosynthesis. The palisade cells can be found beneath the upper epidermis which is a thin layer, meaning that light can easily be absorbed. 

They will also absorb carbon dioxide which is an essential part of the photosynthesis process and the ideal location means that the chloroplast locations ensure that the carbon dioxide doesn’t have to travel long. 

The palisade cells have small spaces to ensure that there is more surface area that is covered by the cells to absorb as much light, gases, and water as possible for photosynthesis.

Thanks to the thinness of the cells, they can allow gases such as carbon dioxide to diffuse easily. 

Chloroplasts contain chlorophyll which provides the plant with energy that is required for a photosynthetic reaction that sees the carbon dioxide and water exchanged to produce oxygen and sugar molecules. 

Observing The Mesophyll Layer Under A Microscope

If you want to explore the mesophyll layer even further, you can do so by observing the layer beneath a microscope. This allows you to look into the specific palisade and mesophyll cells and explore the various structures and functions for yourself. 

To observe the mesophyll cells under a microscope, you will need to obtain the following:

  • Alcohol at 30%, 50%, 70%, and 96%
  • Cassava cork
  • Clamp-on hand sliding microtome
  • Compound microscope
  • Glass slides and cover slips for the microscope
  • Preservation liquid that consists of 70% alcohol and glycerin
  • Safranin-O
  • Young leaf

How To Observe Mesophyll Cells

Once you have gathered the correct equipment and materials, you will need to collect a sample that can be observed under the microscope.

Normally, an instrument such as a vibratome is used to slice thin samples, however, when it comes to mesophyll cells, it is best to follow these instructions:

1. Use A Cassava Cork To Retrieve The Sample

Cassava corks are a great way to cut the leaf and obtain your sample. Make sure that the cassava has been cleaned and dried to ensure that it can slice an appropriate sample that can then be observed.

You will need to make sure that the sample can be held in between the sliced cork, while also making sure that the cork itself can fit within the mini microtome hole. 

2. Inserting The Cassava Cork Into The Microtome

Now you need to insert the cassava cork into the microtome hole by using the blade to extract several sample slices. These slices should be so thin that they appear almost transparent in appearance. 

3. Collect The Sample

Once you have cut the slices, you need to carefully collect the samples using a clean needle that is placed on the tip of a paintbrush. Bear in mind that it is okay if the sample is still attached to the blade. 

4. Dehydrate The Sample Using Alcohol

Now, use the alcohol to dehydrate the samples that you have extracted. Use the 30%, 50%, 70%, and 96% in that order for around 30 seconds each. 

5. Extracting The Sample

Extract the sample from the alcohol and make sure that all traces of the alcohol has been completely drained off the sample. 

6. Placing The Sample In The Peservation Liquid

Now place your sample in the preservation liquid that contains 70% alcohol and glycerin. This mixture should contain stains such as 1% Safranin-O.

7. Placing The Sample On The Glass Slide

The sample now needs to be placed on a glass slide and then covered with a cover slip. Make sure that you prevent sample dehydration by placing a few drops of preservation liquid if the sample is dry. 

8. Observe

The sample is ready to be observed, and you should be able to see the mesophyll cells clearly beneath the palisade cells. 

Frequently Asked Questions

What Is The Main Function Of The Mesophyll Cells?

The main function of the mesophyll cell is to allow carbon dioxide to move freely during photosynthesis. This helps the plant to thrive and survive, making mesophyll a hugely important component part of the plant.

They are located just under the palisade cells and above the lower epidermis to ensure that light is being absorbed by the palisade cells and that there is a clear pathway for carbon dioxide and other materials to pass through. 

What is mesophyll’s role in photosynthesis?

When it comes to photosynthesis, mesophyll is one of two significant components alongside the bundle-sheath leaf cells.

Mesophyll cells contain a carbon-fixation pathway that allows the carbon dioxide to be converted into bicarbonate, which in turn is then added to the three-carbon acid phosphoenolpyruvate, known as PEP via the phosphoenolpyruvate carboxylase enzyme.

Do Mesophyll Cells Have Mitochondria?

Mesophyll cells can contain mitochondria, especially when the leaf is contained within dark conditions. Mitochondria can change the intracellular positions of the leaf when responding to light illumination.

The light-dependent positioning of mitochondria is similar to that of chloroplasts.

Conclusion

In conclusion, learning about mesophyll cells is essential when learning about photosynthesis. This is because mesophyll cells are an integral part of a leaf as they allow carbon dioxide to pass through the cellular structure during photosynthesis. 

While the mesophyll cells are known for their spongy appearance and layering, they are combined with the palisade cells to form the mesophyll layer.

The mesophyll cells provide a pathway for carbon dioxide, while the palisade cells contain 70% of chloroplasts to absorb as much light as possible during photosynthesis. 

Understanding what the mesophyll cells are and what their function is as well as the other components found within the mesophyll layer is essential when learning and understanding how the photosynthesis process takes place.

This is because while the mesophyll cells and palisade cells can be found within the mesophyll layer, they have very different functions which serve the photosynthesis process in different ways.

Jennifer Dawkins

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