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Lesson 10 Parts of a Leaf

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Course: Science 10 [5 cr] - AB Ed copy 1
Book: Lesson 10 Parts of a Leaf
Printed by: Guest user
Date: Sunday, 7 September 2025, 6:43 PM

Table of contents

  Introduction

How do the cells in the leaf support photosynthesis?


A10.1 Photosynthesis
The leaf is where the majority of photosynthesis takes place in plants. This means leaves have their own system with tissues and specialized cells that focus on the process of photosynthesis. Remember, photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into glucose (a type of sugar used for energy) and oxygen. The chemical equation for this process is

«math» «msub» «mi»CO«/mi» «mn»2«/mn» «/msub» «mo»§#160;«/mo» «mfenced» «mi mathvariant=¨normal¨»g«/mi» «/mfenced» «mo»+«/mo» «msub» «mi mathvariant=¨normal¨»H«/mi» «mn»2«/mn» «/msub» «mi mathvariant=¨normal¨»O«/mi» «mo»§#160;«/mo» «mfenced» «mi mathvariant=¨normal¨»l«/mi» «/mfenced» «mo»+«/mo» «mi»Sunlight«/mi» «mo»§#8594;«/mo» «msub» «mi mathvariant=¨normal¨»C«/mi» «mn»6«/mn» «/msub» «msub» «mi mathvariant=¨normal¨»H«/mi» «mn»12«/mn» «/msub» «msub» «mi mathvariant=¨normal¨»O«/mi» «mn»6«/mn» «/msub» «mo»§#160;«/mo» «mfenced» «mi mathvariant=¨normal¨»s«/mi» «/mfenced» «mo»+«/mo» «msub» «mi mathvariant=¨normal¨»O«/mi» «mn»2«/mn» «/msub» «mo»§#160;«/mo» «mfenced» «mi mathvariant=¨normal¨»g«/mi» «/mfenced» «/math»

In this way, plants create their own food and do not need to eat to survive like animals do.

In this lesson, you will learn the different specialized tissues and cells needed for photosynthesis. You will also learn where they are located in the leaf and complete an activity around this.

  Did You Know?


A10.2 Fossil of a fern

Today, the air is made up of 78% nitrogen, 21% oxygen, and less than 1% carbon dioxide. When Earth was first formed, there was little to no oxygen on the planet, but as plants evolved, they took the carbon dioxide present and converted it into oxygen for other life forms to use.


  Targets

By the end of this lesson, you will be able to

        • describe how the cells of the leaf system have a variety of specialized structures and functions
        • identify the structure and function of the epidermis, including guard cells, palisade tissue cells, spongy tissue cells, and phloem and xylem vascular tissue cells that support the process of photosynthesis

          Virtual Lab


        Photosynthesis Lab © Explore Learning
        Background Information:

        This lab gives you an idea of how much oxygen is produced through photosynthesis and the factors that affect production.

        1. Launch the Gizmo by clicking on the play button. Print students can access the Gizmo in the Online Resources for Print Students section of their online course.


        1. This part of the Gizmo allows you to play with the carbon dioxide present, temperature, and light intensity to see how those factors affect the production of oxygen. You can see the amount of oxygen produced by reading the measurements in the oxygen tube or looking at the oxygen flow reading.
        2. Change the three variables and see how they affect the oxygen output.
        3. Record the ideal «math» «msub» «mi»CO«/mi» «mn»2«/mn» «/msub» «/math», temperature, and light intensity you found. The ideal «math» «msub» «mi»CO«/mi» «mn»2«/mn» «/msub» «/math», temperature, and light intensity are the values of those variables that allow for the most amount of oxygen to be produced.

        ©Explore Learning
        A10.3 Where to read oxygen flow
        1. Switch to the “Color” tab.
        2. In this set up, you can see which colour of light and temperature produces the most oxygen. Move the carbon dioxide level up to 1000 ppm, and the light intensity to 100%

        ©Explore Learning
        A10.4 How to switch tabs
        1. Now move the light wavelength around until you find the colour of light that produces the most oxygen.
        2. Once you have found the light wavelength, move the temperature up and down until you find the temperature that produces the most oxygen.
        3. Please return to the top of this page and click on analysis to complete the analysis questions.


        1. What were the best conditions for photosynthesis with the white light?
        Having 81 to 88% intensity and 1000 ppm of carbon dioxide were the best conditions. This makes sure the plant has all the light and carbon dioxide needed to perform photosynthesis, ensuring these factors are not limiting that process. You will learn more about how plants are affected by light in this lesson.

        1. What was the ideal colour of light for photosynthesis?
        Blue light (or a wavelength of 450 nm) is the ideal light for photosynthesis.

        1. What was the ideal temperature for photosynthesis in the different coloured lights?
        Around 23 to 25 degrees Celsius was the best temperature no matter what light colour was used. You will learn more about how temperature affects photosynthesis in this lesson.

          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.

          The Leaf is for Photosynthesis

        The leaf is designed with photosynthesis in mind.



        A10.13 Cross section of a plant leaf
        The leaf is a photosynthesizing machine! The entire structure of the leaf is designed to catch as much sunlight as possible and to allow for the gases needed by photosynthesis to enter. Each type of cell in the leaf has a specific function to carry out in regards to photosynthesis. The tissues in the leaf that are made up of these cells have the specialized function of making food for the rest of the plant.

        Plants, just like animals, still undergo cellular respiration, even while performing photosynthesis. In the next lesson, we will look at how cells are specialized to allow for gas exchange and cellular respiration to occur.

        Scroll down to complete a virtual lab on plant structure.




         

          Digging Deeper

        A10.14 Coca plant leaves

        In ancient civilizations, including Indigenous cultures, the coca plant (famous as it produces cocaine) was used as an anesthetic. In South America, the Incans were using the coca plant as a painkiller and in preparation for surgery long before western medicine started researching the plant in 1884. Go to the following link for more information on the uses of the coca plant. https://en.wikipedia.org/wiki/Coca#Traditional_uses

        Learn More






        Virtual Lab

        Microscope Lab - Plant Structure and Function


        Background Information:

        Structures often look very different under a microscope than they do in diagrams. This virtual lab will give you practice identifying the structures we have talked about in a microscope setting. 

        If you need a refresher on how to use the virtual microscope, please review Exercise 1 under Lab 1.  This microscope has an ocular lens magnification of 10x.

        1. Click on the play icon to open the virtual lab. Print students can access the Virtual Microscope in the Online Resources for Print Students section of their online course.
        2. Click on Exercise 3 under Lab 1
        3. Click on the procedures tab found on the right side of the screen.  This will open the procedures.  You will need to complete both procedures in this lab.
        4. Follow the directions found in the procedures. Remember, finding these tiny structures can take time. Some are very difficult to see, so try not to get frustrated! It is ok if you cannot find a structure or do not understand what you are seeing. Diagrams and real cells are very different things.
        5. Please return to the top of this activity and click on analysis to complete the analysis questions.
        1. Include the images or drawings you took of your cells in Procedure 1 in your notes to study from at a later date.  For more information on how to draw proper scientific diagrams, see page 481 in your textbook.


        ©Lord of Konrad, via Wikimedia Commons
        Caption: A10.16 Leaf cross section with labels


        1. Include the images or drawings you took of your cells in Procedure 2 in your notes to study from at a later date.  For more information on how to draw proper scientific diagrams, see page 481 in your textbook.

        1. What is the total magnification used for the diagrams you created for each procedure?

        In procedure 1 the total magnification used was 100x.  The ocular lens has a magnification of 10x and the 10x objective lens was used.
        In procedure 2 the total magnification used was 400x.  The ocular lens has a magnification of 10x and the 40x objective lens was used.

        1. What was your estimated size of an open stomata?  How does that compare to the estimated size of one of the surrounding cells? Using the knowledge you have gained in this course, do those estimated sizes make sense according to the stomata's function?

        The estimated size of the open stomata is 0.02 mm wide.  The estimated size of a surrounding epidermal cell is 0.1 mm wide.  This makes sense as the stomata needs to be wide enough to allow for transpiration and gas exchange, but cannot be too wide.  If it was too wide, too much water would escape through transpiration.  Different species of plants living in different conditions will have slightly different sizes of stomata as well. 


        1.6 Assignment

        Unit 1 Assignment Lessons 10-13

        It is now time to complete the Lesson 10 portion of 1.6 Assignment. Click on the button below to go to the assignment page.

        1.6 Assignment