Introduction to Photosynthesis - Online Tutor, Practice Problems & Exam Prep

Photosynthesis is a redox reaction where carbon dioxide (CO₂) is reduced to glucose (C₆H₁₂O₆) and water (H₂O) is oxidized to oxygen (O₂). This process occurs in chloroplasts, utilizing sunlight, CO₂, and H₂O to produce glucose and oxygen. The chemical equations for photosynthesis and cellular respiration are nearly opposites, highlighting their interdependence. Photosynthesis produces glucose and oxygen, which are essential for cellular respiration, while the latter generates CO₂ and H₂O, necessary for photosynthesis.

Introduction to Photosynthesis

In this video, we're going to begin our introduction to photosynthesis. Photosynthesis is the process that uses energy from sunlight to synthesize or build sugars such as glucose. You can see that within the word photosynthesis itself because the root photo refers to light, such as sunlight. And of course, synthesis refers to the ability to synthesize or build something, and in this case, it's going to be sugars such as glucose.

As we'll see down below in our image, the process of photosynthesis uses carbon dioxide gas, or CO2 from the atmosphere, water or H2O, and light energy or sunlight. It uses those three things to make glucose, whose chemical formula is C6H12O6, and oxygen gas, whose chemical formula is O2. Recall from our previous lesson videos when we introduced different organelles that the chloroplasts are green organelles that function as the site of photosynthesis. Photosynthesis is associated with chloroplasts, whereas cellular respiration is associated with mitochondria.

Also recall that photosynthetic organisms or organisms capable of performing photosynthesis are also called autotrophs. This is because autotrophs are able to make their own food without having to consume other living organisms. So, autotrophs include photosynthetic organisms.

Let's take a look at our example image down below to examine the overall chemical equation for photosynthesis. In this image, we can notice that, on the left, we have the chloroplast organelle. When we zoom into the chloroplast, we can see that it functions as the site of photosynthesis. As mentioned above, photosynthesis takes carbon dioxide gas, or CO2 from the atmosphere, water or H2O, and sunlight or solar energy, which comes from the sun. It converts these three relatively simple reactants into sugars such as glucose. Glucose's chemical formula is C6H12O6. Also, oxygen gas is created as a byproduct and would either be released into the environment by the plant or used by the plant itself.

I'll talk more and more about photosynthesis as we move forward in our course. So I'll see you all in our next video.

The main product of photosynthesis is:

a) Glucose.

b) Oxygen.

c) Carbon dioxide.

d) Water.

e) Sunlight.

• A. Glucose.
• B. Oxygen.
• C. Carbon dioxide.
• D. Water.
• E. Sunlight.

Photosynthesis is a Redox Reaction

In this video, we're going to talk about how photosynthesis is really just a redox reaction, which recall from our previous lesson videos just means that it involves the transfer of electrons between molecules. And so once again, the overall chemical equation for photosynthesis is a redox reaction. And recall from our previous lesson videos, redox reactions we can remember by remembering Leo the lion goes ger, and that's because Leo reminds us of substances that lose electrons are oxidized, whereas substances that gain electrons are reduced. And so if you remember Leo the lion goes ger, you'll be good on the redox reactions. And so really photosynthesis is a redox reaction, and what we'll see is that by the end of the process of photosynthesis, carbon dioxide or CO2 is going to get reduced. And so that means that it is going to gain electrons. Whereas water on the other hand, we'll see is going to get oxidized, which means that water is going to lose electrons.

And so let's take a look at our example image down below at the chemical equation for photosynthesis to get a better understanding of this. And so what you'll notice is that over here we have carbon dioxide gas, which is one of the reactants of photosynthesis, and it turns out that there are 6 carbon dioxide gases molecules that are going to react, and there are also going to be 6 water molecules that are going to react. And so the carbon dioxide, water, and sunlight or solar energy are the reactants, and the products are going to be a sugar such as glucose whose chemical formula is C6H12O6, and this is the chemical structure of glucose right here. And then also 6 oxygen gas molecules are going to be produced as well. And so this here represents the entire process of photosynthesis, and what you'll notice is that the carbon dioxide here is actually getting reduced meaning that it is going to gain electrons as it's used to form glucose. And the oxygen I'm sorry, the water molecule here is going to get oxidized as it's converted into oxygen gas. And so that means the water molecule is going to be losing electrons. It's going to be, essentially providing or supplying the electrons, that are needed to reduce carbon dioxide and form glucose.

And so we'll be able to talk more and more about photosynthesis and exactly where and how this process works, but, what you'll notice is that this image here looks very similar to an image that we showed you when we talked about cellular respiration. And so in our next video, what we're going to do is compare and contrast the chemical equation for photosynthesis with the chemical equation for cellular respiration. So I'll see you all in that video.

Which of the following reactants is reduced during the process of photosynthesis?

a) Oxygen gas.

b) Photons of light.

c) Carbon Dioxide.

d) Water.

• A. Oxygen gas.
• B. Photons of light.
• C. Carbon dioxide.
• D. Water.

Photosynthesis vs. Cellular Respiration

In this video, we're going to compare and contrast photosynthesis versus cellular respiration. And so what you may have noticed is that photosynthesis and cellular respiration seem kind of similar when you compare their chemical equations. It turns out that photosynthesis and cellular respiration are both very ancient pathways that have been around for 1,000,000,000 years. They are actually really highly connected to one another, and this is because each process produces the reactants that are necessary for the other process. For example, photosynthesis produces products that are used as the reactants for cellular respiration, and cellular respiration produces products that are used as the reactants for photosynthesis. We'll be able to see this down below in our image. Additionally, photosynthesis and cellular respiration are almost exactly the opposite of each other in terms of their overall chemical equations. We'll be able to see that down below in our image as well.

So, in our example, we're going to be looking at the connection between cellular respiration and photosynthesis. Taking a look at the top half of the image up here, notice that it's occurring inside of the chloroplast organelle. This is, of course, the chemical equation for photosynthesis that we recently talked about in our last lesson video. Photosynthesis takes carbon dioxide, water, and sunlight energy from the atmosphere and converts those things into sugars such as glucose and oxygen gas as a byproduct. The products of photosynthesis, which are glucose and oxygen, are actually used by mitochondria. Notice that glucose and oxygen here are being used by the mitochondria, and one thing to note about this image here of the mitochondria is that it's actually flipped around so that the reactants are here on the right, and the arrow is going from right to left here. These over here are the products of what is known as cellular respiration, which we already covered in our previous lesson videos. The reactants here of the mitochondria of cellular respiration are the products of photosynthesis. You'll see that cellular respiration converts oxygen and glucose and converts them into the products of carbon dioxide, water, and a lot of ATP energy. Carbon dioxide and water are products of cellular respiration but are used as the reactants for photosynthesis. Each process is going to produce the reactants that are needed for the other process.

You can also see that these two equations, the equation for photosynthesis and the equation for cellular respiration, are almost exactly opposites of each other. The reason for that is because notice that carbon dioxide, water, and energy are all reactants for photosynthesis, whereas carbon dioxide, water, and energy are all products for cellular respiration. Remember, they're products because the arrow's going from right to left here. In photosynthesis, glucose and oxygen are produced as products, but in cellular respiration, glucose and oxygen are reactants. So when you compare these two equations side by side, they do line up very similarly. The only difference where they don't line up so similarly is in the type of energy that's used or produced. Cellular respiration is producing ATP, whereas photosynthesis is using solar energy. Another thing that you'll notice is that the substances being oxidized or reduced are flipped as well. In photosynthesis, carbon dioxide is being reduced to glucose. Down below in cellular respiration, glucose is being oxidized to carbon dioxide. In photosynthesis, water is being oxidized to oxygen, whereas down below in cellular respiration, oxygen is being reduced to water, and they are reversed in that respect.

One thing that helps me remember which substances are oxidized and reduced is that I know that photosynthesis is going to be synthesizing something, which is going to be a glucose molecule. Glucose is synthesized, using carbon dioxide. It's able to take carbon dioxide gas from the atmosphere and use that carbon dioxide gas to build glucose. Glucose has many more chemical bonds in it than carbon dioxide. These chemical bonds are made using electrons. So, carbon dioxide needs to gain a lot of electrons to make all of the chemical bonds that are found in glucose, which helps me remember that carbon dioxide has to be reduced. Ultimately, water is going to be oxidized, meaning that water is going to lose electrons and be used to produce oxygen. Now in cellular respiration, I know that glucose, having many chemical bonds, needs to be broken down, stripped of electrons, and lose electrons. When it loses electrons, it's converted into carbon dioxide. Oxygen, acting as the final electron acceptor in cellular respiration, gains the electrons, is reduced, and is converted into water. So these are some ways to help you remember that photosynthesis and cellular respiration are similar to each other, almost exact opposites. The only difference is in the type of energy used or produced. Sunlight energy is used in photosynthesis, whereas ATP energy is produced in cellular respiration. Otherwise, they are pretty much exactly the opposite of each other.

This concludes our comparison of photosynthesis and cellular respiration, and we'll be able to get some practice as we move forward in our course. We'll also continue to talk more and more about photosynthesis. See you all in our next video.

Energy used to power photosynthesis & ultimately cellular respiration originates from which energy source?

a) Glucose.

b) ATP.

c) Carbon dioxide.

d) The sun.

• A. Glucose.
• B. ATP.
• C. Carbon dioxide.
• D. The sun.

Here’s what students ask on this topic:

What is the overall chemical equation for photosynthesis?

The overall chemical equation for photosynthesis can be represented as:

$6{\mathrm{CO}}_2+6H_{2}O+\mathrm{light}\to C_6{H}_{12}{O}_6+6O_2$

This equation shows that six molecules of carbon dioxide (CO₂) and six molecules of water (H₂O) react in the presence of light energy to produce one molecule of glucose (C₆H₁₂O₆) and six molecules of oxygen (O₂).

How are photosynthesis and cellular respiration related?

Photosynthesis and cellular respiration are interdependent processes. Photosynthesis converts carbon dioxide (CO₂), water (H₂O), and sunlight into glucose (C₆H₁₂O₆) and oxygen (O₂). Cellular respiration, on the other hand, uses glucose and oxygen to produce carbon dioxide, water, and ATP energy. Essentially, the products of photosynthesis serve as the reactants for cellular respiration, and vice versa. This cyclical relationship highlights the balance of energy and matter in biological systems.

What role do chloroplasts play in photosynthesis?

Chloroplasts are the organelles within plant cells where photosynthesis occurs. They contain chlorophyll, the pigment that captures light energy. Inside the chloroplasts, the light-dependent reactions convert light energy into chemical energy, producing ATP and NADPH. These energy carriers are then used in the Calvin cycle, which takes place in the stroma of the chloroplasts, to synthesize glucose from carbon dioxide and water.

What is a redox reaction in the context of photosynthesis?

A redox reaction involves the transfer of electrons between molecules. In photosynthesis, carbon dioxide (CO₂) is reduced to glucose (C₆H₁₂O₆), meaning it gains electrons. Conversely, water (H₂O) is oxidized to oxygen (O₂), meaning it loses electrons. This electron transfer is crucial for converting light energy into chemical energy stored in glucose.

What are autotrophs and how are they related to photosynthesis?

Autotrophs are organisms that can produce their own food from inorganic substances. They do not need to consume other organisms for energy. Photosynthetic autotrophs, such as plants, algae, and some bacteria, use photosynthesis to convert light energy, carbon dioxide (CO₂), and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂), thus sustaining themselves and contributing to the energy flow in ecosystems.