Learn what photosynthesis is and what it does. Explore why photosynthesis is important. Understand the benefits of photosynthesis for both humans and animals.
Photosynthesis Overview, Benefits & Importance
Table of Contents
- What Is Photosynthesis?
- What Does Photosynthesis Do?
- Why Is Photosynthesis Important?
- Lesson Summary
Animals acquire the energy they need to live from the food they eat. For instance, when a person eats a slice of bread, the bread is broken down into simple sugars within the digestive system. These simple sugars are then broken apart in a process called cellular respiration to produce adenosine triphosphate (ATP), a source of energy.
Plants are unable to move around and ingest food. Instead, they produce their own stores of energy through a process known as photosynthesis. Photosynthesis is a chemical reaction that converts carbon dioxide, water, and sunlight into glucose and oxygen. While plants are the most well-known organisms that utilize photosynthesis, other organisms like photosynthetic bacteria and algae also rely on photosynthesis to live. There are even species of plants that are non-photosynthetic. In this lesson, investigate photosynthesis in more detail to understand the following learning objectives:
- What does photosynthesis do?
- Where does photosynthesis take place within a cell?
- How does photosynthesis relate to cellular respiration?
- Why is photosynthesis important to humans and animals?
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Earlier it was stated that photosynthesis is a chemical reaction that converts water, carbon dioxide, and sunlight into glucose and oxygen. But what does photosynthesis do at a cellular level and how does it work? Plants absorb water from the surrounding environment through their roots. This water travels up specialized structures in the plant tissue to areas where photosynthesis can occur. At these sites, carbon dioxide is brought into the plant from the outside environment. Photosynthetic organisms utilize a specialized pigment called chlorophyll to absorb red and blue light waves travelling through the air. When the energy from this light is absorbed, electrons from water molecules are transferred to the carbon dioxide molecules. This reaction results in the formation of new chemicals, what was once water and carbon dioxide become glucose and oxygen. This glucose can then be utilized by the plants as an energy source and excess oxygen is expelled from the plant's body.
Where Does Photosynthesis Take Place?
Photosynthesis takes place in specialized structures called chloroplasts, which are small organelles within plant cells. These chloroplasts contain a number of important chemicals and structures including thylakoids, which appear as small, stacked discs full of chlorophyll. The thylakoids are where the energy collected from chlorophyll pigments is absorbed which results in the splitting of water molecules. While oxygen split from water is expelled from the cell, the remaining energy (generated from built up hydrogen ions) is used to fix carbon dioxide and transform it into storable glucose. Carbon dioxide fixation occurs within the stroma, or inner layer of the chloroplast that surrounds the thylakoids.
Chloroplasts filled with chlorophyll are what gives plants their green coloration. While they occur in large numbers within leaves, chloroplasts are found in plant cells throughout the plant's body. In other photosynthetic organisms such as photosynthetic bacteria (cyanobacteria) and algae, chloroplasts may occur throughout the body as well but do not always result in a green color due to differences in their chlorophyll.
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Cellular Respiration
Photosynthesis occurs via light-dependent and light independent reactions. The light-dependent reactions occur when energy absorbed from light splits water molecules into hydrogen and oxygen. While oxygen is expelled from the cell, hydrogen ions continue to build and enter processes that turn them into two usable forms of energy: ATP and NADH. The light-independent processes then use this energy to transform carbon dioxide into a usable source of energy via the Calvin cycle.
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The glucose that's formed through the Calvin cycle serves as the photosynthetic organism's food source. But once that glucose is formed, how might a plant utilize that as a stable source of energy? The transformation of a glucose molecule back into a source of energy occurs through a process known as cellular respiration, which was briefly introduced in the introduction of this lesson. Cellular respiration breaks a glucose molecule down into water, carbon dioxide, and a large amount of energy that can be used for a number of processes involved in growth and maintenance. All living organisms with cells must undergo some type of cellular respiration in order to generate a type of usable energy.
If all organisms go through cellular respiration, then do animals use photosynthesis? No. While plants and other photosynthetic organisms must utilize solar energy to produce their sugar, animals are able to ingest materials from the world around them. Thus, they take in the sugar needed to maintain bodily processes by eating and not photosynthesis.
It goes without saying that photosynthesis is crucial for the organisms that utilize it. Without photosynthesis these organisms would be unable to produce the sugars needed to generate energy for growth, development, and reproduction. However, the organisms that utilize photosynthesis are not the only ones that benefit from its outcomes. In fact, all ecosystems (and thus all organisms) benefit from photosynthesis. By utilizing carbon dioxide as a resource for generating sugar, photosynthetic animals play a large role in the reduction of carbon-dioxide based pollutants in the atmosphere. This means that photosynthesis may play a major role in the reduction of atmospheric pollutants related to climate change. In addition to atmospheric benefits, other benefits impact humans and other animals directly.
Why Is Photosynthesis Important to Humans?
At its core, photosynthesis is responsible for the oxygen that makes up the breathable air humans depend on. Without the waste oxygen produced during the light-dependent reactions within chloroplasts, the atmosphere would not contain enough oxygen to support human life.
In addition, photosynthesis results in the growth of plant tissues. Plants are highly important organisms that are used in nearly all aspects of human life. Hardened woods are used for building materials to construct shelters, plant tissues and fruits serve an important dietary role, and thousands of plants are researched and incorporated into medicinal practices.
Why Is Photosynthesis Important to Animals?
Why is photosynthesis important to animals? Photosynthesis offers similar benefits to animals as it does to humans. Again, photosynthesis provides the oxygen needed to support animal life. On a dietary role, photosynthesis provides the energy needed to support a number of trophic levels that shape natural food webs. The sugars stored in plants serve as grazing and foraging material for primary consumers, such as deer and rabbits. This energy is used to build animal tissues within these primary consumers, which is then consumed by secondary consumers (predators). With each new consumer, a fraction of the energy created by photosynthetic organisms is used to support an entirely new level of the food chain.
Cellular respiration is the process all living organisms utilize to turn the energy in food into usable energy (adenosine triphosphate (ATP)) to support and maintain life. While animals cannot absorb energy from the sun and thus must consume food to obtain energy, plants are able to generate their own source of chemical energy through a process known as photosynthesis. Photosynthesis starts with light-dependent reactions when solar light energy absorbed by a pigment called chlorophyll breaks down water molecules to generate energy (in the form of ATP and NADP) and oxygen. This process occurs within structures called thylakoids, which are disk-shaped structures found within the photosynthetic organelles, or chloroplasts.
This energy is then used to fuel a process called the Calvin cycle, which is a light-independent reaction that transforms carbon dioxide into glucose. This process occurs within the inner layer (stroma) of the chloroplast. Thus, photosynthesis converts water, solar energy, and carbon dioxide into sugar and oxygen. Photosynthesis creates all of the energy that fuels living organisms. Animals that eat plants acquire their energy from the stored sugar in plants, and animals that eat those animals obtain that same energy. Thus, all levels of a food web are still fueled by the energy developed by photosynthetic organisms. While plants are the most well-known photosynthetic organisms, other organisms such as cyanobacteria and algae are also capable of photosynthesis.
Video Transcript
What Is Photosynthesis?
Plants have leaves and humans have legs. It's easy to imagine that the processes that happen inside plants have nothing to do with us. But the truth is that we wouldn't be alive today without them.
Photosynthesis is a process where plants use light from the sun, water from the roots, and carbon dioxide from the air and turn it into energy to allow them to live. It's probably the most important process that happens inside plants, because without it, plants everywhere would die off rapidly and probably go completely extinct, not to mention taking us with them!
When you look at photosynthesis in more detail, it's an example of something called a chemical reaction. A chemical reaction is a process where the arrangement of the atoms in a substance is changed; atoms are rearranged to create a new substance. Chemical reactions can be described using chemical equations. Here is the chemical equation for photosynthesis:
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The equation says that carbon dioxide is combined with water, which with the addition of light energy, produces glucose (energy the plant can use) and oxygen. The glucose is the important part for plants, because that's what they use to live (to grow, repair, reproduce, etc.) but humans gain multiple benefits from plants also. Let's talk about some of those benefits.
Photosynthesis and Animals
Probably the most obvious benefit that photosynthesis has for animals, like humans, is that photosynthesis is the reason that we have plants that we can eat. Without photosynthesis all plants would die, and that includes the fruits, vegetables, and leaves that form part (or in some cases all) of the diet of animals.
But, let's say you hate eating vegetables. Maybe you're practically a carnivore. Even you still have plants to thank for your existence. The energy that you eat when you eat meat originally came from plants. Animals like chickens and cows eat plants, and that's how their meat gets energy in the first place. But even if you were to eat a predator, like a crocodile or lion (not that many people would), that energy came from those predators eating animals that in turn eat plants. All the energy on Earth that allows animals to live originally came from the sun, and was absorbed by photosynthesizing plants.
However, that isn't the only benefit of photosynthesis for animals. There's a product other than glucose that comes out of photosynthesis: oxygen. Animals breathe oxygen every minute of every day, and we breathe out carbon dioxide. It's photosynthesis that turns that carbon dioxide back into oxygen. That's why rainforests are sometimes described as the lungs of the planet, even though that's not literally true. If you took away all the green plants in the world tomorrow, we wouldn't run out of oxygen in a hurry, but it would eventually happen. So, it's pretty clear that the very air we breathe is thanks to photosynthesis.
Last of all, plants have indirect uses for humans. We use plants for shelter, to create raw materials like wood and rubber, and plants are sources of many medicines. None of these uses of plants will be possible if those plants did not photosynthesize, because without photosynthesis, the plants would die. Plants are absolutely vital to animal life in general, but especially to humans.
Lesson Summary
Let's take a couple of moments to review what we've learned. Photosynthesis is a process where plants use light, water, and carbon dioxide and turn it into energy in the form of glucose. Photosynthesis also produces oxygen. This process can be described with a chemical equation, because photosynthesis is a chemical reaction, which is a process where the arrangement of the atoms in a substance is changed.
Photosynthesis is vital for animals on Earth, not just plants. Animals often eat plants. Animals sometimes eat other animals, but those animals further down the food chain ate plants. The energy we get from the food we eat originally came from plants, which absorbed energy from the sun. Photosynthesis is also important because of the oxygen it produces. They recycle the carbon dioxide we breathe out and turn it back into oxygen so that we never run out.
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