good thinking photosynthesis

Site Navigation

Good thinking — photosynthesis: blinded by the light, object details.

What is photosynthesis?

Photosynthesis is arguably the most important biological process on earth. By liberating oxygen and consuming carbon dioxide, it has transformed the world into the hospitable environment we know today. Directly or indirectly, photosynthesis fills all of our food requirements and many of our needs for fiber and building materials. The energy stored in petroleum, natural gas and coal all came from the sun via photosynthesis, as does the energy in firewood, which is a major fuel in many parts of the world. This being the case, scientific research into photosynthesis is vitally important. If we can understand and control the intricacies of the photosynthetic process, we can learn how to increase crop yields of food, fiber, wood, and fuel, and how to better use our lands. The energy-harvesting secrets of plants can be adapted to man-made systems which provide new, efficient ways to collect and use solar energy. These same natural "technologies" can help point the way to the design of new, faster, and more compact computers, and even to new medical breakthroughs. Because photosynthesis helps control the makeup of our atmosphere, understanding photosynthesis is crucial to understanding how carbon dioxide and other "greenhouse gases" affect the global climate. In this document, we will briefly explore each of the areas mentioned above, and illustrate how photosynthesis research is critical to maintaining and improving our quality of life.

Photosynthesis and food. All of our biological energy needs are met by the plant kingdom, either directly or through herbivorous animals. Plants in turn obtain the energy to synthesize foodstuffs via photosynthesis. Although plants draw necessary materials from the soil and water and carbon dioxide from the air, the energy needs of the plant are filled by sunlight. Sunlight is pure energy. However, sunlight itself is not a very useful form of energy; it cannot be eaten, it cannot turn dynamos, and it cannot be stored. To be beneficial, the energy in sunlight must be converted to other forms. This is what photosynthesis is all about. It is the process by which plants change the energy in sunlight to kinds of energy that can be stored for later use. Plants carry out this process in photosynthetic reaction centers. These tiny units are found in leaves, and convert light energy to chemical energy, which is the form used by all living organisms. One of the major energy-harvesting processes in plants involves using the energy of sunlight to convert carbon dioxide from the air into sugars, starches, and other high-energy carbohydrates. Oxygen is released in the process. Later, when the plant needs food, it draws upon the energy stored in these carbohydrates. We do the same. When we eat a plate of spaghetti, our bodies oxidize or "burn" the starch by allowing it to combine with oxygen from the air. This produces carbon dioxide, which we exhale, and the energy we need to survive. Thus, if there is no photosynthesis, there is no food. Indeed, one widely accepted theory explaining the extinction of the dinosaurs suggests that a comet, meteor, or volcano ejected so much material into the atmosphere that the amount of sunlight reaching the earth was severely reduced. This in turn caused the death of many plants and the creatures that depended upon them for energy.

Photosynthesis and energy. One of the carbohydrates resulting from photosynthesis is cellulose, which makes up the bulk of dry wood and other plant material. When we burn wood, we convert the cellulose back to carbon dioxide and release the stored energy as heat. Burning fuel is basically the same oxidation process that occurs in our bodies; it liberates the energy of "stored sunlight" in a useful form, and returns carbon dioxide to the atmosphere. Energy from burning "biomass" is important in many parts of the world. In developing countries, firewood continues to be critical to survival. Ethanol (grain alcohol) produced from sugars and starches by fermentation is a major automobile fuel in Brazil, and is added to gasoline in some parts of the United States to help reduce emissions of harmful pollutants. Ethanol is also readily converted to ethylene, which serves as a feedstock to a large part of the petrochemical industry. It is possible to convert cellulose to sugar, and then into ethanol; various microorganisms carry out this process. It could be commercially important one day.

Our major sources of energy, of course, are coal, oil and natural gas. These materials are all derived from ancient plants and animals, and the energy stored within them is chemical energy that originally came from sunlight through photosynthesis. Thus, most of the energy we use today was originally solar energy!

Photosynthesis, fiber, and materials. Wood, of course, is not only burned, but is an important material for building and many other purposes. Paper, for example, is nearly pure photosynthetically produced cellulose, as is cotton and many other natural fibers. Even wool production depends on photosynthetically-derived energy. In fact, all plant and animal products including many medicines and drugs require energy to produce, and that energy comes ultimately from sunlight via photosynthesis. Many of our other materials needs are filled by plastics and synthetic fibers which are produced from petroleum, and are thus also photosynthetic in origin. Even much of our metal refining depends ultimately on coal or other photosynthetic products. Indeed, it is difficult to name an economically important material or substance whose existence and usefulness is not in some way tied to photosynthesis.

Photosynthesis and the environment. Currently, there is a lot of discussion concerning the possible effects of carbon dioxide and other "greenhouse gases" on the environment. As mentioned above, photosynthesis converts carbon dioxide from the air to carbohydrates and other kinds of "fixed" carbon and releases oxygen to the atmosphere. When we burn firewood, ethanol, or coal, oil and other fossil fuels, oxygen is consumed, and carbon dioxide is released back to the atmosphere. Thus, carbon dioxide which was removed from the atmosphere over millions of years is being replaced very quickly through our consumption of these fuels. The increase in carbon dioxide and related gases is bound to affect our atmosphere. Will this change be large or small, and will it be harmful or beneficial? These questions are being actively studied by many scientists today. The answers will depend strongly on the effect of photosynthesis carried out by land and sea organisms. As photosynthesis consumes carbon dioxide and releases oxygen, it helps counteract the effect of combustion of fossil fuels. The burning of fossil fuels releases not only carbon dioxide, but also hydrocarbons, nitrogen oxides, and other trace materials that pollute the atmosphere and contribute to long-term health and environmental problems. These problems are a consequence of the fact that nature has chosen to implement photosynthesis through conversion of carbon dioxide to energy-rich materials such as carbohydrates. Can the principles of photosynthetic solar energy harvesting be used in some way to produce non-polluting fuels or energy sources? The answer, as we shall see, is yes.

Why study photosynthesis?

Because our quality of life, and indeed our very existence, depends on photosynthesis, it is essential that we understand it. Through understanding, we can avoid adversely affecting the process and precipitating environmental or ecological disasters. Through understanding, we can also learn to control photosynthesis, and thus enhance production of food, fiber and energy. Understanding the natural process, which has been developed by plants over several billion years, will also allow us to use the basic chemistry and physics of photosynthesis for other purposes, such as solar energy conversion, the design of electronic circuits, and the development of medicines and drugs. Some examples follow.

Photosynthesis and agriculture. Although photosynthesis has interested mankind for eons, rapid progress in understanding the process has come in the last few years. One of the things we have learned is that overall, photosynthesis is relatively inefficient. For example, based on the amount of carbon fixed by a field of corn during a typical growing season, only about 1 - 2% of the solar energy falling on the field is recovered as new photosynthetic products. The efficiency of uncultivated plant life is only about 0.2%. In sugar cane, which is one of the most efficient plants, about 8% of the light absorbed by the plant is preserved as chemical energy. Many plants, especially those that originate in the temperate zones such as most of the United States, undergo a process called photorespiration. This is a kind of "short circuit" of photosynthesis that wastes much of the plants' photosynthetic energy. The phenomenon of photorespiration including its function, if any, is only one of many riddles facing the photosynthesis researcher.

If we can fully understand processes like photorespiration, we will have the ability to alter them. Thus, more efficient plants can be designed. Although new varieties of plants have been developed for centuries through selective breeding, the techniques of modern molecular biology have speeded up the process tremendously. Photosynthesis research can show us how to produce new crop strains that will make much better use of the sunlight they absorb. Research along these lines is critical, as recent studies show that agricultural production is leveling off at a time when demand for food and other agricultural products is increasing rapidly.

Because plants depend upon photosynthesis for their survival, interfering with photosynthesis can kill the plant. This is the basis of several important herbicides, which act by preventing certain important steps of photosynthesis. Understanding the details of photosynthesis can lead to the design of new, extremely selective herbicides and plant growth regulators that have the potential of being environmentally safe (especially to animal life, which does not carry out photosynthesis). Indeed, it is possible to develop new crop plants that are immune to specific herbicides, and to thus achieve weed control specific to one crop species.

Photosynthesis and energy production. As described above, most of our current energy needs are met by photosynthesis, ancient or modern. Increasing the efficiency of natural photosynthesis can also increase production of ethanol and other fuels derived from agriculture. However, knowledge gained from photosynthesis research can also be used to enhance energy production in a much more direct way. Although the overall photosynthesis process is relatively wasteful, the early steps in the conversion of sunlight to chemical energy are quite efficient. Why not learn to understand the basic chemistry and physics of photosynthesis, and use these same principles to build man-made solar energy harvesting devices? This has been a dream of chemists for years, but is now close to becoming a reality. In the laboratory, scientists can now synthesize artificial photosynthetic reaction centers which rival the natural ones in terms of the amount of sunlight stored as chemical or electrical energy. More research will lead to the development of new, efficient solar energy harvesting technologies based on the natural process.

The role of photosynthesis in control of the environment. How does photosynthesis in temperate and tropical forests and in the sea affect the quantity of greenhouse gases in the atmosphere? This is an important and controversial issue today. As mentioned above, photosynthesis by plants removes carbon dioxide from the atmosphere and replaces it with oxygen. Thus, it would tend to ameliorate the effects of carbon dioxide released by the burning of fossil fuels. However, the question is complicated by the fact that plants themselves react to the amount of carbon dioxide in the atmosphere. Some plants, appear to grow more rapidly in an atmosphere rich in carbon dioxide, but this may not be true of all species. Understanding the effect of greenhouse gases requires a much better knowledge of the interaction of the plant kingdom with carbon dioxide than we have today. Burning plants and plant products such as petroleum releases carbon dioxide and other byproducts such as hydrocarbons and nitrogen oxides. However, the pollution caused by such materials is not a necessary product of solar energy utilization. The artificial photosynthetic reaction centers discussed above produce energy without releasing any byproducts other than heat. They hold the promise of producing clean energy in the form of electricity or hydrogen fuel without pollution. Implementation of such solar energy harvesting devices would prevent pollution at the source, which is certainly the most efficient approach to control.

Photosynthesis and electronics. At first glance, photosynthesis would seem to have no association with the design of computers and other electronic devices. However, there is potentially a very strong connection. A goal of modern electronics research is to make transistors and other circuit components as small as possible. Small devices and short connections between them make computers faster and more compact. The smallest possible unit of a material is a molecule (made up of atoms of various types). Thus, the smallest conceivable transistor is a single molecule (or atom). Many researchers today are investigating the intriguing possibility of making electronic components from single molecules or small groups of molecules. Another very active area of research is computers that use light, rather than electrons, as the medium for carrying information. In principle, light-based computers have several advantages over traditional designs, and indeed many of our telephone transmission and switching networks already operate through fiber optics. What does this have to do with photosynthesis? It turns out that photosynthetic reaction centers are natural photochemical switches of molecular dimensions. Learning how plants absorb light, control the movement of the resulting energy to reaction centers, and convert the light energy to electrical, and finally chemical energy can help us understand how to make molecular-scale computers. In fact, several molecular electronic logic elements based on artificial photosynthetic reaction centers have already been reported in the scientific literature.

Photosynthesis and medicine. Light has a very high energy content, and when it is absorbed by a substance this energy is converted to other forms. When the energy ends up in the wrong place, it can cause serious damage to living organisms. Aging of the skin and skin cancer are only two of many deleterious effects of light on humans and animals. Because plants and other photosynthetic species have been dealing with light for eons, they have had to develop photoprotective mechanisms to limit light damage. Learning about the causes of light- induced tissue damage and the details of the natural photoprotective mechanisms can help us can find ways to adapt these processes for the benefit of humanity in areas far removed from photosynthesis itself. For example, the mechanism by which sunlight absorbed by photosynthetic chlorophyll causes tissue damage in plants has been harnessed for medical purposes. Substances related to chlorophyll localize naturally in cancerous tumor tissue. Illumination of the tumors with light then leads to photochemical damage which can kill the tumor while leaving surrounding tissue unharmed. Another medical application involves using similar chlorophyll relatives to localize in tumor tissue, and thus act as dyes which clearly delineate the boundary between cancerous and healthy tissue. This diagnostic aid does not cause photochemical damage to normal tissue because the principles of photosynthesis have been used to endow it with protective agents that harmlessly convert the absorbed light to heat.

Conclusions

The above examples illustrate the importance of photosynthesis as a natural process and the impact that it has on all of our lives. Research into the nature of photosynthesis is crucial because only by understanding photosynthesis can we control it, and harness its principles for the betterment of mankind. Science has only recently developed the basic tools and techniques needed to investigate the intricate details of photosynthesis. It is now time to apply these tools and techniques to the problem, and to begin to reap the benefits of this research.

Written by and Copyright ©1996 Devens Gust Professor of Chemistry and Biochemistry, Arizona State University

A  translation  of this article into Belorussian by Martha Ruszkowski is available

Learn more about Devens Gust

How scientists are helping plants get the most out of photosynthesis

Postdoctoral Researcher, Centre for Tropical Medicine and Global Health, University of Oxford

Researcher of Implementation Science, University of Oxford

Executive Director, Fraunhofer IME

Disclosure statement

Jonathan Menary receives funding from the European Union

Sebastian Fuller receives funding from the European Commission and the UK National Institute for Health and Care Research

Stefan Schillberg receives funding from the European Union

University of Oxford provides funding as a member of The Conversation UK.

View all partners

Photosynthesis is the starting point for almost every food chain, sustaining most life on Earth. You would be forgiven, then, for thinking nature has perfected the art of turning sunlight into sugar. But that isn’t exactly true. If you struggle with life goals, it might reassure you to know even plants haven’t yet reached their full potential.

Every evolved trait is a trade-off between the benefit it provides and its cost in energy . The plants we domesticated for food are only as good at converting sunlight to sugar as they had to be to survive and reproduce. From a given amount of sunshine, most plants convert less than 5% of that light energy into biomass, and under some conditions, less than 1%.

We now have the knowledge and the tools to maximise photosynthesis in a range of food crops – but scientists aren’t just studying how we help plants become better at photosynthesis out of curiosity. Climate change-driven weather such as drought and flooding is destroying crops and threatening crop yields around the world. This research is about making sure we can grow enough food to feed ourselves.

Many people think of plants as nice-looking greens. Essential for clean air, yes, but simple organisms. A step change in research is shaking up the way scientists think about plants: they are far more complex and more like us than you might imagine. This blossoming field of science is too delightful to do it justice in one or two stories.

This article is part of a series, Plant Curious , exploring scientific studies that challenge the way you view plantlife.

Plants such as wheat sometimes mistakenly make a toxic substance called 2-phosphoglycolate which then has to be recycled inside the plant, costing it energy. Scientists call this photorespiration . It happens when an enzyme crucial to the photosynthesis process, rubisco , mistakenly latches on to an oxygen molecule instead of carbon dioxide.

Rubisco makes this mistake up to 40% of the time. It happens because there is now a lot more oxygen in the atmosphere than in the past, put there by the very first photosynthesisers, cyanobacteria – microscopic organisms found in water. Rising temperatures cause more photorespiration too.

If we could prevent this mistake, it would leave plants more energy for photosynthesis.

Capturing sunlight

Our research project, PhotoBoost , is looking at how to create a kind of internal bypass that reduces photorespiration in rice and potato plants, two of the world’s most important crops.

In the same way a coronary bypass diverts blood around narrow or clogged arteries in humans, the photorespiratory bypass gives plants the genetic tools they need to minimise rubisco’s mistake. Genes from cyanobacteria make this and other photosynthetic improvements possible because they host an array of enzymes for better sunlight management.

Other researchers are looking to plants such as maize, which have evolved their own means of dealing with photorespiration, as a source of inspiration – and genes – for rice .

We’re also improving the speed at which plants respond to changes in light intensity, as this affects photosynthesis too. Plants shut off their photosynthetic machinery if they get too much sun (when light is more intense), after which they can be slow to restart photosynthesising when it gets cooler again – for example, when clouds roll over.

A research group in the US recently showed that speeding up this photoprotection process in soybean can lead to a 33% increase in seed yield.

On PhotoBoost, we’re talking to researchers, agronomists and farmers all around the world to understand how to match the needs of society with this new frontier in plant science. According to Elizabete Carmo-Silva and Ana Moreira Lobo, colleagues at Lancaster University: “Climate change, declining yields and water stress constitute major challenges for food production this century.”

Their team investigates plant responses to light and temperature, paying particular attention to the rubisco enzyme. Higher yield is perhaps the most obvious gain from improving photosynthesis, but it will also help make plants more resilient to drought and heat stress.

A new tool in the crop breeder’s arsenal, gene editing , allows scientists to turn genes on and off, testing the effect they have on plant performance. Once we know their function, these genes can be suppressed, promoted or, as has been done in commercial crops since the 1990s , introduced through genetic modification.

At the Universidade Nova de Lisboa in Portugal, Nelson Saibo and Isabel Abreu told us the tools that plant breeders have are more “fine tuners” these days. Their team is using gene editing to improve photosynthesis in rice.

The potato farmers we recently spoke to in the east of England saw greater photosynthesis efficiency as a route to freeing up land for nature – for example, planting trees on ancient forest sites or restoring peatland in the Fens – as more efficient plants mean you need less of them to give the same crop yield. Their major concern was whether major UK retailers would be willing to champion genetically engineered crops.

As well as Photoboost, the European Union is funding other photosynthesis programmes through the Gain4crops (sunflower) and Capitalise (tomato, maize and barley) projects. Improving photosynthesis isn’t a silver bullet for many of the agricultural problems we face. But combining knowledge and new tools will help us get the most out of light.

• Climate change
• Photosynthesis
• Cyanobacteria
• Photorespiration
• Plant Curious

Want to write?

Write an article and join a growing community of more than 189,400 academics and researchers from 5,038 institutions.

Register now

• Why Does Water Expand When It Freezes
• Gold Foil Experiment
• Faraday Cage
• Oil Drop Experiment
• Magnetic Monopole
• Why Do Fireflies Light Up
• Types of Blood Cells With Their Structure, and Functions
• The Main Parts of a Plant With Their Functions
• Parts of a Flower With Their Structure and Functions
• Parts of a Leaf With Their Structure and Functions
• Why Does Ice Float on Water
• Why Does Oil Float on Water
• How Do Clouds Form
• What Causes Lightning
• How are Diamonds Made
• Types of Meteorites
• Types of Volcanoes
• Types of Rocks

Photosynthesis

What is photosynthesis.

It is the process by which green plants, algae, and certain bacteria convert light energy from the sun into chemical energy that is used to make glucose. The word ‘photosynthesis’ is derived from the Greek word phōs, meaning ‘light’ and synthesis meaning ‘combining together.’

Jan Ingenhousz, the Dutch-born British physician and scientist, discovered the process of photosynthesis.

Where does Photosynthesis Occur

Photosynthesis takes place mainly in the leaves of green plants and also in the stems of herbaceous plants as they also contain chlorophyll. Sometimes it also occurs in roots that contain chlorophyll like in water chestnut and Heart-leaved moonseed. Apart from plants, photosynthesis is also found to occur in blue-green algae.

What Happens During Photosynthesis

It involves a chemical reaction where water, carbon dioxide, chlorophyll, and solar energy are utilized as raw materials (inputs) to produce glucose, oxygen, and water (outputs).

Stages of the Process

Photosynthesis occurs in two stages:

1) The Light-dependent Reaction

• Takes place in the thylakoid membranes of chloroplasts only during the day in the presence of sunlight
• High-energy phosphate molecules adenosine triphosphate ( ATP ) and the reducing agent NADPH are produced with the help of electron transport chain

2) The Light-independent or Dark Reaction ( Calvin cycle )

• Takes place in the stroma of chloroplast in the absence of light that helps to fix carbon
• ATP and NADPH produced in the light reaction are utilized along with carbon dioxide to produce sugar in the form of glucose

Factors Affecting the Rate of Photosynthesis

• Intensity of Light: The higher intensity of light increases the rate of photosynthesis
• Temperature:  Warmer the temperature, higher the rate of photosynthesis. The rate is highest between the temperatures of 25° to 35° C, after which it starts to decrease
• Concentration of Carbon dioxide: Higher concentration of carbon dioxide increases the rate of photosynthesis until it reaches a certain point, beyond which no further effects are found   

Although all the above factors together interact to affect the rate of photosynthesis, each of them individually is also capable of directly influencing the process without the other factors and thus called limiting factors.

Importance of Photosynthesis

It serves two main purposes that are essential to support life on earth:

• Producing food for organisms that depend on others for their nutrition such as humans along with all other animals
• Synthesizing oxygen by replacing carbon dioxide in the atmosphere

Ans. Photosynthesis is an endothermic reaction because it absorbs the heat of the sun to carry out the process.

Ans. The oxygen in photosynthesis comes from splitting the water molecules.

Ans. Chlorophyll is the main light-absorbing pigment in photosynthesis.

Ans. The role of water is to provide oxygen in the form of oxygen gas to the atmosphere.

Ans. Sunlight is the source of energy that drives photosynthesis.

Ans. The easiest way to measure the rate of photosynthesis is to quantify the carbon dioxide or oxygen levels using a data logger. The rate of photosynthesis can also be measured by determining the increase in the plant ’s biomass (weight).

Ans. Photosynthesis is an energy-requiring process occurring only in green plants, algae, and certain bacteria that utilizes carbon dioxide and water to produce food in the form of carbohydrates. In contrast, cellular respiration is an energy-releasing process found in all living organisms where oxygen and glucose are utilized to produce carbon dioxide and water.

Ans. Glucose produced in photosynthesis is used in cellular respiration to make ATP.

Article was last reviewed on Tuesday, April 21, 2020

Related articles

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Save my name, email, and website in this browser for the next time I comment.

Popular Articles

Join our Newsletter

Fill your E-mail Address

Related Worksheets

• Privacy Policy

© 2024 ( Science Facts ). All rights reserved. Reproduction in whole or in part without permission is prohibited.

• History & Society
• Science & Tech
• Biographies
• Animals & Nature
• Geography & Travel
• Arts & Culture
• Games & Quizzes
• On This Day
• One Good Fact
• New Articles
• Lifestyles & Social Issues
• Philosophy & Religion
• Politics, Law & Government
• World History
• Health & Medicine
• Browse Biographies
• Birds, Reptiles & Other Vertebrates
• Bugs, Mollusks & Other Invertebrates
• Environment
• Fossils & Geologic Time
• Entertainment & Pop Culture
• Sports & Recreation
• Visual Arts
• Demystified
• Image Galleries
• Infographics
• Top Questions
• Britannica Kids
• Saving Earth
• Space Next 50
• Student Center

photosynthesis summary

Learn how photosynthesis works and why it’s important.

photosynthesis , Process by which green plants and certain other organisms transform light into chemical energy. In green plants, light energy is captured by chlorophyll in the chloroplasts of the leaves and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds (simple and complex sugars) that are the basis of both plant and animal life. Photosynthesis is crucial for maintaining life on Earth; if it ceased, there would soon be little food or other organic matter on the planet, and most types of organisms would disappear.

Photosynthesis consists of a number of photochemical and enzymatic reactions. It occurs in two stages. During the light-dependent stage (“light” reactions), chlorophyll absorbs light energy, which excites some electrons in the pigment molecules to higher energy levels; these leave the chlorophyll and pass along a series of molecules, generating formation of NADPH (an enzyme) and high-energy ATP molecules. Oxygen , released as a by-product, passes into the atmosphere through pores in the leaves. NADPH and ATP drive the second stage, the “dark” reactions (or Calvin cycle, discovered by Melvin Calvin ), which do not require light. During this stage glucose is generated using atmospheric carbon dioxide.

INFOGRAPHIC

Photosynthesis.

Learn about the process that plants, algae, and some bacteria use to make their own food and the oxygen we breathe.

Biology, Ecology

Loading ...

Media credits.

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, specialist, content production, last updated.

October 19, 2023

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

Photosynthesis

Plants are autotrophs, which means they produce their own food. They use the process of photosynthesis to transform water, sunlight, and carbon dioxide into oxygen, and simple sugars that the plant uses as fuel. These primary producers form the base of an ecosystem and fuel the next trophic levels. Without this process, life on Earth as we know it would not be possible. We depend on plants for oxygen production and food.

Biology, Earth Science, Chemistry, Ecology

• Distance Learning
• Director's Circle
• Sustainability
• Smithsonian Science for the Classroom
• Smithsonian Science for Global Goals
• Smithsonian Science Stories
• STC Curriculum
• Explore Smithsonian
• Free Resources
• Smithsonian Science for Makerspaces
• Girls and Women in STEM
• Smithsonian Science for Computational Thinking
• Women in STEM eBook Series
• Space STEM Resources
• Space STEM Career Resources
• Smithsonian Science for NC and SC Classrooms
• Smithsonian Science Education Academies for Teachers
• Good Thinking!
• Quick Tips for Teachers
• English Learners in STEM
• Upcoming Events
• Action Planning Institute
• Building Awareness for Science Education
• Strategic Planning Institute
• Next Steps Institute
• STEM Diversity
• Zero Barriers in STEM
• Network for Emergent Socio-Scientific Thinking (NESST)
• Where We Are
• Smithsonian Science for Summer School (S4)
• Always Thinking Like A Scientist (ATLAS)
• STEM Literacy Project
• Success Stories
• France in Focus
• Smithsonian Science for Global Goals Research
• Smithsonian Youth STEM Exchange
• STEMvisions Blog
• What is Photosynthesis

When you get hungry, you grab a snack from your fridge or pantry. But what can plants do when they get hungry? You are probably aware that plants need sunlight, water, and a home (like soil) to grow, but where do they get their food? They make it themselves!

Plants are called autotrophs because they can use energy from light to synthesize, or make, their own food source. Many people believe they are “feeding” a plant when they put it in soil, water it, or place it outside in the Sun, but none of these things are considered food. Rather, plants use sunlight, water, and the gases in the air to make glucose, which is a form of sugar that plants need to survive. This process is called photosynthesis and is performed by all plants, algae, and even some microorganisms. To perform photosynthesis, plants need three things: carbon dioxide, water, and sunlight.

Just like you, plants need to take in gases in order to live. Animals take in gases through a process called respiration. During the respiration process, animals inhale all of the gases in the atmosphere, but the only gas that is retained and not immediately exhaled is oxygen. Plants, however, take in and use carbon dioxide gas for photosynthesis. Carbon dioxide enters through tiny holes in a plant’s leaves, flowers, branches, stems, and roots. Plants also require water to make their food. Depending on the environment, a plant’s access to water will vary. For example, desert plants, like a cactus, have less available water than a lilypad in a pond, but every photosynthetic organism has some sort of adaptation, or special structure, designed to collect water. For most plants, roots are responsible for absorbing water. 

The last requirement for photosynthesis is an important one because it provides the energy to make sugar. How does a plant take carbon dioxide and water molecules and make a food molecule? The Sun! The energy from light causes a chemical reaction that breaks down the molecules of carbon dioxide and water and reorganizes them to make the sugar (glucose) and oxygen gas. After the sugar is produced, it is then broken down by the mitochondria into energy that can be used for growth and repair. The oxygen that is produced is released from the same tiny holes through which the carbon dioxide entered. Even the oxygen that is released serves another purpose. Other organisms, such as animals, use oxygen to aid in their survival. 

If we were to write a formula for photosynthesis, it would look like this: 

6CO 2 + 6H 2 O + Light energy → C 6 H 12 O 6 (sugar) + 6O 2 

The whole process of photosynthesis is a transfer of energy from the Sun to a plant. In each sugar molecule created, there is a little bit of the energy from the Sun, which the plant can either use or store for later. 

Imagine a pea plant. If that pea plant is forming new pods, it requires a large amount of sugar energy to grow larger. This is similar to how you eat food to grow taller and stronger. But rather than going to the store and buying groceries, the pea plant will use sunlight to obtain the energy to build sugar. When the pea pods are fully grown, the plant may no longer need as much sugar and will store it in its cells. A hungry rabbit comes along and decides to eat some of the plant, which provides the energy that allows the rabbit to hop back to its home. Where did the rabbit’s energy come from? Consider the process of photosynthesis. With the help of carbon dioxide and water, the pea pod used the energy from sunlight to construct the sugar molecules. When the rabbit ate the pea pod, it indirectly received energy from sunlight, which was stored in the sugar molecules in the plant. 

Humans, other animals, fungi, and some microorganisms cannot make food in their own bodies like autotrophs, but they still rely on photosynthesis. Through the transfer of energy from the Sun to plants, plants build sugars that humans consume to drive our daily activities. Even when we eat things like chicken or fish, we are transferring energy from the Sun into our bodies because, at some point, one organism consumed a photosynthetic organism (e.g., the fish ate algae). So the next time you grab a snack to replenish your energy, thank the Sun for it! 

This is an excerpt from the  Structure and Function  unit of our curriculum product line, Science and Technology Concepts TM  (STC). Please visit our publisher,  Carolina Biological , to learn more. 

[BONUS FOR TEACHERS] Watch "Photosynthesis: Blinded by the Light" to explore student misconceptions about matter and energy in photosynthesis and strategies for eliciting student ideas to address or build on them.

Related Tags

View the discussion thread.

• Behind the Scenes

Popular Posts

• It’s All About the Tilt: Seasons Misconceptions Debunked
• Are All Snowflakes Really Different? The Science of Winter
• What Are Clouds?
• What is the Winter Solstice?

Featured Authors

• Brian Mandell, PhD
• Ashley Deese
• Kate Echevarria
• Katya Vines, PhD
• Jean Flanagan
• October (1)
• November (1)
• December (2)
• January (1)
• February (2)
• September (3)
• October (7)
• November (4)
• December (3)
• January (4)
• February (4)
• September (4)
• October (2)
• November (2)
• December (1)
• January (3)
• September (6)
• October (3)
• January (2)
• October (6)
• November (5)
• December (4)
• February (6)
• September (2)
• February (1)
• December (5)
• September (1)
• October (5)
• February (5)
• Terms of Use
• Google Plus

7th Grade - Photosynthesis

Quiz   by carolina carner.

Feel free to use or edit a copy

includes Teacher and Student dashboards

Measure skills from any curriculum

Tag the questions with any skills you have. Your dashboard will track each student's mastery of each skill.

• edit the questions
• save a copy for later
• start a class game
• automatically assign follow-up activities based on students’ scores
• assign as homework
• share a link with colleagues
• print as a bubble sheet

Our brand new solo games combine with your quiz, on the same screen

Correct quiz answers unlock more play!

• Q 5 Plants are an organic compound because they contain elements carbon, hydrogen, and other elements such as oxygen, phosphorus, nitrogen or sulfur. they contain two or more elements that don’t include carbon. they have 24 atoms 30 s
• Q 6 The use of energy from sunlight to convert water and carbon dioxide to sugar is called photosynthesis meditation condensation precipitation 30 s
• Q 7 In addition to water and carbon dioxide, photosynthesis requires chlorophyll and oxygen chlorophyll and dirt light and chlorophyll light and sugar 30 s
• Q 8 Chlorophyll is a blue pigment red pigment yellow pigment green pigment 30 s
• Q 9 The products of photosynthesis are sugar and carbon dioxide sugar and oxygen hydrogen and oxygen water and carbon dioxide 30 s
• Q 10 The reactants in photosynthesis are oxygen and water carbon dioxide and water carbon dioxide and glucose sugar and oxygen 30 s
• Q 11 The sugar (glucose) that is made during photosynthesis for the plant has what kind of stored energy in it? electrical light chemical 30 s

Teachers give this quiz to your class

Photosynthesis Quiz: Test Your Knowledge!

• Share to Facebook
• Share to Twitter
• Share via Email

Age Ranges:

This quiz about photosynthesis was designed to uncover various misconceptions that students often have, starting with GCSE level misconceptions and moving onto undergraduate level misconceptions.

This quiz was compiled with the kind assistance of Prof Howard Griffiths, Department of Plant Science, University of Cambridge and Dr Mark Winterbottom, Faculty of Education, University of Cambridge.

Correct answers are in bold.

[Misconception – Plants ingest all of their food from the soil. Gases do not have mass.]

1. Where does most of a plant’s biomass come from? Put a tick against the answer which makes the greatest contribution to plant mass:

a) from the soil b)   from carbon dioxide from the air and water from the soil c) from nutrients in the soil d) from water

[Misconception – Plants photosynthesise during the day, whereas they respire at night.]

2. At midday, what is happening in the leaf of a plant? (tick one answer)

a) Respiration b) Photosynthesis c) Mainly photosynthesis and some respiration d) None of the above

3. At midnight, what is happening in the leaf of a plant? (tick one answer)

a) Respiration b) Photosynthesis c) Photosynthesis and respiration d) None of the above

[Misconception – Plants photosynthesise, whereas animals respire (plants do not respire).]

4. In which organisms does photosynthesis happen? (tick one answer)

a) Plants b) Animals c) Plants and animals d) None of the above

5. Which of the following need oxygen to survive? (tick one answer) a) Plants b) Animals c) Plants and animals d) None of the above

[Misconception – the major photosynthetic product from photosynthesis is glucose]

6. The end product(s) of photosynthesis in plants are oxygen plus: (tick one answer)

a) Glucose b) Starch c) Starch and Sucrose d) Water

[Misconception – Photosynthesis is the opposite of respiration]

7. Thinking about photosynthesis and respiration in plants, which statement is correct: (tick one answer)

a) Photosynthesis is the opposite of respiration b) Photosynthesis and respiration both occur in plants c) Only photosynthesis occurs in plants d) Respiration for maintenance and growth only occurs in the dark

[Misconception – All the energy captured in photosynthesis is used to synthesise carbohydrates]

8. Light energy captured by photosynthesis is used in a plant for the synthesis of: (tick one answer)

a) Carbohydrates b) Carbohydrates, Fatty acids and Proteins c) Fatty Acids and Proteins d) None of the above

[Misconception – pure oxygen is bubbled from aquatic plants in the light]

9. The gas evolved in bubbling pond weed in the light is: (tick one answer)

a) pure carbon dioxide b) pure oxygen c) air enriched with O 2  plus CO 2  and N 2 d) none of the above

[Misconception – the ‘dark reaction’/light independent stage/ Calvin cycle only occurs in the dark]

10. Photosynthesis takes place in two separate but dependant series of steps, the light reactions and the photosynthetic carbon reduction cycle; this second cycle (also known as the dark reaction / light independent stage / or the Calvin-(Benson-Bassham)* cycle) of photosynthesis occurs:

a) Only in the dark in intact plants b) In the light and dark in intact plants c) Only in the light in intact plants, although will work in the dark in a test-tube d) None of the above

(*now we are trying to recognise the contribution from Calvin’s co-workers)

[Misconception- Photorespiration occurs in the light, and (dark) respiration in the dark]

11. During the aforementioned photosynthetic carbon reduction cycle, some oxygen also interacts with the primary enzyme to produce a waste product (phosphoglycollate). Photorespiration is a salvage pathway which recovers some of this carbon, the rest being released in a process called “photorespiration”. Photorespiration occurs: (tick one answer)

a)    Instead of conventional respiration processes in the light b)    At a higher rate than conventional respiration processes in the light c)    To generate ATP for maintenance and growth

[Misconception – the use of water split during photosynthetic light reactions to provide oxygen dehydrates a leaf]

12. Water used in photosynthetic light reactions: (tick one answer)

a)    Is a significant proportion of leaf water b)    Leads to dehydration and drought stress; c)    Only uses 2 mols H 2 O per mol O 2  evolved, relative to 1000 water vapour mols transpired

[Misconception – Photosystem I and II occur in pairs, coupled by the electron transport components in chloroplast thylakoid membranes]

13. The “Z” scheme in photosynthesis represents: (tick one answer)

a)   Photosystems I and II, and electron transport components, that are evenly distributed throughout higher plant chloroplast thylakoid membranes b)   How Photosystems I and II are spatially separated between thylakoid stacks and intrathylakoid lamellae, coupled by mobile electron carriers which shuttle back and forth through the membrane c)   Shows how electrons are dislodged from chlorophyll by photons and transferred through the pigment bed to each reaction centre

[Misconception – (untouched) Rainforests, and forests in general, provide the O2 we breathe every year (in the past they did, as carbon was sequestered and buried in soils and as fossil fuel reserves)]

14. Rainforests are often described as the ‘lungs of the earth’ which statement is correct: (tick one answer)

a) we need them to renew the oxygen we breathe each year b) purify pollutants from the air c) are virtually carbon/oxygen neutral as respiration = photosynthesis across an annual cycle in an untouched forest d) not sure

[Misconception – the Ozone hole causes global warming (it is caused by atmospheric pollutants interacting with sunlight)]

15. Stratospheric Ozone is thinning and a “hole” occurs over Antarctica, which: (tick one answer)

a)    causes global warming by increasing radiation absorbed from sunlight b)    is caused by CO2 emissions c)    allows dangerous uv radiation to penetrate causing cancer and blindness in animals d)    leads to atmospheric warming due to uv radiation

What's included?

• Photosynthesis misconceptions quiz - without answers
• Photosynthesis misconceptions quiz - with answers
• Photosynthesis

Related content

Teaching resources.

• A-level set practicals - factors affecting rates of photosynthesis
• Interviews with scientists - Photosynthesis to Feed the World?
• Investigating Photosynthesis with the SAPS / NCBE Photosynthesis Kit

Critical Thinking Questions

• ATP and NADPH are forms of chemical energy produced from the light dependent reactions to be used in the light independent reactions that produce sugars.
• ATP and NADPH are forms of chemical energy produced from the light independent reactions, to be used in the light dependent reactions that produce sugars.
• ATP and NADPH are forms of chemical energy produced from the light dependent reactions to be used in the light independent reactions that produce proteins.
• ATP and NADPH are forms of chemical energy produced from the light dependent reactions to be used in the light independent reactions that use sugars as reactants.
• NADPH and ATP molecules are produced during the light-independent reactions and are used to power the light-dependent reactions.
• Sugar and ATP are produced during the light-dependent reactions and are used to power the light-independent reactions.
• Carbon dioxide and NADPH are produced during the light-independent reactions and are used to power the light-dependent reactions.
• NADPH and ATP molecules are produced during the light-dependent reactions and are used to power the light-independent reactions.

Examine the illustration of the photosynthesis equation. How does the equation relate to both photosynthesis and cellular respiration, and what is the connection between the two processes?

• Photosynthesis utilizes energy to build carbohydrates, while cellular respiration metabolizes carbohydrates.
• Photosynthesis utilizes energy to metabolize carbohydrates, while cellular respiration builds carbohydrates.
• Photosynthesis and cellular respiration both utilize carbon dioxide and water to produce carbohydrates.
• Photosynthesis and cellular respiration both metabolize carbohydrates to produce carbon dioxide and water.
• When photons strike photosystem (PS) I, pigments pass the light energy to chlorophyll, molecules that excite electrons, which are then passed to the electron transport chain. The cytochrome complex then transfers protons across the thylakoid membrane and transfers electrons from PS-II to PS-I. The products of the light-dependent reaction are used to power the Calvin cycle to produce glucose.
• When photons strike photosystem (PS) II, pigments pass the light energy to chlorophyll a molecules that in turn excite electrons, which are then passed to the electron transport chain. The cytochrome complex transfers protons across the thylakoid membrane and transfers electrons from PS-I to PS-II. The products of the light-dependent reaction are used to power the Calvin cycle to produce glucose.
• When photons strike photosystem (PS) II, pigments pass the light energy to chlorophyll a molecules that excite electrons, which are then passed to the electron transport chain. The cytochrome complex transfers protons across the thylakoid membrane and transfers electrons from PS-II to PS-I. The products of the light-dependent reaction are used to power the Calvin cycle to produce glucose.
• When photons strike photosystem (PS) II, pigments pass the light energy to chlorophyll a molecules that excite electrons, which are then passed to the electron transport chain. The cytochrome complex transfers protons across the thylakoid membrane and transfers electrons from PS II to PS I. The products of the light-independent reaction are used to power the Calvin cycle to produce glucose.
• Because UV rays and X-rays are high-energy waves, they penetrate the tissues and thus damage cells.
• Because UV rays and X-rays are long-wavelength waves, they penetrate the tissues and thus damage cells.
• Because UV rays and X-rays are low-energy waves, they cannot penetrate tissues and thus damage cells.
• Because UV rays and X-rays are low-frequency waves, they can penetrate tissues and thus damage cells.
• Photosynthesis is not possible.
• Photosynthesis is possible.
• Photosynthesis is possible only with blue light.
• Photosynthesis is possible only with green light.
• After splitting water in PS-I, high-energy electrons are delivered through the chloroplast electron transport chain to PS-II.
• After the photosynthesis reaction, released products like glucose help in the transfer of electrons from PS-II to PS-I.
• After splitting water in PS-II, high-energy electrons are delivered through the chloroplast electron transport chain to PS-I.
• After the completion of the light-dependent reactions, the electrons are transferred from PS-II to PS-I.
• This event will have no effect on the rate of photosynthesis in the leaf.
• Photosynthesis in the leaf will slow down or possibly stop.
• Photosynthesis in the leaf will increase exponentially.
• Photosynthesis in the leaf will first decrease and then increase.
• The product of the Calvin cycle is glyceraldehyde-3 phosphate and RuBP is regenerated.
• The product of the Calvin cycle is glyceraldehyde-3 phosphate and RuBisCO is regenerated.
• The product of the Calvin cycle is a 3-PGA molecule and glyceraldehyde-3 phosphate is regenerated.
• The product of the Calvin cycle is glyceraldehyde-3 phosphate and oxygen is regenerated.
• by using CAM photosynthesis and by closing stomatal pores during the night
• by using CAM photosynthesis and by opening stomatal pores during the night
• by using CAM photosynthesis and by keeping stomatal pores closed at all times
• by bypassing CAM photosynthesis and by keeping stomatal pores closed at night
• The prey of lions are generally herbivores, which depend on heterotrophs.
• The prey of lions are generally smaller carnivorous animals, which depend on non-photosynthetic organisms.
• The prey of lions are generally herbivores, which depend on autotrophs.
• The prey of lions are generally autotrophs, which depend onother autotrophs.
• It takes three turns to fix enough oxygen to export one G3P molecule.
• It takes three turns to produce RuBisCO as an end product.
• It takes three turns to produce ATP and NADPH for fixation of G3P.
• It takes three turns to fix enough carbon to export one G3P molecule.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/biology-ap-courses/pages/1-introduction

• Authors: Julianne Zedalis, John Eggebrecht
• Publisher/website: OpenStax
• Book title: Biology for AP® Courses
• Publication date: Mar 8, 2018
• Location: Houston, Texas
• Book URL: https://openstax.org/books/biology-ap-courses/pages/1-introduction
• Section URL: https://openstax.org/books/biology-ap-courses/pages/8-critical-thinking-questions

© Jul 10, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.