Test And Quizzes for Biology, Pre-AP, Or AP Biology For Teachers And Students
Find what you need to study
5 min read • december 28, 2022
Photosynthesis is a chemical process with the following equation: H2O + CO2 → C6H12O6 + O2 .
Both plants and photosynthetic bacteria are capable of this complex conversion process. The overall reaction is spurred by the energy from a photon of light striking a pigment in the chloroplast . It is thought that photosynthesis first evolved in prokaryotic cells .
Photosynthesis is broken down into two major steps which are dependent on one another: light-dependent reactions and light-independent reactions ( Calvin Cycle ). Both of these processes occur in the chloroplast of a photosynthetic organism.
Image courtesy of WikiMedia Commons .
Light-dependent reactions occur in the thylakoid membranes of the chloroplast . These are the “pancakes” of the chloroplast , as they look like a stack of flattened disks. The thylakoid membranes possess important pigments called chlorophyll . This pigment has electrons in it that are excited when energy is input by a photon of light . There are many pigments, but for photosynthesis , we'll focus more on chlorophyll , the main one.
When light strikes the chloroplast , an electron from a molecule of chlorophyll is excited and travels through the electron transport chain . In the process, a concentration gradient of hydrogen ions is formed. This will be used later to produce ATP through ATP synthase . The electron lost from chlorophyll is replaced by an electron from water. This creates more hydrogen ions and the production of oxygen , which is released from the plant.
Light-Dependent Reactions (Electron Transport Chain)
When light hits the pigments, it'll hit Photosystem II first, which is embedded in the internal membrane of the chloroplast and excites electrons. This causes H+ ions to move into the thylakoid space and to replenish electrons, the light splits water, called photolysis , into two H+ ions and 1/2 of O2 and electrons, which replaces the missing electrons in Photosystem II . Why are the electrons missing then? Well, it's because the electrons continue to jump down the thylakoid membrane, bumping into Photosystem I , and thus leaving Photosystem II . With the electrons going down the thylakoid membrane, hydrogen ions continue to be pumped into the membrane.
Because there a lot of hydrogen ions inside the thylakoid space, it's natural for the H+ ions to want to leave the thylakoid space. But the only way for these ions to leave is to go through a transport protein called ATP (adenosine triphosphate) synthase, where ADP (adenosine diphosphate) is phosphorylated (add another phosphate) when H+ goes through it.
Other electrons from Photosystem I bind to an electron carrier, such as NADPH . Electron carriers transport electrons in the form of a hydrogen ion. These electrons can then be used in other processes. In this case, the electrons will be used to form bonds in the Calvin Cycle .
Image courtesy of Giphy .
The ATP and electron carriers produced during the light-dependent reactions are essential to the production of glucose in the light-independent reactions . The production of oxygen is toxic to the plants but provides the rest of the world with the opportunity to breathe.
Light-Independent Reactions (Calvin Cycle)
The light-independent reactions are named due to the fact that they do not require light in order to proceed. This set of reactions is also referred to as the Calvin Cycle . These reactions take place in the stroma of the chloroplast , or the gooey space in between the thylakoid pancakes. With the help of ATP and NADPH , CO2 is turned into sugar.
In the Calvin Cycle , carbon dioxide is converted into an organic carbon source, most often modeled by glucose . The first step of this reaction involves the enzyme ribulose bisphosphate carboxylase, abbreviated as rubisco . This enzyme is responsible for carbon fixation , taking carbon dioxide from the air and converting it into an organic, usable form.
After carbon dioxide has been fixed, the process begins to convert it into glucose . This involves the creation of a lot of bonds. In order to make bonds, electrons and energy are required. This is where the electron carriers and ATP from the light-dependent reactions come into play.
By using the energy from ATP and the electrons from the electron carriers, a number of enzymes are able to convert organic carbon into glyceraldehyde-3-phosphate, or G3P . G3P is a precursor for a number of carbohydrates such as starch , cellulose , and glucose . The cell can use this to create a number of important energy and structural components.
Also important, the ATP that is used is broken down into ADP and a phosphate group which can be recycled and rebonded in the light-dependent reactions . Similarly, the electron carrier NADPH becomes NADP+ after dropping off the hydrogen. This can then be refilled with an electron in the light-dependent reactions .
Photosynthesis is hard to understand and visualize, but it's an important part of the AP curriculum. Study tips include trying to draw out the process yourself and explain it to a friend or yourself.
Image Courtesy of Slide Player
Understanding the Electron Transport Chain can be the most challenging, so really make sure you understand what causes what. Remember, the sole purpose of photosynthesis is creating sugar. Also, NADPH represents a "loaded dumptruck" with electrons.
© 2024 Fiveable Inc. All rights reserved.
- 8.1 Overview of Photosynthesis
- 1.1 The Science of Biology
- 1.2 Themes and Concepts of Biology
- Chapter Summary
- Review Questions
- Critical Thinking Questions
- Test Prep for AP® Courses
- 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks
- Science Practice Challenge Questions
- 3.1 Synthesis of Biological Macromolecules
- 3.2 Carbohydrates
- 3.4 Proteins
- 3.5 Nucleic Acids
- 4.1 Studying Cells
- 4.2 Prokaryotic Cells
- 4.3 Eukaryotic Cells
- 4.4 The Endomembrane System and Proteins
- 4.5 Cytoskeleton
- 4.6 Connections between Cells and Cellular Activities
- 5.1 Components and Structure
- 5.2 Passive Transport
- 5.3 Active Transport
- 5.4 Bulk Transport
- 6.1 Energy and Metabolism
- 6.2 Potential, Kinetic, Free, and Activation Energy
- 6.3 The Laws of Thermodynamics
- 6.4 ATP: Adenosine Triphosphate
- 6.5 Enzymes
- 7.1 Energy in Living Systems
- 7.2 Glycolysis
- 7.3 Oxidation of Pyruvate and the Citric Acid Cycle
- 7.4 Oxidative Phosphorylation
- 7.5 Metabolism without Oxygen
- 7.6 Connections of Carbohydrate, Protein, and Lipid Metabolic Pathways
- 7.7 Regulation of Cellular Respiration
- 8.2 The Light-Dependent Reaction of Photosynthesis
- 8.3 Using Light to Make Organic Molecules
- 9.1 Signaling Molecules and Cellular Receptors
- 9.2 Propagation of the Signal
- 9.3 Response to the Signal
- 9.4 Signaling in Single-Celled Organisms
- 10.1 Cell Division
- 10.2 The Cell Cycle
- 10.3 Control of the Cell Cycle
- 10.4 Cancer and the Cell Cycle
- 10.5 Prokaryotic Cell Division
- 11.1 The Process of Meiosis
- 11.2 Sexual Reproduction
- 12.1 Mendel’s Experiments and the Laws of Probability
- 12.2 Characteristics and Traits
- 12.3 Laws of Inheritance
- 13.1 Chromosomal Theory and Genetic Linkages
- 13.2 Chromosomal Basis of Inherited Disorders
- 14.1 Historical Basis of Modern Understanding
- 14.2 DNA Structure and Sequencing
- 14.3 Basics of DNA Replication
- 14.4 DNA Replication in Prokaryotes
- 14.5 DNA Replication in Eukaryotes
- 14.6 DNA Repair
- 15.1 The Genetic Code
- 15.2 Prokaryotic Transcription
- 15.3 Eukaryotic Transcription
- 15.4 RNA Processing in Eukaryotes
- 15.5 Ribosomes and Protein Synthesis
- 16.1 Regulation of Gene Expression
- 16.2 Prokaryotic Gene Regulation
- 16.3 Eukaryotic Epigenetic Gene Regulation
- 16.4 Eukaryotic Transcriptional Gene Regulation
- 16.5 Eukaryotic Post-transcriptional Gene Regulation
- 16.6 Eukaryotic Translational and Post-translational Gene Regulation
- 16.7 Cancer and Gene Regulation
- 17.1 Biotechnology
- 17.2 Mapping Genomes
- 17.3 Whole-Genome Sequencing
- 17.4 Applying Genomics
- 17.5 Genomics and Proteomics
- 18.1 Understanding Evolution
- 18.2 Formation of New Species
- 18.3 Reconnection and Rates of Speciation
- 19.1 Population Evolution
- 19.2 Population Genetics
- 19.3 Adaptive Evolution
- 20.1 Organizing Life on Earth
- 20.2 Determining Evolutionary Relationships
- 20.3 Perspectives on the Phylogenetic Tree
- 21.1 Viral Evolution, Morphology, and Classification
- 21.2 Virus Infection and Hosts
- 21.3 Prevention and Treatment of Viral Infections
- 21.4 Other Acellular Entities: Prions and Viroids
- 22.1 Prokaryotic Diversity
- 22.2 Structure of Prokaryotes
- 22.3 Prokaryotic Metabolism
- 22.4 Bacterial Diseases in Humans
- 22.5 Beneficial Prokaryotes
- 23.1 The Plant Body
- 23.4 Leaves
- 23.5 Transport of Water and Solutes in Plants
- 23.6 Plant Sensory Systems and Responses
- 24.1 Animal Form and Function
- 24.2 Animal Primary Tissues
- 24.3 Homeostasis
- 25.1 Digestive Systems
- 25.2 Nutrition and Energy Production
- 25.3 Digestive System Processes
- 25.4 Digestive System Regulation
- 26.1 Neurons and Glial Cells
- 26.2 How Neurons Communicate
- 26.3 The Central Nervous System
- 26.4 The Peripheral Nervous System
- 26.5 Nervous System Disorders
- 27.1 Sensory Processes
- 27.2 Somatosensation
- 27.3 Taste and Smell
- 27.4 Hearing and Vestibular Sensation
- 27.5 Vision
- 28.1 Types of Hormones
- 28.2 How Hormones Work
- 28.3 Regulation of Body Processes
- 28.4 Regulation of Hormone Production
- 28.5 Endocrine Glands
- 29.1 Types of Skeletal Systems
- 29.3 Joints and Skeletal Movement
- 29.4 Muscle Contraction and Locomotion
- 30.1 Systems of Gas Exchange
- 30.2 Gas Exchange across Respiratory Surfaces
- 30.3 Breathing
- 30.4 Transport of Gases in Human Bodily Fluids
- 31.1 Overview of the Circulatory System
- 31.2 Components of the Blood
- 31.3 Mammalian Heart and Blood Vessels
- 31.4 Blood Flow and Blood Pressure Regulation
- 32.1 Osmoregulation and Osmotic Balance
- 32.2 The Kidneys and Osmoregulatory Organs
- 32.3 Excretion Systems
- 32.4 Nitrogenous Wastes
- 32.5 Hormonal Control of Osmoregulatory Functions
- 33.1 Innate Immune Response
- 33.2 Adaptive Immune Response
- 33.3 Antibodies
- 33.4 Disruptions in the Immune System
- 34.1 Reproduction Methods
- 34.2 Fertilization
- 34.3 Human Reproductive Anatomy and Gametogenesis
- 34.4 Hormonal Control of Human Reproduction
- 34.5 Fertilization and Early Embryonic Development
- 34.6 Organogenesis and Vertebrate Formation
- 34.7 Human Pregnancy and Birth
- 35.1 The Scope of Ecology
- 35.2 Biogeography
- 35.3 Terrestrial Biomes
- 35.4 Aquatic Biomes
- 35.5 Climate and the Effects of Global Climate Change
- 36.1 Population Demography
- 36.2 Life Histories and Natural Selection
- 36.3 Environmental Limits to Population Growth
- 36.4 Population Dynamics and Regulation
- 36.5 Human Population Growth
- 36.6 Community Ecology
- 36.7 Behavioral Biology: Proximate and Ultimate Causes of Behavior
- 37.1 Ecology for Ecosystems
- 37.2 Energy Flow through Ecosystems
- 37.3 Biogeochemical Cycles
- 38.1 The Biodiversity Crisis
- 38.2 The Importance of Biodiversity to Human Life
- 38.3 Threats to Biodiversity
- 38.4 Preserving Biodiversity
- A | The Periodic Table of Elements
- B | Geological Time
- C | Measurements and the Metric System
In this section, you will explore the following questions:
- What is the relevance of photosynthesis to living organisms?
- What are the main cellular structures involved in photosynthesis?
- What are the substrates and products of photosynthesis?
Connection for AP ® Courses
As we learned in Chapter 7, all living organisms, from simple bacteria to complex plants and animals, require free energy to carry out cellular processes, such as growth and reproduction. Organisms use various strategies to capture, store, transform, and transfer free energy, including photosynthesis. Photosynthesis allows organisms to access enormous amounts of free energy from the sun and transform it to the chemical energy of sugars. Although all organisms carry out some form of cellular respiration, only certain organisms, called photoautotrophs, can perform photosynthesis. Examples of photoautotrophs include plants, algae, some unicellular eukaryotes, and cyanobacteria. They require the presence of chlorophyll, a specialized pigment that absorbs certain wavelengths of the visible light spectrum to harness free energy from the sun. Photosynthesis is a process where components of water and carbon dioxide are used to assemble carbohydrate molecules and where oxygen waste products are released into the atmosphere. In eukaryotes, the reactions of photosynthesis occur in chloroplasts; in prokaryotes, such as cyanobacteria, the reactions are less localized and occur within membranes and in the cytoplasm. (The structural features of the chloroplast that participate in photosynthesis will be explored in more detail later in The Light-Dependent Reactions of Photosynthesis and Using Light Energy to Make Organic Molecules.) Although photosynthesis and cellular respiration evolved as independent processes—with photosynthesis creating an oxidizing atmosphere early in Earth’s history—today they are interdependent. As we studied in Cellular Respiration, aerobic cellular respiration taps into the oxidizing ability of oxygen to synthesize the organic compounds that are used to power cellular processes.
Information presented and the examples highlighted in the section support concepts and learning objectives outlined in Big Idea 1 and Big Idea 2 of the AP ® Biology Curriculum Framework, as shown in the table. The learning objectives listed in the Curriculum Framework provide a transparent foundation for the AP ® Biology course, an inquiry-based laboratory experience, instructional activities, and AP ® exam questions. A learning objective merges required content with one or more of the seven science practices.
Use this first part of the chapter to present an overview that will be filled out and completed in the later two portions. This will introduce the students to the biochemistry that they need to know and give them a chance to build up their understanding of the material.
Importance of Photosynthesis
Use this section to stress the importance of the interdependence between different species and the role played by photosynthesis in bringing energy to the living organisms. A number of terms, such as photoautotroph, heterotrophy, and chemoautotroph will be introduced here.
Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. In brief, the energy of sunlight is captured and used to energize electrons, whose energy is then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis almost 200 million years ago.
Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis ( Figure 8.2 ). Because they use light to manufacture their own food, they are called photoautotrophs (literally, “self-feeders using light”). Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”), because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds; hence, they are referred to as chemoautotrophs .
The importance of photosynthesis is not just that it can capture sunlight’s energy. A lizard sunning itself on a cold day can use the sun’s energy to warm up. Photosynthesis is vital because it evolved as a way to store the energy in solar radiation (the “photo-” part) as energy in the carbon-carbon bonds of carbohydrate molecules (the “-synthesis” part). Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. When a top predator, such as a wolf, preys on a deer ( Figure 8.3 ), the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to light, to photosynthesis, to vegetation, to deer, and finally to wolf.
Science Practice Connection for AP® Courses
Think about it.
- Why do scientists think that photosynthesis evolved before aerobic cellular respiration?
- Why do carnivores, such as lions, depend on photosynthesis to survive? What evidence supports the claim that photosynthesis and cellular respiration are interdependent processes?
- The first Think About It question is an application of Learning Objective 1.15 and Science Practice 7.2 because students are describing the evolution of two energy-procuring processes that today are present in different organisms.
- The second Think About It question is an application of Learning Objective 2.5 and Science Practice 6.2 because you are explaining how the interdependent processes of photosynthesis and cellular respiration allow organisms to capture, store, and use free energy.
- Aerobic cellular respiration requires free oxygen, which was not available in the Earth’s atmosphere until photosynthetic organisms produced enough oxygen as waste to support developing aerobic respiration.
- Carnivores at the top of the food chain eat herbivores that eat photoautotrophs. So no matter where you are in the food chain, every species depends on photosynthesis to convert light energy to chemical energy. In ecosystems that lack photosynthetic organisms (such as by forests burned by forest fire), organisms on all levels of the food chain die off.
The structures, substrates and products of photosynthesis are introduced in this section. Remind them that Figure 8.5 can also be read from right to left, if cellular respiration is the subject. This should help the students to connect the two pathways of photosynthesis and cellular respiration.
Obtain diagrams of leaf structures to illustrate the content of this section. Try to bring in some leaves for students to look at. They have all seen lots of leaves, but probably never examined them for structural detail. A simple magnifying glass should allow them to see the inner structures discussed in this section.
Main Structures and Summary of Photosynthesis
Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates ( Figure 8.4 ). After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (G3P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.
The following is the chemical equation for photosynthesis ( Figure 8.5 ):
Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved.
In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll . The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimize water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes.
In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast . For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane). Within the chloroplast are stacked, disc-shaped structures called thylakoids . Embedded in the thylakoid membrane is chlorophyll, a pigment (molecule that absorbs light) responsible for the initial interaction between light and plant material, and numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen . As shown in Figure 8.6 , a stack of thylakoids is called a granum , and the liquid-filled space surrounding the granum is called stroma or “bed” (not to be confused with stoma or “mouth,” an opening on the leaf epidermis).
- Rate of photosynthesis will be inhibited as the level of carbon dioxide decreases.
- Rate of photosynthesis will be inhibited as the level of oxygen decreases.
- The rate of photosynthesis will increase as the level of carbon dioxide increases.
- Rate of photosynthesis will increase as the level of oxygen increases.
The Two Parts of Photosynthesis
There are different terms that have been used for these reactions. Go over each pair of terms and discuss how they apply to the pathways.
Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light independent-reactions. In the light-dependent reactions , energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. In the light-independent reactions , the chemical energy harvested during the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide. Therefore, although the light-independent reactions do not use light as a reactant, they require the products of the light-dependent reactions to function. In addition, several enzymes of the light-independent reactions are activated by light. The light-dependent reactions utilize certain molecules to temporarily store the energy: These are referred to as energy carriers. The energy carriers that move energy from light-dependent reactions to light-independent reactions can be thought of as “full” because they are rich in energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. Figure 8.7 illustrates the components inside the chloroplast where the light-dependent and light-independent reactions take place.
Link to Learning
Click the link to learn more about photosynthesis.
- The light reactions produces ATP and NADPH, which are then used in the Calvin cycle.
- The light reactions produces NADP + and ADP, which are then used in the Calvin cycle.
- The light reactions uses NADPH and ATP, which are produced by the Calvin cycle.
- The light reactions produce only NADPH, which is produced by the Calvin cycle.
Everyday Connection for AP® Courses
Photosynthesis at the grocery store.
Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle ( Figure 8.8 ) contains hundreds, if not thousands, of different products for customers to buy and consume.
Although there is a large variety, each item links back to photosynthesis. Meats and dairy link, because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from starchy grains, which are the seeds of photosynthesis-dependent plants. What about desserts and drinks? All of these products contain sugar—sucrose is a plant product, a disaccharide, a carbohydrate molecule, which is built directly from photosynthesis. Moreover, many items are less obviously derived from plants: For instance, paper goods are generally plant products, and many plastics (abundant as products and packaging) are derived from algae. Virtually every spice and flavoring in the spice aisle was produced by a plant as a leaf, root, bark, flower, fruit, or stem. Ultimately, photosynthesis connects to every meal and every food a person consumes.
- at the base
- near the top
- in the middle, but generally closer to the top
- in the middle, but generally closer to the base
As an Amazon Associate we earn from qualifying purchases.
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/8-1-overview-of-photosynthesis
© Jan 8, 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.
Investigation: What Factors Affect Photosynthesis
Background and PreLab
Photosynthesis fuels ecosystems and replenishes the Earth's atmosphere with oxygen. Like all enzyme-driven reactions, the rate of photosynthesis can be measured by either the disappearance of substrate, or the accumulation of products. The equation for photosynthesis is:
6CO 2 + 6H 2 O ------light--------> C 6 H 12 O 6 + 6O 2 + H 2 0
The rate of photosynthesis can be measured by:
1) measuring O2 production 2) measuring CO2 consumption
Leaf Structure and Function
In this investigation, you will use a system that measures the accumulation of oxygen in the leaf. Consider the anatomy of the leaf as shown below.
The leaf is composed of layers of cells. The spongy mesophyll layer is normally infused with gases, oxygen and carbon dioxide. Leaves (or disks cut from leaves) will normally float in water because of these gases. If you draw the gases out from the spaces, then the leaves will sink because they become more dense than water. If this leaf disk is placed in a solution with an alternate source of carbon dioxide in the form of bicarbonate ions, then photosynthesis can occur in a sunken leaf disk. As photosynthesis proceeds, oxygen accumulates in the air spaces of the spongy mesophyll and the leaf becomes buoyant and floats. Oxygen and carbon dioxide are exchanged through openings in the leaf called stoma.
While this is going on, the leaf is also carrying out cellular respiration. This respiration will consume the oxygen that has accumulated and possibly cause the plant disks to sink. The measurement tool that can be used to observe these counteracting processes is the floating (or sinking) of the plant disks. In other words, the buoyancy of the leaf disks is actually an indirect measurement of the net rate of photosynthesis occurring in the leaf tissue .
1) To design and conduct an experiment to explore factors that affect photosynthesis. 2) To connect and apply concepts, including the relationship between cell structure and function, strategies for capture and stores of energy, and the diffusion of gases across membranes.
Experimental Question: What factors affect the rate of photosynthesis?
PreLab Questions - these should be completed BEFORE the scheduled lab
1. How can the rate of photosynthesis be measured?
2. Where in the cells of the leaf do you find air spaces?
What is the function of the stomata?
3. What will happen if you remove the air from these spaces?
4. How will air return to these spaces?
5. Instead of carbon dioxide, what will be used as the reactant in this lab?
6. List any factors that you think may affect the rate of photosynthesis. Consider environmental factors that you could manipulate during the lab.
Part 1: Basic Procedure for Measuring the Rate of Photosynthesis
Materials: baking soda, liquid soap, plastic syringes, leaves (spinach or ivy), hole punch, cups or beakers, timer, light source
Troubleshooting: Gently swirl the solution to dislodge disks which may become stuck to the bottom. If no disks float within 5 minutes, add a couple more drops form your soap solution and start the time over again. Place you beaker as close to the light as possible.
To make comparisons between experiments, a standard point of reference is needed. Repeated testing of this procedure has shown that the point at which 50% of the disks are floating (the median or ET 50 ) is a reliable and repeatable point of reference. In this case, the disks floating are counted at the end of each time interval. The median is chosen over the mean as the summary statistic.
The median will generally provide a better estimate of the central tendency of the data because, on occasion, a disk fails to rise or takes a very long time to do so. A term coined by G. L Steucek and R. J Hill (1985) for this relationship is ET50, the estimated time for 50% of the disks to rise. That is, rate is a change in a variable over time. The time required for 50% of the leaf disks to float is represented as Effective Time = ET 50 .
Graph your data for the experimental group. Determine the ET 50 for your leaf disks and determine the ET 50 for your data.
What is the relationship between sodium bicarbonate and photosynthesis rate? This is your CLAIM .
Provide evidence that supports this claim; summarize data by referencing ET50.
Provide reasoning that linke the evidence and the claim and explains why this relationship exists.
Part 2: Design and Conduct Your Own Investigation
Now that you have mastered the floating disk technique, you will design an experiment to test another variable that may affect the rate of photosynthesis. You will collect data, analyze data and present your findings in the form of a LAB REPORT. As you conduct your investigation, you may want to take photos to include in your report. Choose from the list of variables below to investigate. (If you have another variable that you would like to try, check with your instructor first.)
light intensity or distance from the light | amount of sodium bicarbonate water temperature | size of leaf disks or shape of leaf disks | color of light
1. Describe your experiment. You may use sketches.
2. Compile your results into a table and graph the results showing the ET 50
3. Summarize the results of the experiment using the CER format.
Other Resources on Photosynthesis
Inquiry Lab with Vernier Probes
Separation of Plant Pigments with Chromatography
How Does Photosynthesis Work
Light Dependent Reaction and Calvin Cycle
If you're seeing this message, it means we're having trouble loading external resources on our website.
If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.
Unit 1: chemistry of life, unit 2: cell structure and function, unit 3: cellular energetics, unit 4: cell communication and cell cycle, unit 5: heredity, unit 6: gene expression and regulation, unit 7: natural selection, unit 8: ecology, unit 9: worked examples of ap®︎ biology free response questions, unit 10: ap®︎ biology standards mappings.