Name: photosynthesis: light, sugars, and carbon
Uploaded: 2019-01-29T11:04:45.000Z
Duration: 4 min 45 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.3.2

Photosynthesis

Have you ever wondered why every autumn leaves on trees change from green to shades of yellow, orange, and red? What gives leaves their bright colors in the first place? The answer lies in the plant organelles called chloroplasts which contain pigments that absorb certain wavelengths in sunlight and reflect others. One particular pigment, chlorophyll, is the most abundant in summer. It absorbs high-energy, purple, blue, and red wavelengths from sunlight, and reflects green wavelengths giving leaves their green appearance. There are other pigments in leaves, such as carotenoids, which reflect red and yellow light. In autumn the leaves stop replenishing their pigments. Since chlorophyll degrades faster than the other pigments, the colors of these carotenoids are unmasked.The presence of different pigments in a green leaf can be demonstrated with chromatography paper, a hydrophilic polymer that separates molecules based on their solubility in a particular solvent. First, leaf extract is loaded onto the paper. When the paper is dipped into an organic hydrophobic solvent, the solvent travels along the paper due to capillary action and along the way it separates different pigments in the leaf extract. The pigments that are the most hydrophobic are carried further up the paper. Whereas hydrophilic pigments bind to cellulose which hinders their movement. After all of the pigments are sorted by their hydrophobicity, we can calculate the retention factor or Rf values. The Rf value is the ratio of the distance traveled by a pigment to the distance traveled by the solvent. Each pigment has a unique Rf value and we can easily identify pigments by comparing calculated values to standards. Photosynthesis, the process by which plants convert carbon dioxide, water and light energy into chemical energy and oxygen, is carried out primarily in the leaves of a plant, and chlorophyll plays a critical role in this process. Chloroplasts contain dozens of chlorophyll molecules, each performing a specific task and interacting in complex ways. Ultimately, light energy causes chlorophyll molecules to give up electrons which are utilized in other metabolic processes. Therefore, chlorophyll needs a continuous supply of electrons to replace the ones it loses. These replacement electrons come from splitting water molecules into protons, electrons and oxygen molecules. At high rates of photosynthesis water is split faster to replenish electrons and oxygen is generated rapidly.This phenomenon helps us to assess the rate of photosynthesis in the lab by simply suspending leaf discs in a bicarbonate solution where bicarbonate acts as a rich source of carbon. At the beginning of the leaf disk experiment the gases are forced out of the leaf discs by applying negative pressure with a vacuum in a syringe. The leaf discs with their gases expelled become heavier and sink to the bottom of the bicarbonate solution when transferred to a beaker. When photosynthesis takes place water in the environment is split in order to replenish chlorophyll electrons. The resulting oxygen makes the discs lighter causing them to float to the surface over time. Environments that allow for higher rates of photosynthesis have discs that float faster.In this lab you will first separate and identify pigments in spinach leaves using chromatography paper. Then you will assess the rate of photosynthesis in water and in bicarbonate solution with a leaf disk experiment.

photosynthesis

<h4>Autotrophs</h4>

Almost all living organisms on Earth depend on photosynthesis, which is the process that converts sunlight energy into a simple sugar called glucose. This molecule can be used as a short-term energy source or to build more complex carbohydrates like starches for long-term energy storage. Autotrophs are organisms that capture light energy using photosynthesis. Also known as primary producers, they provide the energy necessary to the organisms that eat them, which are known as consumers.

Organisms that can photosynthesize are rather diverse, including cyanobacteria, some protists such as algae, as well as plants. In eukaryotic cells, photosynthesis takes place in an organelle called the chloroplast, which appear green due to its high content of the pigment chlorophyll. Pigments are molecules that absorb light at certain wavelengths. The light that is not absorbed by a pigment is reflected as visible light that can be observed as the color of the pigment. Plants produce multiple pigments with various functions that absorb light from the sun at different wavelengths. For example, chlorophyll absorbs light at red and blue wavelengths while it reflects wavelengths that correspond to green. Some other pigments such as carotenoids, anthocyanins, and betalains commonly reflect light at low-energy wavelengths between 600 and 800 nm, and thus appear yellow to red. In temperate regions, the decrease in chlorophyll in autumn reveals these pigments when leaves change color to reds, yellows, and oranges.

<h4>Chloroplasts</h4>

Chlorophyll is the primary pigment in chloroplasts used in photosynthesis, whereas other pigments help channeling light energy to chlorophylls or protect the cell against light damage. Photosynthesis consists of two pathways, which are known as the light-dependent and light-independent reactions and occur at distinct locations within chloroplasts. These organelles contain three membranes: an outer membrane, an inner membrane, and the innermost thylakoid membrane, which forms long, disc-shaped folds within the chloroplast. The fluid-filled space between the inner and thylakoid membranes is called the stroma. The light-dependent reactions start when the energy in sunlight excites the electrons of chlorophyll pigments that are embedded within the thylakoid membrane. These high-energy electrons are then passed from one electron carrier molecule to another within the thylakoid membrane, collectively known as the electron transport chain. Each transfer within the electron transport chain takes the electron to a lower energy state, therefore releasing energy. Some of this energy is harnessed to synthesize small, energy-rich molecules such as Adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). The lost electron of the chlorophyll is replaced through hydrolysis (which means water splitting), when hydrogen and oxygen atoms are separated. Hydrogen atoms generated by hydrolysis donate their electrons to the chlorophyll whereas the oxygen molecules are released into the atmosphere. Stream of electrons through hydrolysis enables chlorophyll pigments to continuously absorb the light energy by repeatedly exciting new electrons and pass them down the electron transport chain.

The light-independent reactions take place in the stroma. This process uses the light energy indirectly by utilizing the energy from ATP and NADPH molecules generated by the light-dependent reactions. During this pathway, carbon dioxide (CO2) is used to build a three-carbon sugar, which then can be turned into glucose or other biomolecules. This process is also known as carbon fixation or carbon sequestration, because the carbon is sequestered from the atmosphere and fixed into biomolecules.

<h4>Photosynthesis and the Environment</h4>

Carbon sequestration during photosynthesis is an important step of the carbon cycle, in which CO2 flows from one reservoir to another at a relatively constant pace. Changes in the CO2 flow rate can shift the balance of it among reservoirs. More importantly, since CO2 is a greenhouse gas, increases in its atmospheric concentration contributes to rising temperatures. Most of this CO2 is emitted by burning fossil fuels, thus returning the carbon dioxide that was sequestered by photosynthesis hundreds of millions of years ago to the atmosphere at an unprecedented rate. Therefore, forests and ocean algae are evermore imperative in cooling the earth by reducing the increased CO2 levels1. This is one of many reasons why deforestation is a serious concern in a changing climate.

Much like how plants use photosynthesis to capture light energy into biomolecules, researchers are investigating artificial photosynthesis to create carbon neutral biofuels as an alternative to fossil fuels. Similar to solar panels, artificial photosynthesis methods obtain energy from the sun, and store it as chemical energy, some of which can be stored for long periods of time, instead of converting it directly to electricity2. Scientists have also been able to produce simple sugars and lactic acid using photosynthetic bacteria3. This approach has wide applications in manufacturing biomolecules, biofuels, and even biodegradable plastics with little to no harmful emissions. In addition, this approach may be used to remove excess CO2 from the atmosphere. A similar concept is being applied in the medical field, where photosynthetic bacteria are being used to produce physiologically active substances and medications, some of which have been applied to cancer diagnosis and treatment4. Future research may increase the efficiency of producing sustainable and carbon neutral molecules while remediating the effects of increased atmospheric CO2 levels.

<h4>References</h4>

<ol class="references">
	<li>Bonan, GB. Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests. Science. 2008, Vol. 320, 5882 (1444-9).</li>
	<li>Liu, C, et al. Water splitting&#8211;biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis. Science. 2016, Vol. 352, 6290 (1210-1213).</li>
	<li>Niederholtmeyer, H, et al. Engineering Cyanobacteria To Synthesize and Export Hydrophilic Products. Appl Env Microbio. 2010, Vol. 76, 11 (3462-66).</li>
	<li>Sasaki, K, et al. Applications of photosynthetic bacteria for medical fields. J Biosci Bioeng. 2005, Vol. 100, 5 (481-8).</li>
</ol>

Autotrophs

Almost all living organisms on Earth depend on photosynthesis, which is the process that converts sunlight energy into a simple sugar called ...

Education

JoVE Lab Manual

Cellular Processes

photosynthesis: light, sugars, and carbon

Photosynthesis turns sunlight into chemical energy in the form of glucose. This process powers most life on Earth by helping autotrophs, or primary producers, make food. The glucose they make can provide quick energy or be stored as starch for later use. Consumers depend on these producers for energy.

Photosynthesis happens in many kinds of organisms. Cyanobacteria, some protists such as algae, and plants can all carry out this process. In eukaryotic cells, it takes place in the chloroplast. Chloroplasts look green because they contain chlorophyll, a pigment that absorbs light at specific wavelengths.

Plants use several pigments to capture light. Chlorophyll absorbs red and blue light and reflects green light. Other pigments, including carotenoids, anthocyanins, and betalains, absorb or reflect different wavelengths and often appear yellow to red. In autumn, when chlorophyll levels drop in temperate regions, these pigments become visible and leaves change color.

Photosynthesis has two main stages: light-dependent reactions and light-independent reactions. These stages happen in different parts of the chloroplast. The chloroplast has an outer membrane, an inner membrane, and an inner thylakoid membrane that forms disc-like folds. The space between the inner membrane and thylakoids is the stroma.

The light-dependent reactions begin in the thylakoid membrane when sunlight excites electrons in chlorophyll. Those electrons move through an electron transport chain, dropping to lower energy levels and releasing energy. The cell uses that energy to make ATP and NADPH. Water splitting, also called hydrolysis, replaces the lost electrons in chlorophyll. This process releases oxygen into the atmosphere and helps keep the flow of electrons going.

The light-independent reactions take place in the stroma. They use ATP and NADPH from the first stage to build a three-carbon sugar from carbon dioxide. That sugar can then be turned into glucose or other biomolecules. This is also called carbon fixation or carbon sequestration because carbon is pulled from the atmosphere and stored in living molecules.

Photosynthesis plays a major role in the carbon cycle. Carbon dioxide moves between reservoirs at a steady pace, but changes in that flow can upset the balance. Because carbon dioxide is a greenhouse gas, more of it in the atmosphere can raise temperatures. Much of the extra carbon dioxide comes from burning fossil fuels, which returns ancient carbon to the air very quickly.

Forests and ocean algae help lower carbon dioxide levels, so deforestation is a serious concern in a changing climate. Scientists are also studying artificial photosynthesis as a way to make carbon-neutral biofuels. Like solar panels, these methods take energy from the sun and store it as chemical energy instead of electricity. Researchers have also used photosynthetic bacteria to make simple sugars, lactic acid, biodegradable plastics, and even medically useful compounds, including substances studied for cancer diagnosis and treatment.

Photosynthesis: Light, Sugars, and Carbon

Photosynthesis turns sunlight into chemical energy in the form of glucose. This process powers most life on Earth by helping autotrophs, or primary producers, make food. The glucose they make can provide quick energy or be stored as starch for later use. Consumers depend on these producers for energy. Photosynthesis happens in many kinds of organisms. Cyanobacteria, some protists such as algae, and plants can all carry out this process. In eukaryotic cells, it takes place in the chloroplast.

cellular respiration

Cellular Energy From Glucose Breakdown

Cellular respiration is the process cells use to release usable energy from biomolecules such as sugars and lipids. Living things need a steady energy supply for growth, repair, movement, defense, and reproduction. Cells use that energy mainly by converting adenosine diphosphate (ADP) to adenosine triphosphate (ATP). Autotrophs and heterotrophs get the molecules for respiration in different ways. Autotrophs, such as plants, algae, and photosynthetic and chemosynthetic bacteria, build...

cell division

Cell Cycle, Mitosis, and Meiosis

Cell division is essential for growth, repair, and reproduction in living organisms. It lets single-celled organisms create a new organism and helps multicellular organisms make new cells for development and for replacing damaged cells. In multicellular species, cell division also makes reproductive cells needed for reproduction. Before a cell divides, it must copy its genetic material and split it into two daughter cells. This process is called the cell cycle. Although the timing can vary...

transpiration

Water Movement in Plants

Water movement in plants depends on transpiration and the vascular system. Plants must move water and dissolved nutrients from the roots to the leaves. They also exchange materials with the environment as part of normal life processes. Vascular plants use bundles of tissues that run from the roots to the tips of the plant. Root hairs absorb water and nutrients, and osmosis moves water into the xylem, the main water-conducting tissue. Water then travels to the tallest parts of the plant and...

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Learn how photosynthesis converts sunlight into glucose, how chloroplasts use pigments and ATP/NADPH, and why carbon fixation matters for climate.

Photosynthesis: Light, Sugars, and Carbon | JoVE K12

Pennsylvania State Academic Standards

Life Science

matter-and-energy-in-organisms-and-ecosystems

Matter and Energy in Organisms and Ecosystems

3.1.9-12.E

3.1.9-12.J

3.1.9-12.K

Louisiana Student Standards for Science

High School

Life Sciences

From Molecules To Organisms: Structures And Processes

HS-LS1-5

Environmental Science

ecosystems-interactions-energy-and-dynamics

Ecosystems: Interactions, Energy And Dynamics

HS-LS2-4

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Cells

Cellular processes

Virginia  Standards of Learning

HIgh School

BIO.2

BIO.2.e

Minnesota Academic Standards in Science

3.1.1 9L.3.1.1.2

3.2.1 9L.3.2.1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

From Molecules to Organisms: Structures and Processes

Ecosystems: Interactions, Energy, and Dynamics

HS-LS2-5

Arizona Science Standards

HS.L2

HS.L2U1.21

HS+B.L2

HS+B.L2U1.8

Next Generation Science Standards

Florida Department of Education

SC.912.L.18

SC.912.L.18.7

SC.912.L.18.9

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS1-5

new-york-state-science-learning-standards

New York State Science Learning Standards

HS-LS1-5.

Georgia Standards of Excellence

Botany

SBO1.

Prepare spinach leaves, chromatography paper, bicarbonate solution, and leaf discs for a high school photosynthesis lab on pigments and floating discs.

Leaf Pigment Prep for Chromatography Labs | JoVE K12

Separate spinach pigments by chromatography, calculate Rf values, and use floating leaf discs to compare photosynthesis in light, dark, bicarbonate, and water.

Spinach Pigments and Leaf Disc Photosynthesis | JoVE K12

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Photosynthesis: Light, Sugars, and Carbon

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