Learning objectives
By the end of this section you will be able to:
- Describe the function and location of photosynthetic pigments in eukaryotes and prokaryotes
- Describe the main products of light-dependent and light-independent reactions
- Describe the reactions leading to the production of glucose in a photosynthetic cell
- Compare and compare cyclic and non-cyclic photophosphorylation
Heterotrophic organisms includeE coliMan is dependent on chemical energy contained mainly in carbohydrate molecules. Many of these carbohydrates are produced byphotosyntheza, a biochemical process by which phototrophic organisms convert solar energy (sunlight) into chemical energy. Although photosynthesis is most commonly associated with plants, microbial photosynthesis is also an important supplier of chemical energy that powers many different ecosystems. In this section, we will focus on microbial photosynthesis.
Photosynthesis occurs in two successive phases: light-dependent reactions and light-independent reactions (Figure 8.19). I amlight-dependent reactionSThe energy of sunlight is absorbed by pigment molecules in photosynthetic membranes and converted into stored chemical energy. INlight-independent reactionS, chemical energy generated in light-dependent reactions, is used to drive the assembly of sugar molecules with CO2; However, these reactions are still light-dependent because the products of the light-dependent reactions required to initiate them are short-lived. Light-dependent reactions produce ATP and NADPH or NADH for temporary energy storage. These energy carriers are used in light-independent reactions to enhance the energetically unfavorable process of "binding" of inorganic CO2in the organic form of sugar.
Lik8.19 The light-dependent reactions of photosynthesis (left) convert light energy into chemical energy, creating ATP and NADPH. These products are used in light-independent CO fixation reactions2, resulting in organic carbon molecules.
Photosynthetic structures in eukaryotes and prokaryotes
TogetherPhototrophy eukariotyczne, Photosynthesis takes place inChloroplast, organelles that arose in eukaryotes as a result of the endosymbiosis of photosynthetic bacteria (seeUnique properties of eukaryotic cells). These chloroplasts are surrounded by a double membrane with an inner and outer layer. Inside the chloroplast is a third membrane that forms disc-shaped stacked photosynthetic structuresThylakoidsS (Figure 8.20). The thylakoid stack is labeled aCereal, and the space surrounding the granum inside the chloroplast is calledStroma.
In contrast, photosynthetic membranes in prokaryotes are not organized into distinct membrane-bound organelles; rather, they are wrinkled areas of the plasma membrane. For example, in cyanobacteria, these folded regions are also called thylakoids. In both cases, other photosynthetic bacterial membranes are embedded in the thylakoid membranesphotosynthetic pigmentMolecules organized into one or more photosystems where light energy is actually converted into chemical energy.
The photosynthetic pigments in photosynthetic membranes are organized intophoto systemS, each consisting of a light-harvesting complex (antenna) and a reaction center. Thelight collection complexIt consists of several proteins and associated pigments, each of which absorbs light energy and can be excited by it. This energy is transferred from one pigment particle to another until finally (about one millionth of a second) it is released into the reaction center. Until now, only energy, not electrons, was transferred between molecules. Thereaction centerit contains a pigment molecule that can be oxidized upon excitation and actually donate an electron. It's on that levelphotosynthezathat light energy is converted into an excited electron.
Different types of light-harvesting pigments absorb unique patterns of wavelengths (colors) of visible light. Pigments reflect or transmit wavelengths that they cannot absorb, which is why they appear to be their respective colors. Examples of photosynthetic pigments (molecules used to absorb solar energy) areBacteriochlorophylls (green, purple or red),carotenoidss (orange, red or yellow),Chlorophyllgreen),Phycocyanin(blue) iPhycoerythrin(Red). Pigment blends allow the body to absorb energy from multiple wavelengths. Since photosynthetic bacteria typically grow in competition with sunlight, each species of photosynthetic bacteria is optimized to take advantage of the wavelengths of light it is normally exposed to, leading to stratification of microbial communities in aquatic and terrestrial ecosystems based on light quality and penetration.
Once the light-harvesting complex transfers energy to the reaction center, the reaction center releases its high-energy electrons into the electron carrier one by oneElectron transport systemand transferring electrons throughETSIt has started. ETS is similar to this inZellatmungand is embedded in the photosynthetic membrane. Ultimately, an electron is used for productionNADHLubNADPH. Theelectrochemical gradientwhich is formed by the photosynthetic membrane is used to generateATPby chemiosmosis in the processphotophosphorylation, another exampleoxidative phosphorylation(Figure 8.21).
Lik8.20 (a) Photosynthesis in eukaryotes occurs in chloroplasts, which contain thylakoids stacked to form a branch. (b) Photosynthetic prokaryotes have wrinkled areas of the plasma membrane that function as thylakoids. (Source: Matt Russell scale data).
Lik8.21 This photo briefly shows how the photo system works. Light Harvesting (LH) pigments absorb light energy and convert it into chemical energy. The energy is transferred from one LH pigment to another until it reaches the pigment in the reaction center (RC) and excites the electron. This high-energy electron is lost from the RC pigment and goes through the electron transport system (ETS), eventually generating NADH or NADPH and ATP. The reduced molecule (H2A) donates an electron and exchanges electrons for electron-poor RC pigment.
Check if you understood correctly
- Where does photosynthesis occur in phototrophic eukaryotes?
Oxygenic and anaerobic photosynthesis
In order for photosynthesis to continue, an electron lost from the pigment of the reaction center must be replaced. The source of this electron (H2A) differentiatesoxygenic photosynthesisfrom plants and algaeanaerobic photosynthesiscarried out by other types of bacterial phototrophs (Figure 8.22). In photosynthesis involving oxygen, H2O undergoes fission and donates an electron to the reaction center. Since oxygen is produced as a by-product and released, this type of photosynthesis is called oxygenic photosynthesis. However, when other reduced compounds serve as electron donors, no oxygen is produced; These types of photosynthesis are called anoxic photosynthesis. Hydrogen sulfide (H2S) tiosiarczanit can serve as an electron donor and generate elemental sulfur and sulfateor as a result.
Photosystems are divided into two types:Photosystem I (PSI)IFotosustav II (PSII)(Figure 8.23). Cyanobacteria and plant chloroplasts have both photosystems, while anaerobic photosynthetic bacteria use only one of the photosystems. Both photosystems are simultaneously excited by light energy. If a cell needs both ATP and NADPH for biosynthesis, it willnoncyclic photophosphorylation. In the electron transfer from the PSII reaction center to the ETS that connects PSII and PSI, the lost electron is replaced from the PSII reaction center by split water. The excited electron of the PSI reaction center is used to reduce NADP+to NADPH and is replaced by an electron leaving the ETS. The flow of electrons in this way is denoted asZ-shema.
When a cell's need for ATP is much greater than its need for NADPH, it can bypass reducing energy productioncyclic photophosphorylation. Only PSI is used during cyclic photophosphorylation; The high-energy electron of the PSI reaction center passes to the ETS carrier and then finally returns to the oxidized pigment of the PSI reaction center, causing its reduction.
Lik8.22 Eukaryotes and cyanobacteria carry out aerobic photosynthesis and produce oxygen while other bacteria carry out anaerobic photosynthesis which does not produce oxygen.
Lik8.23 (a) PSI and PSII are located on the thylakoid membrane. The high-energy electron from PSII is donated to the ETS, which generates the proton motive force for ATP synthesis via chemiosmosis, ultimately replacing the electron lost from the PSI reaction center. The PSI reaction center electron is used to generate NADPH. (b) When both ATP and NADPH are needed, noncyclic photophosphorylation (in cyanobacteria and plants) provides both. The flow of electrons described here is called the Z-scheme (shown in yellow in [a]). When the cellular demand for ATP exceeds the need for NADPH, cyanobacteria and plants use only PSI, and their reaction center electron is donated to the ETS to generate the proton driving force for ATP synthesis.
Check if you understood correctly
- Why would a photosynthetic bacterium have different pigments?
Light-independent reactions
By converting solar energy into chemical energy and temporarily storing it in ATP and NADPH molecules (with lifetimes of millionths of a second), photoautotrophs have the fuel they need to build multi-carbon carbohydrate molecules that can last for hundreds of millions of years. for long-term energy storage. Carbon comes from CO2, a gas that is a byproduct of cellular respiration.
TheThe Calvin-Bensonov cycle(named after Melvin Calvin [1911–1997] and Andrew Benson [1917–2015]), a biochemical pathway used to fix CO2it occurs in the cytoplasm of photosynthetic bacteria and in the stroma of eukaryotic chloroplasts. Thelight-independent reactionThe phases of the Calvin cycle can be broken down into three basic phases: fixation, reduction, and recovery (seeAppendix Cdetailed description of the Calvin cycle).
- fixation: EnzymesRibulozabisphosphoran-carboxylase (RuBisCO)catalyzes the addition of CO2DoRybulozabisfosforan (RuBP). This leads to production3-phosphoglycerynian(3-PGA).
- Reduction: Six molecules of ATP and NADPH (from light dependent reactions) are used to convert 3-PGA to glyceraldehyde 3-phosphate (G3P). Some of the G3P is then used to make glucose.
- Regeneration: Remaining G3P not used for glucose synthesis is used to regenerate RuBP, allowing the system to continue producing CO2fixation. Three more ATP molecules are used in these regeneration reactions.
Photoautotrophic plants and bacteria make extensive use of the Calvin cycle, and the RuBisCO enzyme is believed to be the most abundant enzyme on earth, accounting for 30-50% of all soluble proteins in plant chloroplasts.1However, in addition to its predominant use in photoautotrophs, the Calvin cycle is also used by many non-photosynthetic chemoautotrophs to fix CO.2. In addition, other bacteria and archaea use alternative systems for CO2fixation. Although most bacteria using alternatives to the Calvin cycle are chemoautotrophic, some photoautotrophic green sulfur bacteria have also been shown to use alternative CO2the method of attachment.
Check if you understood correctly
- Describe the three phases of the Calvin cycle.
FAQs
What is photosynthesis in microbiology? ›
Photosynthesis is the process by which microorganisms utilize carbon dioxide and water in the presence of sunlight to produce glucose and oxygen. These organisms can convert light energy from the sun into chemical energy in a photosynthetic reaction.
What percent of photosynthesis is performed by microorganisms? ›As much as a third of the earth's photosynthesis is performed by microorganisms in the oceans. Six bacterial phyla include photosynthetic members (Blankenship, 2002; Jones, 2009; Golbeck, 2010; see Chapter 50).
What are the 4 types of photosynthetic bacteria? ›They are proteobacteria (also known as purple bacteria), heliobacteria, Chloroflexi (filamentous bacteria also known as green non-sulfur bacteria), Chlorobi (green sulfur bacteria) and cyanobacteria.
What is the equation for photosynthesis in bacteria? ›While different organisms may have differences during oxygenic photosynthesis, they all follow the general equation of, carbon dioxide + water + light energy → carbohydrate + oxygen.
What is the process of photosynthesis? ›During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose.
How do you explain photosynthesis? ›photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.
Where does 80% of photosynthesis take place? ›Most of the photosynthesis (80%) which takes place on this earth is carried out by algae present in fresh water and ocean water. At least a half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis.
What is the average rate of photosynthesis? ›There is a total of 7000 x 109 tonnes of carbon dioxide in the atmosphere and photosynthesis fixes 100 x 109 tonnes per year. So 15% of the total carbon dioxide in the atmosphere moves into photosynthetic organisms each year.
Does photosynthesis occur in microorganisms? ›In microorganisms, photosynthesis occurs in unicellular algae and in photosynthesizing bacteria such as cyanobacteria and green and purple sulfur bacteria.
What are 3 types of organisms go through photosynthesis? ›Plants, algae, and cyanobacteria, known as photoautotrophs, are the only organisms capable of performing photosynthesis.
What 3 types of organisms can perform photosynthesis? ›
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.
What are photosynthesis bacteria called? ›Examples of photosynthetic bacteria are Cyanobacteria, Chlorobi (green sulfur bacteria), Proteobacteria (also known as purple bacteria), and Chloroflexi (filamentous bacteria also known as green non-sulfur bacteria), Proteobacteria (also known as purple bacteria), etc.
What is the conclusion of bacterial photosynthesis? ›Conclusion. Bacterial photosynthesis occurs in purple bacteria, green sulphur bacteria, phototrophic helicobacter, and acidobacteria. Light energy is converted to chemical energy in this process, and the carbohydrate formed is stored as food.
What factors affect the rate of photosynthesis? ›The main factors affecting rate of photosynthesis are light intensity, carbon dioxide concentration and temperature.
What generally photosynthesis in bacteria and plants are respectively? ›The process of photosynthesis in bacteria and plants is different. Bacterial photosynthesis is mostly an anoxygenic process, here O2 is not evolved, whereas plant photosynthesis is an oxygenic process and O2 is evolved during the process.
What are the 4 main steps of photosynthesis? ›- Absorption of light.
- Transfer Of Electron.
- Production Of ATP.
- Carbon Fixation.
Photosynthesis is an endothermic reaction. This means it cannot occur without energy (from the Sun). The light required is absorbed by a green pigment called chlorophyll in the leaves. Chlorophyll is found in chloroplasts in plant cells , particularly the palisade and spongy mesophyll cells .
What are the 7 steps of photosynthesis in order? ›- Carbon Dioxide Assimilation.
- Reductive Pentose Synthesis.
- Regeneration of Carbon Acceptor Molecules.
In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll. Chloroplasts are surrounded by a double membrane and contain a third inner membrane, called the thylakoid membrane, that forms long folds within the organelle.
Why is photosynthesis important? ›The primary function of photosynthesis is to convert solar energy into chemical energy and then store that chemical energy for future use. For the most part, the planet's living systems are powered by this process.
What is an example of a photosynthesis? ›
Examples of photosynthesizing organisms: Green plants, cyanobacteria (earlier termed as blue-green algae), and different types of algae that essentially carry out phytoplankton photosynthesis.
What plant does the most photosynthesis? ›Most of the photosynthesis (80%) which takes place on this earth is carried out by algae present in fresh water and ocean water. At least a half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis.
Where is photosynthesis highest? ›Maximum absorption of light by chlorophyll a occurs in red and blue regions of the absorption spectrum. So that, the rate of photosynthesis is maximum in red and blue light of the visible spectrum. Minimum photosynthesis takes place in the green light.
What time does photosynthesis take place? ›In most plants, photosynthesis fluctuates throughout the day as stomata open and close. Typically, they open in the morning, close down at midday, reopen in late afternoon and shut down for good in the evening. Carbon dioxide is plentiful in the air, so it is not a limiting factor in plant growth.
Is photosynthesis 100% efficient? ›The photosynthetic efficiency is dependent on the wavelength of the light absorbed. Photosynthetically active radiation (400–700 nm) constitutes only 45% of the actual daylight. Therefore the maximum theoretical efficiency of the photosynthesis process is approximately 11%.
How do you measure photosynthesis? ›Leaf photosynthetic rate is measured by enclosing a leaf in a closed, transparent chamber and measuring the decrease in carbon dioxide concentration as a function of time. Light flux density is measured outside of the chamber and must be corrected for the chamber transmittance, which is 0.9.
What is the highest rate of photosynthesis? ›As photosynthesis occurs at all wavelengths of the visible spectrum, its rate is highest in polychromatic light, that is white light, which is a combination of different wavelengths.
Why do microorganisms conduct photosynthesis? ›Some bacteria are able to use a process called photosynthesis to convert energy from sunlight into another form of energy they can use to grow. Within the bacteria, structures known as photosystems are responsible for absorbing light and transferring the energy to other molecules.
What is the microbial metabolism of photosynthesis? ›Bacterial photosynthesis is a light-dependent, anaerobic mode of metabolism. Carbon dioxide is reduced to glucose, which is used for both biosynthesis and energy production. Depending on the hydrogen source used to reduce CO2, both photolithotrophic and photoorganotrophic reactions exist in bacteria.
In which microorganisms does photosynthesis take place? ›Photosynthesis occurs only in some bacteria such as cyanobacteria, which is a diverse group of cyanobacteria. They are also known as blue-green bacteria. In higher-order plants, photosynthesis occurs in the chloroplast. Bacteria do have chloroplasts.
Does photosynthesis occur in all living organisms? ›
Only certain organisms, called autotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that can absorb light and convert light energy into chemical energy.
What organisms do not carry out photosynthesis? ›Animal cells and fungal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms, as well as the non-photosynthetic protists, rely on other organisms to obtain their energy. These organisms are heterotrophs.
What are the 2 types of photosynthesis? ›- Oxygenic photosynthesis.
- Anoxygenic photosynthesis.
- A It is the source of energy and food for all organisms.
- B It releases oxygen into the environment which is utilised by organisms.
- C It sustains all the food chains in an ecosystem. Photosynthesis is the source of energy and food for all organisms directly and indirectly.
Some types of bacteria are autotrophs. Most autotrophs use a process called photosynthesis to make their food. In photosynthesis, autotrophs use energy from the sun to convert water from the soil and carbon dioxide from the air into a nutrient called glucose.
Do all fungi do photosynthesis? ›Unlike plants, fungi are unable to source their energy from the sun via photosynthesis. Instead, most fungi (except for lichens) release enzymes into the environment that digest organic matter and then absorb it.
Is bacterial photosynthesis a process? ›Process of bacterial photosynthesis: Bacterial photosynthesis is based on cyclic photophosphorylation mechanism and only one pigment system (PS-I) is involved. During the process, bacteriochlorophyll absorbs light and this light energy raises the chlorophyll molecule to an excited state.
Why is bacterial photosynthesis unique? ›None of the anoxygenic phototrophic bacteria have the ability to use water as an electron donor (or cannot oxidize water), and so perform photosynthesis using sulfide, hydrogen or organic substrates. Therefore, photosynthesis by these bacteria is without the evolution of oxygen.
What does bacteria release during photosynthesis? ›Photosynthetic bacteria contain different photosynthetic pigments and can convert sunlight into the energy they need for their metabolism and to release hydrogen.
Which bacteria produce oxygen during photosynthesis? ›Cyanobacteria or blue-green algae are aquatic and photosynthetic. They are unicellular and very small-sized bacteria that can grow in colonies. During photosynthesis, cyanobacteria can produce oxygen.
Which type of organism produce 70% of the oxygen made in photosynthesis? ›
Prochlorococcus and other ocean phytoplankton are responsible for 70 percent of Earth's oxygen production.
Is 90% of photosynthesis carried out by algae? ›Photosynthesis takes place sequentially in several steps. There is an evolutionary inheritance of red and green plastids in eukaryotic algae, which makes algae of oceans 85 - 90% of photosynthetic efficiency.
What percentage of oxygen is produced by microorganisms? ›Did you know that 20% of the oxygen we breathe comes from the ocean? Tiny bacteria called prochlorococcus are hard at work turning carbon dioxide into the oxygen we breathe through photosynthesis.
Are majority of bacteria photosynthetic? ›The majority of bacteria are heterotrophic i.e. can not prepare their own food. Heterotrophic bacteria feed on dead plants and animals, thus they are referred to as decomposers.
What is the main type of photosynthesis used by 85% of plants called? ›In fact, nearly 85% of the world's plant species utilize C3 photosynthesis. These plants produce a three-carbon intermediate called 3-phosphoglyceric acid (3-PGA). 3-PGA reacts with rubisco, an enzyme found in chloroplasts, to initiate carbon fixation in C3 plants.
What is the #1 thing that organisms get from photosynthesis? ›Oxygen is given off by green plants in the process of photosynthesis. Green plants are the lungs of the earth! All animals inhale oxygen and exhale carbon dioxide. Plants take in carbon dioxide and give off oxygen as they make food.
What organism is responsible for the most photosynthesis? ›Photosynthesis is mainly carried out by green plants and certain algae. But most of the Photosynthesis occurring on the Earth's surface is done by Algae.
What is 9 10 of photosynthesis carried out by? ›So the correct option is 'Algae/phytoplankton of the ocean'.
Where is maximum photosynthesis? ›When light having a wavelength ranging between 400-and 700 nm is absorbed by the plant, the rate of photosynthesis is the highest. Red light is absorbed effectively by chlorophyll which ranges within this wavelength. It is utilized in the maximum amount.
What percent of energy comes from photosynthesis? ›Therefore, the estimated maximum energy efficiency of photosynthesis is the energy stored per mole of oxygen evolved, 117 kcal, divided by 450—that is, 117/450, or 26 percent.
What produces 80% of the world's oxygen? ›
Plankton that are plants, known as phytoplankton, grow and get their own energy through photosynthesis and are responsible for producing an estimated 80% of the world's oxygen.
What are microorganisms that require 10% CO2 for growth termed? ›Strict anaerobes do not grow in 10% CO2 in air; microaerophilic bacteria can grow in 10% CO2 in air or under aerobic or anaerobic conditions, and facultative organisms can grow in the presence or absence of air.
What are microbes requiring oxygen levels of 2 to 10% called this? ›A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O2; typically 2–10% O2) for optimal growth. A more restrictive interpretation requires the microorganism to be obligate in this requirement.
Do all bacteria need photosynthesis? ›Yes, photosynthesis occurs in some bacteria, e.g. purple and green-sulphur bacteria and cyanobacteria. Photosynthetic pigments are present within the membrane infoldings of bacteria as they lack chloroplasts. Cyanobacteria or cyanobacteria contain chlorophyll and may perform oxygenic photosynthesis like plants.
Is photosynthesis in bacteria the same as in higher plants? ›The process of photosynthesis in bacteria and plants is different. Bacterial photosynthesis is mostly an anoxygenic process, here O2 is not evolved, whereas plant photosynthesis is an oxygenic process and O2 is evolved during the process.
Do all photosynthetic bacteria produce oxygen? ›None of the anoxygenic phototrophic bacteria have the ability to use water as an electron donor (or cannot oxidize water), and, thus, perform photosynthesis using sulfide, hydrogen or organic substrates. Therefore, photosynthesis by these bacteria does not involve oxygen.