Photosynthesis Quiz

Photosynthesis is a biological process that converts light energy into chemical energy, which is used by plants and other organisms. It produces carbohydrates such as sugars and starches from carbon dioxide and water. The process is performed by photoautotrophs, which include most plants, algae, and cyanobacteria. Photosynthesis is responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth. The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide. Today, the average rate of energy capture by photosynthesis globally is approximately 130 terawatts. Photosynthesis is vital for climate processes as it captures carbon dioxide from the air and then binds carbon in plants and further in soils and harvested products. Photosynthesis occurs in two stages: light-dependent reactions and light-independent reactions. The light-dependent reactions capture the energy of light and use it to make the hydrogen carrier NADPH and the energy-storage molecule ATP. The light-independent reactions use these products to capture and reduce carbon dioxide. Photosynthesis in plants occurs primarily in organelles called chloroplasts, which contain chlorophyll and other pigments. Photosynthetic bacteria have proteins that gather light for photosynthesis embedded in cell membranes. Different wavelengths of light support different types of photosynthetic organisms. The Z-scheme is the process by which light-dependent reactions occur in plants. The photosynthetic action spectrum depends on the type of accessory pigments present. Water is the source of electrons for photosynthesis in green plants and cyanobacteria.Photosynthesis: Stages, Efficiency, and Evolution

Light-dependent reactions:

• Conversion of light energy to chemical energy in the form of ATP and NADPH
• Oxygen is a waste product
• Chlorophyll and other pigments absorb light and pass the energy to reaction centers
• ATP and NADPH are used in the light-independent reactions
• Hydrogen ions are released and contribute to ATP synthesis
• Majority of organisms on Earth use oxygen for cellular respiration

Light-independent reactions:

• Enzyme RuBisCO captures CO2 from the atmosphere and uses NADPH to produce three-carbon sugars
• Sugars are used to form other organic compounds or as fuel in cellular respiration
• Carbon concentrating mechanisms are used in hot and dry conditions to increase CO2 concentration
• C4 plants chemically fix CO2 in mesophyll cells and release it in bundle sheath cells for fixation by RuBisCO
• CAM plants fix CO2 at night and store it as malic acid, then use it for fixation during the day
• Cyanobacteria possess carboxysomes to concentrate CO2

Efficiency:

• Photosynthetic efficiency of plants is 3-6%
• Efficiency varies with light frequency, intensity, temperature, and CO2 concentration
• Chlorophyll fluorescence can measure light reaction, infrared gas analyzers can measure dark reaction
• Quantum walk phenomenon increases efficiency of energy transport of light
• Early photosynthetic systems were anoxygenic and used various other molecules than water as electron donors

Evolution:

• Fossils suggest photosynthesis began 3.4 billion years ago

• Oxygenic photosynthesis became important around 2 billion years ago

• Symbiotic relationships exist between some animals and photosynthetic algae

• Chloroplasts likely originated from symbiotic relationships between early eukaryotic cells and photosynthetic prokaryotesPhotosynthesis: Key Discoveries, Processes, and Factors

• Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy to produce food.

• Some animals, such as sea slugs, can also perform photosynthesis through symbiosis with algae.

• The endosymbiotic theory suggests that photosynthetic bacteria were acquired by early eukaryotic cells to form the first plant cells, which may explain the origin of chloroplasts.

• There are several photosynthetic eukaryotic lineages, including the Archaeplastida and the photosynthetic Paulinella, which acquired their plastids through primary endosymbiosis, and the "red lineages" and the "green lineages," which have either a red or green algal origin.

• Cyanobacteria, formerly called blue-green algae, are the only prokaryotes performing oxygenic photosynthesis, and the biochemical capacity to use water as the source for electrons in photosynthesis evolved once in a common ancestor of extant cyanobacteria.

• The overall photosynthetic equation has been known since the 19th century, and key discoveries have been made by scientists such as Jan van Helmont, Joseph Priestley, and Jean Senebier.

• Cornelis Van Niel made key discoveries explaining the chemistry of photosynthesis, and Robert Emerson discovered two light reactions by testing plant productivity using different wavelengths of light.

• Melvin Calvin, Andrew Benson, and James Bassham elucidated the path of carbon assimilation in plants, which is known as the Calvin cycle, and Rudolph A. Marcus discovered the function and significance of the electron transport chain.

• Factors influencing photosynthesis include the amount of light available, the amount of leaf area a plant has to capture light, the rate at which carbon dioxide can be supplied to the chloroplasts, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis.

• The radiation climate within plant communities is extremely variable, and the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation have been investigated.

• Factors that affect the efficiency of photosynthesis include the type of photosynthesis, the rate of carbon dioxide diffusion, the efficiency of energy transfer from light-harvesting pigments to the reaction center, and the rate of electron transport.

• Photosynthesis is an important process for the biosphere as it provides the main input of free energy and is one of four main ways in which radiation is important for plant life.

• Advances in understanding photosynthesis have led to the development of new technologies, such as artificial photosynthesis, which aims to mimic natural photosynthesis to produce renewable energy.Title: Key Concepts in Photosynthesis

• Temperature affects the rate of carbon assimilation in photosynthesis, which has two sets of reactions; light-dependent and temperature-independent, and light-independent and temperature-dependent.

• Blackman's experiments illustrate the concept of limiting factors, and light wavelength is another limiting factor in photosynthesis.

• Cyanobacteria have a light-harvesting complex called Phycobilisome, which has different pigments surrounding the reaction center to combat the problem of not receiving the required wavelengths for photosynthesis.

• The rate of sugar production by photosynthesis increases with rising carbon dioxide concentrations until limited by other factors.

• RuBisCO, the enzyme that captures carbon dioxide in photosynthesis, binds to both carbon dioxide and oxygen and will bind oxygen instead of carbon dioxide when the carbon dioxide concentration is low, causing photorespiration.

• Photorespiration uses energy but does not produce sugars, and is disadvantageous to plants for several reasons.

• The salvaging pathway for the products of RuBisCO oxygenase activity is commonly known as photorespiration, characterized by light-dependent oxygen consumption and the release of carbon dioxide.

• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy.

• The process occurs in two stages: the light-dependent reactions in the thylakoid membrane and the light-independent reactions in the stroma of the chloroplasts.

• Chlorophyll is the primary pigment involved in capturing light energy during photosynthesis.

• Photosynthesis is essential for life on Earth as it provides the oxygen we breathe and is the basis of the food chain.

• The efficiency of photosynthesis can be increased by genetic engineering and other methods, which is important in the context of climate change and food security.