Photosynthesis Flashcards
Photosynthesis
Biological process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose molecules.
Chlorophyll
Green pigment found in the chloroplasts of plants. It plays a crucial role in photosynthesis by absorbing light energy from the sun and converting it into chemical energy. Chlorophyll molecules are responsible for capturing photons of light during the light-dependent reactions of photosynthesis, initiating the process of energy transfer that ultimately leads to the production of glucose and oxygen.
Stomata
Stomata are tiny pores on plant surfaces, mainly leaves, that regulate gas exchange, allowing carbon dioxide to enter for photosynthesis and oxygen to exit. They also help in controlling water loss through transpiration.
Stroma
Fluid-filled interior of chloroplasts in plant cells where the Calvin cycle, the process of converting carbon dioxide into glucose, takes place.
Thylakoids
Membrane-bound compartments within chloroplasts where light-dependent reactions of photosynthesis occur. They contain chlorophyll and other pigments that capture light energy to produce ATP and NADPH.
Grana
Stacks of thylakoid membranes in chloroplasts, where light-dependent reactions of photosynthesis occur.
Light reactions
Initial stage of photosynthesis that occur in the thylakoid membranes of chloroplasts. During these reactions, light energy is absorbed by chlorophyll and other pigments, generating high-energy electrons that are passed along an electron transport chain.
This process leads to the production of ATP and NADPH, which are used to power the subsequent light-independent reactions (Calvin cycle) and convert carbon dioxide into glucose. Additionally, light reactions release oxygen as a byproduct of water splitting.
Wavelength
Distance between two consecutive peaks or troughs of a wave. It determines the color and energy of electromagnetic radiation, with shorter wavelengths corresponding to higher energy and longer wavelengths to lower energy.
Electromagnetic spectrum
The electromagnetic spectrum comprises all forms of electromagnetic radiation, from high-energy gamma rays to low-energy radio waves, each with different wavelengths and energies.
Calvin cycle
Biochemical reactions that occur in the stroma of chloroplasts during photosynthesis. This cycle converts carbon dioxide from the atmosphere into glucose and other organic molecules using ATP and NADPH generated by the light-dependent reactions.
The Calvin cycle involves several key steps, including carbon fixation, reduction, and regeneration of the starting molecule, ribulose-1,5-bisphosphate (RuBP). It is essential for producing carbohydrates, which serve as energy sources for plants and other organisms.
Photon
A photon is the basic unit of light and other forms of electromagnetic radiation, carrying energy without mass and traveling at the speed of light.
Photosystem
A photosystem is a molecular complex in chloroplasts and certain prokaryotes that captures light energy and converts it into chemical energy during photosynthesis.
How the light reactions generate ATP and NADPH
Absorption of Light: Photons of light are absorbed by chlorophyll and other pigments in Photosystem II (PSII) and Photosystem I (PSI) within the thylakoid membranes of chloroplasts.
Electron Excitation: The absorbed light energy excites electrons in chlorophyll molecules, causing them to move to a higher energy state.
Water Splitting: In PSII, the excited electrons are transferred to an electron acceptor molecule, leaving behind positively charged chlorophyll molecules. These electrons are replaced by the splitting of water molecules, releasing oxygen as a byproduct.
Electron Transport Chains: The excited electrons are passed through a series of electron transport chains in both PSII and PSI. As the electrons move along these chains, they release energy, which is used to pump protons (H⁺ ions) from the stroma into the thylakoid lumen.
Proton Gradient Formation: The pumping of protons creates a concentration gradient, with a higher concentration of protons in the thylakoid lumen compared to the stroma.
ATP Synthesis: The protons in the thylakoid lumen flow back into the stroma through ATP synthase complexes embedded in the thylakoid membrane. This flow of protons drives the phosphorylation of adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), a process known as chemiosmosis.
NADPH Formation: Meanwhile, the electrons that reach Photosystem I (PSI) are re-energized by another photon of light and passed through a second electron transport chain. At the end of this chain, the electrons are transferred to the electron carrier molecule NADP⁺, along with protons from the stroma, to form NADPH.
The calvin cycle: making sugar from carbon dioxide
Carbon Fixation: Carbon dioxide is combined with a five-carbon molecule, forming two molecules of 3-phosphoglycerate (3-PGA).
Reduction: ATP and NADPH from the light reactions convert 3-PGA into glyceraldehyde-3-phosphate (G3P).
Regeneration of RuBP: Some G3P molecules regenerate the starting molecule, ribulose-1,5-bisphosphate (RuBP).
Sugar Production: Remaining G3P molecules are used to produce glucose and other carbohydrates, which serve as energy sources for the plant.
