Biology Chapter 10: Photosynthesis Flashcards

Photosynthesis Overview

• Autotrophs are self-feeders that synthesize their own glucose, whereas heterotrophs are consumers reliant on other organisms for organic compounds.
• Granum consists of a stack of thylakoids, while stroma is a thick fluid within chloroplasts where sugars are synthesized during the Calvin cycle.

Oxygen Production

• 18O isotope tracing demonstrated that oxygen released during photosynthesis originates from water.

Light Reactions

• Light energy is converted into chemical energy in the light reactions.
• Water is split, releasing electrons (e-), hydrogen ions (H+), and O2; electrons reduce NADP+ to form NADPH, while H+ ions help synthesize ATP.

Calvin Cycle

• ATP and NADPH fuel the Calvin cycle, converting three CO2 molecules into one net G3P molecule, a precursor to glucose.
• Inputs of the thylakoid are light and water, while the stroma inputs CO2 and outputs sugar.

Light Absorption

• Absorption spectra signify the range of light wavelengths a pigment captures; chlorophyll b absorbs from 410-510 nm in purple and blue ranges.
• Action spectra measure the effectiveness of various wavelengths for photosynthesis, noting that green light is least effective since it is reflected.

Photosystems

• Photosystems consist of a reaction-center complex surrounded by light-harvesting complexes, enabling energy absorption over broad wavelengths.
• Photosystem I (P700) and II (P680) are designated by the preferred wavelengths they absorb.

Electron Transport Chain

• Electrons travel from the primary electron acceptor of PSII through a sequence of carriers to PSI, where energy from their movement is used to pump H+ ions and create a gradient.
• Key players in the electron flow include plastoquinone (Pq), cytochrome complex, and ferredoxin (Fd).

Chemiosmosis

• Chemiosmosis refers to ion movement across membranes, generating ATP through a proton gradient facilitated by ATP synthase.
• Both photosynthesis and cellular respiration utilize similar chemiosmotic processes but differ in their sources of protons and ATP synthase locations.

Carbon Fixation

• RuBisCO catalyzes the initial step of carbon fixation in the Calvin cycle, converting CO2 and RuBP into 3-phosphoglycerate (3-PGA).
• The cycle requires three turns to net one G3P, with five G3P molecules reconfigured to regenerate RuBP.

Photorespiration and Plant Types

• C3 plants' initial product of carbon fixation is 3-phosphoglycerate.
• Photorespiration occurs under stress from closed stomata, causing rubisco to bind O2 instead of CO2, leading to carbon loss and decreased yields.

C4 and CAM Photosynthesis

• C4 plants initially produce a 4-carbon compound using PEP carboxylase to efficiently fix CO2 without engaging in photorespiration by separate spatial pathways.
• CAM plants fix CO2 at night, converting it to organic acids, which are released during the day for the Calvin cycle, aiding water conservation in arid conditions.

Plant Structures and Functions

• The most abundant organic molecule in plants is cellulose, which serves as a key structural component.
• Sucrose acts as a transport molecule for photosynthate, providing energy for cellular respiration and building blocks for various organic compounds.

Summary of Processes

• The Calvin cycle occurs in the stroma, using ATP and NADPH to convert CO2 into G3P while returning ADP and NADP+ to the light reactions.
• Light reactions take place in the thylakoid membranes, generating ATP and NADPH while splitting water and releasing oxygen.

Comparisons and Differences

• Both C4 and CAM plants convert CO2 to organic acids but do so through different timing and structural methods.
• The adaptation of C4 plants allows them to thrive in high-temperature environments with minimized photorespiration effects.