C3 Plant Metabolism vs. C4 Metabolism

Photochemical reactions of photosynthesis are the light reactions of plants. The chemical equation is 2 H2O + 2 NADP+ +2 ADP + 2 PI – 2 NADPH2 + 2 ATP + O2. Special adaptations plants have evolved include extended and broad, lateral leaves that absorb more radiation for photosynthesis. The organelle responsible for photosynthesis is the Chloroplast. The chloroplasts contain many different pigments that allow for light absorption. Chlorophyll is a main pigment and stable molecule that has the ability to gain and lose electrons; therefore able to pass on excited electrons to other molecules. Photochemical reactions occur in the Thylakoids and Thylakoid Membrane. 3 things occur in excited pigments: energy is transferred to a reaction center, heat is produced and energy is lost, fluorescence releases photons and energy is lost.

The Enzymatic reactions of photosynthesis are processes that involve the dark reactions and do not require light. These processes take place in the stroma, aqueous medium. Photorespiration in the Glycolate pathway is an inefficient process that increases in hot temperature and low humidity climates and: fixes O2 instead of CO2, a major disadvantage of C3 photosynthesis.
NADPH and ATP are important in both types of photosynthesis because they are the energy that combine with carbon dioxide and water to produce glucose and oxygen. Photosynthesis= 6 CO2 + 6 H2O + energy -> C6H12O6 + 6 O2. Photosynthesis is a biological process in which solar energy is used to form chemical bonds. Photosynthesis is important for many reasons including oxygen evolving photosynthesis producing and regulating atmospheric oxygen for respiration and forming the ozone layer, protecting Earth from UV radiation.

The main differences between C3 and C4 grasses:
C3 Metabolism:
used by all plants,
the most prevalent and primitive pathway,
evolved with climates of high CO2 and low O2
C4 Metabolism:
PEPcase Phosphoenolopyruvate carboxylase (higher affinity for CO2 and none for O2) is the initial receptor of CO2 instead of Rubisco,
occurs in Mesophyll cells and Bundle Sheath cells (contain chloroplasts) surrounding the Xylem and Phloem (veins),
is an adaptation that solves the problem of photorespiration,
evolved 7-9 million years ago in a period with high O2 concentration

C3 and C4 grasses are highly linked to different environments because of different advantages/disadvantages the C3 and C4 photosynthesis/pathways evolved. The advantages of C4 Photosynthesis include no photorespiration, CO2 fixation is resistant to heat and drought, higher water use efficiency. Disadvantages include cold sensitivity (therefore evolving to be warm season plants); and contain more bundle sheath cells (high in fiber)/less mesophyll so are more fibrous than C3 grasses. Photosynthesis relies on Rubisco to fix CO2; factors affecting Carboxylation (acquisition of CO2 by Rubisco) include Rubisco quantity/activity, CO2 concentration, acceptor concentration (RuBP), protoplasm hydration, temperature, and minerals (P). Since C4 is reliant on PEPcase as an initial receptor and not Rubisco, it evolved to reduce photorespiration before carboxylation occurs. C3 pathway evolved during a time in history where the atmosphere was high in CO2, low in O2; while C4 pathway evolved during a period that the atmosphere was high in O2. So climatic conditions influence what environments C3 and C4 grasses grow in. Areas with higher O2 concentration will have more C4 grasses because of their adaptation to photorespiration (a disadvantage of C3 photosynthesis), in hot and humid environments. The C3 pathway is more evolutionarily ancient because it speciated before the C4 pathway. The C4 evolved this adaptation due to natural selection making them more fit for environments the C3 grasses can not survive in.

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