Types of Photosynthesis: C3, C4 and CAM

Dark reaction – Calvin cycle
Second step of photosynthesis is called Calvin’s cycle. Because it does not require light, so it is called dark reaction. During dark reaction, the ATP and NADPH generated by light reaction are consumed to fix carbon dioxide into organic carbohydrates. The first fixed carbohydrate is a three carbon compound 3-phosphoglycerate (3PGA). The final product is a high-energy 3 carbon compound glyceraldehyde-3-phosphate (G3P) which can be used to synthesize a broad range of organic molecules. An important intermediate molecule for carbon dioxide fixation is ribulose bisphosphate (RuBP), and the enzyme catalyzing the CO2 fixation is Rubisco.

Comparison of some characteristics of C3 plants with C4 and CAM plants. C3 crop examples are given.

Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of organic carbohydrates from carbon dioxide and water. Photosynthesis takes place in chloroplasts and can be divided into two steps: light reactions which require light and dark reactions which do not require light. During light reaction, light energy is captured by photosystems and electrons are transferred among the electron receptors. ATP and NADPH are generated. During dark reactions, CO2 is fixed using ATP and NADPH generated by the light reactions and organic carbohydrates are synthesized via the Calvin Cycle. When the CO2 is first fixed into a 3 carbon compound 3PGA, it is called C3 pathways and these plants are called C3 plants. The disadvantage of C3 plants is that they undergo photorespiration and thus waste some energy gained in light reactions. C4 cycle is the pathway adopted by C4 plants to bypass photorespiration.


Explain the difference between C3, C4, and CAM plants

Structure of Chloroplasts
Chloroplasts are specialized organelles in plant cells for the purpose of photosynthesis. Each cell may contain 1-1000 copies of chloroplasts. Chloroplasts are double membrane structure with stacked disc-like membrane structure (called thylakoids) inside the stroma. Light reactions of photosynthesis occur in thylakoids, and dark reactions occur in stroma.


Second step of photosynthesis is called Calvin’s cycle


In a C3 leaf, mesophyll cells are arranged in parallel rows with well formed chloroplasts.
C4 Photosynthesis
Occurs in plants in hot & dry conditions.

C4 Photosynthesis PowerPoint Presentation - SlideServe


Light Reactions
Calvin Cycle Reactions
- the organelles that carry on photosynthesis
a double membrane surrounds a fluid-filled area called the stroma.
a third membrane system within the stroma forms flattened sacs called
Stacks of thylakoid (plural, grana)
Chlorophyll
a pigment that is found in the thylakoids
absorbs solar energy to be used in photosynthesis
Thylakoid Membrane
contains complexes that convert solar energy into a chemical form useable by the enzymes in the stroma
Stroma
enzyme rich area in which carbon dioxide is reduced to a carbohydrate

This carbohydrate is the only source of energy for most organisms on Earth.
Electrons are removed from water and energized by solar energy
Photosynthetic Pigments
Chlorophylls and Carotenoids
Other types of Photosynthesis
C3 Photosynthesis
Occurs where temperature and rainfall tend to be moderate.
the first detectable molecule after carbon dioxide fixation is a C3 molecule composed of three carbon atoms.

Question about the C4 cycle (photosynthesis)? | Yahoo …


Avoid the uptake of O2 by rubisco, which would compete with carbon dioxide for the active site on rubisco.
C4 Photosynthesis
C4 plants have a different structure than C3 plants.
Chloroplasts are found in both the mesophyll cells and the bundle sheath cells
the mesophyll cells are arranged concentrically around the bundle sheath cells
the mesophyll cells shield the bundle cells from the oxygen
the Calvin cycle occurs only in the bundle sheath cells
Carbon dioxide is not taken directly from the air
the carbon dioxide is fixed in mesophyll cells producing a C4 molecule.