PHOTOSYNTHESIS AND CARBOHYDRATE PRODUCTION Lecture 12 PHOTOSYNTHESIS AND CARBOHYDRATE PRODUCTION

Photosynthesis and Carbohydrate Production The Photosynthetic Process Photosynthetic Reaction Factors Affecting Photosynthesis Source-Sink Relations Metabolism Carbohydrate Production

Photosynthesis and Carbohydrate Production “It is the business of agriculture to harvest the light energy that is used to produce food, fiber, and usable stuffs produced by agricultural plants and animals” National Academy of Science, 1975 Question of the Day – How does a corn kernel weighing 0.15 g, become a mature plant weighing 6-7 Kg in 90 days?

The Photosynthetic Process Occurs in tissues within chloroplasts in plant cells Requirements are: Green leafy tissue, healthy plants Light, solar energy CO2 & H2O Net primary production from photosynthesis 1.41 x 1011 metric tons of carbon per year 3.9 billion metric tons of carbon per day 8 trillion pounds/day

In Photosynthesis, always remember that light energy is being converted to chemical energy or food.

The Plant Cell

Photosynthetic Reaction – Generalized 6 CO2 + 12H2O  C6H12O6 + 6H2O + 6O2 ^ green tissue light

CO2 from the atmosphere around the leaf, enters the stomate, travels to a photosynthetic cell where glucose is produced

Photosynthetic Reaction – Generalized Resources used: Water, nutrients CO2, light energy Energy provided: Chemical bond energy Products produced: Sugars, lipids, amino acids (proteins) , many others

Amino acids are the components of proteins and there are 20 in nature Amino acids are the components of proteins and there are 20 in nature. Look carefully and you will see why nitrogen (N) is so important in plants and animals.

Photosynthetic Reaction – Generalized Endothermic reaction: 114 Kcal/mole CO2 Total photosynthesis: Total CO2 uptake Net photosynthesis: (Measured CO2 uptake)-(respiration losses) Photosynthesis beyond losses from respiration

Photosynthetic Reaction – Generalized Photosynthesis: H2O + CO2  CH2O + O2 Respiration: CH2O + O2  H2O + CO2 Note! These are almost the exact opposite reaction

Factors Affecting Photosynthesis Light quality Action spectrum of photosynthesis and growth Function of chlorophyll in plant cells

Factors Affecting Photosynthesis Light intensity Sun leaves vs. shade leaves Photosynthetic light response curve(Fig 7.7, p. 151) Dark respiration Occurs at night, no photosynthesis Compensation point When respiration = photosynthesis Saturation point Light exists in surplus

Continued from previous slide Light Intensity - Maximum photosynthetic rate Determined by chloroplasts per leaf

Factors Affecting Photosynthesis Day length Time of year – photo period CO2 concentration Hardly ever limiting Temperature Temperature response curve Hot temps can be limiting Extreme cold also be limiting

Factors Affecting Photosynthesis Water Water stress guard cells become flaccid stomates close gas exchange stops factors affect water flow through xylem Drought incipient or prolonged

Factors Affecting Photosynthesis Source – Sink relationships Sources Net exporters of photosynthetic products (leaves) Sinks Net importers of photosynthetic products (roots, shoots)

Factors Affecting Photosynthesis Stages of leaf development Heterotrophs (sinks) 1 – 10% full size Autotrophs (sources) 10 – 15% full size (unfolding) Exporters (sources) 25% of full size (expanding) Senescing (source/sink transition) Aging, slowing down on photosynthesis

Factors Affecting Photosynthesis Plant metabolism Anabolism Plant products (carbohydrates, oils, proteins) being produced or assembled energy storage Catabolism Plant products (carbohydrates, oils, proteins) being broken down Energy release

Factors Affecting Photosynthesis Carbohydrate production via photosynthesis Light reaction Splitting of H2O Release of H, O2, e-, ATP

Factors Affecting Photosynthesis Carbohydrate production via photosynthesis C3 vs. C4 photosynthetic pathways Slightly different pathways C4 experience less net respiration losses, they recycle much of the respired CO-2 Examples: C4 – corn, sorghum, bermudagrass C3 – soybean, barley, rice, cotton

The End

The Plant Cell