Ch. 8.1: Photosynthesis Overview Plants use sunlight to make food (glucose).

Plants and Photosynthesis Plants are autotrophs (producers) - make their own food. Plant cells have chloroplasts which can capture light energy and convert it into chemical energy – stored in glucose.

Photosynthesis + + The Process H2O CO2 Energy Calvin Cycle Chloroplast ATP and NADPH2 Which splits water Light is Adsorbed By Chlorophyll Calvin Cycle ADP NADP Chloroplast Used Energy and is recycled. O2 + C6H12O6 Light Reaction Dark Reaction

Chemical Equation for Photosynthesis

Chloroplast – the Photosynthetic Organelle in Plant Cells

Chloroplast site of photosynthesis. Chloroplasts are concentrated in the mesophyll tissue found in the leaf. Mesophyll tissue is present right under the epidermis of the leaf and consists of Palisade tissue + spongy tissue.

Gases: Where Does the O2 Come From? CO2 is taken into the leaf through stomata for photosynthesis. O2 is released out of the leaf through stomata as a product of photosynthesis. In order to determine whether the O2 gas product came from the reactant CO2 or from H2O, scientists used tracer (radio-isotopic) Oxygen, first in CO2 and then in H2O as follows:

Fate of Atoms in Photosynthesis CO2  becomes part of glucose (C6H12O6) H2O  is split into H and O; O2 is released as a gas; H’s become part of glucose.

Two Stages of Photosynthesis Photosynthesis occurs in two stages. Light reactions (during day-time only, in the thylakoid membrane) Calvin Cycle (both day and night, in the stroma), which are linked together by NADPH and ATP.

Light Reaction Light reaction – is dependent on light and occurs only during the day in nature. Where: thylakoid membrane of the chloroplast. Light reactions involve: a) Splitting of water to produce O2 gas and H for glucose. b) Production of ATP = chem. Energy NADPH (carries H, also energy).

Calvin Cycle independent of light and occurs during the day and the night. Where: stroma of the chloroplast. Calvin Cycle involves the production of ‘food’ as glucose, by using CO2, ATP energy and NADPH.

Light Used in Photosynthesis Chlorophyll pigments can absorb only some wavelengths of the visible light from the electromagnetic spectrum. Visible light consists of the following colors or wavelengths in order of increasing wavelengths / decreasing energy: Violet Blue  Green  Yellow  Orange Red. Chloroplasts absorb mainly blue-violet and red-orange lights. Green light is reflected and transmitted by green plants – hence, they appear green.

Light Photon = a discrete packet of light energy. The shorter the wavelength, the greater the energy….and vice-versa.

Photosynthesis + + H2O CO2 Energy Calvin Cycle Chloroplast O2 C6H12O6 ATP = chemical energy NADPH – carries Hydrogen (NADP + H) + H2O CO2 Energy ATP and NADPH2 Which splits water Light is Adsorbed By Chlorophyll Calvin Cycle ADP NADP Chloroplast Used Energy and is recycled. O2 + C6H12O6 Light Reaction “Dark” Reaction

Photosynthesis and Cellular Respiration Both Photosynthesis and Cellular Respiration are reverse of each other. Photosynthesis is an endergonic reaction (energy required for rxn) Cellular Respiration is an exergonic reaction (energy released during rxn)

The Flow Of Biological Energy Photosynthesis cellular respiration carbohydrates/ energy rich O2 chloroplast mitochondria CO2 + H2O ATP for: (energy poor) movement/cell activity