BIO 200 Chapter 7, Fall 2015

Biochemical Pathways – Photosynthesis CHAPTER 7 Photosynthesis Autotrophs Plants Autotrophic bacteria Algae 99.9% of all life on earth relies on photosynthesis for their energy Photosynthesis and chloroplasts  Photosynthesis occurs in Chloroplasts  Chloroplasts contain the pigment that captures the energy in light = Chlorophyll  Chlorophyll is found in membranous sacs called thylakoids  A stack of thylakoid is called a granum (pl. grana).  Grana are suspended in a fluid-filled space called the stroma. Photosynthesis An overview of photosynthesis Light-capturing events – The pigment chlorophyll absorbs certain wavelengths of light and some of its electrons become excited. An overview of photosynthesis Light-capturing events Light-dependent reactions – These reactions use the energy in the excited electrons to make ATP and NADPH. An overview of photosynthesis Light-capturing events Light-dependent reactions Light-independent reactions – ATP and NADPH from the light reactions are used to reduce carbon dioxide to make glucose. Visible light spectrum  Visible light – Combinations of different wavelengths of light – Can be seen as different colors  Pigments are molecules that absorb light – Each pigment absorbs certain wavelengths of light – The wavelengths that they do not absorb, they reflect  Chlorophyll: The main photosynthetic pigment – Two forms; Chl a and Chl b – Absorb light in the blue and red portions of the spectrum – Reflect green wavelengths Other types of pigments  Accessory pigments = Carotenoids  Absorb blue and green wavelengths  Reflect orange and yellow  Chlorophyll + accessory pigments – Organized into photosystems that harvest the energy from many wavelengths of light  When pigments absorb light – Some of their electrons become “excited” Photosynthesis Photosynthesis Photosynthesis Glyceraldehyde-3-phosphate: The product of photosynthesis  Used to recycle ribulose needed in the Calvin cycle  Used to make glucose  Used to make the sugars needed to build ATP, DNA and RNA  Can be converted into lipids  Can be broken down in glycolysis  Can be converted into amino acids to make proteins Other aspects of plant metabolism  Plant cells can use the organic molecules produced in photosynthesis to make – Fats, proteins and other carbohydrates – Toxins for their protection  Many of these are useful medicines.  Some can be used as natural insecticides. – Vitamins  Molecules that we cannot make, but that we need