Chapter 13.1 Photosynthesis

Capturing Light Energy Photosynthesis – is the process by which plants make their own food. Plant cells have organelles called chloroplasts Chloroplasts are surrounded by two membranes Inside the chloroplast another membrane form stacks called grana Grana contain the green pigment called chlorophyll. Sunlight is made up of many wavelengths. Chlorophyll absorbs many of these wavelengths. It reflects more wavelengths of green light, this is why plants look green.

Making Sugar The light energy capture by chlorophyll is used to help form glucose molecules. In turn, O2 is given off by the plant cells Photosynthesis is a complicated process that is summarized by the following equation.

6 molecules of CO2 and six molecules of O2 are needed to form one molecule of glucose and six molecules of oxygen.

Getting Energy from Sugar Glucose molecules store energy. Plant cells use this energy for their processes To get energy plant cells break down glucose and other food molecules in a process called cellular respiration. During this process, plant cells use O2. The cells give off CO2 and O2. Excess glucose is converted to another sugar called sucrose and stored as a starch.

Gas Exchange CO2 enters the plant leaves through stomata and O2 leaves through this opening. An opening in the leaf’s epidermis and cuticle. The stoma is surrounded by two guard cells that act like double doors opening and closing the stoma. Water also exists the leaf in this way this is called transpiration.

Why is Photosynthesis Imporat?