An overview of photosynthesis Section 8.2

Light Visible spectrum of light ranges from red to violet Our eyes are able to process these wavelengths and produce colours We see reflected colours

Pigments Photosynthetic organisms capture energy from the sunlight with pigments Chlorophyll absorbs light in red and blue part of spectrum Green part is reflected Why leaves appear green

Why do leaves turn brown in fall? Chlorophyll breaks down before carotenoids These orange and red accessory pigments are then exposed for everyone to see

Chloroplasts Contain sac like photosynthetic membranes called thylakoids Interconnected and arranged as grana Chlorophyll is located in thylakoid membranes Stroma – fluid filled portion of chloroplast

How do Chloroplasts work? Chlorophyll absorbs light energy very well This energy is transferred to electrons in the chlorophyll molecule This makes a large supply of high energy electrons Driving force for photosynthesis

Why are the high energy electrons important? In a chemical sense, these electrons are highly reactive – they act as fuel A carried is needed to take them where it is needed to go This carrier, or taxi, is NADP+ and a H+ ion Nicotinamide adenine dinucleotide phosphate Conversion of NADP+ and H+ to NADPH stores some of the suns light energy Acts as a starting point for chemical energy formation

Overview of Photosynthesis Photosynthesis uses the suns energy to convert water and carbon dioxide into high energy sugars and products

Light dependent and Light independent reactions Light dependent reactions use energy from the sun Water needed, converted into H+ ions and source of electrons Oxygen is a by – product NADPH and ATP generated Reactions occur in thylakoid membrane

Light independent reactions Glucose is produced via the Calvin Cycle ATP and NADPH are used to produced high energy sugars from carbon dioxide Light independent reactions rely on the products of the light dependent reactions!

Writing assignment Write a paragraph explaining why plants require light. Describe how light is used to produce energy in a form that cells can use.