Chapter 7 1 Plants are autotrophs meaning they sustain themselves they are self feeders Producers feed the consumer of the biosphere Heterotrophs cannot make their own food but must consume plants or animals or decompose organic material Because autotrophs use the light plants and other photosynthesizes are specifically called photoautotrophs 2 In the chloroplast of two membranes encloses an inner compartment which is filled with a thick fluid called stroma Carbon dioxide enters the leaf and oxygen exits by way of tiny pores called stomata Suspended in the stroma is a system of interconnected membranous sacs called thylakoids In many places thylakoids are concentrated in stacks called grana 3 Co2 becomes reduced to sugar as electrons along with hydrogen ions H from water are added to it Meanwhile water molecules are oxidized that is they lose electrons along with hydrogen ions Recall that oxidation and reduction always go hand and hand 4 Photosynthesis converts light energy to chemical energy and stores it in chemical bonds of sugar molecules which can provide energy for later use or raw materials for biosynthesis The two stages light reaction and the Calvin cycle occur in the Chloroplast The two stages are interdependent because the reactions produce no sugar sugar is not made until the Calvin cycle The splitting of water is necessary because when it splits it provides a source of electrons and giving off O2 as a by product 5 Chlorophyll a absorbs mainly blue violet and red light It looks blue green because it reflects mainly green light Chlorophyll b is very similar it absorbs mainly blue and orange light and reflects olive green Chloroplasts also contain pigments called carotenoids which are various shades of yellow and orange Green is least effective at driving photosynthesis because it is mostly transmitted and reflected not absorbed by photosynthesis pigments 6 Electrons are added to the primary electron acceptor in photosystem two from a water molecule The water molecule loses its hydrogen s from this and the resulting oxygen binds with another oxygen to create oxygen gas The electron in the primary electron acceptor is excited by sunlight and moves to the top of the primary electron acceptor where it has a ton of energy It moves down a chain of proteins and loses energy This energy is used to pump hydrogen ions against the concentration gradient from a low concentration in the stroma to a high concentration in the thylakoid interior space The electron then reaches the primary electron acceptor in photosystem one and is re excited by sunlight It gains a ton of energy and goes through the same process of losing energy which Chapter 7 is used to pump hydrogen ions against the concentration gradient When the electron has lost enough energy it is then picked up by a molecule called NAD When NAD picks up two electrons it becomes NADPH and moves to the Calvin Cycle Meanwhile there is a high concentration of hydrogen ions in the thylakoid interior space and a low concentration in the stroma The hydrogen ions pass through a protein at the end of the electron transport chain called ATP synthase Hydrogen ions flow through it with the concentration gradient from the thylakoid interior space into the stroma Since they are flowing with the concentration gradient energy is released which is used to bind and ADP with a phosphate group to make ATP This process is called chemiosmosis The Calvin cycle which consumes the NADPH and ATP occurs in the stroma 7 Calvin cycle depends on the ATP and NADH produced through the light reactions which can only occur when sunlight is present and mostly during the day as the moon doesn t provide enough light energy CO2 ATP and NADPH are inputs of the Calvin cycle For the net synthesis of one G3P molecule the Calvin cycle consumes nine ATP and six NADHP molecules For the net synthesis of one G3P molecule the Calvin cycle uses three CO2 8 C3 plants use co2 directly from the air because the first organic compound produced is the three carbon compound 3 PGA C4 plants have special adaptations that save water without shutting down photosynthesis C4 plants keep their stomata closed when its hot which is most of the time to prevent the release of water CAM plants conserve water by opening the stomata and admitting CO2 mainly at night