1 Photosynthesis & Cellular Respiration How plants get Energy

2 Photosynthesis Photosynthesis - the process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen

Photosynthesis There are two main steps in Photosynthesis. Light reaction Calvin Cycle 3

4 The Photosynthesis Equation The equation for photosynthesis is: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 carbon dioxide + water sugars + oxygen Light

5 Light Energy Light is a form of energy –chlorophyll absorbs light. –The energy is transferred directly to electrons in the chlorophyll molecule raising the energy levels of these electrons. –high-energy electrons are what make photosynthesis work

6 Inside a Chloroplast photosynthesis takes place inside chloroplasts. Plant Plant cells Chloroplast

7 Inside a Chloroplast Chloroplasts contain thylakoids—saclike photosynthetic membranes. Thylakoids are arranged in stacks known as grana. A singular stack is called a granum. Stroma – space outside of the thylakoids Granum Chloroplast Stroma Single thylakoid

8 Light and Pigments photosynthesis requires chlorophyll –pigments - light-absorbing molecules that gather the sun's energy The main pigment in plants is chlorophyll. There are two main types of chlorophyll: –chlorophyll a –chlorophyll b

9 Light and Pigments Chlorophyll does not absorb light in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green. Estimated Absorption (%) Chlorophyll b Chlorophyll a Wavelength (nm)

10 Inside a Chloroplast Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast in the thylakoid membrane. Chloroplast Photosystems

Light Reaction Sep 1 Light energy forces electrons in the chlorophyll a molecules to become excited. This means that have more energy than usual. 11

Light Reaction Step 2 The electrons leave the chlorophyll a molecule and are accepted by the primary electron acceptor. This begins the start of the electron transport chain and activates the Hydrogen pumps. Hydrogen is pumped into the Thylakoid. 12

Light Reaction However, certain electrons are donated to NADP (cousin to NAD) instead of heading down the chain. NADP takes and electron and a Hydrogen. 13

Light Reaction SO…. Where did the electrons that were lost come from? Water! An enzyme in the Thylakoid breaks two water molecules down into four hydrogen ions (H + ), their 4 electrons and O 2. 14

Light Reaction An enzyme in the Thylakoid breaks two water molecules down into four hydrogen ions (H + ), their 4 electrons and O 2. This is why plants don’t need to take in O 2. They make it by splitting water! 15

Calvin Cycle Now that the plant has made energy it is going to use that energy to make a simple sugar. But WE NEED CARBON to make sugar. Plants take in CO 2 and turn it into sugar! 16

Calvin Cycle Step 1 We need three CO 2 to get started. We start by hooking the carbon from each CO 2 up to a 5 carbon chain with phosphates at each end. This now make a 6 carbon chain with phosphates at each end. We create three of these at a time. 17

Calvin Cycle Step 2 Each carbon chain breaks in half. You now have 6 three carbon chains with a phosphate at each end. 18

Calvin Cycle Step 3 The ATP and NADPH created in photosynthesis gives a phosphate and a hydrogen to each of the three carbon chains. There is now a phosphate attached at each end. 19

Calvin Cycle Step 3 Cont. The three carbon chains now give off a phosphate. Yes we gained 6 phosphates to lose 6 phosphates. CRAZY! But this give the three carbon chains the energy needed to rearrange slightly. 20

Calvin Cycle Step 4 One of the new three carbon chains leaves to become a carbohydrate. We have made a molecule of sugar!!! The rest of the 3 carbon chains use 3 ATPs to recombine into the 5 carbon chains. 21

22 Inside a Chloroplast Chloroplast Light H2OH2O O2O2 CO 2 Sugars NADP + ADP + P Calvin Cycle Light- dependent reactions Calvin cycle

23 Photosynthesis Reactions –light-independent reactions (Calvin cycle) takes place in the stroma ATP and NADPH not stable enough to store the energy they carry for more than a few minutes uses ATP and NADPH energy to build high-energy sugars for long term storage

24 Factors Affecting Photosynthesis Many factors affect the rate of photosynthesis, including: Water Temperature Intensity of light

25 Comparing Photosynthesis and Cellular Respiration The energy flows in photosynthesis and cellular respiration take place in opposite directions.

26 Comparing Photosynthesis and Cellular Respiration On a global level, photosynthesis and cellular respiration are also opposites. –Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. –Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.