PHOTOSYNTHESIS Chapter 6

The main form of energy from the sun is in the form of electromagnetic radiation Visible radiation (white light) used for photosynthesis Remember : ROY G. BIV? Living things require energy to stay alive. The main energy input is fr/ sun. Wavelength - (crest to crest) The sun produces many wavelengths but only visible radiation is used for photosynthesis.

Why are plants green? pigment a compound that absorbs light different pigments absorb different wavelengths of white light. chlorophyll is a pigment that absorbs red & blue light so green is reflected or transmitted. Chlorophyll is located in the thylakoid membranes So, Plants are green because the green wavelength is reflected, not absorbed. Photosynthesis cannot occur w/out chlorophyll.

2 types of chlorophyll Chlorophyll a – involved in light reactions Chlorophyll b – assists in capturing light energy – accessory pigment Carotenoids – accessory pigments – captures more light energy Red, orange & yellow

The electromagnetic wavelengths and the wavelengths that are absorbed by the chlorophyll

Photosynthesis is - conversion of light energy into chemical energy that is stored in organic compounds (carbohydrates > glucose) Used by autotrophs such as: Plants Algae Some bacteria (prokaryotes) Remember… Autotrophs (producers) – produce energy fr sunlight Heterotrophs (consumers) – get energy fr eating autotrophs or heterotrophs- Bacteria example - cyanobacteria

glucose - energy-rich chemical produced through photosynthesis C6H12O6 Biochemical pathway – series of reactions where the product of one reaction is consumed in the next E.g. photosynthesis product is glucose which is used in cellular respiration to make ATP (carbohydrate) glucose (sugar is carbohydrate).

Photosynthesis equation Light energy 6CO2 + 6H2O C6H12O6 + 6O2 Chlorophyll Reactants: Carbon dioxide and water Products: glucose and oxygen which is a byproduct In words… 6 carbon dioxide molecules plus 6 water molecules with sunlight in the presence of chlorophyll will yield glucose and oxygen

Where does photosynthesis take place? Mainly occurs in the leaves: a. stoma - pores b. mesophyll cells Mesophyll Cell Chloroplast Stoma

Stomata (stoma) Pores in a plant’s cuticle through which water vapor and gases (CO2 & O2) are exchanged between the plant and the atmosphere. Guard Cell Oxygen (O2) Stoma Carbon Dioxide (CO2) Found on the underside of leaves

Chloroplast Organelle where photosynthesis takes place. Stroma Outer Membrane Thylakoid Granum Inner Membrane Thylakoid stacks are connected together

Parts chloroplasts – membrane organelle that absorbs light energy Thylakoids – flattened sacs contain pigment - chlorophyll Grana (pl: granum) – layered thylakoids (like pancakes) Stroma – solution around thylakoids Stomata – pore on underside of leaf where O2 is released and CO2 enters

Energy for Life on Earth Sunlight is the ULTIMATE energy for all life on Earth Plants store energy in the chemical bonds of sugars Chemical energy is released as ATP during cellular respiration

Structure of ATP ATP stands for adenosine triphosphate It is composed of the nitrogen base ADENINE, the pentose (5C) sugar RIBOSE, and three PHOSPHATE groups The LAST phosphate group is bonded with a HIGH ENERGY chemical bond This bond can be BROKEN to release ENERGY for CELLS to use

Photosynthesis SUN Photosynthesis can be divided into two stages: 1. Light Reaction - Produces energy from solar power (photons) in the form of ATP and NADPH. 2. Calvin Cycle Also called Carbon Fixation,Uses Co2 & energy (ATP and NADPH) from light reaction to make sugar (glucose).

2 stages of photosynthesis- The Process of Photosynthesis does NOT Happen all at Once; it occurs in  THREE STAGES: NADP+ is organic compound that accepts electrons (Nicotinamide adenine dinucleotide phosphate)

STAGE 1: Light Reaction (Electron Flow) Occurs in the Thylakoid membranes

Photosystem I and II Step 1 – light excites e- in photosystem II Step 2 – e- move to primary e- acceptor Step 3 – e- move along electron transport chain (etc) Step 4 – light excites e- in photosystem I Step 5 – e- move along 2nd (etc) End – NADP+ combine H+ to make NADPH Step 1 – light excites e- in chlorophyll a of photosystem II Step 2 – e- move to a primary e- acceptor (redox occurs) Step 3 – e- transferred along electron transport chain Step 4 – light excites e- in chlorophyll a of photosystem I Step 5 – e- from photosystem I are transferred along a 2nd electron transport chain End – combine with NADP+ and H+ to make NADPH

Chemiosmosis – synthesis of ATP Powers ATP synthesis Takes place across the thylakoid membrane Uses ETC and ATP synthase H+ move down their concentration gradient forming ATP from ADP Concentration of protons is greater in thylakoid than stroma Concentration gradient is potential energy (remember: concentrations move fr high to low) ATP Synthase converts potential energy of/ protons concentrated gradient into chem energy of ATP across thylakoid membrane ATP synthase – multifunctional protein - carrier protein that harnesses energy in thylakoid membrane AND enzyme b/c it catalyzes ATP How? Makes ATP by adding phosphate group to ADP (adenosine diphosphate)

ELECTRON TRANSPORT CHAIN ANIMATION http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html

STAGE 2: CALVIN CYCLE Biochemical pathway in photosynthesis that produces organic compounds (Glucose) using ATP & NADPH from the light reactions of photosynthesis Carbon fixation – carbon atoms from CO2 are bonded or ‘fixed’ into carbohydrates occurs in stroma The Calvin cycle – part of photosynthesis that fix carbon from atmospheric CO2 into organic compounds – carbohydrates - sugar. Remember – sugar is C6H12O6 The Calvin cycle reactions do not require light directly, but reduction of CO2 to sugar requires the products of the light reactions