Photosynthesis and Cellular Respiration

Photosynthesis Needed in order for life to survive on Earth Photosynthesising organisms contain chloroplasts that trap the Sun’s energy converted into chemical energy and stored as sugars and carbohydrates Other products produced by the Sun’s energy are oxygen, ATP and heat

Cellular Respiration Used by plants, animals and other multicellular organisms The break down of energy-rich compounds to release stored energy broken down inside the mitochondria This makes ATP

ATP Supplies the energy for cellular activities Used rapidly so cells must be constantly creating it Used for: active transport, movement of chromosomes, movement of muscles, cilia or flagella, etc.

ATP produces energy by breaking a bond to a phosphate group this produces ADP (adenosine diphosphate) and a free phosphate group ATP → ADP + P This process works in reverse to create more ATP

Oxidation and Reduction When atom or molecule loses an electron, it is said to be oxidized When an atom or molecule gains an electron, it is said to be reduced Electrons lost by one atom or molecule are gained by another Atoms or molecules in their reduced form have more energy

Chloroplasts leaves are the primary photosynthetic organs of plants contain chlorophyll inside chloroplasts

have two membranes: outer membrane and an inner membrane the membranes enclose an interior space filled with a protein-rich semi liquid material known as stroma thylakoids: membrane-bound sacs found within the stroma these thylakoids stack on top of one another to form columns called grana

most chloroplasts have about 60 grana which each have about 30-50 thylakoids (each chloroplast has 1800-3000 thylakoids) grana are connected by unstacked thylakoids called lamellae photosynthesis occurs partly within the stroma and partly in the thylakoid membrane thylakoid membranes enclose a space called the thylakoid lumen

Chlorophyll All photosynthetic organism contain chlorophyll the two main types of chlorophyll: chlorophyll a (blue-green) and chlorophyll b (yellow-green) they absorb photons with energies in the blue-violet and red regions and reflect everything else

Chlorophyll a and b chlorophyll a is the only pigment that can transfer the energy from sunlight to photosynthesis chlorophyll b acts as an accessory pigment (“helper”) to catch the photons a misses and transfer the energy absorbed to a there are other compound, carotenoids, are also “helper” pigments

Why do leaves change color? in winter there is not enough light or water for photosynthesis to occur plants begin to break down the chlorophyll they have and stop making more the green color disappears and other colors start to appear (yellow, orange, red) these colors were always there they were just covered up by the green chlorophyll

Mitochondria Mitochondria enable cells to extract energy from food (where cellular respiration occurs) Are bound by two membranes The fluid filled space of the inner membrane is the matrix The inner membrane has many folds known as cristae to increase the surface area

The Process of Photosynthesis Section 5.2

Plants

Various energy containing molecules are formed during photosynthesis: 1) Glucose - energy storage in most cells 2) ATP (adenosine triphosphate) - used by all living cells for immediate energy

3) NADPH - starts as NADP+ (nicotinamide dinucleotide phosphate)

Light-dependent reactions Light-independent reactions Throughout the process of photosynthesis there are two different types of reactions that occur: Light-dependent reactions Makes ATP and NADPH Light-independent reactions Uses the ATP and NADPH to make glucose

Light-Dependent Reactions http://www.youtube.com/watch?v=BK_cjd6Evcw Requires sunlight in order to work require chlorophyll; occur in the thylakoid involves photosystems photosystems I and II responsible for capturing light energy

solar energy is captured when an electron in a chlorophyll molecule absorbs a photon (photosystem II) electrons go from low energy to high energy the “excited” electron is removed from photosystem II and passed through an electron transport chain

Once the excited electron has left photosystem II there are four steps that occur The electron that left photosystem II needs to be replaced before more light can be absorbed This is done through photolysis (ie. splitting of H2O)

Step 2: The electron in the electron-transport chain is passed from molecule to molecule As it is passed along it releases energy This energy pull hydrogen ions from the stroma into the thylakoid lumen

Step 3: Light hits photosystem I An electron in this photosystem is ‘excited’ and passed onto the smaller electron transport chain

Step 4: The electron that went from photosystem I to the next electron transport chain is used to reduce NADP+ to make NADPH

Chemiosmosis The H+ ions in the thylakoid lumen are unable to escape except through special proteins called ATP synthase complexes As the H+ ions move through this complex they release energy The complex uses some of this energy to combine ADP with Pi making ATP This ATP then moves onto the light- independent reaction to make glucose

Light-Independent Reactions

Light-Independent Reactions https://www.youtube.com/watch?v=c2ZTumt pHrs does not require light Also known as the Calvin-Benson cycle Will occur when enough NADPH and ATP have been produced Figure 5.14, page 177

Occurs in three stages: Step 1: Fixing Carbon Dioxide 6 Carbon dioxide molecules bond to 6 five- carbon compounds known as RuBP (ribulose bisphosphate) This makes 6 six carbon compounds that are unstable Breaks into 12 three-carbon compounds

Step 2: Reduction The 3-carbon compounds are activated by ATP (given energy) and then reduced by NADPH (given more energy) The 12 molecules are now known as G3P 2 G3P molecules move on to make glucose, 10 go to Step 3

Step 3: Replacing RuBP Remaining G3P will be used to make more RuBP ATP will help break and reform the chemical bonds to make the 5-carbon RuBP