Almost all energy used by life comes from the sun The sun produces light in the form of Photons which act like particles and waves - posses energy

Overview of Photosynthesis Photosynthesis takes places in three stages 1.capturing energy from sunlight 2.using the captured energy to produce ATP and NADPH 3.using the ATP and NADPH to make carbohydrates from CO 2 in the atmosphere

Chemistry of Photosynthesis 6 CO H 2 O + light  C 6 H 12 O H 2 O + 6 O 2 Photosynthesis converts atmospheric carbon into organic carbon (which can be used by other organisms

Pigments in plants absorb light energy

Pigments are arranged into photosystems -Light energy is absorbed by electron in pigments -This “excites” an electron -The electron is passed until it finds a pigment adjacent to a water splitting enzyme

Anatomy of a leaf

Plants use two photosystems

Products of photosynthesis: Plants produce both ATP and NADPH the excited electrons flow through both photosystems and end up in NADPH high energy electrons generated by photosystem II are used to make ATP and are then passed along to photosystem I to drive the production of NADPH

Photosystem II generates ATP via a H+ gradient

Photosytem I produces NADPH (holds high energy electron)

ATP and NADPH from photosynthesis are used to “fix” carbon -A 5 carbon sugar is converted into 2 3 carbon molocules using CO2 -3 carbon molecules are converted into glucose using ATP and NADPH -5 carbon sugar is rebuilt from the byproducts using ATP

-6 CO2 molecules are used to generate 1 glucose molecule -most of the molecules in the Calvin cycle are recycled

Some plants can’t photosynthesize in hot weather

Carbon fixation in C 4 plants -C4 plants can use a different starting molecule (4 carbons) which O2 doesn’t compete with -C4 plants can store CO2, so carbon fixation can take place even when it stomata are closed

Products built by plants (photosynthesis) are consumed by animals (any non-photosynthetic cell) The process of aerobic respiration requires oxygen and carbohydrates C 6 H 12 O O 2  6 CO H 2 O + energy The products are carbon dioxide, water, and energy (heat or ATP)

Aerobic respiration takes place in mitochondria

Step 1: Glycolosis -Glucose is converted into 2 pyruvate molecules -Glyclosis occurs outside of the mitochondria

Glycolosis, like most energy producing reactions, is complex -Glycolosis does not require oxygen -Relatively little ATP is produced

Products of glycolosis -CO2 is produced (waste) -A high energy electron is captured by bonding a H+ to NAD+ -Pyruvate is converted to acetyl-CoA (2 carbon molecule)

NADH and NAD + are used by cells to carry hydrogen atoms and energetic electrons

Step 2: the Krebs cycle -Acetyle- CoA is combined with other molecules -AcoA is completely converted to CO2 -Other molecules are recycled The original glucose molecule, made from CO2 by plants, has now been completely converted back to CO2

The Krebs cycle is also complex -More ATP is produced than during glycolosis -O2 is combined with carbons from AcoA to produce CO2 (aerobic) -More NADH is produced (holds a high energy electron)

Step 3: Oh look! High energy electrons are used to move protons against their concentration gradient (just like in photosynthesis)!

Proton gradient is used to generate (tons of) ATP -At the end of the electron transport chain, O2 is used to combine the electron with a proton and make H2O -This, combined with the proton pump in the electron transport chain, keeps the concentration of H+ low in the inner mitochondria

Glucose Is Not the Only Food Molecule Cells also get energy from foods other than sugars The other organic building blocks undergo chemical modifications that permit them to enter cellular respiration

Summary of energy flow through cells