Photosynthesis Anderson Spring 2017 College of the Redwoods

Photosynthesis Anderson Spring 2017 College of the Redwoods

How do plants get energy? Cellular Respiration C 6 H 12 O 6 sugar Photosynthesis + 6 O 2 oxygen 6 CO 2 + 6 H 2 O carbon dioxide water 6 CO 2 + 6 H 2 O + ATP carbon dioxide light water C 6 H 12 O 6 sugar energy + 6 O 2 oxygen

Autotroph/Heterotroph • Autotroph – organism that produces its own food • auto = self, troph = feeder • Plants (and some bacteria and algae) are photoautotrophs uses sunlight and carbon from CO 2 to synthesize energy • Heterotroph – organisms that must obtain energy and carbon from food by consuming other organisms • hetero = other, troph = feeder • Dependent on autotrophs

Leaf Cross-Section Photosynthesis occurs in the mesophyll (middle layer) CO 2 exchange happens through openings on bottom of leaf, called stomata

Chloroplasts Organelle in which photosynthesis takes place • Thylakoid – membrane-bound disc structure that contains chlorophyll (green) • Granum – stack of thylakoids • Stroma – space around granum

What is Light Energy? • Longer wavelengths carry less energy; shorter carry more • Sunlight emits broad range of electromagnetic radiation

Visible Light Spectrum • White light – light that contains all wavelengths of light • The colors we see are the light that’s NOT absorbed • When we see green, all light except for green is being absorbed

Chlorophyll Pigments • Chlorophyll a – absorbs from violet and red range • Chlorophyll b – absorbs from blue and red-orange • Carotenoid – absorbs from bluegreen (looks red, orange, yellow) • Not all plants are equal! (but all plant lives matter)

Photons • Individual bundles of electromagnetic energy • Can provide energy to electrons (makes them move) • Basic unit of all light

Structure of Chlorophyll

Let’s tie all that nonsense together • Plants make their own food from sunlight energy – photoautotrophs • Sunlight contains tiny particles, called photons, that make up light • These photons have energy! • The photons in the light hit the chlorophyll pigments in plant leaves, green light is reflected, all other absorbed • A reaction occurs which is the

Stages of Photosynthesis • Stage 1 – Light Reactions • Energy from sun light splits water to produce oxygen • Reduces NADP+ to NADPH, which will then carry high energy electrons to Calvin Cycle • Stage 2: Calvin Cycle • Carbon dioxide and the high energy electrons from NADPH are used to create carbohydrates (glucose) • Called the “dark cycle” because sunlight is not necessary

Light-Dependent Reactions • Photosystem – grouping of pigment molecules (chlorophyll) and proteins • Exists in thylakoid membrane • Photon is “absorbed” by the chlorophyll and causes chlorophyll to become excited • The electron breaks free from chlorophyll – “donates” electron • The electron must be replaced – this is done by splitting water into oxygen and hydrogen ions (each water molecule releases 2 electrons) H 2 O ½ O 2 + 2 H+

Photosystems • In eukaryotes and some prokaryotes, there’s 2 photosystems: • Photosystem II and Photosystem I (named by discovery, not order of function)

Photosystem II 1. Light energy absorbed and enters reaction center – chlorophyll excited 2. Electron captured by acceptor 3. Water split, electrons replace donated ones from chlorophyll, O 2 released as byproduct 4. Electrons are passed to photosystem I

Photosystem I 5. Once electrons re passed to photosystem I, electrons are captured by acceptor 6. Excited electrons oxidize NADP+ to NADPH (another energy storing molecule)

ATP Synthase • Electrochemical gradient of H+ ions created through electron transport chain • ATP synthase uses gradient to diffuse H+ out of thylakoid space

End Result of Light-Dependent 2 H 2 O 2 O 2 + 2 H 2 – oxygen is the byproduct 1 NADPH 1 ATP So where does the carbon come from to make the glucose?

Calvin Cycle • Reactions of photosynthesis that use energy stored from light-dependent reactions (ATP and NADPH) to form glucose • CO 2 enters chloroplasts by diffusion (enters cell through stomata) • Calvin cycle occurs in stroma (space between membrane and thylakoids) • In addition to CO 2, Ru. Bis. CO (an enzyme), and Ru. BP (5 carbon molecule) are needed

Calvin Cycle Stage 1: • Carbon fixation – CO 2 and Ru. BP (5 carbons) create 6 carbon compound, catalyzed by Ru. Bis. CO • The 6 -carbon compound immediately breaks into 2 3 -carbon compounds (3 PGA)

Calvin Cycle Stage 2: • 3 -PGA (3 -carbon molecule) reduced by NADPH and ATP • Results in G 3 P, NADP+ and ADP • 1 ATP and 1 NADPH used for each 3 -PGA molecule • 1 G 3 P leaves cycle to make glucose

Calvin Cycle Stage 3: • Remaining G 3 P molecules regenerate Ru. BP (5 3 -carbon molecules rearrange to make 3 5 -carbon molecules) • 3 more ATP used, making 3 ADP • And the cycle is ready for the next CO 2 • Takes 6 turns to make 1 glucose (or 2 with 3 CO 2 to start)

How do prokaryotes do it without chloroplasts? • Remember: prokaryotes lack membrane-bound organelles, such as chloroplasts • Prokaryotic photosynthetic autotropic organisms have infoldings of plasma membrane for chlorophyll attachment and photosynthesis

One organism’s waste is another organism’s energy • Carbon dioxide is “waste” for animals, plants need carbon dioxide for photosynthesis • Oxygen is “waste” for plants, animals need oxygen for cellular respiration 6 CO 2 + 6 H 2 O carbon dioxide water C 6 H 12 O 6 + 6 O 2 sugar oxygen C 6 H 12 O 6 sugar + 6 O 2 oxygen 6 CO 2 + 6 H 2 O carbon dioxide water

Plants Undergo Cellular Respiration Too! • Carbohydrates are energy storage molecules • Plants store their glucose as starch • The ATP from the light-reactions of photosynthesis is enough to fuel the Calvin cycle, not the whole plant cell • Plants have mitochondria too! Cellular respiration provides more ATP • When there’s little or no light, plants get their energy from cellular respiration (take in O 2 and release CO 2)

Do Plants Sleep? • During the night, when there’s no sunlight, plants consume oxygen to undergo cellular respiration (use their carbohydrate energy stores) • They will be using oxygen and releasing CO 2, just like we do • But! Plants take up much more CO 2 during photosynthesis than they release at night • So the next time a 5 year old asks you this question, you can tell them, “No, they don’t really sleep. They’re just doing other things at night that they don’t do during the day. ”

Don’t listen to our President, global warming is real!