(BIOL 101) Module 2: Lesson 10 - Photosynthesis

“self-feeders”; “producers”; organisms that use photosynthesis; synthesize organic compounds from CO₂ & H₂O

autotrophs

conversion of light energy —→ chemical energy —→ stored in sugars or other organic compounds; forms the basis of almost all life on Earth

photosynthesis

“other-feeders”; feed on other organisms; consists of consumers & decomposers; need organic molecules & oxygen to make energy

heterotrophs

organelle for capturing solar energy & converting it to chemical energy

chloroplasts

double membrane surrounding the chloroplast organelle

outer/inner membrane of chloroplast

semi-fluid interior of the chloroplast

stroma

flattened membranes; form stacks within the chloroplast

thylakoids

a stack of thylakoids

granum

pigments found in the thylakoid membrane; drive photosynthesis

chlorophyll

Any green part of a plant contains ____

chlorophyll & chloroplasts

waxy coating outside of the leaf; helps prevent water loss

cuticle

contains chloroplasts; site of photosynthesis

palisade mesophyll

structural portion of the leaf

spongy mesophyll

opening on the underside of the leaf; used for gas exchange

stoma

cells that open & close the stoma

guard cells

Photosynthesis Equation

6CO₂ + H₂O—→ C₆H₁₂O₆ + 6O₂

Carbon diOxide + Water —→ Glucose + Oxygen

COW GO! •

occur when sun is out; happen in thylakoids; goal = to capture solar energy; water is split into hydrogens (energy molecules) & oxygens (waste products); hydrogen are kept, oxygen are thrown away

light dependent reactions

NO light needed; happen in the stroma; goal = to build sugars; combine carbons & oxygens from carbon dioxide with hydrogen to make glucose; ex. Calvin Cycle

light independent reactions

____ will result in a transfer energy by exciting electrons in the object; pigments can do this

light absorption

___ will result in perceived color of the object.

light reflection

a graph plotting a pigment’s light absorption vs. wavelength

absorption spectrum

a machine that passes individual wavelengths of light through a solution & measures amount of light transmitted

spectrophotometer

rate of photosynthesis; combined action of all pigments

action spectrum

main pigment; absorbs more blue wavelengths

chlorophyll a

“helper” pigment; absorbs more indigo wavelengths

chlorophyll b

protective pigments; absorb more green & blue wavelengths; broaden the spectrum of absorbed light; present in spring/summer (masked by chlorophyll a & b); last longer in fall than the other pigments; appear yellow & orange; may absorb excess light energy to prevent production of oxygen radicals (photoprotection)

carotenoids

formed from chlorophyll a, chlorophyll b, & carotenoids

photosystem

Plants have multiple ____ that absorb light of different ____

pigments; wavelengths

discovered second but used first in process; captures solar energy that energizes electrons to move —→ water splits to replace electrons that moved to photosystem I → makes ATP from the transfer of energized electrons to photosystem I

photosystem II

receives electrons from photosystem II → captures solar energy to energize electrons → electrons passed along until they’re taken up by an electron carrier (NADP+ → NADPH) → carriers take electrons to stroma to build sugars in the Calvin cycle

photosystem I

ETC

electron transport chain

electron carriers for photosynthesis

NADPH

With each step in the ETC —→ enzymes associated pump a H⁺ ions across the thylakoid membrane → sets up concentration gradient → H+ ions pumped through ATP synthase causing it to turn & create ATP

Making ATP in Light reactions

ATP making enzyme

ATP synthase

caused by concentration gradient; H⁺ ions move back across membrane (down concentration grad.) via ATP synthase; each turn of it produces 1 ATP

chemiosmosis

most common; exs. photosystem I & II

noncyclic pathways

Reactants for Light Reactions in Photosynthesis

water & light/solar energy

Products for Light Reactions in Photosynthesis

NADPH & ATP

in many prokaryotes & in eukaryotes; also used in time of stress & low water; use ONLY photosystem I; for cells needing extra ATP production; photoexcited electron from photosystem I can go back to 1st ETC & make ATP instead of NADPH

cyclic pathways

takes place in the stroma of the chloroplast; uses ATP & NADPH to fix carbon dioxide: carbon dioxide taken from air → turned into carbon (sugar); ONLY done in photosynthesis; 3 stages — fixation of carbon, reduction, generation of RuBP

Calvin cycle

CO₂ combines w/ RuBP molecule (5 carbons) → form a 6-carbon compound & release O₂ → 6-carbon compound is UNSTABLE → splits into 2 three-carbon compounds (3-PGA); reaction driven by Rubisco enzyme

fixation (of carbon)

the 2 three carbon-compounds (3-PGA) are reduced with ATP & NADPH → turn into 2 different three-carbon compounds (G3P); 2 G3P’s can make one glucose molecule

reduction

5 carbon molecule that's ruining my day

RuBP

enzyme responsible for combining RuBP & CO₂

rubisco

three carbon compounds prior to ATP & NADPH getting involved

3-PGA

three carbon compounds post ATP & NADPH getting involved

G3P

G3P molecules fuse back together to regenerate RuBP via ATP → process starts over; note that a G3P molecule cannot be released from the Calvin Cycle without at least 6 G3P (5 to replace RuBP & 1 disperesed), each cycle creates 2 G3P

regeneration of RuBP

Normal plants; undergo photosynthesis; require stomata to be open for gas exchange

C3 plants

caused by dry/arid environments; stomata stays closed —→ O₂ level inside plant rises; very bad because plant burns through ATP w/o producing sugars; 2 types of plants in these environments are able to minimize this: C4 Plants & CAM Plants

photorespiration

can do photosynthesis via spatial separation of light reactions & Calvin Cycle; have different leaf arrangements

C4 plants

can do temporal (time) separation of light reactions & Calvin Cycle; stomata only opens at night

CAM plants