Campbell Biology 12th edition: Chapter 10

chloroplasts (def.)

the organelle where photosynthesis occurs

Photosynthesis (def.)

the process of taking light energy to chemical energy (opposite of cellular respiration)

Autotrophs

photosynthetic organisms get carbon through carbon dioxide

Photoautotrophs

true photosynthetic organisms get carbon from carbon dioxide and get energy from light (most primary producers)

Heterotrophs

depended on organic compounds for carbons (humans)

examples of photosynthetic organisms

Plants

Cyanobacteria

Multicellular alga

Unicellular eukaryotes

Purple sulfur bacteria

major locations of photosynthesis in plants

leaves; they have large surface area for sunlight

mesophyll

interior tissue of the leaf

contains 30-40 chloroplasts

stomata

pore on the leaf; where carbon dioxide enters and oxygen leaves

chloroplast (components)

stroma

double membrane organelle

thylakoids

grana/granum

chlorophyll

stroma

fluid in chloroplasts

thylakoids

flat membrane sacks that hold chlorophyll

grana/granum

grana (singular)

granum (plural)

a stack of thylakoids

chlorophyll

the photosynthetic pigment (one of them)

photosynthesis formula

a complex series of reactions

carbon dioxide water and light energy produce glucose oxygen and water

- endergonic process (brings in molecules)

6CO2 + 12H2O + light energy ---> C6H12O6 + 6O2 + 6H2O

photosynthesis components

light reaction (the photo part)

Calvin cycle (the synthesis part)

light reactions properties

- in the thylakoids

-Split H2O release O2

-Reduce the electron acceptor NADP+(electron acceptor) to NADPH (stores energy)

-Generate ATP from ADP by phosphorylation

Calvin Cycle

-in the stroma

-forms sugar from CO2 using ATP and NADPH

- ATP NADPH form first system that drive production of glucose

-anabolic reaction

light dependent reaction

set of reactions in photosynthesis that use energy from light to produce ATP and NADPH

light independent reaction

Calvin Cycle

set of reactions in photosynthesis that do not require light energy; receives ATP and NADPH to make glucose

ATP and NADP

produced by light reaction that goes to Calvin cycle that generates glucose

electromagnetic energy

light

a.k.a electromagnetic radiation

- travels in rhythmic waves

wavelength

the distance between crests of electromagnetic waves

determines the type of electromagnetic energy

Electromagnetic spectrum

All of the frequencies or wavelengths of electromagnetic radiation; presented in a chart

visible light

the colors we can see; 380-750nm wavelength

short wavelength

high energy

long wavelength

low energy

photons

small light packages or particles

pigment/light behavior

some pigments will absorb physical light and other wavelengths will be reflected off;

the reflected pigment is visible to us the others are not

Spectrophotometer

able to tell which pigment can be absorbed

Absorption spectrum

a graph plotting a pigments light absorption versus wavelength

absorption spectrum of chlorophyll a

suggest that violet-blue and red work best for photosynthesis

action spectrum

profiles the relative effectiveness of different wavelengths of radiation in driving a process

pigments in chloroplasts

chlorophyll a

Chlorophyll b

Carotenoids

Carotenoids

a separate group of accessory pigments

chlorophyll b

an accessory pigment

chlorophyll a

the key light-capturing pigment

when pigment absorbs light

goes from a ground state to an excited state which is unstable

excited electrons fall down

back to the ground state

excess energy is released as heat

excitation of isolated chlorophyll molecule

emit light, an afterglow called fluorescence

and heat energy

Light harvesting complexes

the pigment molecules bound to a proteins

Photosystem

composed of a reaction center complex and a light harvesting complex

Photosystem II

first photosystem; P680 nanometers

Photosystem I

second photosystem; P700 nanometers

reaction center complex

where proteins hold a special chlorophyll a molecule and a primary electron acceptor

primary electron acceptor

in the reaction center;

will accept excited electrons (reduced)

two routes for electron flow in light reactions

cyclic and linear electron flow

linear electron flow

the primary pathway, involves both photosystems and produces ATP and NADPH using light energy

P680+

the strongest known biological oxidizing agent

made from photon energy transport through pigments in Photosystem II

H+ in light reaction

released into the thylakoid space

biproduct of light reaction

O2

P680

the special pair of chlorophyll a molecules in PSII

P700

the special pair of chlorophyll a molecules in PSI

cyclic electron flow

electrons cycle back from Fd to the PS I reaction center via a plantacyanin molecule

only PSI

- produces ATP but not NADPH

-no oxygen is released

- evolved b4 linear electron flow

-protects from light-induced damage

ex. bacteria

3 phases of Calvin cycle

carbon fixation

reduction

regeneration

carbon fixation

-catalyzed by rubisco

- CO2 is combined with an organic molecule

- produces 3-PGA molecules

rubisco

starting catalyst in the Calvin Cycle

Regeneration

- regenerates RuBP

- G3P continues and becomes RuBP through use of ATP

Reduction

- uses energy from ATP and NADPH to convert 3-PGA molecules into G3P (3C)

- exports G3P to make glucose

RuBP

CO2 acceptor; regenerated in Calvin Cycle

Leaves in hot climates

close their stomata to save water for photosynthesis

- experiences photorespiration

photorespiration

- not good for all plants

- when the stomata in plants close

- traps in oxygen and cant get Co2

- limits damaging light reaction products (occur in absence of Calvin Cycle)

why photorespiration is bad

on a hot, dry day it can drain as much as 50% of the carbon fixed by Calvin Cycle

C3 plants

-adds O2 instead of CO2 in the Calvin cycle

-consumes oxygen and organic fuel to produce CO2

-doesn't make ATP or sugar

- rubisco makes (2 C) compound

photorespiration theory

- evolution based on rubisco's presence during earth's oxygen low atmosphere

C4 plants

- minimizes cost of photorespiration

- incorporates co2 into (4C compound)

- two types of cells

two cell types in C4 plants

bundle-sheath cells

mesophyll cells

bundle-sheath cells

arranges in tight packed sheaths; around the veins of the leaf

mesophyll cells

loosely packed between the bundle sheath and the leaf surface

sugar production in C4 plants

1. production of 4C precursors is catalyzed by PEP carboxylase in mesophyll cells

2. 4C compounds are exported to bundle-sheath cells

3. In bundle-sheath cells, release CO2 used in Calvin cycle

increasing levels of CO2

may affect C3 and C4 plants differently

(changing abundance)

C3 and C4 photosynthesis

C4 photosynthesis uses less water and resources than C3

GMO rice

went form C3 to C4 plant to carry out photosynthesis

- 30-50% increase in yield

CAM plants

- open stomata at night (get Co2 into their organic acids within vacuoles)

- close during day (use stored Co2 in Calvin Cycle)

- similar to C4

- pathway separated initial step of carbon fixation from Calvin cycle