Intro to & Light Dependent Photosynthesis

why is photosynthesis important?

• autotrophs: photosynthetic organisms that make their own food

• heterotrophs: eat other organisms, autotrophs, wouldn’t have source a food or energy

what is photosynthesis?

• CO₂ + H₂O + light energy → C₆H₁₂O₆ + O₂

• conversion of light energy

• carbon dioxide and water converted into high energy compound: glucose

• occurs more in the palisade mesophyll but also the spongy mesophyll, in chloroplasts

guard cells and stomata

• The stoma opens during the day and closes at night (usually)

• Sunlight activates a proton pump in the guard cells causing H+ to exit the cells

• the influx of K+ ions draws water into the guard cell making them turgid

• The swelling of the guard cells opens the stoma

label

1. outer membrane

2. inner membrane

3. stroma lamellae

4. grana/granum: stack of thylakoids, stacking increases surface area

5. intermembrane space

6. thylakoid

7. stroma: like matrix, jelly like substance

photosystem ETLAR

• primary electron accepter

• transmembrane proteins

• light harvesting unit in photosynthesis

• contains antenna complex

• contain chlorophyll a that acts as a reaction centre

• PSII comes before PSI

noncyclic electron flow 

• electrons dont cycle back to PSI in chloroplast

• electrons move through PSII then PSI then to NADP+

• predominant → primary way of flow

• Z patterns 

• most efficient for plant

cyclic electron flow

• uses PSI only, electrons cycle back to it

• No NADPH or Oxygen produced

• only ATP produced 

• limited energy

two stages that photosynthesis can occur in

• light dependent reactions: thylakoid

• light independent reactions: calvin cycle, dark reactions

stage one of photosynthesis: beginning of photosynthesis (summary)

• Converts solar energy into chemical energy

• photons of light hit thylakoid

• Light is absorbed by chlorophyll

• drives the transfer of electrons to NADP+

• 1 ATP is produced through photophosphorylation

photon

fundamental particle of light

different pigments of a photosystem

• in order highest to lowes

• carotenoids: pinkish redish

• chlorophyll b: yellow

• chlorophyll a: green

label

1. light

2. carotenoids

3. chlorophyll b

4. chlorophyll a 

5. reaction center

6. antenna complexes

7. light

8. reaction center 

9. antenna complexes

stage one, reaction details of electrons

• noncyclic 

• light dependent

• Z pattern

• light hits PS II first, photons received

• electrons become energized and move to electron accepter molecule in etc

• water is split to replace those electrons: oxygen, two hydrogen and 2 electrons

• first electrons move to PSI

• creates high proton concentration in stroma

• protein pumps protons from stroma to thylakoid space

• protons move through atp synthase (diffusion) and release energy

• energy used to produced atp from adp + phosphate

how is NADPH produced?

• electrons from PS I gain energy from light

• electrons become energized and escape PS I

• energized electrons and proton reduce NADP+ to NADPH

what molecule is in reaction centre of PSII?

P680 that gains energy from light and loses an electron to become P680+

what energy is absorbed at PSI reaction centre?

P700