ch17 - chloroplast and light dependent reaction

What occurs during photosynthesis and what is the chemical reaction? 

photosynthesis is an endothermic reaction in which light energy (absorbed by chlorophyll from the sun) is used to convert H2O and CO2 into glucose, released oxygen as a byproduct

6CO2 + 6H2O → C6H12O6 + 6O2

What occurs during aerobic cellular respiration and what is the chemical reaction? 

Respiration is an exothermic process where complex organic molecules (glucose) is broken down into small inorganic molecules (water and carbon dioxide), releasing chemical energy in the form of ATP, as well as thermal energy/metabolic heat which dissipates

C6H12O6 + 6O2 → 6CO2 + 6H2O

What is the link between photosynthesis and cellular respiration?

-both of these processes occur in plants

-the raw materials of one are the products of the other and vice versa 

What are the 2 stages of photosynthesis and where do they occur?

1. Light dependent reaction which occurs in the thylakoid membrane 

2. Light independent reaction which occurs in the stroma

what is another name for light dependent reaction 

Z scheme

what is another name for light independent reaction 

Calvin cycle

What is the site of photosynthesis?

Chloroplasts

What are the 2 functions of chloroplast ?

To absorb light energy 

To convert light energy into chemical energy

What are the 7 structures in the chloroplast  

Thylakoids

Grana

Intergranal lamella

Stroma

Starch grains

Ribosomes

Chloroplast DNA

what is the function of these 7 structures

Thylakoids - flattened membranous sacs that contain photosystems with photosynthetic pigments 

Grana - stacks of thylakoids

Intergranal lamella - extensions that connect grana together 

Stroma - the fluid within the chloroplast 

Starch grains - energy storage/ it stores glucose molecules 

Ribosomes - for protein synthesis to create the enzymes coded by chloroplast DNA

Chloroplast DNA - contains its own DNA that has genes which code for enzymes involved in photosynthesis

What are photosystems and how many are there and their names? 

> they are clusters within the thylakoid membrane that contain the photosynthetic pigments

> there are two:

Photosystem I 

Photosystem II 

What are photosynthetic pigments?

Pigments found within photosystems which absorb light

What are the 3 photosynthetic pigments and name their functions?

Chlorophyll a - main pigment, absorbs red & blue light and reflects green light (which is why most plants look green)

Chlorophyll b - accessory pigment 

Xanthophylls and carotenoids - accessory pigment 

What is the function of accessory pigments?

they absorb other wavelengths of light to chlorophyll A which broadens the spectrum of light taken in 

What do both photosystems have and what pigments do they contain 

Light harvesting system = contains chlorophyll a, chlorophyll b, and xanthophylls + carotenoids

Reaction centre = contains two chlorophyll A molecules

How do the light harvesting system and reaction centres work together?

> light harvesting system absorbs the light energy which is transferred to the reaction centre 

> reaction centre emits high-energy electrons

What is absorbed by photosystem I and II?

Light energy from the sun 

What is the role of light energy absorbed by the photosystems?

Light energy excites electrons in Photosystem I and Photosystem II, boosting them to higher energy levels

light dependent reaction

What molecule enters and is then broken down at Photosystem II?

Water molecules enter the thylakoid membrane into photosystem II and are broken down through photolysis

What is photolysis and what does it produce?

Photolysis is the splitting of water to produce 1/2Oxygen molecule and 2hydrogen molecules, protons and 2 electrons

What happens to the oxygen released during photolysis?

Oxygen is released as a byproduct

What happens to the protons released during photolysis?

Protons are used later during noncyclic phosphorylation 

What happens to the electrons released during photolysis and why are they important?

They enter Photosystem II and become excited by light energy

-they replace the electrons lost from PSII

What are electron carriers?

Electron carriers are proteins that make up the ECT, they take up excited electrons and transport them through the electron transport chain

What happens to electrons as they move through the electron transport chain?

As electrons move through the electron transport chain, they release energy which is used to actively pump protons from the stroma into the thylakoid lumen generating a proton gradient

Where do electrons arrive after passing through the electron transport chain from Photosystem II?

Photosystem I

What happens to electrons at Photosystem I?

Electrons at Photosystem I absorb more light energy and become re-excited

What are the two possible pathways for electrons after excitation at Photosystem I?

Electrons can either go into cyclic photophosphorylation OR go into noncyclic photophosphorylation

what is meant by photophosphorylation

synthesis of ATP from ADP and Pi using light energy

What is cyclic photophosphorylation?

electrons travel back down the ETC to PS1 to become reexited and then reenter ETC, this process occurs continually so protons are released which builds a proton gradient so more ATP is made

What is noncyclic photophosphorylation?

where electrons meet up with the previously released protons at the enzyme NADP reductase to reduce NADP into NADPH/ reduced NADP

which involves PSI and PSII and which only PSI

cyclic - PSI only

noncyclic - PSI and PSII

where are the atp synthase found

throughout the membrane, after each ETC

How does ATP synthase produce ATP?

protons diffuse down electrochemical gradient from thylakoid lumen to stroma through ion channel center in ATP synthase enzyme, this releases energy which is used to phosphorylate ADP into ATP

what different ways is the proton gradient generated for atp synthase

cyclic - from electrons travelling down etc which releases energy used to pump protons from stroma into thylakoid lumen

noncyclic - from etc and photolysis of water

how is the proton gradient maintained

thylakoid membrane is impermeable to protons so they can only diffuse through atp synthase enzyme

what is the final electron acceptor

NADP

What is the purpose of the light-dependent stage?

use light energy to produce ATP and NADPH/reduced NADP, these products are then used as the reactants for calvin cycle/ LIR

What are the products of the light-dependent stage that are then used in the light independent stage/ calvin cycle?

ATP and NADPH