Ch. 7 - Photosynthesis

Aristotle (384-322 BCE) contributions

Thought plants derived food from the soil

Jan Baptista van Helmont (1577-1644) contributions

Later concluded that plants grew from water, and not the soil

Joseph Priestly (1733-1804) contributions

Concluded that plants added "dephlogisticated air", or oxygen, that allows a candle to burn after 10 days of adding oxygen to the air.

photosynthesis definition

the metabolic process where light energy is converted into chemical energy

photosynthesis purpose

makes organic compounds from inorganic molecules, like CO2

summarized photosynthesis equation

6 H2O + 6 CO2 + light energy ---> (with chlorophyll and enzymes ---> C6H12O6 + 6 O2 + heat

photosynthesis occurs in...

any living green photoautotrophic organism

main categories of phototrophic organisms

plants (main focus)
algae
some bacteria

photosynthesis occurs in the...

chloroplasts
except for prokaryotes

the nature of light travels as...

waves
particles (photons)

photons

discrete packet of energy

eelctromagnetic spectrum

entire range of electormagnetic energy

the shorter the wavelength...

the more energy there is

the longer the wavelength...

the less energy there is

visible light

light from 380 nm to 750 nm that drives photosynthesis
also produces the colors we see in the plant

Which color contains more energy: violet or red light?

Violet; shorter wavelength = more energy transmitted within the same time

When light hits an object, the light may be...

reflected
transmitted
absorbed

reflection

light bounces off of the object

transmission

light goes through the object and makes it through the other side

absorption

light goes through the object and stays within the object

Do plants use green light?

No, chlorophyll a, the primary pigment used in photosynthesis, is green to our eyes; therefore, it is reflecting that green light so that it may look green to us

pigment

any substance that absorbs light

color that reflects all wavelengths of visible light

white

color that absorbs all wavelengths of visible light

black

absorption spectrum

the specific pattern of wavelength a pigment absorbs from visible light

How can we ID pigments?

by their absorption spectrum

primary pigment definition

the pigment that drives photosynthesis

primary pigment name

chlorophyll a

secondary / accessory pigment

pigments that transfer absorbed energy to the primary pigment

secondary / accessory pigment example

chlorophyll b
carotenoids

How do accessory pigments improve efficiency of photosynthesis?

They extend the range of light a plant can capture.

Englemann Experiment (1883)

Took filament w/ green algae on it, and looking at the rate of oxygen produced with oxygen-seeking bacteria, who moved to where oxygen was being produced the most.
Was able to see which wavelengths of light plants performed the best

list of photosynthetic pigments

chlorophyll a, b, and c
bacteriochlorophyll
chlorobium chlorophyll
carotenoids
phycobilin

chlorophyll a description

bright green primary pigment of photosynthesis
about 75% of all chlorophyll content in plants
aborbs best in blue-violet and red ranges
found in eukaryotes and cyanobacteria

chlorophyll b description

olive green accessory pigment that transfers energy to chlorophyll a
absorbs best in blue and orange red
found in plants, green algae, euglenoids (type of protist)

chlorophyll c description

found in brown algae and diatoms
accessory pigment, used instead of chlorophyll b
absorbs best in blue and orange red

bacteriochlorophyll

found in purple bacteria
several different kinds
cannot extract electrons from water, and therefore do not produce oxygen

chlorobium chlorophyll

found in green sulfur bacteria
cannot extract electrons from water either

carotenoids

red, yellow, orange accessory pigments
found in all chloroplasts and cyanobacteria
helps absorb harmful UV radiation from light
carotenes, xanthophylls, fucoxanthin (gives the "brown" in brown algae)
changing colors of leaves, as chlorophyll breaks down and carotenoids are able to show through

phycobilins

found in red algae and cyanobacteria (phycocyanin, phycoerythrin)

two stages of photosynthesis

light dependent reactions (the "photo")
calvin cycle (the "synthesis")

light dependent reactions overall purpose

light-dependent reactions convert light energy into chemical energy, which will be used to drive the Calvin cycle to produce sugar

light dependent reactions

mostly within thylakoid membranes of the chloroplasts
keeps so many processes together in order for the reactions to have a greater chance of occurring

photosystems

chlorophylls and other pigments found in clusters of many pigments

photosystems consist of _______________ and ______________________.

antennae complex
reaction center

antennae complex

contains pigments (chlorophyll a, chlorophyll b, carotenoids)
absorbs photons of light and passes the energy from molecule to molecule until it reaches the reaction center

reaction centers

contains chlorophyll a and a primary electron accepter

how do reaction centers transfer energy to the electron acceptor?

photon of energy causes electron from chlorophyll a to get energized and break free from the molecule
that electron gets donated to the primary electron acceptor

Photosystem I optimal absorption peak

700 nm (P700)

Photosystem II optimal absorption peak

680 nm (P680)

order of photosystems when performing light reactions

II, then I

True or false: photosystems work together, but not simultaneously.

False, they do work simultaneously and together.

three fates of energy from an electron that returns to a lower state

- released as heat and light (fluorescence)
-energy is transferred from one chlorophyll molecule to the next
- electron and most energy transferred to electron transfer molecules in electron transport chain

fluorescence

electron goes back to ground state in a billionth of a second, and energy is released as heat and energy, giving a glow.

Which three options of energy fate from electron moving from excited state to ground state is the least useful?

fluorescence

Why is fluorescence a bad choice for plants (why should they avoid this?)

They want to contain this energy and transform it into glucose, ATP, or NADPH.

An excited electron from chlorophyll a is transferred to ______________________ in __________________________

a primary electron acceptor
an electron transport system

How are chlorophyll a electrons replaced?

by electrons from the splitting of water

water splitting

releases two electrons, two H+, and one O
protons are later used in photosynthesis

What happens to the oxygen atom from water splitting?

gets released asa byproduct into the atmosphere

electron transport chain (ETC)

series of proteins embedded in thylakoid membrane

pheophytin

first protein in ETC
chlorophyll derivative

quinones

part of ETC
able to pick up 1 or 2 e-

cytochromes b6/f

works as proton pump across the thylakoid membrane

ferredoxin (Fd)

iron-sulfur proteins

plastocyanin

copper containing protein

flow of electron in ETC

PS II
cytochromes b6/f
PS I
NADP reductase

pH on outside of thylakoid membrane

pH 8

pH on inside of thylakoid membrane

pH 4

ATP synthesis by Phosphorylation

Protons diffuse through ATP synthase, which forms ATP from ADP (two phosphate groups to three phosphate groups)

Oxygen is a product of the light-dependent reaction. What reactant contains this oxygen?

Water (H2O) splitting causes the product of the light-dependent reaction.

Electrons are passed through the electron transport system of Photosystem II and I. What supplies the electrons to Photosystem II?

The electrons are supplied by the chlorophyll a molecules within the reaction center. Once the electrons are used up in these pigments, water splitting regenerates these electrons.

Where are the electrons at the end of the light-dependent reaction?

The electrons are part of the NADPH molecules, as they are needed to reduce NADP+.

Describe the energy conversion during the light-dependent reaction. (Where is the energy at the beginning of the light-dependent reaction, and where is the energy at the end of the reaction?)

It starts out as light energy exciting electrons, and then ends with the ATP and NADPH molecules.

Calvin cycle

light independent reactions

Calvin cycle location

stroma of chloroplasts (fluid substance that surrounds the thylakoids and grana)

Calvin cycle reactant

carbon (from CO2)
energy from ATP
high-energy electron NADPH

Calvin cycle products

energy-rich sugar molecules

Calvin cycle is organized in three stages:

carbon fixation
phosphorylation/reduction
regeneration of RuBP

Calvin Cycle alternate name

C3 pathway

carbon fixation

incorporation from atmospheric CO2 (inorganic carbon) into the carbon in organic compounds

First phase of Calvin cycle steps

Take in 3 CO2 and rubisco --> short-lived intermediate

Second phase of Calvin cycle steps

six 3-phosphoglycerate --> 6 ATP to ADP --> six 1,3 bisphosphoglycerate --> 6 NADPH to 6 NADP+ and 6 inorganic phosphate --> six G3P
results in 1 G3P which makes glucose and other organic compounds

Third phase of Calvin cycle steps

5 G3P from fast step stays in cycle --> 3 ATP to ADP --> RuBP --> rubisco

First phase of Calvin cycle function

carbon fixation

Second phase of Calvin cycle function

reduction

Third phase of Calvin cycle function

regeneration of CO2 acceptor, RuBP

How many "turns" of the Calvin cycle need to produce one carbohydrate?

6
CO2 only supplied 1 carbon, but needs 5 more to form a carbohydrate

Electrons are passed through photosynthesis. What supplies the electrons for the Calvin Cycle?

NADPH supplies the electrons

Describe the energy conversions that occur during the Calvin Cycle. [Where is the energy at the beginning of the Calvin Cycle, and where is the energy at the end of the Calvin Cycle?

The energy starts with the ATP molecules, and once the phosphate group gets taken off, it is brought into the sugars, turning ATP into ADP.

In what form did carbon enter the Calvin Cycle, and in what form did it leave the Calvin Cycle?

CO2 (inorganic) --> glucose / other sugars (organic)

What happens to the ADP and NADP+ produced in the Calvin Cycle?

They are brought back to the light-dependent reactions to regain the energy needed for ATP and the electron needed for NADPH.

Plants use glucose for:

Cellular respiration,
carbon skeletons to make all other macromolecules

Photosynthetic organisms are the only life forms that:

convert light energy into chemical energy

Why is carbon fixation important for not only plants, but the rest of life?

That’s why we can live – we are using their food and nutrients to live.

Most of the ______________ in the Earth's atmosphere originated from the (term) produced as a waste product of photosynthesis

oxygen

What is the path of carbon in photosynthesis?

CO2 --> glucose (and other macromolecules)

What is the path of electrons in photosynthesis?

H2O --> NADPH --> glucose (and other macromolecules)

What does the enzyme rubisco (or ribulose bisphosphate carboxylase/oxygenease) catalyze?

RuBP and CO2 rxn

Why are most plants called c3 plants?

They use the Calvin cycle.