Week 2- Primary productivity as metabolic processes and photosynthesis

What is the simple symbol equation for photosynthesis

6CO₂ + 6H₂O ——> C₆H₁₂O₆ + 6O₂

What is the word equation for photosynthesis

Carbon Dioxide + Water ——> Glucose + Oxygen

What is oxidation

Loss of electrons

• Gets positive

What is reduction

Gain of electrons

• Gets negative

What is a REDOX reaction

Reduction and oxidation reaction takes place at the same time

When will a product be accumulated and a substrate become depleted

When there is an imbalance

Are photosynthesis and respiration redox reactions

Yes they are both REDOX reactions

Globally what is there more of: photosynthesis or respiration

Global excess of photosynthesis- in order for oxygen to be in room there must be an imbalance and therefore photosynthesis takes place first

For enough carbon to be fixed what must their be a big sources of

• Big source of energy

• Big source of electrons

• Big source of carbon

160 W m^-2 of electromagnetic radiation reaches Earth how much does this surpass other energy sources by

5 orders of magnitude

How much solar energy do photosynthetic processes convert to chemical energy

0.13%

Define an autotroph

Organisms use simple inorganic molecules and produce organic compounds

Define a phototroph

Use light as energy source

Define a chemoautotroph

Use various chemicals as a source of energy

Define a heterotroph

Organisms gain energy and carbon by breaking down organic matter

Define a mixotroph

Can be autotrophic and heterotrophic i.e. mixed nutrition

e.g. Venus fly trap

Define primary production

Formation of chemical energy in living organisms

Things that have sunlight as a source

Electrons Carbon

Inorganic - litho CO₂- autotroph

Organic- organ Organic- heterotroph

Give an example of a photolithoautotrophic reaction

Oxygenic photosynthesis

Give an example of a photolithoautotroph

Cyanobacteria, phytoplankton, algae, purple bacteria, green sulphur bacteria

Why does oxygenic photosynthesis dominate over an oxygenic/anaerobic photosynthesis

Due to the abundance of water

Which anoxgenic/anaerobic photolithoauthotrophs are there

purple sulfur bacteria, green sulfur bacteria

What is the difference between anoxygenic and oxygenic photosynthesis

Anoxygenic don’t use water and don’t generate oxygen

Where do anoxygenic photosynthesisers get electrons from

Other reduced substances often sulfur compounds e.g. H₂, H₂S, S

Are chemoautotrophs prokaryote or eukaryote

Prokaryote

What are chemoautotrophs

Bacteria/archaea that obtain energy from oxidation of some substance

Why do chemoautotrophs generally have a low growth rate

Don’t provide as much energy as photosynthesis/heterotrophy

Why are chemoautotrophs important in global nitrogen cycle

Nitrogen oxidising bacteria contibute N cycling by oxidising ammonium ions to nitrite ions and nitrite to nitrate ions

Why are chemoautotrophs important at deep sea vents

Around deep sea vents dissolved minerals and gases support a variety of chemoautotrophs that are pp that support heterotrophs like tube worms

Why are chemoautotrophs important in deep biosphere

Hydrogen oxidising bacteria support heterotrophic bacteria/fungi in pores of rocks

Why is autotrophic carbon fixation a crucial component in global carbon cycle

Provides organic carbon used by life on earth

What is the most abundant way to fix carbon

Calvin Basaam (used by phytoplankton)

It was originally though it was only biochemical autotrophic CO₂ fixation process but there are other processes

What are carbon fixation carbon sources

• CO₂

• Methane (CH₄)

• Methanol (CH₃OH) or methyl amine (CH₃NH₂₎

How many known ways are there to fix/incorporate CO₂ into organic material

6 ways

Why is CBB cycle the most used way of carbon fixation

It is the most oxygen tolerant

Why are anaerobic chemoautotrophs not so common way for carbon fixation

They are energy efficient but oxygen sensitive

What are the main differences between photosynthesis and respiration

• Photosynthesis is simple inorganic to complex organic whereas respiration is complex organic to simple inorganic

• Photosynthesis is energetically uphill respiration is energetically downhill

Define photosynthesis

Conversion of light energy to chemical energy

What are the two stages of photosynthesis

Light reaction

Light independent (dark) reaction

What is the equation for photolysis in the light reaction

2H₂O + Light —→ O₂ + 4H⁺ + 4e^-

• Oxygen is a waster product

• Light used to split water

What is the equation for light independent reaction to form carbohydrate by reducing CO₂

CO₂+ 2H⁺ +2e^{- ——→} CH₂O

• No light requirement

• The CO₂ is reduced

How are light and dark reactions linked

With energy and electron carriers

What energy carrier is the product of light reaction

ATP

What is ATP

Adenosine triphosphate

ATP —→ ADP + Pi + Energy

• Phosphate ion is released to create ADP to create ion

What is the main electron carrier in photosynthesis

NADPH or NADP⁺

NADPH ——> NADP⁺ + H⁺ + 2e^-

Here it is oxidised and releases electrons

How is NADPH and ATP created from light reaction which is then used in dark

2H₂O + 2NADP⁺ + 3ADP + 3Pi ——> O₂ + 2NADPH + 2H⁺ + 3ATP

• Oxygen waste

How is the NADPH and 3ATP created then used in dark reaction

CO₂ + 2NADPH + 2H⁺ + 3ATP ——> (CH₂O) + H₂O + 2NADP⁺ + 3ADP + 3Pi

• CO₂ is fixed to form carbohydrates

What is the photosynthetic apparatus in eukaryotic cells

Chloroplasts

What is the photosynthetic apparatus in prokaryotic cells

Cyanobacterium

Where do light reactions occur

Thylakoid membrane

What is the photolysis equation

2H₂O ——> 2O₂ + 4H⁺ + 4e^-

What is the donor in photolysis

Water is oxidised (loses an electron)

What is the acceptor in photolysis

NADPH is reduced (gains an electron)

How do you split water

Need energy from sunlight

+0.82 V needed

Light reactions are photochemical catalysed oxidation- reduction reactions. What catalyses this

Photosystems (PSI and PSII)

What is in photosystems

Pigment protein complexes

Where water is split

Convert light to chemical energy

Describe the Z Scheme

At photosystem II P680 (a special chlorophyll molecule)gets excited then loses electron to become P680⁺.

Leaves and enters photosystem I and the electron is replaced by water as P680⁺ is a very oxidising species.

P700 absorbs light and creates enough potential to form P700⁺ to generate enough charge for NADP⁺ to convert to NADPH

How is ATP made from ADP

As e- goes down electron transport chain. Hydrogen ions are generated on ones side and move to other side of membrane. There is hen a conc gradient of hydrogen ions.

= Charge potential used to create ATP from ADP

In the light reaction what are the waste and useful products

Useful: 4 electrons and 8 photons

Waste: Oxygen

What is CO₂ used for in dark reaction

From carbohydrates using reductant (NADPH) and energy (ATP)

What is the net reaction of the Calvin Cycle

CO₂ + 2H₂O + 8 photons ——> CH₂O + H₂O + O₂

What are the four main phases of Calvin cycle

1. Carboxylation phase

2. Reduction phase

3. Regeneration phase

4. Product synthesis

What is the carboxylation phase of Calvin cycle

5C molecule + CO₂ is catalysed by RuBisCo to create a 6C unstable molecule

This is then split into two 3C molecules

What is the reduction phase of Calvin Cycle

3C + 3C + 2ATP + 2ATP + NADPH + NADPH———> 3C + 3C + ADP + ADP + P + P + NADP⁺ + NADP⁺

What is the regeneration phase of RuBp

3C + 3C + 3C + 3C + 3C + 3ATP ——> 5C + 5C + 5C + 3ADP + 2P

What is product syntheis s

Sugars and carbs converted to fats, fattu acids, amino acids and organic acids

When does photorespiration take place

Instead of fixing carbon

Why can RuBisCO be inefficient

Not evolved to tolerate oxygen strongly and can react with oxygen leading to photorespiration

What does a cell require for RuBisCo to overcome inefficiency

• High concentrations of RuBisCO

• High CO₂ concentrations at active site