Biology: Photosynthesis and Respiration

Autotrophs

Organisms able to carry out photosynthesis and use simple organic molecules to synthesise complex molecules. Energy obtained from light

Heterotrophs

Organisms which obtain organic molecules through digestion and absorption to provide energy for growth.

Site of LDR

Thylakoid membrane (products released into stroma)

Site of LIR

In stroma

Photosynthetic pigment

Chemicals that absorb light energy (photons) found in thylakoid membrane of chloroplasts

Axes for absorption spectra

X: Wavelength of light Y: Light absorbed

Axes for Action spectra

X: Wavelength of light Y: Rate of photosynthesis

Oxidation

Loss of e^- /H or gain of O₂

Reduction

Gain of e^-/H or loss of O₂

Excitation and photoionisation

-Light energy is absorbed by chlorophyll

-Electrons excited and released

-Electron acceptor is reduced/chlorophyll is oxidised

Photolysis of water

Water molecules split using light:

2H₂O → 4H⁺+4e^-+O₂

-Electrons replace those lost from cholorphyll

Non-cyclic photophosphorylation and chemiosmosis

-PSII (680nm) electrons form ETC to PSI (700nm)

-Chemiosmosis takes place with energy from ETC

-Proton gradient down ATP synthase into stroma and forms ATP from ADP and Pi

Reduction of NADP (NCPP)

PSI absorbs more light and photoionisation tasks place. NADP is combined with H⁺ and e^- (H atom) to form NADPH

Properties of ATP

• only releases small amounts of energy (30.5 KJ/mol)

• small, soluble and easily transported and broken down

• cannot pass out of a cell

• used in phosphorylation (transfer of phosphates to other chemicals)

Light Independent Reaction

1) CO₂ combines with RuBP to form x2 GP (using Rubisco)

2) GP reduced to TP (using NADPH and ATP per GP)

3) 1/6th of TP used to make organic compounds and the rest to regenerate RuBP (using ATP)

Substrate level phosphorylation

Producing ATP by addition of phosphate group in Krebs and glycolysis

Anabolic reaction

Metabolic reactions which build large molecules from small

Catabolic reactions

Metabolic reactions that hydrolyse large molecules into small

Effect of decreased CO₂ on calvin cycle

More RuBP and less GP (as less CO₂ to be fixed) → less TP as a result

Effect of reduced light intensity on calvin cycle

LDR cannot take place so no NADPH or ATP so more GP but less TP → less RuBP as a result

Effect of increased temperature on calvin cycle

Oxygen competes with CO₂ for Rubisco enzyme and photorespiration takes place instead. RuBP increases as no fixation but GP and TP is decreased. Rubisco will denature at very high temperatures

Products of glycolysis (from one glucose molecule)

• net gain of 2x ATP (2 broken down and 4 formed) and x2 NADH

• 2x pyruvate

Stages of glycolysis

1) Glucose is phosphorylated twice (glucose phosphate and hexose bisphosphate with ×2 ATP→ADP+Pi)

2) Triose Phosphate oxidised into pyruvate by 2x ADP+Pi→ATP and NAD→NADH per molecule

Site of glycolysis

Cytoplasm of cell

Site of Link reaction

In mitochondrial matrix

Stages of Link reaction

1) Decarboxylation and oxidation of pyruvate to form acetate(using NAD→NADH)

2)Acetate combined with coenzyme A forming acetyl CoA

Products of Link reaction (per glucose molecule)

• x2 CO₂

• x2 NADH

• x2 acetyl CoA

Site of Krebs cycle

Mitochondrial Matrix

Stages of Krebs cycle

1) Acetyl CoA combines with oxaloacetate to form 6C (citrate)

2) Citate is decarboxylated and oxidised forming NADH and 5C intermediate

3)5C intermediate is decarboxylated and oxidised to form x2 NADH, x1 FADH and synthesises ATP from ADP and Pi and oxaloacetate (4C)

Products of Krebs cycle (per cycle)

• x2 CO₂

• x3 NADH

• x1 FADH

• x1 ATP

(per glucose would be doubled)

Site of Oxidative Phosphorylation

Cristae of the mitochondria

Stages of Oxidative Phosphorylation

1) H atoms released from reduces coenzymes and split into H⁺ and e^- to form ETC

2) Energy from ETC pumps H⁺ from mitochondiral matrix to intermembrane space across cristae

3) Chemiosmotic theory means protons move down ATP synthase back into matrix to form ATP

4) at the end of the electron transport chain, protons combine with oxygen (final electron acceptor) to form water

Products of Oxidative Phosphorylation

• ATP

• NAD/FAD

• H₂O

What is biomass measured in?

Mass of Carbon per given area per given time e.g. Kg m^-2 years^-1

Anerobic respiration in plants and yeast

• Glycolysis to produce pyruvate

• Pyruvate decarboxylated to produce ethanal

• Ethanal is reduced to ethanol by NADH being oxidised to NAD

(Alcoholic fermentation - irreversible)

Anerobic respiration in animals and some bacteria

Lactate fermentation - reversible due to Cori cycle

-Glycolysis to produce pyruvate

-Pyruvate reduced to lactate and NADH is oxidised to NAD