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CHAPTER 11

LEAF PHYSIOLOGY

MR. GENARO ³yhong´ ALDERITE

JR.,MSERM

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Metabolism- refers to all chemical processes

that occur in living material.

Types:

1. Anabolism

2. Catabolism

Plant Metabolic processes:

a. Photosynthesis

b. Cellular Respiration

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Photosynthesis- is a process that

converts carbon dioxide into organic

compounds, especially sugars, using theenergy from sunlight.

-occurs in plants, algae, and many species

of Bacteria, but not in Archaea.* Photoautotrophs

* Chemoautotrophs

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2 Parts of Photosynthesis:

1. Light ±dependent reaction

2. Light ±independent reaction

Light-dependent reaction ( PHASE I)

- occur in the thyllakoid membrane- uses light energy to split water ( photolysis). =

chlorophyll is required

- oxygen from water is released in the form of 

oxygen gas ( O2)

- the hydrogen (H+) from the split water are

transported by carrier molecules into Phase II.

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Light Independent Reaction ( Phase II)

- occur in the stroma ( the fluid filled area of a

chloroplast outside of the thylakoid

membranes)

- involves combining of hydrogen from the

carrier molecules in Phase I with carbondioxide and previously formed organic (

carbon containing) molecules.

- this reaction requires ATP.- this results in the formation of glucose and

the recycling of organic molecules required to

start Phase I.

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Phase II- Calvin Acid Cycle

3 CO2 + 6 NADPH + 5 H2O + 9 ATP

Glyceraldehyde 3-Phosphate(GAP) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi

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1. The enzyme RuBisCO

catalyses the carbo-

xylation of Ribulose-1,5bisphosphate, a 5-carbon compound, bycarbon dioxide (a totalof 6 carbons) in a two-step reaction.

-The initial product of the reaction is a six-carbon intermediate sounstable that itimmediately splits inhalf, forming twomolecules of glycerate

3-phosphate, a 3-carbon compound.

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2. The enzymephosphoglycerate

kinase catalyses thephosphorylation of 3PGA by ATP (whichwas produced in thelight-dependent stage).

-1,3bisphosphogly-cerate (glycerate-1,3-bisphosphate)and ADP are theproducts.

*However, note that two

PGAs are produced for every CO2 that entersthe cycle, so this steputilizes 2ATP per CO2 fixed.

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3. The enzyme G3Pdehydrogenase

catalyses the reductionof 1,3BPGA by NADPH

(which is another productof the light-dependentstage).

*Glyceraldehyde 3-

phosphate (also G3P,GP, TP, PGAL) isproduced, and theNADPH itself wasoxidized and becomesNADP+. Again, twoNADPH are utilized per 

CO2 fixed

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Three Significant Reasons of Photosynthesis:

1. Conversion of Light into chemical energy

2. Release of Oxygen

3. Production of Food

General chemical equation for 

photosynthesis

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Cellular Respiration

- chemical energy ( ATP) is made available

through the breakdown of the simple food,glucose.

Two Types:

a. Aerobic Cellular Respiration

b. Anaerobic Cellular Respiration

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 Anaerobic respiration- requires free oxygen

which results in a more complete breakdown

of food and the release of a maximumamount of energy.

Three Parts:

1. Glycolysis2. Kreb¶s cycle ( Citric Acid Cycle)

3. Electron Transport Chain

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Glycolysis- conversion of glucose into pyruvic

acid and results in the production of a small

amount of ATP and the release of a fewhydrogens and electrons.

General chemical equation:

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Kreb Cycle- continues the metabolism of 

pyruvic acid through the number of steps.

- Carbon dioxide , hydrogen molecules andelectrons are released at different steps.

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Electron Transport Chain- hydrogens and

electrons are accepted by oxygen forming

water.- Most energy is released in electron

transport.

Summary of Aerobic respiration:

C6H12O6 + 6O2 6CO2 +6H20 + Energy

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 Anaerobic Respiration

- takes place in the absence of free oxygen

and results in the formation of more complexend products such as alcohol, methane and

lactic acid.