To Investigate the Influence of Light Intensity on the Rate of Photosynthesis

Textbook Diagram: set up of the investigation.

• Place a funnel over Elodea, pondweed, in a beaker of pond water at 25°C.
• The funnel is raised off the bottom on pieces of blue-tack. This allows continuous free diffusion of CO₂ to Elodea.
• Invert a test tube full of water over the stem of the funnel to collect any gas from the Elodea.
• Place the beaker on a hot plate at 25°C.
• Maintain and monitor the temperature of the water with a thermometer.
• Excess sodium bicarbonate is placed in the water to give a constant saturated solution of CO₂.
• Place the lamp (the only light source) at a predetermined distance from the plant.
• Use a light meter to measure the light intensity at this distance. Record the light intensity.
• Allow the plant five minutes to adjust to the new conditions.
• Count the number of oxygen bubbles given off by the plant in a five-minute period.
• Repeat the count twice more and calculate the average of the three readings. This is the rate of photosynthesis at that particular light intensity.
• The gas should be checked to prove that it is indeed oxygen — it relights a glowing splint.
• Repeat at different light intensities by moving the lamp to different distances.
• Run a control: identical set up but at a constant light intensity.
• Result: no change in the rate of photosynthesis.
• Conclusion: change in light intensity causes a change in the rate of photosynthesis.
• Graph the results placing light intensity on the x-axis.

Note: make sure you know the shape of this graph and are able to interpret it.

Respiration

Respiration is the enzymatic-controlled release of energy from organic compounds in a living cell.

Definitions

Aerobic Respiration
The enzymatic-controlled release of energy from organic compounds using free molecular oxygen.

Anaerobic Respiration
The enzymatic-controlled release of energy from organic compounds in a living cell using substances other than free molecular oxygen as electron acceptors.

Fermentation
The enzymatic controlled release of energy form organic compounds yielding simpler organic compounds.

The energy released by respiration is of very little value unless it is used to produce ATP.

ATP
Adenosine triphosphate (ATP) is the most abundant short-term energy store and immediate source of energy for cell work.

ATP: adenine + ribose sugar + three phosphate groups	Adenine + Riboseis called Adenosine
ATP = A + P + P + P	A: adenosine P: phosphate

ATP releases energy when the last phosphate is removed
A + P + P + P ATP		A + P + P + energy + P (free) ADP + energy + P (free)	ADP: adenosine diphosphate

ATP can be remade by the addition of a phosphate onto ADP, i.e., by the phosphorylation of ADP.
The phosphorylation of ADP requires energy. Respiration is one source of energy to produce ATP.

Living cells use up ATP at a very fast rate — a human cell needs about 2 million a second.
In order to maintain constant energy, a supply of ATP must be replaced as it is used.

Note: Light is the energy source to make ATP in the light dependent stage of photosynthesis.
ATP is made during pathway 1 and pathway 2 of the light stage.
The ATP from the light stage is used to drive the dark phase reactions in the production of glucose.

Aerobic Respiration: Glucose + Oxygen? Carbon Dioxide + Water + Energy (38 ATP)
C6H12O6 + 6O2? 6CO2 + 6 H2O + Energy (38 ATP)

Fermentation
Plants and Fungi: Glucose? 2 Ethanol + 2 Carbon Dioxide + Energy (2 ATP)
Animals and some Bacteria: Glucose? 2 Lactic Acid + Energy (2 ATP)

Lactic acid is a colourless liquid miscible with water.

In fermentation the glucose is only partially broken down.
A lot of energy is still available in ethanol and lactic acid.

Note: ethanol is one member of the family of chemicals called the alcohols; ethanol is the alcohol of beer, wine and spirits.

(Anaerobic respiration is incorrectly known as fermentation.)

Aerobe: an organism that lives and grows only in the presence of free oxygen; it respires aerobically.

Anaerobe: an organism that can live and grow in the absence of free oxygen, it can produce ATP without free oxygen.

• Obligate Anaerobe: an organism that is not capable of aerobic respiration (free oxygen is toxic to some of these).
• Facultative Anaerobe: an organism that is usually respires aerobically but can survive by anaerobic respiration in the absence or shortage of free oxygen.

Aerobic Respiration of Glucose (6C)

Stage 1: Glycolysis

• Takes place in the cytosol – the non-organelle part of the cytoplasm.
• Oxygen not used and its presence not required.
• Net production of 2ATPs.
• Two pairs of hydrogen atoms are ‘donated’ to NAD+.
• The six carbon glucose is converted to two pyruvates.
• Pyruvate is a three carbon compound.
• A compled enzyme pathway is involved in glycolysis.

Stage 2. Formation of acetyl co-enzyme A
Takes place in the mitochondrion – the presence of free oxygen is essential.

• Pyruvate enters the mitochondrion.
• Pyruvate loses a carbon dioxide and a pair of hydrogen atoms.
• Pyruvate is thus converted to an two carbon acetyl group.
• Co-enzyme A links to the acteyl group forming acetyl coenzyme A.

Krebs Cycle

• Acetyl co-enzyme A combines with a four carbon compound in the mitochondrion.
• A six carbon is formed with the release of co-enzyme A.
• Loss of two carbon dioxides and pairs of hydrogen regenerates the four carbon compound.
• One ATP is produced for each turn of the Krebs cycle.
• The hydrogen pairs become involved in the Electron Transport System.

Electron Transport Chain

• NAD+ is the hydrogen acceptor.
• NAD+ takes a hydrogen pair forming NADH + H+.
• The H+ (hydrogen ion or proton) enters into solution.
• NADH passes two electrons to the Electron Transport Chain in the mitochondrion.
• The electrons travel to oxygen releasing energy which is used to make ATP.
• About three ATPs are produced for each pair of electrons.
• At the end of the chain electrons, oxygen and hydrogen ions from solution form water.

Aerobic Respiration of Glucose – ATP Account

• Glycolysis: 2 ATPs
• Krebs Cycle: 2 ATPs
• Electron Transport Chain: 34 ATPs

Total: 38 ATPs.

NAD+

• NAD+ is a hydrogen acceptor – it takes on electrons and hydrogen ions.
• NAD+ transfers the electrons and hydrogen ions to other substances in certain cellular activities.
• NAD+ collects electrons from many diverse sources and passes them on to electron transport chains.
• As the electrons pass along the electron transport chain ATP is synthesised.

Fermentation

The enzymatic controlled release of energy form organic compounds yielding simpler organic compounds and does not involve electron transport.

The two pairs of hydrogen removed from glucose during glycolysis are donated to pyruvate, one pair to each pyruvate.

Pyruvate + 2H? Lactic Acid (animals, some bacteria) - Lactic Acid Fermentation
Pyruvate + 2H? Ethanol + Carbon Dioxide (plants, fungi and some bacteria) - Alcoholic Fermentation.

Advantages of Fermentation

• Permits survival of some organisms in oxygen deficient environments.
• Supply of extra ATP when the aerobic system cannot meet the demand for ATP

Disadvantages of Fermentation

• The organic end products (lactic acid, ethanol) are toxic.
• Inefficient: only 2 ATPs per glucose - much chemical remains in the organic end products.

Role of Micro-organisms in Industrial Fermentation

• Industrial fermentation: the growing micro-organisms in a liquid medium under any conditions.
• There are a wide variety of micro-organisms with a very extensive range of organic compounds of value to us.
• Culturing of specific micro-organisms in carefully controlled favourable conditions can yield a rich harvest of important and useful organic substances – ethanol, acetone, lactic acid (cheese, yoghurt), ethanoic acid (vinegar), antibiotics, vitamins, amino acids, insecticides, enzymes, citric acid, carbon dioxide and methane (natural gas).

Bioprocessing With Immobilised Cells

Bioprocessing is the use of biological materials (organisms, cells, organelles, enzymes) to carry out manufacturing or treatment prodedures of commercial or scientific interest.

Immobilised cells are not free in solution – for example they cam be held in a bead of soft permeable gel or coat the internal surface of a porous solid.

Teztbook Diagram: Bioreactor setup.

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