Photosynthesis

• Converts light energy from the sun to chemical energy, stored in simple sugars
  • From simple sugars, all other biomolecules are formed (e.g. fats, proteins)
• Produces oxygen into the air for cellular respiration of all living things

Formulas

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Process

Entry of into leaf

• is used in photosynthesis, conentration of decreases, becomes lower than concentration in the atmospheric air
• diffuses through the stoma into the system of air spaces in the leaf
• dissolves into thin film of water on the surface of mesophyl cells
  • Higher concentration of in the water
• Dissolved in the water then dissolves into the cells

Light dependent stage

• Light energy Chemical energy
• Light energy is used for photolysis of water
  • Splits water () into and
  • bonds with and forms (Chemical energy!!)***
  • is released during photosynthesis

Light independent stage

• Hydrogen (*** ) is then used to reduce to form 6-carbon sugars + water

Fates of Glucose

Celluar respiration

• Used as energy for celluar respiration to carry out cell metabolic activities

Excess glucose

• Stored as starch in the leaf
  • Starch is more compact
  • Insoluble, can be stored without affecting water potential of cell

Converted to other biological molecules

• Lipids
• Other carbohydrates
• Proteins

Factors affecting photosynthesis

• Carbon dioxide concentration
• Light intensity
• Temperature
• pH

Limiting factor

• Factor that affects the rate of reaction if its quantity is changed

Carbon Dioxide concentration

• Atmospheric carbon dioxide is at 0.04%, which is a limiting factor under normal environmental conditions

Experiments

Find out if is Necessary for Photosynthesis

Measuring Rate of Photosynthesis

Translocation Studies

Aphid Stylet Experiment

• Aphid’s mouthpart will penetrate a single sieve tube of a phloem when it is feeding on a stem
• We can anaesthetise a feeding aphid and cut its body away from its mouthpart to analyse the phloem sap
• Conclusion: Phloem is the tissue involved in the translocation of the plant’s food substances

Ringing Experiment

• Cut off a complete ring of bark from the main stem of a woody twig A
• Set up a control using an unringed twig B
• Ensure that the bottom end of both twigs are in contact with water
• Observe the twigs daily
• Observation: Bulge formed above the cut on twig A
• Explaination:
  • The removal of phloem prevents the translocation of food substances to the region below the ring
  • Accumulation of sucrose in the region reduces water potential
  • Water from xylem enters the phloem, resulting in swelling

Radioactive Tracing

• Cover leaf with plastic bag and supply radioactive carbon in the form of
• After photosynthesis has occurred, cut a thin section from the stem and place it on x-ray film
• Observation: Only the area with the phloem will be darkened
• Explanation:
  • When radioactive Carbon-14 is used for photosynthesis, it will produced radioactive sucrose