Photosynthesis Light Independent Stage

Light Independent Stage of Photosynthesis

• ATP and reduced NADP (NADPH H+) produced in the light dependent stage are essential for the light independent stage, also known as the Calvin cycle.
• This stage does not require light directly but relies on products from the light dependent stage, halting when light is absent.
• Occurs in the stroma of chloroplasts and was described by Melvin Calvin and his team.
• The Calvin cycle consists of several enzyme-controlled stages.

Stages of the Calvin Cycle

• Carbon dioxide enters the leaf through stomata, dissolves in surrounding water, and diffuses into the stroma of chloroplasts.
• In the stroma, carbon dioxide reacts with ribulose bisphosphate (RuBP) using the enzyme ribulose bisphosphate carboxylase (rubisco), forming an unstable six-carbon compound.
• This six-carbon compound splits into two molecules of glycerate 3-phosphate (GP), a three-carbon compound.
• One ATP molecule from the light dependent reaction converts GP into triose phosphate (TP), also a three-carbon sugar.
• Reduced NADP contributes hydrogen to reduce GP to TP.
• Triose phosphate molecules pair up to form six-carbon (hexose) sugars.
• Six-carbon sugars can polymerize to create starch, a storage carbohydrate.
• Five out of every six TP molecules regenerate RuBP using remaining ATP, ensuring the cycle continues.

Synthesis of Organic Compounds

• Plants synthesize various organic molecules, including carbohydrates, lipids, and proteins, from Calvin cycle compounds.
• Carbohydrates like sucrose are created by combining glucose and fructose; glucose serves as a respiratory substrate.
• Starch (storage carbohydrate) and cellulose (cell wall component) are formed by polymerizing glucose differently.
• Lipids consist of glycerol and fatty acids derived from triose phosphate and glycerate 3-phosphate, respectively.
• Lipids serve for storage and structural functions in cell membranes.
• Proteins, essential for cell structure and enzymatic functions, are composed of amino acids produced from glycerate 3-phosphate through acetyl coenzyme A and Krebs cycle intermediates.

Light Independent Stage of Photosynthesis

• ATP and reduced NADP (NADPH H+) produced in the light dependent stage are essential for the light independent stage, also known as the Calvin cycle.
• This stage does not require light directly but relies on products from the light dependent stage, halting when light is absent.
• Occurs in the stroma of chloroplasts and was described by Melvin Calvin and his team.
• The Calvin cycle consists of several enzyme-controlled stages.

Stages of the Calvin Cycle

• Carbon dioxide enters the leaf through stomata, dissolves in surrounding water, and diffuses into the stroma of chloroplasts.
• In the stroma, carbon dioxide reacts with ribulose bisphosphate (RuBP) using the enzyme ribulose bisphosphate carboxylase (rubisco), forming an unstable six-carbon compound.
• This six-carbon compound splits into two molecules of glycerate 3-phosphate (GP), a three-carbon compound.
• One ATP molecule from the light dependent reaction converts GP into triose phosphate (TP), also a three-carbon sugar.
• Reduced NADP contributes hydrogen to reduce GP to TP.
• Triose phosphate molecules pair up to form six-carbon (hexose) sugars.
• Six-carbon sugars can polymerize to create starch, a storage carbohydrate.
• Five out of every six TP molecules regenerate RuBP using remaining ATP, ensuring the cycle continues.

Synthesis of Organic Compounds

• Plants synthesize various organic molecules, including carbohydrates, lipids, and proteins, from Calvin cycle compounds.
• Carbohydrates like sucrose are created by combining glucose and fructose; glucose serves as a respiratory substrate.
• Starch (storage carbohydrate) and cellulose (cell wall component) are formed by polymerizing glucose differently.
• Lipids consist of glycerol and fatty acids derived from triose phosphate and glycerate 3-phosphate, respectively.
• Lipids serve for storage and structural functions in cell membranes.
• Proteins, essential for cell structure and enzymatic functions, are composed of amino acids produced from glycerate 3-phosphate through acetyl coenzyme A and Krebs cycle intermediates.

General Features of Water

• Water is a dipolar molecule with an oxygen atom carrying a slight negative charge (Ƨ -) and hydrogen atoms carrying slight positive charges (Ƨ +).
• Polarity leads to the formation of hydrogen bonds, where water molecules are attracted to one another.
• Oxygen is more electronegative than hydrogen, causing uneven electron sharing; this results in the partial charges in the molecule.
• As an excellent solvent, water enables the transport of polar molecules and ions, dissolving substances like oxygen, carbon dioxide, amino acids, and glucose.
• Water has high melting and boiling points due to the significant energy required to break hydrogen bonds connecting the molecules.
• High surface tension arises from stronger cohesion between water molecules compared to their adhesion with air, forming a 'skin' on the surface.

Properties of Water

• Acts as an excellent solvent for ions and polar molecules, facilitating biochemical reactions in living cells by allowing reactants to dissolve and move freely.
• Maintains the stability of cell membranes, essential for cellular function.
• Functions as a transport medium:
  • In animals, water carries digested food, hormones, antibodies, and waste in blood and lymphatic systems.
  • In plants, water transports salts through xylem and sugars in phloem.

High Specific Heat Capacity

• Water has a high specific heat capacity, requiring 4200 joules to raise 1 kg of water by 1°C.
• This property enables water to resist temperature changes, stabilizing environments:
  • Lakes and oceans experience slow temperature change, providing a stable habitat for aquatic life.
  • Maintains constant temperatures in the bodies of living organisms, essential for biochemical reactions and optimal enzymatic activity.

Density and Freezing Point

• Ice floats on liquid water, creating an insulating layer, which protects aquatic life from freezing conditions.
• Low-density ice reduces the risk of aquatic organisms freezing completely during cold temperatures.

Cohesion and Surface Tension

• Cohesion refers to water molecules sticking together due to hydrogen bonds, contributing to water's overall cohesion.
• Adhesion is the attraction between water molecules and different substances, enhancing water interaction with the environment.
• High surface tension minimizes surface area due to stronger hydrogen bond attractions among water molecules compared to the attraction to air.

Implications for Aquatic Life

• Transparency of water allows sufficient light penetration for photosynthesis in aquatic organisms.
• Insulating properties from floating ice help maintain underlying water temperatures.
• High specific heat capacity makes water more resistant to temperature fluctuations, benefiting the functioning of enzymes in aquatic environments.

Transport of Molecules

• Water’s polar nature enables it to dissolve ions and polar compounds effectively.
• The positive hydrogen ends attract negatively charged ions (anions), while the negative oxygen end attracts positively charged ions (cations), facilitating nutrient transport in organisms.