Biology: Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration

• Metabolic pathways are biological processes involving matter and energy, examples include cellular respiration and photosynthesis
• Photosynthesis stores energy from the sun in glucose, which is then released in cellular respiration
• Photosynthesis and respiration cycle; each product is used by the next in a continuous process

Metabolic Pathways and Enzymes

• Metabolism is the sum of all the processes within a cell

• Metabolic pathways are categorized as either anabolic (build larger molecules from subunits) or catabolic (break down larger molecules into smaller pieces)

• Enzymes are protein catalysts that accelerate reactions by lowering activation energy. This allows reactions to occur at biological temperatures.

• Enzymes are required because of the need to maintain efficiency and speed up reactions inside of biological systems.

• Activation energy is the energy required to start a reaction

Oxidation and Reduction

• Oxidation is a reaction where an atom or molecule loses electrons, leading to a loss of energy
  • LEO: Losing Electrons = Oxidation
• Reduction is the reaction where an atom or molecule gains electrons and gains energy
  • GER: Gains Electrons = Reduction
• Oxidation and reduction always occur simultaneously

Chloroplasts

• Chloroplasts are the sites for photosynthesis in plant cells
• Contains thylakoids, flattened sacs that have grana (stacks of thylakoids)
• Chlorophyll is the green pigment in chloroplasts found in the stroma

Mitochondria

• Mitochondria are the sites for cellular respiration in both plant and animal cells
• Contains inner and outer membranes with the matrix in between
• Matrix contains the necessary chemicals and proteins for breaking down carbohydrates to produce ATP.

Photosynthesis

• Heterotrophs (like animals) ingest their food
• Autotrophs (like plants) produce their own food
• Photosynthesis transforms light energy into chemical energy in glucose, using inorganic raw materials (water and CO2)

Photosynthetic Pigments and Absorption

• Light exists in various wavelengths, each representing its energy content
• Plants absorb wavelengths in the visible light spectrum via pigments like chlorophyll and carotenoids
• Chlorophyll A is the primary pigment involved in photosynthesis, followed by Chlorophyll B
• Carotenoids are accessory pigments that aid in photosynthesis by capturing a wider range of wavelengths.
• Absorption spectra and action spectra determine the effectiveness of a wavelength in photosynthesis.

The Reactions of Photosynthesis

• Light-Dependent Reactions: These reactions happen in thylakoid membranes.
  • Light energy (photons) from the sun is trapped and used to make ATP and NADPH
  • Water is split to produce electrons, oxygen, and hydrogen ions (photolysis)
  • The energized electrons move through electron transport chains, creating an electrochemical gradient.
  • This gradient drives the creation of ATP through ATP synthase.
• Light-Independent Reactions (Calvin Cycle):
  • These reactions occur in the stroma of the chloroplast.
  • Carbon dioxide is fixed to RuBP to synthesize the sugar G3P (later glucose)
  • Requires ATP and NADPH (formed in light-dependent reactions).

Overall Costs

• ATP and NADPH are required per CO2 molecule fixation, to generate G3P.
• The Calvin Cycle consumes 9 ATP and 6 NADPH to synthesize one G3P.
• Factors such as light intensity, temperature, and CO2 all affect the rate of photosynthesis.

Explore the key concepts of photosynthesis and cellular respiration in this quiz. Understand how these metabolic pathways interact, the role of enzymes, and the importance of energy transformations. Test your knowledge of the continuous cycles that sustain life.