Photosynthesis and Respiration in Plants

Photosynthesis and Respiration

• Green plants utilize sunlight to convert carbon dioxide and water into glucose (a sugar), a process called photosynthesis. This process releases oxygen as a byproduct. The chemical equation for photosynthesis is 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
• Photosynthesis takes place primarily in chloroplasts, organelles within plant cells that contain the green pigment chlorophyll, which absorbs light energy.
• Light-dependent reactions occur in the thylakoid membranes of the chloroplasts, capturing light energy and producing ATP and NADPH.
• Light-independent reactions (the Calvin cycle) occur in the stroma of the chloroplasts, using ATP and NADPH to convert carbon dioxide into glucose.

Respiration in Plants

• In respiration, plants break down glucose (or other sugars) in the presence of oxygen to release energy in the form of ATP. This energy fuels various cellular processes. The equation for respiration is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP.
• Plant respiration occurs continuously, day and night, in all living plant cells.
• Respiration is a catabolic process (the breakdown of complex molecules), involving multiple enzymatic steps that release energy.
• Cellular respiration has three main stages: glycolysis, the Krebs cycle (citric acid cycle), and the electron transport chain.

Relationship between Photosynthesis and Respiration

• Photosynthesis and respiration are interconnected and complementary processes. Photosynthesis produces the glucose that respiration breaks down to release energy.
• The products of one process are the reactants of the other. This reciprocal relationship is fundamental to the carbon cycle in ecosystems.
• During the day, if photosynthesis exceeds respiration, the plant increases its net glucose production, storing the excess as starch.
• At night, when photosynthesis stops, respiration uses stored starch for energy.

Factors affecting photosynthesis and respiration

• Light intensity, carbon dioxide concentration, and temperature are key factors influencing photosynthetic rates.
• Light intensity is essential because chlorophyll needs light to initiate electron transfer and produce ATP and NADPH. Higher light intensity usually leads to faster photosynthesis.
• Carbon dioxide is the main source of carbon in the Calvin cycle. Increased carbon dioxide generally boosts photosynthetic rates.
• Temperatures are vital; optimal temperatures promote enzyme activity in both processes. Extreme high or low temperatures can slow down both processes.
• Oxygen concentration affects respiration rates. Higher oxygen concentrations usually lead to higher respiration rates, excluding factors like toxins.
• Water availability impacts both processes, affecting cellular functions, structural integrity, and cooling. Water uptake is crucial for both chemical and structural processes in plants.

Storage Products

• Plants store excess glucose as starch.
• Starch is stored in various plant parts (roots, stems, leaves) for future energy use.