Photosynthesis in Plants

Photosynthesis

• Photosynthesis allows plants to produce carbohydrates from raw materials using light energy.
• Chlorophyll, a green pigment located in chloroplasts, converts light energy into chemical energy for synthesizing glucose and other carbohydrates.
• Carbohydrates are utilized and stored in several ways:
  • Starch serves as an energy reserve.
  • Cellulose is used to form cell walls.
  • Glucose fuels respiration for energy.
  • Sucrose is transported throughout the plant.
• The word equation for photosynthesis is: Carbon Dioxide + Water → Glucose + Oxygen.
• The balanced chemical equation is: 6CO2 + 6H2O → C6H12O6 + 6O2.
• Photosynthesis requires chlorophyll, light, and carbon dioxide.
• Light intensity, carbon dioxide concentration, and temperature all influence the rate of photosynthesis.
• Submerged aquatic plants with hydrogencarbonate indicator solution help to understand photosynthesis rate relative to environmental factors.
• Insufficient Light intensity, carbon dioxide concentration, or temperature, can limit photosynthesis.

Leaf Structure

• Most leaves are broad and thin, increasing the surface area for light absorption and facilitating gas exchange.
• Dicotyledonous leaf structures include:
  • Stomata and guard cells control gas exchange.
  • Spongy and palisade mesophyll cells are where photosynthesis occurs.
  • Air spaces facilitate gas diffusion.
  • Vascular bundles (xylem and phloem) transport water and nutrients.
  • Chloroplasts are distributed within mesophyll cells to maximize light capture.
  • The upper and lower epidermis protect the leaf.
  • The waxy cuticle reduces water loss through evaporation.

Mineral Nutrition

• Nitrate ions are essential for synthesizing amino acids, which are used to produce proteins.
• Magnesium ions are vital for the synthesis of chlorophyll.

Uptake and Transport of Water and Ions

• Root hair cell structure enhances water and ion absorption.
• Water Pathway: Root hair cells → Root cortex cells → Xylem → Mesophyll cells.
• Staining is useful for observing the water's route in a cut stem.

Transpiration and Translocation

• Transpiration entails water vapor loss from leaves.
• Water evaporates from mesophyll cell surfaces into air spaces, then diffuses out via stomata as water vapor.
• Transpiration is affected by:
  • Wind speed: Increased speed raises transpiration rate.
  • Temperature: Higher temperatures increase transpiration rate.
  • Humidity: High humidity decreases transpiration rate.
  • Light intensity: Greater intensity increases transpiration rate.
• Wilting occurs as a result of excessive water loss, which reduces turgor pressure in cells.
• Water movement in xylem: Transpiration pull draws water, utilizing cohesion between water molecules.
• Translocation is the transportation of sucrose and amino acids in the phloem.
  • Sources are where these substances are produced or released.
  • Sinks are where they are used or stored.
• Tissues in transverse sections of non-woody dicotyledonous roots and stems:
  • Xylem
  • Phloem
  • Cortex
• Xylem’s Functions:
  • Water and mineral ion transport
  • Support
• Xylem vessel structures include:
  • Thick walls with lignin
  • Absence of cell contents
  • Cells linked end-to-end without cross walls

Human Gas Exchange

• Features of human gas exchange surfaces include:
  • Large surface area to increase the rate of diffusion.
  • Thin surface to reduce the diffusion distance.
  • Good blood and air supply.
• Atmospheric air composition:
  • Approximately 78% nitrogen
  • Approximately 21% oxygen
  • Small % of other gasses
• Expired air has more carbon dioxide and less oxygen compared to inspired air
• Key structures in the gas exchange system:
  • Larynx
  • Trachea
  • Lungs
  • Bronchi
  • Bronchioles
  • Alveoli
  • Capillaries
• Alveoli facilitate gas exchange with a large surface area, thin walls, and a rich blood supply.
• Components involved in breathing:
  • Ribs
  • Intercostal muscles (internal and external)
  • Diaphragm
• Breathing mechanism: Ribs and intercostal muscles, along with the diaphragm, alter thorax volume and pressure to move air into and out of the lungs.
• Physical activity increases breathing rate and depth.
• Goblet cells, ciliated cells, and mucus protect against pathogens and capture particles in the gas exchange system.

Respiration

• Respiration is the process where living cells release energy from glucose.
• Energy uses in living organisms:
  • Muscle contraction
  • Protein synthesis
  • Cell division
  • Active transport
  • Growth
  • Nerve impulse transmission
  • Maintaining body temperature
• Temperature impacts respiration rate in yeast.

Aerobic Respiration

• Aerobic respiration releases substantial energy from glucose by using oxygen.
• The word equation is: Glucose + Oxygen → Carbon Dioxide + Water.
• The balanced chemical equation is: C6H12O6 + 6O2 → 6CO2 + 6H2O.

Anaerobic Respiration

• Anaerobic respiration releases a small amount of energy from glucose without oxygen.
• Word equation for human anaerobic respiration: Glucose → Lactic Acid.
• Word equation for anaerobic respiration in yeast: Glucose → Ethanol + Carbon Dioxide.
• Lactic acid buildup during intense exercise leads to EPOC (oxygen debt).
• The oxygen debt is resolved by:
  • Elevated heart rate to transport lactic acid from muscles to the liver.
  • Deeper, faster breathing to supply oxygen for lactic acid breakdown in the liver.