Optimizing Plant Growth: Photosynthesis and Greenhouse Factors

Posted on Jan 17, 2025 in Biology

Optimizing Plant Growth in Greenhouses

In many countries where temperature and environmental conditions may not maximize the rate of photosynthesis, plants are grown in greenhouses to control the limiting factors.

Controlled Conditions in Greenhouses:

  1. Temperature:
    • Sunlight heats the inside of the glasshouse.
    • The glass prevents a significant amount of this heat from escaping.
    • Electric heaters are used in cold weather.
  2. Light:
    • The glass allows sunlight to enter.
    • Artificial lights can be used when light intensity is low.
    • Blinds can block out intense light, and shading lowers the temperature in tropical countries.
  3. Carbon Dioxide:
    • Carbon dioxide can be pumped in to increase its concentration.
    • Alternatively, burning butane or natural gas can increase carbon dioxide levels.
  4. Water:
    • Many greenhouses have automatic watering systems using sprinklers.

These factors are monitored and controlled by computers and sensors.

Investigating Gas Exchange in Aquatic Plants

  • Use hydrogencarbonate indicator solution to investigate the effect of gas exchange of an aquatic plant kept in light and dark conditions.
  • During photosynthesis, carbon dioxide is used, and oxygen is released.
  • During aerobic respiration, oxygen is used, and carbon dioxide is released.
  • Like all living cells, plant cells perform aerobic respiration continuously. However, photosynthesis only occurs in the presence of light. This leads to two predictions involving gas exchange: at low light intensities, plants will release carbon dioxide overall, and at high light intensities, plants will release oxygen overall.
  • Hydrogencarbonate is used to estimate the carbon dioxide concentration in the water.
  • Low carbon dioxide concentration results in a purple color, normal atmospheric concentration results in a red color, and high concentration results in an orange color.
  • When acidity increases, pH decreases, and CO2 concentration decreases, resulting in an orange/yellow color. When acidity decreases, pH increases, and CO2 concentration increases, resulting in a purple color.
  • Hydrogencarbonate indicator reacts to changes in CO2 in the air.
  • Example Results:
    • Black paper cover: yellow
    • Tissue paper cover: pink
    • No cover: purple
    • Boiled water: orange
  • Procedure:
    1. Half-fill three boiling tubes with water.
    2. Place a 5cm length of pondweed in boiling tubes 1 and 2, and none in boiling tube 3.
    3. Add some hydrogen carbonate indicator to each boiling tube.
    4. Place boiling tube 1 in a dark cupboard and boiling tubes 2 and 3 next to a window.
    5. After a few hours, record the color of the indicator in each boiling tube.

Expected Results:

  • Pondweed in dark conditions: orange (rate of photosynthesis is less than the rate of respiration).
  • Pondweed in light conditions: purple (rate of photosynthesis is greater than the rate of respiration).
  • No pondweed in light conditions: red (control tube).

Leaf Structure and Photosynthesis

The structure of the leaf includes chloroplasts, cuticle, guard cells and stomata, upper and lower epidermis, palisade mesophyll, spongy mesophyll, vascular bundles, xylem, and phloem in the leaves of a dicotyledonous plant.

Adaptations of Leaf Structure for Photosynthesis:

  • Palisade mesophyll cells are packed tightly together near the upper surface of the leaf to maximize the absorption of light where its intensity is highest.
  • There are many chloroplasts in the palisade mesophyll cells to absorb as much light as possible.
  • Stomata (usually in the lower epidermis) open to allow carbon dioxide to diffuse into the leaf for photosynthesis.
  • Leaves are thin, allowing for faster diffusion of carbon dioxide to the palisade and spongy mesophyll cells.
  • There are large air spaces between the spongy mesophyll cells, making it easy for carbon dioxide to diffuse to all the mesophyll cells.
  • Xylem in veins brings water and ions to the mesophyll cells.

Essential Mineral Ions for Plant Growth

Plants need mineral ions, which are absorbed from the soil in small quantities as ions by active transport.

  • Nitrate ions: Used for making amino acids, which are used to make proteins. Proteins are required for growth, so a deficiency will result in poor growth.
  • Magnesium ions: Used for making chlorophyll. A deficiency causes leaves to turn yellow, a condition known as chlorosis.

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