Photosynthesis and Plant Nutrition Practice Flashcards

Photosynthesis: Fundamentals and Processes

• Definition: Photosynthesis is the fundamental biological process through which plants manufacture simple sugars from inorganic raw materials.

• The Photosynthesis Equation:

  • Word Equation: $\text{carbon dioxide} + \text{water} \xrightarrow[\text{chlorophyll}]{\text{light}} \text{glucose} + \text{oxygen}$
  • Balanced Chemical Equation: $6CO_{2} + 6H_{2}O \xrightarrow{\text{chlorophyll}} C_{6}H_{12}O_{6} + 6O_{2}$

• Essential Components for Photosynthesis:

  • Chlorophyll: A green pigment required to capture light energy.
  • Light: Provides the external source of energy.
  • Carbon Dioxide ($CO_{2}$): An inorganic raw material obtained from the atmosphere.
  • Water ($H_{2}O$): An inorganic raw material essential for the reaction.

• Limiting Factors:

  • Definition: A limiting factor is a component present in the environment in short supply that restricts life processes.
  • Key Factors: The rate of photosynthesis is affected by varying light intensity, $CO_{2}$ concentration, and temperature.
  • Greenhouse Productivity: To increase plant productivity, greenhouse systems utilize $CO_{2}$ enrichment, optimum light levels, and optimum temperatures.

• Experimental Investigations:

  • Investigating the necessity of chlorophyll, light, and $CO_{2}$ using appropriate controls.
  • Measuring the effects of varying light, $CO_{2}$, and temperature on the rate of photosynthesis (e.g., using submerged aquatic plants).
  • Investigating gas exchange in aquatic plants in light versus dark conditions using hydrogen carbonate indicator solution.

• Fate of Carbohydrates:

  • Synthesis: Carbohydrates are synthesized during the process.
  • Use and Storage: Carbohydrates made during photosynthesis are used as energy sources or stored for future use within the plant.

Classifying Nutrition: Autotrophic vs. Heterotrophic

• Definition of Nutrition (Feeding): Nutrition is the intake of inorganic and organic substances from which organisms obtain energy and raw materials for growth and development.

• Autotrophic Nutrition:

  • Etymology: Derived from the Greek words autos ("self") and trophe ("nourishing").
  • Mechanism: Autotrophs (producers) like plants and algae make their own food. They use inorganic materials ($CO_{2}$ and $H_{2}O$), an external energy source (sunlight), and chlorophyll to build organic molecules including glucose, starch, fats, and proteins.

• Heterotrophic Nutrition:

  • Mechanism: Heterotrophs (consumers) like animals and fungi must acquire and take in all organic substances needed to survive.
  • Process: They obtain and digest organic molecules (proteins, fats, starch, and other carbohydrates) to use as a source of energy and as building materials for growth.

Internal Leaf Structure and Adaptations

• Leaf Anatomy Standards: Learners must identify the cellular and tissue structure of a dicotyledonous leaf in cross-section.
• Functional Significance of Structures:
  • Chloroplast Distribution: Positioned for maximum light absorption for photosynthesis.
  • Stomata: Functions in opening and closure for gas control.
  • Mesophyll Cells: Adapted specifically for gaseous exchange.
  • Vascular Bundles: Consist of xylem and phloem, which are responsible for the transport of materials throughout the plant.

Essential Mineral Nutrients and Their Importance

• Iron ($Fe$):

  • Classification: Micronutrient (required in very small amounts).
  • Absorption Form: Iron ions.
  • Importance: Essential for chlorophyll synthesis, a constituent of electron carriers, and required for the formation of certain enzymes.
  • Deficiency (Iron Chlorosis): Starts with yellowing of new upper leaves while veins remains green, creating a "spidery look." Progression leads to older leaves turning yellow, then whitish, followed by die-back and stunted growth of the entire plant.

• Magnesium ($Mg$):

  • Classification: Macro-nutrient (required in relatively large amounts).
  • Absorption Form: Magnesium ions ($Mg^{2+}$).
  • Importance: Required for chlorophyll synthesis, acts as an enzyme activator, and forms part of the middle lamellae in plant cells.
  • Deficiency: Yellowing of older (lower) leaves occurs first, specifically between the veins and around the edges. If unchecked, the leaf and plant will die.

• Phosphorus ($P$):

  • Classification: Macro-nutrient.
  • Absorption Form: Phosphate ions.
  • Importance: Synthesizes nucleotides for DNA and RNA; forms high-energy compounds like ATP; component of cell membranes (phospholipids); increases early growth and root formation; improves water and nutrient absorption; encourages flower and fruit production.
  • Deficiency: Results in stunted growth (especially roots) and brown areas on leaves and petioles. Indicators include small plants, little flower production, weak roots, and a bright green or purplish cast (purpling of the leaves, particularly the leaf veins).

• Nitrogen ($N$):

  • Classification: Macro-nutrient.
  • Absorption Form: Nitrates.
  • Importance: Required for amino acid and protein synthesis; chlorophyll synthesis; nucleotide and nucleic acid synthesis; and the synthesis of hormones like auxin.
  • Deficiency: General chlorosis (yellowing of all leaves); small leaves that drop prematurely; stunted growth; thin, weak stems; and pale green or yellow leaves due to the inability to make sufficient chlorophyll.

Investigative Procedures in Plant Nutrition

• Effect of Mineral Deficiency on Plant Growth:
  • Context: Nitrogen stimulates chloroplasts, which are essential for photosynthesis. Lack of enough nitrogen makes plants yellow and leads to death from lack of food.
  • Fertilizers: Compounds like ammonium or nitrate fertilizers (e.g., urea, organic fertilizers, or synthetic formulas like $34-0-0$) are added to stimulate growth.
  • Methodology:
    1. Collect $30$ maize or mahangu seedlings of the same age and height.
    2. Prepare three liquid nutrient mediums with varying nitrate ion concentrations: High, Medium, and Low.
    3. Plant seedlings in separate pots with soil.
    4. Divide the plants into three groups. Each group receives only one type of nitrate mixture.
    5. Apply approximately one cup of the assigned liquid medium to each pot.