Plant nutrition

• What is the external structure of a dicotyledonous leaf composed of?


  Upper and lower epidermis, vascular bundles, chloroplasts, palisade mesophyll, and spongy mesophyll.

  
• What are the functions of the upper epidermis in a dicot leaf?

  • Layer of transparent cells (no chloroplasts)
  • Allows light to pass through to mesophyll cells
  • Protects the inner cells of the leaf
  • Produces the cuticle

  
• What is the role of the cuticle in a dicot leaf?

  • Waxy, waterproof layer covering the upper epidermis
  • Reduces water evaporation from the leaf

  
• What is the function of the lower epidermis in a dicot leaf?

  • Layer of transparent cells (no chloroplasts)
  • Allows light to pass through to mesophyll cells
  • Protects the inner cells of the leaf
  • Sometimes produces a cuticle

  
• What are the two types of mesophyll cells in a dicot leaf and their functions?

  • Palisade mesophyll cells:
  • Located just below the upper epidermis
  • Most photosynthesis occurs here
  • Spongy mesophyll cells:
  • Located just above the lower epidermis
  • Facilitate gaseous exchange and also participate in photosynthesis

  
• What are vascular bundles in a dicot leaf composed of?

  Xylem and phloem.

  
• What is the function of xylem in a dicot leaf?

  • Transports inorganic substances (water and mineral ions)

  
• What are stomata and their function in a dicot leaf?

  • Small pores located between epidermal cells in the lower epidermis
  • Controlled by guard cells
  • Allow gaseous exchange (carbon dioxide and oxygen) and transpiration

  
• How do guard cells function in a dicot leaf?

  • Control the opening and closing of stomata
  • Contain few chloroplasts for some photosynthesis
• What are the adaptations of leaf structure for photosynthesis?

  • Large surface area for maximum light absorption
  • Thin structure for light penetration and reduced diffusion distance
  • Transparent epidermis to allow light through
  • Palisade mesophyll cells are closely packed and contain many chloroplasts
  • Spongy mesophyll cells have air spaces for gas exchange

  
• How do chloroplasts adapt for photosynthesis in mesophyll cells?

  • Can move towards light
  • Can move away from high light intensity to avoid damage

  
• What is autotrophic nutrition in plants?


  • Process where plants (producers) use inorganic materials (carbon dioxide and water) and sunlight to build organic molecules like glucose during photosynthesis

  
• What is the word equation for photosynthesis?

  • Carbon dioxide + water + (chlorophyll & light energy) → glucose + oxygen

  
• What is the balanced chemical equation for photosynthesis?

  • $6CO_2 +$$6H_2O \rightarrow 6O_2 +$$C_6H_{12}O_6$

  
• What is the role of chlorophyll in photosynthesis?

  • Green pigment found in chloroplasts
  • Transfers energy from light to chemical energy for carbohydrate synthesis

  
• How are carbohydrates synthesized during photosynthesis?

  • Requires light energy, water, and carbon dioxide
  • End product is glucose and oxygen
  • Light energy is absorbed by chloroplasts and transformed into chemical energy

  
• How are carbohydrates used in plants?

  • As glucose for respiration
  • As starch for energy storage
  • As sucrose for transport in phloem
  • As cellulose for building cell walls
  • As nectar to attract pollinators
  • For making amino acids and chlorophyll

  
• What is the importance of minerals in plants?

  • Required for growth, development, and repair
  • Essential minerals include iron, magnesium, phosphate, and nitrate
• What happens during nitrate ion deficiency in plants?

  • Yellowing of leaves
  • Stunted growth and weak stems
  • Inability to produce sufficient chlorophyll

  
• What is the role of magnesium in plants?


  • Needed for synthesis of chlorophyll

  
• What is the starch test on leaves used for?

  • To test whether a plant has started photosynthesis
  • Presence of starch indicates photosynthesis has occurred

  
• What materials are needed for the starch test on leaves?

  • Green leaf exposed to sunlight
  • Beaker of water
  • Alcohol (e.g., ethanol)
  • Forceps, Bunsen burner, tripod with gauze, test tube, and iodine solution

  
• What is the first step in the starch test on leaves?

  • Boil the leaf in water for 1 minute to break down cell walls and membranes

  
• What is the purpose of placing the leaf in alcohol during the starch test?

  • To remove chlorophyll and make the leaf colorless for iodine staining

  
• How are magnesium ions absorbed by plants?

  Magnesium ions are absorbed from the soil.

  
• What is magnesium needed for in plants?

  Magnesium is needed for the synthesis of chlorophyll in plants.

  
• What happens to leaves when there is a magnesium deficiency?

  Yellowing of leaves will occur.

  
• What is the consequence of insufficient chlorophyll in plants?

  Without sufficient chlorophyll, there is no photosynthesis.

  
• What is the first product produced during photosynthesis?

  The first product produced is simple sugars.

  
• How is starch related to photosynthesis?

  Presence of starch implies presence of photosynthesis.

  
• What materials are needed for the starch test on leaves?

  • Green leaf exposed to sunlight
  • Beaker filled with water
  • Alcohol (e.g. ethanol)
  • Forceps
  • Bunsen burner
  • Tripod with gauze
  • Test tube
  • Petri dish / white tile
  • Iodine solution

  
• What are the steps of the starch test on leaves?

  1. Boil leaf in water for 1 minute.
  2. Place leaf in alcohol and boil until decolourised.
  3. Rinse leaf in hot water.
  4. Spread leaf on Petri dish and cover with iodine solution.
  5. Observe color change to test for starch presence.

  
• Why do we boil the leaf in water during the starch test?

  Boiling breaks down cell walls, membranes, enzymes, and cytoplasm.

  
• What is the purpose of placing the leaf in alcohol during the starch test?

  To remove chlorophyll from the leaf.

  
• What does a blue-black color indicate when testing for starch?

  A blue-black color indicates that starch is present.

  
• What is the significance of light in photosynthesis?

  Light is necessary for starch formation and thus for photosynthesis.

  
• How can you demonstrate that light is essential for photosynthesis using a geranium plant?

  By destarching the plant and wrapping a leaf in aluminum foil before exposing it to sunlight.

  
• What happens to the leaf that was covered with foil after testing for starch?

  The covered portion will stain brown, indicating no starch formation.

  
• How can you show that carbon dioxide is essential for photosynthesis?

  By covering a plant with a container of soda lime to absorb CO2 and then testing for starch.

  
• What does it indicate if leaves stain brown after testing for starch in a CO2-deprived environment?

  It indicates that no starch was formed due to lack of carbon dioxide.