Plant Nutrition: Photosynthesis, Leaf Structure & Water Uptake
Plant Nutrition: Photosynthesis and More
Plant Nutrition:
Photosynthesis is the process by which plants convert inorganic raw materials into organic matter using sunlight as an energy source.
Note: Organic matter is the one that contains carbon, except for CO2 and carbonates.
In photosynthesis, there is an energy conversion from light energy to chemical energy stored in glucose.
Chlorophyll is a pigment that absorbs light energy.
Word Equation: Carbon Dioxide + Water → Glucose + Oxygen
Balanced Equation: 6CO2 + 6H2O -(light)→ C6H12O6 + 6O2
Need for Chlorophyll in Photosynthesis
Use a variegated plant.
De-starch the plant by placing it in the dark for 48 hours.
Place the plant in the light.
Take one leaf of the plant and remove its chlorophyll by boiling it in alcohol.
Make the test for starch on the leaf using iodine.
Results: The leaf stays blue-black where it had chlorophyll.
Conclusion: Starch is stored where there is chlorophyll, meaning that chlorophyll is needed for the process.
Need for Light in Photosynthesis
Cover one part of the leaf with aluminum foil.
De-starch the plant by placing it in the dark for 48 hours.
Place the plant in light.
Take the leaf of the plant and remove its chlorophyll by boiling it in alcohol.
Make the test for starch on the leaf using iodine.
Explain the Need for CO2 in Photosynthesis
Erlenmeyer flask with KOH (potassium hydroxide) to absorb CO2.
– De-starch the plant.
– Place one leaf of the plant in a flask with KOH.
– Place the plant in the light.
– Make the test for starch on the leaf.
Results: The leaf will stain yellow with iodine.
Conclusion: CO2 is needed for photosynthesis.
Cross Section of the Leaf
1. Waxy cuticle: This gives the leaf a waterproof layer, which lets in light.
2. Upper epidermis: Provides an upper surface. Layer of cells.
3. Palisade cells (vertical): Packed full of chloroplasts. Layer of cells.
4. Spongy mesophyll: Collection of damp, loosely packed cells.
5. Lower epidermis: The layer of cells on the lower surface.
6. Air space inside the leaf: Allows contact between air and moist cell surfaces.
7. Stoma: A hole in the leaf through which gases diffuse.
8. Guard cells: Change shape to close the stoma.
Palisade and spongy cells belong to the mesophyll tissue, so they are called Palisade mesophyll and spongy mesophyll cells.
Intake of CO2 by the Leaf
– CO2 is taken in by the leaf through the stomata by diffusion.
– CO2 circulates among air spaces to reach every cell.
– Oxygen is released out through stomata.
In cell respiration, oxygen is taken into the leaf and CO2 out of the leaf through stomata.
Xylem and Phloem
Xylem: Vessels through which water circulates in the plant. Water is taken up by the roots and goes up to the leaves through the xylem.
Phloem: Vessels through which carbohydrates circulate from the leaves to different parts of the plant. Carbohydrates circulate as sucrose along the phloem.
Position of xylem and phloem in a transverse section of a leaf, stem, and root.
Uptake of Water
The plant takes water from the soil through the roots by the process of osmosis.
The root is branched, and root cells have root hairs to increase the surface area of absorption.
Function of root and root hairs:
- Increase the surface area of absorption.
- Anchor the plant to the soil.
Once water is absorbed by the roots, it is transported through the xylem to the leaves.
Then, water is eliminated as water vapor through the stomata of the leaves. This is known as Transpiration. Transpiration is the elimination of water vapor through the stomata of the leaves.
Factors That Affect the Rate of Transpiration
Temperature: Increased temperature increases the rate.
Humidity: Increased humidity decreases the rate.
Wind: Increased wind increases the rate.
Light intensity: Increased light increases the rate.