Basic Plant Physiology3 MAIN PLANT FUNCTIONS1. PhotosynthesisThe word photosynthesis is derived from the Greek language, “ph?s” means”light” and “synthesis” means “putting together”. The process of photosynthesisoccurs in the green leaves of plants. It is a process in which green plants containingchlorophyll turn water, sunlight, and Carbon dioxide into food, glucose, and Oxygen.
Photosynthesis has a huge responsibility in the creation and maintenance of Earth’soxygen content, and provides all organic compounds and most of the energynecessary for life on Earth.Photosynthesis is a chemical reaction that uses light energy and is the mostimportant chemical reaction on Earth.This occurs in organelles called chloroplasts, which are present inphotosynthetic cells or mesophyll cells. Although photosynthesis is performeddifferently by different plant species, the process always begins when energy fromlight is absorbed by proteins called reaction centers, containing green chlorophyllpigments.Figure 4.1 Diagram of PhotosynthesisLightenergyOxygenWaterOxygen and water vapor exitthe leaf through the stomata.Water loss from leaves iscalled transpiration.
Excess sugar is storedas starch (food) in theroots.CarbondioxideCO2 enters through thestomata, an opening inthe leaf’s epidermis andcuticle.Water is absorbedthrough the roots andcarried throught thestem to the rest of theplant. A plant’s rootsreplace water lost duringtranspiration.Chlorophyll absorbs green wavelengths from the sun, makingplants look green.Water, CO2 andSunlight combinein the leaf tomake sugarNatural Farming Gardening: Management of Plants, Soil, and Water2.
Transpiration3. Nutrient Uptake and TransportTranspiration is the evaporation of water from aerial parts of plants suchas leaves, stems, and flowers. This occurs through tiny pores over the leaf surfacecalled stomata, as they open for the passage of Carbon dioxide and Oxygenduring photosynthesis. Transpiration cools plants, changes osmotic pressure ofcells, and enables mass flow of mineral nutrients and water from roots to shoots.All plants require minerals that we call nutrients. This nutrient uptake is theprocess by which nutrients enter the cellular material, usually following the samepath as water.
The path taken is soil, roots, stems, and leaves. The nutrients andwater are used in their destination to make more complex molecules and help inperforming normal metabolic functions. The water reaches the leaves again whereit transpires from the plant and also goes to play its part in photosynthesis, and thewhole process begins again.Figure 4.2 Diagram of TranspirationWater evaporates fromleaf surfaceWater travelsthrough plantsWater absorbedby rootsCO2, the source of carbonfor photosynthesis, diffusesinto leaves from the airthrough stomata.Roots absorb H2O andminerals from the soil.
Roots take in O2 andexpel CO2. The plant usesO2 for cellular respirationbut is a net O2 producer.Through stomata, leavesexpel H2O and O2.CO2CO2H2OH2OO2O2MineralsFigure 4.3 Diagram of Nutrient Uptake and Transport78 The Essentials of Natural Farming in Philippine Context 79