Biology Semester II |
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| Sections: |
Introduction | Section 1 | Section 2 | Section 3 |
| Section Three: |
Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10 |
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Biology: Plant Hormones, Nutrition, and Transport: Part Five Plant Nutrition There is an old saying: you are what you eat. Unlike animals who obtain their energy from what they eat, plants obtain their nutrition from the soil and the atmosphere. So obviously this saying does not apply to plants! Using sunlight as an energy source, plants can modify sugars during photosynthesis to make all the organic macromolecules they need. However, plants must take up various minerals through their root systems and transport them through the xylem tissue to other areas of the plant body for use. These minerals make up the “plant food” we give to our houseplants. A (plant) balanced diet Carbon (C), hydrogen (H), and oxygen (O) are the essential elements to plants. They make up 96 percent of a plant's dry weight. Without these three nutrients, the plant cannot make sugar, which is composed of C, H, and O. The carbon that plants use comes from carbon dioxide. Hydrogen is stripped from water molecules during photosynthesis. The oxygen is derived from atmospheric oxygen (O2), carbon dioxide (CO2), or water (H2O). A nutrient is considered to be essential if it has an identifiable nutritional role that no other element can substitute. If there is a lack of the essential element, the plant will die. Plants obtain nitrogen, potassium, and phosphorous from the soil and are the plants' primary macronutrients. Nitrogen is an important part of amino acids and nucleotides (such as ATP and the bases of DNA and RNA molecules). Plants cannot use nitrogen (as N2) directly from the air. Instead, this nitrogen must be altered by bacteria into organic nitrogen in the form of ammonium (NH4+) or nitrate (NO3-) ions. Phosphorous is also vital to a plant. It is a component of ATP and the nucleic acids. An inorganic source of phosphorous is apatite, a group of phosphate minerals commonly found in rocks. Apatite weathers at Earth’s surface, which releases phosphorous into the environment. Plants absorb the element from the soil. Calcium, magnesium, and sulfur are the secondary macronutrients plants need in lesser quantities. Calcium is an important co-factor in some enzyme reactions. It also acts as a second messenger to activate plant hormones in response to environmental stimuli. Sulfur is part of coenzyme A (from the Krebs cycle), as well as a component of some amino acids. Magnesium’s chief role is as the metal in chlorophyll, the green pigment essential for photosynthesis. Micronutrients are nutrients plants need in very small quantities. Some micronutrients are toxic in large quantities. These include iron, manganese, copper, zinc, boron, and chlorine. Though needed in very small amounts, these micronutrients play a number of vital functions. Copper, a metallic ion, activates enzymes. Without copper, certain enzymes will not function. Magnesium and iron play roles in electron transfer systems. Zinc is needed to produce functional pollen grains. Boron is essential to the growth of pollen tubes that provide access for sperm cells to the egg cell. A complete fertilizer provides all three primary macronutrients and some of the secondary and micronutrients. The label of the fertilizer will list numbers, for example 5-10-5. These numbers refer to the percent by weight of the primary macronutrients.Soils play a role Soil is weathered, decomposed rock and mineral (geological) fragments mixed with air and water. Fertile soil contains the nutrients in a readily available form that plants require for growth. The roots of the plant act as miners by moving through the soil and bringing needed minerals into the plant roots.
Plants use these minerals in:
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