Introduction
Plants play important roles in our daily life. Plants are the major organism undergoing photosynthesize, which support the majority of animal lives.
Plant Nutrition
Plants absorb nutrients from air and soil. According to the amount the plant requires, the plant nutrients can be classified as macronutrients and micronutrients. Primary macronutrients include nitrogen (N); phosphorus (P), and potassium (K), secondary macronutrients include calcium (Ca), magnesium (Mg), and sulfur (S). There are total 9 micronutrients: boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn). Macronutrients are usually not proficient in cultivation soil and need to be supplied in fertilizer. Other ways to obtain nutrients include Nitrogen fixation by bacteria, carnivorous feeding and symbiotic associations with fungi. Natural community recycles nutrients.
Transportation of water, minerals and food
Root absorbs nutrients from the soil. These nutrients are transported upwards via xylem. The driving force is the evaporation from leaves via guard cells. This process (evaporation of water via guard cells pulls up water from root) is called transpiration. On the contrary to transpiration, leaves make carbohydrates and these need to be supplied to roots and stems. This transportation occurs in phloem in vascular tissue and it is both directions, downwards and upwards.
Plant Hormones
There are 5 major plant hormones: auxin, gibberellins (Gas), cytokinins, ethylene and abscisic acids (ABA). Auxin is produced by apical tissues and developing leaves, the function is for cell division and elongation. Auxin is also the cause of apical dominance, phototropism and gravitropism. Cytokinins are another group of plant hormones that can stimulate cell division. Cytokinins are derivatives of the purine adenine. Function of cytokinins includes stimulate cell division; the major source is the roots and apical meritstem. Cytokinins are opposite to auxin in that they move upward and they promote growth of lateral buds. They prevent leaf senescence and are Essential for plant cell culture. Gibberellins include over 30 structurally related compounds. The function of Gibberellins includes promoting stem elongation, breaking dormancy of seeds, buds and stimulate flowering in mature plants. Abscisic acids are the major plant hormone response to stress. The main function includes bud dormancy, seed maturation and dormancy, abscission of leaves and fruits (opposite to auxin) and closing of stomata. Ethylene is the only gas form of plant hormone, it is produced by fruit. Major function of ethylene includes promoting fruit ripening and stimulates senescence and abscission in leaves and fruits.
Plant Defense
Plants developed both physical and chemical defense strategy. The physical barriers include cuticle wax on surface of leaves, trichomes, spines and bark. The chemical barrier is secondary metabolites or chemical toxins which could cause problems for the predators, for example, isoprene, phenolic compounds and alkaloids. Plants also developed a systemic response when they are wounded, in such a condition as insects attacking. Upon attacking, plants first synthesize a small peptide called systemin which then triggers a series of biochemical reaction to release proteinase inhibitors which are toxic to insects. Upon infection by plant virus, plants can undergo a hypersensitive response (HR) which leads to programmed cell death on the infected sites. There is a gene-for-gene theory for plant defense against virus. Basically, to every pathogen avirulence (avr) gene, there is a corresponding R gene (resistance gene) in plant to trigger HR. HR is commonly followed by a slower response that leads to systemic acquired resistance (SAR). SAR occurs when a hormone, which may be salicylic acid, travels from the infection site to nearby tissues and triggers the expression of a specific set of genes.
Plant reproduction
Plants adopt two pathways to reproduce themselves: sexual and asexual reproduction approaches. Sexual Reproduction involves male gametes (sperms) and female gametes (eggs), they combine together to form zygotes. After that, female structures house the embryo during development. Asexual reproduction refers to offspring produced by mitosis and therefore they are genetically identical to parent. Flowers are the reproductive organs for plants. The reproduction process typically includes flower blossom, pollination, seed development and seed maturation.
