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IB Biology Notes - 9.1 Plant structure and growth
Although copper deficiencies or toxicities rarely occur, it is best to avoid either extreme as both can have a negative impact on crop growth and quality.Function of Copper: Copper activates some enzymes in plants which are involved in lignin synthesis and it is essential in several enzyme systems. It is also required in the process of photosynthesis, is essential in plant respiration and assists in plant metabolism of carbohydrates and proteins.
Tropisms are directional movement responses which occur due to external environmental stimuli. The direction of the stimulus affects the direction of movement. Tropisms can either be negative or positive. Positive tropisms are the directional movement towards the stimulus while negative tropisms are the directional movement away from the stimulus. Examples of stimuli causing tropisms in plants are gravity and light. Roots will grow towards gravity while the plant shoot will grow upwards in the opposite direction. The directional movement of plants in response to light is called phototropism. As seen with gravity, the plant's roots will grow away from the light, into the soil (negative phototropism) while the plant shoot will grow towards the light (positive phototropism). Positive phototropism seen at the tips of plant shoots is made possible due to plant hormones called auxins. Auxins are produced at the tips of plant shoots and then translocate to the darker side of the shoot tip and stem which is receiving less light. This translocation is made possible via auxin efflux carriers which are unevenly distributed in the plant tissue. Once auxins reach the shaded side of the plant, they cause the elongation of cells so that the shaded side grows faster than the brighter side, thereby promoting the bending of the plant shoot towards the light. Auxins do so by binding to auxin receptors on cells. The binding of auxin causes the transcription of certain genes within those cells and therefore the production of specific proteins which affect growth. Auxins allow the expelling of protons (hydrogen ions) into the cell walls of the cells on the shaded side, decreasing the pH inside the cells and in doing so activate specific enzymes which break down cellulose microfibrils within the cell wall. This loosens the cell wall and allows cell elongation. So to conclude, auxins are very important in the control of plant growth towards the light and thereby allow the plant to increase its rate of photosynthesis.
Role of Magnesium in Plant Culture | PRO-MIX
The plant meristem is a type of tissue found at several locations on plants. This tissue is composed of cells which are totipotent. This means that these cells are able to divide and make all the types of cells of that particular plant at any given time. Meristem tissue allows continuous growth and the formation of new organs. Apical meristems are found at the tips of roots and shoots. The apical meristem is responsible for the elongation of roots and stems. It allows the stem to grow taller and the roots to increase in length. Also, the shoot apical meristem allows the formation of new leaves and flowers. The growth in height of the stem is important for photosynthesis while the lengthening of the roots is important for the plant to anchor deep into the soil and it is also vital for the uptake of water and nutrients found in deeper soil layers. The growth taking place at apical meristems is called primary growth. In addition, plants also grow by increasing the diameter of their stems and roots. This is called secondary growth and is a result of cell devision in the lateral meristems. It allows extra xylem and phloem tissue production and it also provides stability for the plant to grow taller.
Many enzymes in plant cells require magnesium in order to perform properly. However, the most important role of magnesium is as the central atom in the chlorophyll molecule. Chlorophyll is the pigment that gives plants their green color and carries out the process of photosynthesis. It also aids in the activation of many plant enzymes needed for growth and contributes to protein synthesis.
Plant Energy Transformations-Photosynthesis
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