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What is a Plant?

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What is a Plant? MOST PLANTS are green because they contain the substance chlorophyll. They use it to trap light energy; this is used during photosynthesis to make food. Plants are usually anchored in a growing medium such as soil. Some, such as mosses and liverworts, are small and delicate. Others, such as the giant redwood trees, are huge. Many plants, such as marigolds and sunflowers, are annuals, which means that they live for just a year. Perennials can live for many years: some bristlecone pine trees, for example, are nearly 5,000 years old. Rainforest vegetation Where a plant lives depends on its growing requirements. Plants of the rainforest, for example, need its humid climate in order to survive and grow. Flowering Plants FLOWERING plants, known as angiosperms, are the most widespread of all plants. Using flowers to reproduce has contributed to this success. Flowers carry the reproductive organs within a ring of petals. After pollination and fertilization, the flowers produce seeds, which are often enclosed and protected by fruits. There are two classes of flowering plants: monocots, such as grasses, in which the seed embryo has only one leaf; and dicots, such as oak trees, in which the seed embryo has two leaves. Flowering plants use a variety of ingenious ways to scatter their seeds. Non-flowering Plants PLANTS that do not use flowers for reproduction include conifers, ferns, and mosses. ...read more.


Anaerobic Respiration A modified form of respiration, anaerobic respiration, does not use oxygen. Anaerobic respiration gives less energy than aerobic respiration, producing a net gain of only two molecules of ATP for each molecule of glucose. It occurs in muscles when prolonged or hard exercise has used up their oxygen supply. It also occurs in many anaerobic microorganisms, such as the tetanus bacterium, and in yeast, which is a type of fungus. Yeast produces ethanol (alcohol) as a by-product of anaerobic respiration, a property exploited in the brewing industry to make wine and beer. Cell Processes THOUSANDS of complex chemical reactions take place inside living cells every second. For example, molecules such as proteins, lipids, and carbohydrates are made by joining smaller molecules together. In plant cells, food is made through a process called photosynthesis. In multicellular organisms, cell division produces cells that become specialized to carry out particular functions. The energy required to fuel all these processes is obtained from glucose molecules, through a process called respiration. Photosynthesis Photosynthesis is a chemical process used by plants and many microorganisms to convert the inorganic compounds carbon dioxide and water into organic compounds (carbohydrates), using the Sun's energy to drive the reaction. It is the most important synthetic process in the living world. About 50 billion tonnes of carbon are fixed into organic compounds by photosynthetic organisms each year, much of this by phytoplankton living in the surface of the oceans. ...read more.


The NADPH and ATP produced during the light reaction are then used to reduce these GP molecules to two molecules of a 3-carbon sugar, glyceraldehyde 3-phosphate (GALP). Some of the sugar molecules are removed to be converted into glucose, and the remainder are converted into new molecules of ribulose biphosphate, allowing the Calvin cycle to be repeated. The glucose molecules are then converted into starch for short-term storage. The products of carbon fixation are not only used for energy - they can also be converted into structural and genetic compounds, such as carbohydrates, proteins, lipids, and nucleic acids. Carbon Fixation in Tropical Plants Certain tropical plants, such as sugar cane and maize, can capture carbon dioxide with a substance called phosphoenol pyruvate (PEP), before releasing the carbon dioxide into the Calvin cycle. These plants are called C4 plants because the immediate product of carbon fixation is a 4-carbon compound. (Other plants are called C3 plants because the first stable product of fixation is the 3-carbon compound GP.) C4 plants have an exceptionally high affinity for carbon dioxide, which enables them to photosynthesize more effectively than C3 plants in very bright sunlight and at high temperatures - conditions often found in tropical environments. Certain desert plants use the C4 system to store carbon dioxide during the day and convert it into carbohydrates at night. This allows them to keep their stomata closed during the heat of the day, preventing water loss, and to open them at night, allowing gas exchange and the Calvin cycle to take place. ...read more.

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