Respiration is a passive process that occurs in all plants. Its purpose is to release energy captured and stored within the plant. Using raw materials from the environment, photosynthesis occurs, providing the materials to be used during respiration. A continuing cycle of capture and release of energy makes life possible for plants even under stressful conditions.
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Plant respiration is the mechanism by which energy stored in the form of glucose, a product of photosynthesis, is released for use in plant metabolism. Photosynthesis uses light energy from the sun along with water and carbon dioxide to produce glucose, or sugar, and releases oxygen into the atmosphere. Respiration releases carbon dioxide.
During respiration, glucose is broken down to become products that will fuel other processes that the plant will use. Respiration is a multi-stage process that can take different pathways depending on the presence or absence of oxygen. Glycolysis breaks glucose into two molecules initially, in the cytoplasm, or the main body of the cell enclosed within the plant cell wall.
The presence or absence of oxygen determines how the process will progress. If oxygen is present, products from glycolysis will be used within the mitochondria, or energy centres, of the cell, to continue respiration. If oxygen is not present, fermentation, a less efficient use of energy, occurs.
During photosynthesis, plants store energy captured during the day, the light reaction, to fuel the process of creating sugar chiefly at night, during the dark reaction of photosynthesis. As the name implies, the dark reaction is independent of the presence of light. Glucose is produced. Glucose will in turn fuel respiration.
Photosynthesis is dependent upon the presence of water, light and carbon dioxide. Plant respiration requires oxygen if the more efficient aerobic respiration is to occur. While carbon dioxide is usually not an issue for photosynthesis, water can be a limiting factor, determining when and if photosynthesis occurs. Fortunately, plants have several adaptations to cope with environmental stress. Let's consider two extremes, the tropical rainforest and the desert.
Rather than being a limiting factor, the overabundance of water causes stress in tropical plants. Too much water can create conditions where bacteria, fungi and mould take hold. Plants will often have a waxy surfaces and smooth bark to keep water from settling on plant surface and encouraging bacterial growth. Conversely, desert plants must seize opportunities to collect water. Some desert plants too, will use waxy surfaces to retain water within. Some plants called succulents store water within their tissues. Spines and needles protect a plant's water stores from animals.
The breakdown of glucose during plant respiration is key to fuelling the process of photosynthesis and plant growth. Plants have evolved to make the most efficient use of its products. Whether or not oxygen is present, plants carry on respiration producing energy. This adaptability of plants is responsible for life on Earth.
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