Respiration is the process in which glucose is utilized to initiate metabolism in plant tissues. This involves the exchange of vital gases such as carbon dioxide (CO2) and oxygen (O2). These gases use water to travel throughout the plants tissues. Each part of the plant relies on respiration for survival and also plays a role in carrying it out. Environmental temperatures and conditions will have a direct effect on the rate of respiration. The climate where a plant lives will dictate how it will use this process for survival.
In foliage plants the leaves play a critical role in respiration. The foliage surface is where the plant draws in sunlight and carbon dioxide. Even a small amount of water is drawn in through the leaves and needles of plants. Small holes on the leaf surface called stomata allow these exchanges to take place.
For photosynthesis to occur the plant must have sunlight, carbon dioxide and water. Sunlight activates the chlorophyll in the leaves and allows it to change into usable molecules. These molecules combine with (CO2) and water to form glucose. Respiration occurs when the cells take these sugars, oxidizes them, and makes them usable to the plant.
For most plants the primary purpose of the stem is to transport needed water, carbohydrates and gases from the foliage to the roots and back. Petioles that connect the leaves to the stem provide the same type of function. Without these stems the plant could not carry out metabolism and produce buds and shoots. Respiration also occurs in the stem tissues during dormant periods to keep cells alive. For some types of plants the stem is the most important part.
The body of a cactus is a type of modified stem. All of the vital processes happen within the stem tissues. The stem is where it takes in sunlight, stores water and makes and stores food. So for cacti the entire respiration process occurs within the stem.
Traditional plant roots have two purposes. One is to anchor the plant and the other is to take in water and nutrients. During dormancy the roots can also absorb air from the soil. Water disperses the molecules needed by each part of the plant to carry out respiration. Bulbs and tubers are modified roots. These enlarged roots have a greater capacity to store what the plant will need to survive.
Respiration can occur inside the bulb during times of dormancy. Some desert plants have enlarged lignotubers attached to their roots. These are swollen pockets that contain water and nutrients similar to bulbs. The lignotubers allow these plants to survive during long periods when photosynthesis cannot occur.