Cellular Respiration in Plants

Respiration is not just a process for animals. Plants consume oxygen and release carbon dioxide the same way as humans and other animals. Their growth, maintenance and reproduction rely on respiration as a way of breaking down the molecules produced during photosynthesis and using them for energy.

Cellular Respiration

• Plants use respiration to convert the energy in glucose molecules produced during photosynthesis into usable energy-containing molecules. The process consumes glucose and oxygen, the same as respiration does in animals and produces energy, carbon dioxide and water.

Glycolysis

• Glycolysis is the first process of cellular respiration. It occurs in the plant cell's cytoplasm, the fluid-filled free space within the cell body. During glycolysis, glucose produced during photosynthesis and released into the cytoplasm is broken down into acid molecules, releasing a small amount of energy in the process, stored in molecules. Oxygen is not involved in glycolysis, making it an anaerobic process.

Krebs Cycle

• The Krebs Cycle, also called the citric acid cycle, converts the acid produced during glycolysis to energy molecules. This process occurs in the cell's mitochondria, an organelle containing layers of membranes folded over many times. These membranes are called cristae. They are equipped with enzymes that can remove the energy in the form of electrons from the energy molecules produced during respiration. The Krebs Cycle also produces carbon dioxide as a waste product.

Electron Transport Chain

• The enzymes contained along the cristae of the mitochondria along with pigment molecules form the electron transport chain. As energy molecules pass through a series of these enzymes and pigments, their electrons are removed and used to pass hydrogen molecules, taken from the energy molecules, across the membrane into the outer section of the mitochondria. Oxygen is an essential component in this process. It is responsible for removing electrons from the chain so they can provide energy to the plant. The electrons are eventually passed along the chain and used to form a new energy molecule that is suited for energy storage. Oxygen bonds with the hydrogen pumped across the membrane and forms water.

Chemiosmosis

• The production of energy-storing molecules is done through a process called chemiosmosis. This occurs as hydrogen is moved across the mitochondria membrane to the outer compartment at the end of the electron transport chain. The build up of positively charged hydrogen on the inside of the membrane creates a disproportionate charge on one side. As a result, the hydrogen is transferred to the more negatively charged outer section of the mitochondria, releasing its energy as it passes. This energy is then used to produce the energy-containing molecules.

Fermentation

• Respiration can still take place without oxygen. This anaerobic process is called fermentation and begins with glycolysis. Because no oxygen is involved in glycolysis, the process still yields acid in anaerobic conditions. During fermentation, glycolysis occurs in the yeast cells, where the acid produced is converted to ethyl alcohol. Yeast cells contain specialized enzymes that are able to carry out this conversion. Fermentation produces energy-storing molecules and carbon dioxide. Bread and alcohol are both produced using fermentation.