12. RESPIRATION IN PLANTS

All living organisms need energy for carrying out daily life activities, be it absorption, transport, movement, reproduction or even breathing.

Living organisms, including plants, require energy to perform various life functions such as moving, reproducing, and metabolizing substances. This energy is vital for the survival and proper functioning of cells.

Think of energy as the fuel that powers a car. Just as a car needs fuel to run, plants and other organisms need energy to grow, move, and carry out their life processes.

We know we eat food for energy – but how is this energy taken from food? How is this energy utilized? Do all foods give the same amount of energy? Do plants ‘eat’? Where do plants get their energy from?

Plants, unlike animals, do not consume food in the traditional sense. Instead, they produce their own food through photosynthesis, using sunlight, carbon dioxide, and water to create glucose, which is a form of stored energy.

Consider plants as solar power stations. They harness sunlight to create energy rather than going to a store to buy food. This process is similar to how solar panels convert sunlight into electricity.

Only green plants and cyanobacteria can prepare their own food; by the process of photosynthesis they trap light energy and convert it into chemical energy that is stored in the bonds of carbohydrates like glucose, sucrose and starch.

Photosynthesis involves converting light energy into chemical energy, which is stored in glucose and other carbohydrates. This transformation takes place in the chloroplasts of green plants and is crucial for life on Earth as it forms the basis of the food chain.

You can think of photosynthesis like baking a cake. Just as you mix ingredients (sunlight, water, and carbon dioxide) to create a finished product (glucose), plants use these ingredients to produce energy-rich carbohydrates.

This chapter deals with cellular respiration or the mechanism of breakdown of food materials within the cell to release energy, and the trapping of this energy for synthesis of ATP.

Cellular respiration is the process where cells break down glucose and other organic molecules to release energy. This energy is then captured in the form of ATP (adenosine triphosphate), which is used by the cell for various functions.

Imagine a vending machine. When you put in a coin (food), the machine releases a snack (ATP) that you can use to fuel your activities, just like ATP fuels cellular processes.

Yes, plants require O2 for respiration to occur and they also give out CO2. Hence, plants have systems in place that ensure the availability of O2. Plants have stomata and lenticels for this purpose.

Plants exchange gases with their environment primarily through stomata, small openings on leaves, and lenticels on stems. While they produce oxygen during photosynthesis, they also need oxygen for respiration, particularly at night when photosynthesis stops.

Think of stomata like windows on a house. They open to let in fresh air (oxygen) for living activities and close to conserve energy, just like how windows can be opened or closed depending on the weather.

Some cells live where oxygen may or may not be available. There are sufficient reasons to believe that the first cells on this planet lived in an atmosphere that lacked oxygen.

Many organisms can survive in environments without oxygen. Fermentation is a process some cells utilize to break down glucose without oxygen, producing energy under anaerobic conditions.

Imagine working out in a closed space where fresh air is limited. Just as your body might switch to anaerobic processes to keep functioning during intense exercise, some cells adapt to low-oxygen environments to survive.

The term glycolysis has originated from the Greek words, glycos for sugar, and lysis for splitting. The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway.

Glycolysis is the initial stage of respiration, where glucose is split into two molecules of pyruvate through a series of ten enzyme-catalyzed reactions. This process happens in the cytoplasm and is essential for cellular respiration.

Think of glycolysis like slicing a loaf of bread into smaller pieces. Just as you break the bread to use for sandwiches, glycolysis breaks glucose down into smaller units that can be further processed for energy production.

During glycolysis, all the energy contained in respiratory substrates is not released free into the cell, or in a single step. It is released in a series of slow step-wise reactions controlled by enzymes, and it is trapped as chemical energy in the form of ATP.

The breakdown of glucose in glycolysis releases energy gradually. This controlled release allows the energy to be captured and used to synthesize ATP, which cells use for energy when needed.

Imagine using a water faucet. If you open it too much, water spills everywhere. But if you control the flow, you fill a cup (ATP) without wasting any water. Similarly, enzymes control energy release in glycolysis to maximize ATP production.

In fermentation, say by yeast, the incomplete oxidation of glucose is achieved under anaerobic conditions by sets of reactions where pyruvic acid is converted to CO2 and ethanol.

Fermentation is an alternative pathway to release energy in the absence of oxygen. In this process, pyruvate is further broken down into carbon dioxide and ethanol (in yeast), providing energy in low oxygen environments.

Think of fermentation like making sauerkraut from cabbage. In a sealed jar without air, the cabbage ferments, producing flavors and nutrients similar to how yeast converts sugars into alcohol in low-oxygen conditions.

Aerobic respiration is the process that leads to a complete oxidation of organic substances in the presence of oxygen, and releases CO2, water, and a large amount of energy present in the substrate.

During aerobic respiration, cells utilize oxygen to fully break down glucose, resulting in carbon dioxide, water, and substantial energy production. This process occurs mostly in the mitochondria of eukaryotic cells.

You can compare aerobic respiration to a car running on premium fuel. Just as a car uses high-quality gasoline to operate efficiently and produce more energy, cells use oxygen to maximize energy extraction from glucose.

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