1.0 Respiration in Plants
Unlike photosynthesis, which only happens in the presence of light, Respiration is a continuous process that occurs in all living cells, 24 hours a day. It is the process of releasing energy from food (glucose).
Respiration: A catabolic process in which complex organic compounds (glucose) are oxidized to release energy in the form of ATP.
The Chemical Equation
The overall process of aerobic respiration can be represented by the following equation:
Key Characteristics of Respiration:
- It is a catabolic process (breaking down process).
- It involves the use of enzymes at every step.
- Energy is released in small steps and stored in ATP (Adenosine Triphosphate) molecules.
- The main site of aerobic respiration is the Mitochondria.
In exams, you may be asked how energy is "recharged." When a cell needs energy, ATP breaks down into ADP (Adenosine Diphosphate) and a phosphate group, releasing energy. During respiration, that ADP is converted back into ATP.
2.0 Types of Respiration
Depending on the availability of oxygen, respiration is classified into two types. In plants, anaerobic respiration is also known as Fermentation.
Anaerobic Equation in Plants
While plants produce Ethanol during anaerobic respiration, animal muscles produce Lactic Acid. This is a major point of difference often asked in ICSE Biology!
Question: Why do seeds fail to germinate if the soil is waterlogged for a long time?
Answer: Water replaces the air in soil pores. Seeds are forced to respire anaerobically, producing Ethanol, which is toxic and eventually kills the embryo.
3.0 Experimental Proof of Respiration
To study respiration in plants, we usually use germinating seeds because they respire much faster than mature plants. For mature plants, experiments must be done in the dark to prevent photosynthesis from interfering with the results.
Experiment 1: To prove CO2 is evolved
- Setup: Germinating seeds are placed in a conical flask with a small test tube containing KOH (Potassium Hydroxide) hanging inside.
- Observation: The KOH absorbs the CO2 produced by the seeds, creating a partial vacuum. This causes the level of water in the delivery tube to rise.
- Conclusion: Germinating seeds give out Carbon Dioxide during respiration.
Experiment 2: To prove Heat is evolved
Since respiration is an exothermic process, it always releases energy in the form of heat.
- 🧪 Flask A: Contains living germinating seeds. Result: Thermometer shows a rise in temperature.
- 🧪 Flask B (Control): Contains boiled/dead seeds soaked in antiseptic (to prevent bacterial respiration). Result: No change in temperature.
In the "Heat Evolution" experiment, you must mention that dead seeds are washed with formalin or carbolic acid. This is to kill any bacteria, ensuring that any heat produced (or not produced) is only from the seeds and not from bacterial decay.
4.0 Comparative Analysis
1. Respiration vs. Photosynthesis
These two processes maintain the balance of oxygen and carbon dioxide in nature.
2. Respiration vs. Combustion (Burning)
Both involve oxidation and release energy, but the "speed" and "control" are very different.
- Respiration: Occurs at body temperature, energy is released in steps, and stored in ATP.
- Combustion: Occurs at high temperatures (ignition point), energy is released all at once as heat and light.
Question: Why is it advised not to sleep under a tree at night?
Answer: At night, photosynthesis stops but respiration continues. The tree takes in oxygen and releases Carbon Dioxide, which can lead to a lack of oxygen for a person sleeping underneath.
- Can you write the balanced chemical equation for aerobic respiration?
- Do you know the end products of anaerobic respiration in plants?
- Can you explain why KOH is used in respiration experiments?
- Do you understand why germinating seeds are used for these experiments?