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Respiration

Respiration

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Respiration is how living things get energy from glucose. It's basically the opposite of photosynthesis. Remember, cells can't use glucose directly for energy. Instead, they turn it into something called ATP, which they can use right away. This process of turning glucose into ATP is called cellular respiration. In A-level biology, we focus on two types of cellular respiration: aerobic and anaerobic.

What is the difference between anaerobic respiration and aerobic respiration?

Let’s explore aerobic and anaerobic respiration to understand their differences.

Aerobic respiration

Aerobic respiration is a process that needs two parts: the cytoplasm and mitochondria. Aerobic makes a lot of ATP, along with carbon dioxide and water. This process has four stages:

  1. Glycolysis: This is the first stage of aerobic respiration. It splits a 6-car3bon molecules stage3 pyv go through to become acetyl coenzyme, which has two carbons.
  2. Krebs cycle: This is the most complicated stage of aerobic respiration. Acetyl coenzyme A enters a of reactions that produce ATP, reduced NAD, and reduced FAD.
  3. Oxidative phosphorylation: This is the final stage of aerobic respiration. It uses the electrons released from the Krebs cycle (attached to reduced NAD and FAD) to create ATP. Water is produced as a by-product.

The overall equation for aerobic respiration is the following:

 

Aerobic respiration summarsed
Aerobic respiration summarsed

Anaerobic respiration

Anaerobic respiration doesn't need oxygen to work. It happens only when there's no oxygen. The process occurs in the cytoplasm. What it produces depends on whether it happens in plants or animals. In animals, it produces lactate or ethanol, while in plants and fungi it produces carbon dioxide. Only a small amount of ATP is made during anaerobic respiration.

Unlike aerobic respiration, anaerobic respiration only has two stages:

The overall equation for anaerobic respiration in animals is:

glucose → lactic acid (or ethanol) + energy

The overall equation for anaerobic respiration in plants or fungi is:

 

Anaerobic respiration summarised
Anaerobic respiration summarised

How do you measure the rate of respiration?

There are a few different ways in which you can measure the rate of respiration.

Redox indicators

Scientists use various methods to measure the rate of respiration, but one of the most common ways is by using redox indicators.

A redox indicator is a substance that changes colour when it is either reduced or oxidised. DCPIP and methylene blue are some of the examples of redox indicators. We use redox indicators to study how temperature and substrate concentration affect the rate of anaerobic respiration in yeast. They can be added to a yeast cell suspension without harming them. By monitoring the colour change of the redox indicator, we can determine the rate of anaerobic respiration. This method is useful for investigating the effects of different variables on the rate of respiration in living organisms.

Aerobic Respiration: Effect of Temperature & Substrate Concentration  (12.2.11) | CIE A Level Biology Revision Notes 2022 | Save My Exams
An outline of the equipment and process of measuring the rate of respiration using redox indicators

If you want to investigate the effect of temperature on the rate of respiration, you can follow these1 Take two suspension them In third test, add distilled water. Add one yeast and glucose to the test tube containing distilled water. The test tube containing distilled water will act as a control for your experiment.

  1. Place all test tubes into a temperature-controlled water bath and leave them there for 5 minutes. Ensure that the water temperature is around 30℃ and is not fluctuating.
  2. Add methylene blue or DCPIP to the test tubes and start the timer immediately. Record the amount of time that each solution takes to become colourless.
  3. Repeat the experiment across a range of temperatures with the same glucose concentration: 35℃, 40℃, 45℃, and 50℃. You can also vary the glucose concentrations at 0.1%, 0.5%, and 1%, but remember to keep the temperature consistent.
  4. Plot a graph of your results for temperature against time and concentration against time. You should find that as the temperature and concentration of glucose increase, the rate of respiration also increases.

By following these steps, you can investigate the effect of temperature on the rate of respiration and determine how different variables affect the process.

Mechanism

During aerobic respiration, dehydrogenation occurs regularly, particularly in both decarboxylation and the Krebs cycle.

The Krebs cycle, which features NAD and FAD being reduced via dehydrogenation
The Krebs cycle, which features NAD and FAD being reduced via dehydrogenation
The Link Reaction in which NAD is reduced via dehydrogenation
The Link Reaction in which NAD is reduced via dehydrogenation

Rate of respiration = 1 / time taken for solution to turn colourless

This equation shows that the faster the solution turns colourless, the higher the rate of respiration. This is because a faster rate of respiration means more hydrogen atoms are being produced and picked up by the redox indicators, leading to a quicker reduction of these indicators.

By using this equation, we can determine the rate of respiration under different conditions, such as varying temperatures or substrate concentrations. This information can help us understand the metabolic processes occurring within living organisms and how they are influenced by different factors. 

Respirometers

To use the respirometer to measure the rate of respiration, follow these steps:

  1. Place a small amount of beads at the bottom of test tube.
  2. Add you want to test to the test tube, making sure it is submerged in the glass beads.
  3. Insert a soda-lime pellet into the test tube, which will absorb any carbon dioxide produced during respiration.
  4. Seal the test tube with a rubber stopper, making sure it is airtight.
  5. Place the test tube in a temperature-controlled water bath at the desired temperature.
  6. Measure the initial volume of air in the test tube by reading the scale on the side of the tube.
  7. Start the stopwatch and record the time.
  8. Monitor the respirometer for a set period of time, such as 15 minutes, and record any changes in the air volume.
  9. Calculate the rate of respiration by dividing the amount of oxygen consumed by the time taken.

By using a respirometer, we can measure the rate of respiration in living organisms and investigate the effects of different factors, such as temperature or substrate concentration. This provides valuable insight into the metabolic processes occurring within organisms and can help us better understand their physiology.

Practical: Respirometer (5.7.14) | OCR A Level Biology Revision Notes 2017  | Save My Exams
A respirometer containing germinating seeds. Note that this is set up in a temperature-controlled water bath

Measuring the rate of respiration in this way can provide important information about the organisms. By investigating the effects of different factors, such as temperature, the rate of respiration, we gain a better understanding of how these processes are regulated and how they contribute to an organism's overall physiology. This knowledge can be applied to various fields, including medicine, agriculture, and ecology, to improve our understanding of the natural world and how it works.

Assessing the rate of respiration in yeast

Measuring the rate of respiration in yeast provides important insights into the metabolic processes that occur in this important organism. By understanding how temperature affects the rate of respiration, we can gain a better understanding of how yeast behaves in different environments, including in food production and fermentation processes. This knowledge can be applied to various industries, including brewing, winemaking, and baking, to ensure that these processes are optimized and produce high-quality products.

Respiration

What are two types of respiration?

Aerobic and anaerobic.Aerobic respiration occurs in both the cytoplasm of the cell and the mitochondria. It requires oxygen and glucose to take place, and produces carbon dioxide, water, and a lot of ATP. Anaerobic respiration occurs exclusively in the cytoplasm, and does not require oxygen to occur. During anaerobic respiration, glucose is converted into two lactate molecules (or ethanol and carbon dioxide in plants or fungi) and a small amount of ATP is produced.

Where does respiration take place?

Glycolysis, the first stage of respiration, takes place in the cytoplasm of the cell. If respiration is anaerobic, fermentation also occurs in the cytoplasm. If respiration is anaerobic, the remaining stages of respiration take place in the mitochondria of the cell.

What is the equation for aerobic respiration?

C6H12O6 + 6O2  6H2O + 6CO2

What is respiration?

Respiration refers to the metabolic process in which cells use glucose and turn it into ATP. Respiration can involve oxygen ( which  is aerobic respiration) but can occur in the absence of oxygen ( which  is anaerobic respiration).

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