Respiration continued

Glycolysis involves the phosphorylation of glucose, followed by the splitting of fructose 1,6-bisphosphate (6C) into two triose phosphate molecules (3C). These are then oxidized to pyruvate (3C), producing ATP and reduced NAD.

The Krebs cycle involves oxaloacetate (4C) accepting a 2C fragment from acetyl coenzyme A to form citrate (6C). Through a series of steps, citrate is converted back to oxaloacetate. Decarboxylation removes carbon dioxide, and dehydrogenation removes hydrogen (reducing NAD and FAD).

Hydrogen atoms split into protons and electrons. Electrons release energy as they pass through the electron transport chain. This energy pumps protons across the inner mitochondrial membrane, creating a gradient. Protons then diffuse back through ATP synthase, driving ATP synthesis. Oxygen is the final electron acceptor, forming water.

The highly folded inner membrane (cristae) increases surface area for electron transport and ATP synthesis. The matrix contains enzymes for the Krebs cycle and link reaction. The intermembrane space accumulates protons for chemiosmosis.

In ethanol fermentation, pyruvate is decarboxylated to acetaldehyde, which is then reduced by reduced NAD to ethanol, regenerating NAD+ so glycolysis can continue. This process allows yeast to produce ATP in the absence of oxygen.

In lactate fermentation, pyruvate is reduced by reduced NAD to lactate, regenerating NAD+ so glycolysis can continue. This process allows muscle cells to produce ATP in the absence of sufficient oxygen, but lactate accumulation causes muscle fatigue.

Aerobic respiration uses oxygen to fully oxidize glucose, extracting all available energy. Anaerobic respiration only partially breaks down glucose, resulting in a much lower ATP yield as the Krebs cycle and oxidative phosphorylation are not utilized.

Rice plants develop aerenchyma in their roots, creating air spaces for oxygen diffusion to submerged tissues. They also undergo ethanol fermentation in roots to produce ATP in the absence of oxygen, and exhibit faster stem growth to reach above the water surface for gas exchange.

Increasing temperature generally increases the rate of respiration in yeast, as enzyme activity increases with temperature, leading to faster metabolic reactions. However, beyond an optimal temperature, enzymes denature and the rate decreases.

A respirometer measures the rate of oxygen consumption. The organism is placed in a sealed chamber, and the decrease in oxygen volume (often indicated by a change in fluid level in a connected manometer) is measured over time. This change reflects the rate of respiration.

The control establishes a baseline for comparison. It contains all components of the experimental setup *except* the variable being tested (temperature). This allows you to isolate and determine the specific effect of temperature on the rate of respiration, excluding other potential factors.