Suppose a mutant of a photosynthetic algae has dysfunctional mitochondria. It would affect its ability to perform -

Photosynthetic algae rely on two primary organelles for their cellular metabolism:

1. Chloroplasts: For photosynthesis, which generates glucose and oxygen from light, carbon dioxide, and water.
2. Mitochondria: For cellular respiration, which breaks down glucose to produce ATP, the energy currency of the cell.

Impact of Dysfunctional Mitochondria:

Dysfunctional mitochondria will impair cellular respiration, leading to various consequences:

1. Reduction in ATP Production:
   • ATP is primarily generated during oxidative phosphorylation in mitochondria.
   • If mitochondria are dysfunctional, the algae would depend on glycolysis for ATP production, which is significantly less efficient (producing only 2 ATP molecules per glucose molecule as opposed to ~30-32 in oxidative phosphorylation).
   • This reduced ATP availability would limit energy-dependent cellular processes such as protein synthesis, ion transport, and cell division.
2. Impaired Carbon Fixation (Indirect Impact):
   • Photosynthesis requires ATP and NADPH produced during the light-dependent reactions in chloroplasts.
   • However, the Calvin cycle (light-independent reactions) relies on the recycling of carbon intermediates and cellular energy balance.
   • Dysfunctional mitochondria may disrupt the overall energy balance, indirectly affecting the Calvin cycle and reducing photosynthetic efficiency.
3. Disruption of Photorespiration:
   • In C3 plants and algae, mitochondria are involved in the photorespiratory pathway, where glycolate is converted to glycine, and subsequently to serine, releasing CO2.
   • Dysfunctional mitochondria can impair this pathway, leading to the accumulation of toxic byproducts like glycolate, which could inhibit photosynthetic efficiency.
4. Inability to Utilize Stored Glucose:
   • Algae store excess glucose as starch or other carbohydrates during photosynthesis.
   • Mitochondria are crucial for breaking down these reserves during periods without light (e.g., at night) to generate ATP.
   • A dysfunctional mitochondrion would prevent the algae from effectively utilizing stored energy, potentially leading to starvation during non-photosynthetic periods.
5. Oxidative Stress:
   • Mitochondria also play a role in managing reactive oxygen species (ROS) produced during cellular metabolism.
   • Dysfunctional mitochondria would result in excessive ROS accumulation, causing oxidative damage to proteins, lipids, and DNA, which can lead to cellular senescence or death.
6. Secondary Metabolic Disruption:
   • Mitochondria are involved in amino acid metabolism, fatty acid oxidation, and the TCA cycle.
   • Dysfunctional mitochondria would lead to disruptions in these pathways, affecting the synthesis of biomolecules required for cellular growth and repair.

The algae's ability to perform crucial life functions would be severely compromised due to dysfunctional mitochondria. Specifically, the effects would manifest as:

1. Reduced ATP availability.
2. Impaired carbon fixation and photorespiration.
3. Inability to utilize energy reserves in the absence of light.
4. Accumulation of ROS, leading to cellular damage.
5. Disruption in secondary metabolism.

Thus, while photosynthesis in chloroplasts may still occur, the algae’s overall metabolic efficiency and survival would be significantly impacted, particularly in conditions where energy demand is high or during dark periods.