Cellular Respiration Processes

Cellular respiration begins with glycolysis in the cytoplasm and continues through several stages in the mitochondria, culminating in oxidative phosphorylation.

Definition: Glycolysis is the initial glucose-breaking process that produces a net yield of 2 ATP and reduces NAD to NADH.

The link reaction connects glycolysis to the Krebs cycle by converting pyruvate to acetyl-CoA in the mitochondrial matrix. The Krebs cycle then generates reduced coenzymes (NADH and FADH2) through a series of reactions.

Highlight: Oxidative phosphorylation occurs on the inner mitochondrial membrane through an electron transport chain, creating a proton gradient that drives ATP synthesis.

Example: The complete oxidation of respiratory substrates produces significant ATP through chemiosmosis, where protons flow through ATP synthase.

Vocabulary: Chemiosmosis refers to the process where the proton gradient drives ATP synthesis through ATP synthase.

Photosynthesis and Light Reactions

The photosynthetic process begins in the specialized organelles called chloroplasts, which contain stacked membrane structures called thylakoids. These thylakoid light dependent reactions occur on the membrane surface while the Calvin cycle takes place in the surrounding stroma.

Definition: Grana are stacks of thylakoid membranes connected by lamellae, increasing surface area for light reactions.

Highlight: The light-dependent reactions produce NADPH and ATP, which are essential for the Calvin cycle, while oxygen is released as a waste product.

The process involves chlorophyll absorbing light energy, exciting electrons that travel down an electron transport chain. This generates ATP through photophosphorylation and produces NADPH through water photolysis.

Example: Carbon dioxide levels fluctuate over 24 hours, with higher concentrations at night due to the absence of photosynthesis while respiration continues constantly.

Vocabulary: The compensation point occurs when photosynthesis rate equals respiration rate.

The Calvin cycle (carbon fixation) combines CO2 with RuBP to form GP, which is then reduced to triose phosphate using ATP and NADPH, ultimately producing glucose and other organic compounds.