5.2.1 Mitochondria & the Need for Energy

The Need for Energy in Cells

Cells require energy in the form of ATP for a variety of essential processes:

1. Active Transport:

• Movement of molecules against their concentration gradient, e.g., $Na⁺/K⁺$pump in nerve cells.

2. Metabolic Processes:

• Synthesis of macromolecules like proteins (from amino acids) and DNA replication.

3. Movement:

• Muscle contraction in animals.
• Cytoplasmic streaming in plant cells.

4. Secretion:

• Energy is needed for vesicle formation and exocytosis during secretion.

5. Cell Division:

• Energy is required for mitosis and meiosis, including spindle fibre formation.

Adaptations of Mitochondria

• Abundance: Cells requiring high amounts of ATP, such as muscle cells, contain a greater number of mitochondria.
• Cristae: Provide a large surface area for electron carriers and ATP synthase in the inner membrane.
• Matrix: Contains enzymes for the Krebs cycle and other stages of respiration.