state that cells use ATP from respiration for energy-requiring processes

Published by Patrick Mutisya · 14 days ago

Cambridge A-Level Biology – Cells as the Basic Units of Living Organisms

Cells as the Basic Units of Living Organisms

Learning Objective

State that cells obtain ATP from respiration to power energy‑requiring processes.

1. The Cell Theory

  • All living organisms are composed of one or more cells.

  • The cell is the smallest unit that can carry out all the processes of life.

  • All cells arise from pre‑existing cells.

2. Energy in Cells

All cellular activities that involve movement, synthesis or transport require energy. This energy is supplied by the molecule adenosine triphosphate (ATP).

3. Production of ATP – Cellular Respiration

Cellular respiration is the series of metabolic pathways that convert the energy stored in glucose into ATP. The overall reaction can be written as:

\$C6H{12}O6 + 6\,O2 \;\longrightarrow\; 6\,CO2 + 6\,H2O + \text{\overline{38} ATP (aerobic)}\$

Key stages of aerobic respiration:

  1. Glycolysis – occurs in the cytoplasm; net gain of 2 ATP.

  2. Pyruvate oxidation – occurs in the mitochondrial matrix; produces NADH.

  3. Krebs cycle – also in the matrix; generates NADH, FADH2 and GTP (equivalent to ATP).

  4. Electron transport chain (ETC) – located on the inner mitochondrial membrane; oxidative phosphorylation produces the majority of ATP (≈34).

4. How ATP Powers Cellular Processes

ATP stores energy in its high‑energy phosphate bonds. When the terminal phosphate is removed (hydrolysis), energy is released and the molecule becomes ADP:

\$\text{ATP} + H2O \;\longrightarrow\; \text{ADP} + Pi + \text{energy}\$

Energy‑requiring (endergonic) processes that depend on ATP include:

  • Active transport of ions and molecules across membranes.

  • Synthesis of macromolecules (proteins, nucleic acids, polysaccharides).

  • Muscle contraction and cell movement.

  • Cell division (mitosis and meiosis).

  • Signal transduction pathways.

5. Summary Table

ProcessLocation in the CellATP Requirement (per cycle)Role of ATP
Active transport (e.g., Na⁺/K⁺ pump)Plasma membrane1 ATP per 3 Na⁺ out, 2 K⁺ inProvides energy to change conformation of pump protein.
Protein synthesis (translation)Ribosome (cytoplasm)\overline{4} ATP equivalents per amino acid addedActivates amino acids (tRNA charging) and drives peptide bond formation.
DNA replicationNucleus\overline{2} ATP equivalents per nucleotide incorporatedHelicase unwinding, polymerase activity, ligation.
Muscle contraction (actin‑myosin cycle)Cytoplasm (muscle fibers)1 ATP per cross‑bridge cycleCauses conformational change in myosin head.

6. Key Terms

  • ATP – Adenosine triphosphate, the universal energy currency of the cell.

  • Cellular respiration – Metabolic pathway that converts glucose and oxygen into ATP, CO₂ and H₂O.

  • Active transport – Movement of substances against a concentration gradient using energy.

  • Oxidative phosphorylation – Production of ATP using the energy released by electron transfer in the ETC.

7. Suggested Diagram

Suggested diagram: Flowchart of cellular respiration showing glycolysis, Krebs cycle, and electron transport chain with ATP yield at each stage.

8. Sample Exam Question

Question: Explain how the ATP produced in cellular respiration is used to drive the active transport of glucose into a plant cell.

Answer outline:

  1. Glucose is transported into the cell by a glucose‑H⁺ symporter.

  2. The symporter uses the proton gradient established by the H⁺‑ATPase pump.

  3. The H⁺‑ATPase pump hydrolyses ATP to pump H⁺ out of the cell, creating an electrochemical gradient.

  4. Energy stored in the gradient allows the symporter to move glucose against its concentration gradient.