These are detailed Revision Notes for Topic 5.2.1 of OCR A-Level (Energy for Biological Processes). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
- Energy Cycles
- ATP synthesis
- P...
Energy for Biological Processes
17.1 Energy Cycles
17.1 Energy cycles
- Energy is needed in cells for:
o Active transport 17.2 ATP synthesis
o Secretion (exocytosis) 17.3 photosynthesis
o Endocytosis
o Anabolism e.g., transcription, translation 17.4 factors affecting photosynthesis
o DNA replication
o Movement (muscle contraction)
o Movement of chromosomes, mitosis, meiosis, cell division
o Activation of molecules (phosphorylation)
- Organisms make use of the energy in the bonds of organic molecules such as glucose.
- These bonds are formed during photosynthesis in plants
- Respiration is where organic compounds are broken down into smaller molecules and the energy released
from the bonds is used to synthesis adenosine triphosphate.
17.2 ATP Synthesis
- ATP is the energy currency of the cell
- ATP is formed from ADP + Pi with an input of energy.
- This energy can be released directly from a substrate within respiration through substrate level
phosphorylation or by oxidative phosphorylation.
- The hydrolysis of ATP releases free energy for use within the cell. Some ‘wasted’ heat energy will also
be released.
- ATP is a universal energy currency because:
o It can move around the cell
o It couples catabolic and anabolic reactions
o Energy is released in small packets
o It is an immediate source of energy
o Rapid turnover
o Used by all organisms
- Chemiosmosis ~ diffusion of protons from high concentration to low concentration through a partially
permeable membrane, releasing energy that is used in the attachment of an inorganic phosphate to
ADP, forming ATP.
17.3 Photosynthesis
- Photosynthesis converts light energy to chemical energy.
- Autotrophs use external energy source (light or chemical) and inorganic molecules to synthesise complex
organic molecules.
- Heterotrophs must ingest and digest complex organic molecules and release their chemical potential
energy.
- Autotrophs produce organic molecules during photosynthesis, so start food chains.
- Inorganic molecules are used to create the larger
organic ones, these molecules bonds contain energy
usually formed using energy from the sun during
photosynthesis. Photosynthesis makes most of the
biomass on earth.
- 6CO2 + 6H2O à C6H12O6 + 6O2
- Grana – flattened membrane compartments, host the
light-dependent stage of photosynthesis
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