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By the end of this topic, you should be able to:
Outline the need for energy in living organisms, as illustrated by active transport, movement and anabolic reactions, such as those occurring in DNA replication and protein synthesis
Describe the features of ATP that make it suitable as the universal energy currency
State that ATP is synthesised by: transfer of phosphate in substrate-linked reactions; chemiosmosis in membranes of mitochondria and chloroplasts
Explain the relative energy values of carbohydrates, lipids and proteins as respiratory substrates
State that the respiratory quotient (RQ) is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen taken in, as a result of respiration
Calculate RQ values of different respiratory substrates from equations for respiration
Describe and carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae)
All living organisms need a constant supply of energy to stay alive. Every cell in your body is constantly using energy to keep you functioning. Without energy, life would simply stop.
Energy is needed for many different processes in living organisms:
1. Active Transport
Active transport is when substances are moved across cell membranes against their concentration gradient. This means moving something from where there is less of it to where there is more of it - like pushing a ball uphill. This requires energy because it goes against the natural direction.
Example: Your cells use active transport to absorb nutrients from your intestines, even when the concentration inside your cells is already higher than in your intestines.
2. Movement
Movement requires energy at different levels:
Inside cells: Proteins and other molecules need to be transported from where they are made to where they are needed. For example, a protein made on a ribosome needs to travel to the Golgi apparatus.
Whole organisms: Muscles need energy to contract. When you walk, run, or even blink, your muscle cells are using energy to make movement happen.
3. Anabolic Reactions
Anabolic reactions are chemical reactions that build large molecules from smaller ones. These reactions always require energy input.
Key examples include:
DNA replication: Making a complete copy of all your DNA before a cell divides requires a lot of energy. Small nucleotide building blocks must be joined together to form the long DNA molecule.
Protein synthesis: Building proteins from individual amino acids is an anabolic process that needs energy. Your cells make thousands of different proteins, and each one requires energy to construct.
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