Energy

Biology: IB Diploma Higher Level, topic 8.2.1

All living organisms require energy in one form or another, usually ATP, to carry out cellular processes.

All living things require energy in one form or another.
Energy is required by most complex metabolic pathways (often in the form of adenosine triphosphate, ATP).
In particular, those pathways responsible for building large molecules from smaller compounds require a lot of energy.
Living organisms would not be able to assemble macromolecules (proteins, lipids, nucleic acids, and complex carbohydrates) from their monomeric subunits without a constant energy input.

It is important to understand how organisms acquire energy and how that energy is passed from one organism to another.
Energy takes a one-way path through ecosystems because energy conversions result in a loss of usable (free) energy through the release of heat. In

Cellular processes such as the building and breaking down of complex molecules occur through stepwise chemical reactions.
Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed.
Just as living things must continually consume food to replenish what has been used, cells must continually produce more energy to replenish that used.
All of the chemical reactions that take place inside cells are the cell’s metabolism.

The relationship between metabolic rate and body mass is typically an inverse one.
The smaller the animal, the higher its metabolism, with mice having a higher metabolic rate than, for example, elephants.
Because mice have a greater surface area-to-volume ratio for their mass than larger animals, they lose heat at a faster rate.
So, mice require more energy to maintain constant body temperature.

Smaller endothermic animal having a higher basal metabolic rate (BMR), per body weight, than a larger endothermic animal.

For organisms to survive, they need to meet the energy needs of their basal metabolic rate.
Any extra energy may be used for growth or stored (e.g as fat).
If an organism has a consistent net loss of energy, it will not be able to grow and will eventually die.

Test yourself on Energy

Which of the following would you expect to have the highest basal metabolic rate per body weight?
What is the typical relationship between metabolic rate and body mass?