Bioenergetics sounds like a very intimidating topic! It's a mix between biology and chemistry, so we describe it as biochemistry - a branch of science that delves into the various chemical processes within living organisms. Bioenergetics focuses on how living Cells often produce, store or consume ATP (adenosine triphosphate), helping us to understand how Cells transfer energy in relation to processes like Respiration and Photosynthesis!
Bioenergetics Definition
Bioenergetics is the process by which cells transform energy from one form to another. This often occurs by producing, storing or consuming a crucial molecule called ATP (adenosine triphosphate). This molecule is found densely in your mitochondria and helps to provide our cells with energy!
Remember that energy cannot be created or destroyed, just transferred from one form to another or stored.
Photosynthesis
Photosynthesis is the process by which plant cells convert light energy into food (chemical energy). This process only occurs in plant cells, not animal cells.
Animal cells do not need to carry out photosynthesis because we can eat food to get energy! Plant cells cannot do this.
Photosynthesis takes place in the chloroplasts of plant cells. These are organelles filled with chlorophyll (the substance that gives Plants their green colour) and are specialised to trap light energy from the sun.
Take a look at the photosynthesis equation:
\[\text{Carbon dioxide} + \text{Water} \xrightarrow{\text{Light energy}} \text{Glucose} + \text{Oxygen}\]
When writing out the equation for photosynthesis, make sure that you add 'light energy' above the arrow. We do not count light energy as a reactant; however, light must be present for the reaction to occur. As it is not a reactant, we cannot put it on the left side of the arrow.
Respiration
Respiration is a vital process that takes place in both Animal and Plant Cells. It is a chemical process that occurs in every cell of an organism. In respiration, energy is released from the breakdown of glucose. Glucose is a carbohydrate (sugar) that comes from the foods we eat daily!
There are two types of respiration - aerobic and anaerobic. The difference between the two is in how much energy can be transferred and how much oxygen is present.
Aerobic Respiration occurs when the cell has a plentiful supply of oxygen (most of your cells will be aerobically respiring as you read this).
Anaerobic Respiration occurs when there is a limited supply of oxygen, for example, when you have to run to catch the bus.
Aerobic Respiration is much more efficient than Anaerobic Respiration, so your cells prefer to respire this way. Our cells only anaerobically respire when necessary, like at the end of a long workout or sprinting.
After respiring anaerobically, our body cells need to recover - this is often described as oxygen debt. You may have experienced this before. After a prolonged period of physical activity, even once we stop, we still have to breathe deeply in order to catch our breath. This act of catching our breath after exercise is repaying our oxygen debt.
Bioenergetics and Metabolism
Metabolism is the term used to describe all of the chemical reactions that are taking place in a cell or the body.
It involves respiration, digestion and absorption alongside many more reactions in the human body, for example. We break metabolic reactions into either anabolic reactions or catabolic reactions. Both of these sorts of reactions are important in metabolism.
Here are some examples of metabolic reactions that occur in the human body; synthesis of glycogen from glucose (anabolic), synthesis of Lipids from Fatty Acids and glycerol (anabolic), and breakdown of Proteins into amino acids in digestion (catabolic).
Have a look at our article on metabolism for more information on this.
The hormonal system plays a vital role in metabolism. Hormones such as thyroxine affect our basal Metabolic Rate. This refers to the speed of metabolism - the speed of reactions in the body.
The thyroid gland releases thyroxine in the neck. It is involved in a Negative Feedback system involving the hypothalamus and pituitary gland - a very complex system involving three different hormones.
Bioenergetic Systems
Bioenergetic systems refer to metabolic reactions that show us the energy flow in living organisms. We have discussed a few of these processes above. The most notable of these processes are respiration and photosynthesis.
Bioenergetic systems have different factors that can limit Energy Transfers within the system. If we take photosynthesis as an example, the following factors can limit the energy transfer in photosynthesis;
To learn more about photosynthesis, have a look at our article on the topic!
We have to look for energy leaks like those mentioned above in these systems. As we discussed in our 'Bioenergetics and Metabolism' section, metabolic reactions can be anabolic or catabolic.
Any reaction that releases energy is said to be exothermic - meaning that catabolic reactions are exothermic.
Any reaction that requires energy is said to be endothermic - meaning that anabolic reactions are endothermic.
Bioenergetics Example
An example of bioenergetics that we could focus on is photosynthesis.
Remember the equation for photosynthesis?
\[\text{Carbon dioxide} + \text{Water} \xrightarrow{\text{Light energy}} \text{Glucose} + \text{Oxygen}\]
Make sure you also understand the symbol equation too:
\[6CO_2 + 6H_2O \xrightarrow{\text{Light energy}} C_6H_{12}O_6 + 6O_2\]
Photosynthesis takes place in plant cells only. Plant cells are densely packed with chloroplasts, the organelle specialised for photosynthesis. It occurs explicitly in the leaves of Plants, in the spongy mesophyll layer.
You can read our article on Plant Organs to find out more about the leaf of plants as well as the other organs found in plants.
Human Bioenergetics
When discussing human bioenergetics, we could discuss respiration (both aerobic and anaerobic), metabolism, digestion, and many more reactions.
We must understand that these reactions have limiting factors just like photosynthesis has many limiting factors. Enzymes catalyse the majority of reactions in the body.
Catalyst: a substance that increases the rate of reaction without getting used up.
Enzyme: a biological catalyst in the form of a protein that speeds up the rate of reactions in the body.
Some limiting factors for respiration could be;
enzyme concentration
temperature
oxygen concentration
Any factors that impact the enzyme activity rate can also affect human bioenergetics.
Have a look at our article on Enzymes to learn more about these factors.
Bioenergetics - Key takeaways
Bioenergetics is the process by which cells transform energy from one form to another.
Respiration takes place in both animal and plant cells. It is the process by which energy is released through the breakdown of ATP.
Photosynthesis takes place in plant cells. It is the process by which plant cells convert light energy into chemical energy.
Metabolism is the sum of all the reactions that take place in the body.
Catabolic reactions involve breaking down reactants.
Anabolic reactions involve building up reactants.
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