Chapters
In this article, we will discuss 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. In addition to this, we will also discuss the sources of energy and how energy is transferred between living organisms. So, let us get started.
Why do we need energy?
All living organisms are made up of cells. Inside these cells, several activities and processes are constantly occurring to maintain life. These activities and processes in living organisms need energy and usable carbon compounds.
Important Activities in Living Organisms
Some of the crucial activities in living organisms are:
- Transport of substances across membranes: It involves active transport by utilizing a sodium-potassium pump in cell membranes. It also includes exocytosis of bacteria that are digested from white blood cells.
- Anabolic reactions: It involves the synthesis of DNA from nucleotides and proteins from amino acids. These reactions need the energy to create large molecules from the smaller ones
- Movement: It involves the cellular movement of chromosomes through the spindle and the mechanical contraction of muscles.
- Maintaining body temperature: All mammals and birds need to maintain a constant body temperature.
In the next section of the article, we will discuss the sources of energy in living organisms.
Sources of energy
The main sources of energy are photosynthesis and respiration.
Photosynthesis
In almost all living organisms, the main source of energy is the sun. Sunlight is essential for the reactions of photosynthesis which stores energy in organic molecules. Sun provides light energy which is converted into chemical potential energy in carbohydrates synthesis. The carbohydrates created are then employed in the synthesis of ATP or are combined and altered to create all the usable organic molecules that are critical for all metabolic processes within the plant. Photosynthesis occurs in the first organism in the food chain like plants and some other small organisms.
Respiration
All living cells release energy by breaking down organic molecules in a process known as respiration. This process includes the transfer of chemical potential energy from nutrient molecules like proteins, carbohydrates, and fats into a usable energy form. This usable energy form can be employed for work within an organism.
Equations of Glucose
Glucose + Oxygen 
carbon dioxide + Water + Energy
What are Autotrophs and Heterotrophs?
The organisms that can synthesize their own usable carbon compounds from carbon dioxide in the atmosphere through photosynthesis are known as autotrophs. On the other hand, heterotrophs cannot do this as they need a supply of already made usable carbon compounds that they will get from their food.
How Energy is Transferred in and Between Organisms?
Life is dependent on continuous energy transfer. Chlorophyll absorbs light in the process of photosynthesis, and this results in the production of ATP. In the process of respiration, different substances are employed as respiratory substrates. The production of ATP in respiration is associated with the hydrolysis of these respiratory substrates.
In both photosynthesis and respiration, the production of ATP occurs when protons diffuse down an electrical gradient by enzyme ATP synthase molecules that are embedded in the cellular organelles’ membranes. All photoautotrophic organisms undergo the process of photosynthesis. On the other hand, the process of respiration occurs in all living organisms. Remember that the processes of respiration and photosynthesis are not perfectly efficient. Biomass and its stored chemical energy transfer from one organism to a consumer are also not perfectly efficient.
Photosynthesis
- Light is absorbed by the chlorophyll resulting in the photoionization of chlorophyll
- During photoionization, some of the released energy from electrons is saved in the formation of ATP and reduced NADP
- The generation of ATP includes a transfer of electrons linked with the transfer of electrons down the chain along with the passages of protons across chloroplast membranes. It is catalyzed by ATP synthase embedded in these membranes
- Protons, electrons, and oxygen are generated through the photolysis of water.
The reaction that does not need light to occur employs reduced NADP from the reaction that is dependent on light to create a simple sugar. The ATP hydrolysis, also from the reaction that is dependent on light, gives energy for this reaction.
Respiration
Respiration generates ATP. The first stage of aerobic and anaerobic respiration is glycolysis which occurs in the cytoplasm and is an anaerobic process. The following stages are included in glycolysis:
- By employing ATP, phosphorylation of glucose to glucose phosphate.
- Triosephosphate production
- Triosephosphate oxidation to pyruvate with a net gain of both ATP and reduced NAD.
In anaerobic respiration, pyruvate can be transformed into ethanol or lactate by utilizing reduced NAD. The oxidized NAD produced in this manner can be employed in glycolysis further. In aerobic respiration, pyruvate from glycolysis enters the mitochondrial matrix through active transport.
Ecosystems and Energy
In any ecosystem, the synthesis of organic compounds occurs from atmospheric or aquatic carbon dioxide. Plants used the majority of synthesized sugar as respiratory substrates. The remaining are employed to create other groups of biological molecules. These biological results in the biomass of the plants. We can measure biomass in terms of carbon or dry mass of tissue per given area. Calorimetry can be used to estimate the chemical energy stored in dry biomass.
- Gross primary production: It refers to the chemical energy stored in plant biomass, in a specific area or volume.
- Net primary production: It refers to the chemical energy stored in plant biomass after respiratory losses to the environment have been considered. In other words, it represents gross production and respiratory losses to the environment.
The net primary production is used for the reproduction and growth of plants. It is also accessible to other trophic levels in an ecosystem like decomposers and herbivores.
The net production of animals that are considered as consumers can be represented as chemical energy stored in ingested food, chemical energy lost to the environment through urine and feces, and losses due to respiration to the environment. Primary and secondary productivity refers to the primary or secondary production rate. It is calculated by considering biomass in a specific area in a given time.
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