Population structure is what the population is composed of, or it shows what is the make up of a population. It divides the different gender of a place or community specifically males and females of different age groups. The population pyramid shows how the males and females of different age group is divided, it is the graphical illustration of the division of the two. Below is an example of a population pyramid. The figure above shows how the two gender with different age groups are divided considerably. The widest bar at the left side means that the largest population in Kentucky are males with the age of 20-24 years old. While on the female side, the largest population among the age groups are 0-4 years old. The reason of the large number of males in Kentucky is because it is the place of a large military installation. So the bars on the side determine the gender and estimate the number of them while the middle part determine the age of the different groups. Population Density is the number of individuals per unit area. Population density can be determined by dividing the population by the area. For example, if the Philippines has a population of 103 million people and an area of 300,000 km so the population density is about 323.33 persons per square kilometer. There are two reasons that can affect population density, the input and the output. The inputs can be high birth rate or immigration. High immigration or birth rate can affect the density if it is not balanced with the output which is death or emigration. If there is high inputs and low output, it can cause overpopulation. Population, Energetic, Biomass and ProductionEnergy flow is the transfer of energy from trophic level to another trophic level. Solar energy is transferred from the sun to the plants or the producers and will be taken in by the primary consumer whereas the energy transfers, it only transfer 90% of energy will be lost due to respiration. So the primary consumer only get 10% of energy while 1% for the secondary consumer and only 0.1% left for the tertiary consumer. A lot of energy is lost between trophic levels, as a result the last consumer receives the lowest energy.