There are various forms of symbiosis. In mutualism both species benefit while in commensalism only one species benefits and the other species is left unaffected. In parasitism, one species is harmed while the other benefits. Last, predation is defined a predator-prey relationship in which one species feeds on another.

It is true we derive energy from eating meat. And it is also true that the cow derives its energy from the grass it eats; however, ultimately the sun provides the raw energy for the grass to synthesize biomolecules that the cow uses to synthesize its biomolecules after eating the grass. When we consume a cow, we convert its energy to energy we can in the form of molecules such as glucose. The ultimate or very first energy source is the sun.

In a standard food pyramid, organisms are divided into trophic levels based on their means of gaining nutrients. As one moves upwards through trophic levels, the number of organisms that can be sustained decreases. This is because energy is lost between each level. Typically, about 90% of the energy in one trophic level is lost during transfer to the next highest level; this leaves on about 10% of the energy to be used by the consumer. Because of this disparity, it is very difficult to maintain large populations at higher trophic levels. This explains why lower level organisms can easily flourish (such as ants), while higher level organisms can easily become endangered (such as tigers).

The water cycle is an important aspect of all ecosystems. It involves biotic and abiotic factors, which play a role in the pathways that move water in the water cycle. The water cycle is a recycling process that has no starting point, nor ending point. It can be divided into three stages: gas, liquid, and solid. The evaporation of water from bodies of water, such as an ocean, returns it to the atmosphere. This water, now in the clouds as vapor, can be converted back to liquid, which is known as condensation. The cooling of vapor in the clouds makes precipitation that is returned to the ground as rain, sleet, hail, and snow.

The next step of the water cycle after evaporation is condensation, causing the water to form clouds after it leaves the ocean. The clouds are then able to transport the water over land and return it to the soil via precipitation.

Most of the planet's water is located in the oceans as salt water. The earth's surface is about 71% covered by the oceans, and those oceans hold about 96% of all the water on earth.

Infiltration is the process by which water can seep or be absorbed into the soil, which makes the soil wet or turns the water into groundwater. If there is something covering the soil, like a road or a sidewalk, then the water cannot be absorbed and instead sits on the hard surface. Parks and gardens allow the soil to be exposed and the water cycle to continue.

Evaporation is the process of water moving from the liquid phase to the gaseous phase and rising into the atmosphere. Once water has evaporated, it rises up into the atmosphere where it cools and forms clouds. During precipitation, this water may turn into river, lake, or ground water, which plants may have access to through their roots. 

When plants lose water through its leaves, it is called transpiration. This happens when it gets too hot and the water they have stored evaporates and escapes from the stomata of their leaves. Respiration refers to the cellular process by which energy is produced. Perspiration is also known as sweating, and is used to prevent overheating. Precipitation is the falling of water (in one of several forms) from the atmosphere.

Evaporation, transpiration and sublimation are the three processes by which water is vaporized and allowed to enter into the atmosphere. Transpiration is the process by which water is lost from plants during photosynthesis and respiration. Evaporation is the process by which water is vaporized by absorbing enough solar energy to break away from the rest of the water molecules, note the body of water does not come to a boil during evaporation. Sublimation is the vaporization of ice into water vapor in much the same way that evaporation occurs.