Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds. It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth. If photosynthesis ceased, there would soon be little food or other organic matter on Earth. And during cellular respiration, a glucose molecule is gradually broken down into carbon dioxide and water. Along the way, some ATP is produced directly in the reactions that transform glucose.
Much more ATP, however, is produced later in a process called oxidative phosphorylation. Biotic factors are all of the living organisms within an ecosystem. These may be plants, animals, fungi, and any other living things. Abiotic factors are all of the non-living things in an ecosystem. Abiotic factors come in all types and can vary among different ecosystems. For example, abiotic factors found in aquatic systems may be things like water depth, pH, sunlight, turbidity (amount of water cloudiness), salinity (salt concentration), available nutrients (nitrogen, phosphorus, etc.), and dissolved oxygen (amount of oxygen dissolved in the water). Abiotic variables found in terrestrial ecosystems can include things like rain, wind, temperature, altitude, soil, pollution, nutrients, pH, types of soil, and sunlight.
Biotic factors that I depend on are cows, pigs, fruits, herbs, and vegetables. Heterotrophs cannot make their own food, so they must eat or absorb it. For this reason, heterotrophs are also known as consumers. Consumers include all animals and fungi and many protists and bacteria. They may consume autotrophs or other heterotrophs or organic molecules from other organisms. Heterotrophs show great diversity and may appear far more fascinating than producers. But heterotrophs are limited by our utter dependence on those autotrophs that originally made our food. If plants, algae, and autotrophic bacteria vanished from earth, animals, fungi, and other heterotrophs would soon disappear as well. All life requires a constant input of energy. Only autotrophs can transform that ultimate, solar source into the chemical energy in food that powers life.
Chemosynthesis, process in which carbohydrates are manufactured from carbon dioxide and water using chemical nutrients as the energy source, rather than the sunlight used for energy in photosynthesis. Most life on earth is fueled directly or indirectly by sunlight. There are, however, certain groups of bacteria, referred to as chemosynthetic autotrophs, that are fueled not by the sun but by the oxidation of simple inorganic chemicals, such as sulfates or ammonia. Chemosynthetic autotrophs are a necessary part of the nitrogen cycle. Some groups of these bacteria are well suited to conditions that would have existed on the earth billions of years ago, leading some to postulate that these are living representatives of the earliest life on earth.
This view has been supported by the discovery of small ecosystems that thrive in the hot (350°C/660°F) water found around hydrothermal vents on the ocean floor. In these ecosystems, the primary producers in the food web are bacteria whose life functions are fueled by inorganic chemicals that seep up from the earth’s crust.