Energy Flow Through Organisms and Ecosystems
Living organisms need a constant supply of energy to stay alive. At the most basic level, energy is required to drive many of the chemical reactions that take place within living cells. If these metabolic reactions stop, then all of the cell's activities stop and it dies. In mammals, large amounts of energy are required to maintain body temperature above that of our surroundings. Inside every cell, the immediate source of energy is ATP or adenosine triphosphate. ATP is the energy 'currency' of a cell. Astonishing amounts of ATP are made every day. When energy is required, the ATP is broken down by hydrolysis and its energy used for whatever the cell needs.
The source of energy for making ATP is other organic molecules such as carbohydrates, lipids, and proteins. These molecules are high in energy which can be released and used to make ATP as they are broken down in the process of respiration. Respiration happens in every living cell, and its whole purpose is to make ATP.
Energy storage in carbohydrates, lipids, and proteins is achieved inside the mesophyll cells of plant leaves. Here, sunlight is captured by chlorophyll in the chloroplasts and is used to supply energy to drive the reactions of photosynthesis. Carbon dioxide from the air and water drawn from the soil react together to produce carbohydrates and, in the process, energy is transferred from sunlight and converted into chemical energy in the carbohydrate molecules. The plant uses these carbohydrate molecules. The plant uses these carbohydrate molecules to make lipids and proteins which also contain some of this energy. When the plant requires energy for its metabolism, it breaks down some of these molecules in respiration and makes ATP.
This is how all living organisms get their energy. Photosynthesis in plants converts sunlight energy into chemical energy in organic molecules. Animals eat plants, obtaining some of this chemical energy in the molecules they take in. Plants and animals then break down these organic molecules in respiration transferring energy to ATP molecules. The ATP can then itself be broken down to release its energy for use in metabolic reactions.
Green plants and other photosynthetic organisms are producers. These other organisms that consume the organic chemicals made by plants are consumers.
Food Chains and Food Webs
The way in which energy flows from producer to consumers can be shown by drawing a food chain. Arrows in the food chain indicate the direction in which the energy flows. In a typical food chain, the is a producer, a primary consumer, a secondary consumer, and a tertiary consumer. These different positions in a food chain are called trophic levels. The interrelationships between many food chains can be drawn as a food web. The food web also shows the importance of a group of organisms called decomposers. Most decomposers live in the soil, and their role in an ecosystem is to feed on detritus (dead organisms and waste material). Decomposers include many bacteria, fungi, and also some larger animals. Sometimes, the term 'decomposer' is used only for bacteria and fungi, which feed saprotrophically, while larger animals are called detritivores.
The source of energy for making ATP is other organic molecules such as carbohydrates, lipids, and proteins. These molecules are high in energy which can be released and used to make ATP as they are broken down in the process of respiration. Respiration happens in every living cell, and its whole purpose is to make ATP.
Energy storage in carbohydrates, lipids, and proteins is achieved inside the mesophyll cells of plant leaves. Here, sunlight is captured by chlorophyll in the chloroplasts and is used to supply energy to drive the reactions of photosynthesis. Carbon dioxide from the air and water drawn from the soil react together to produce carbohydrates and, in the process, energy is transferred from sunlight and converted into chemical energy in the carbohydrate molecules. The plant uses these carbohydrate molecules. The plant uses these carbohydrate molecules to make lipids and proteins which also contain some of this energy. When the plant requires energy for its metabolism, it breaks down some of these molecules in respiration and makes ATP.
This is how all living organisms get their energy. Photosynthesis in plants converts sunlight energy into chemical energy in organic molecules. Animals eat plants, obtaining some of this chemical energy in the molecules they take in. Plants and animals then break down these organic molecules in respiration transferring energy to ATP molecules. The ATP can then itself be broken down to release its energy for use in metabolic reactions.
Green plants and other photosynthetic organisms are producers. These other organisms that consume the organic chemicals made by plants are consumers.
Food Chains and Food Webs
The way in which energy flows from producer to consumers can be shown by drawing a food chain. Arrows in the food chain indicate the direction in which the energy flows. In a typical food chain, the is a producer, a primary consumer, a secondary consumer, and a tertiary consumer. These different positions in a food chain are called trophic levels. The interrelationships between many food chains can be drawn as a food web. The food web also shows the importance of a group of organisms called decomposers. Most decomposers live in the soil, and their role in an ecosystem is to feed on detritus (dead organisms and waste material). Decomposers include many bacteria, fungi, and also some larger animals. Sometimes, the term 'decomposer' is used only for bacteria and fungi, which feed saprotrophically, while larger animals are called detritivores.
Energy losses along food chain
Whenever energy is transferred from one form, or from one system, to another some is always lost as heat. As energy passes along a food chain large losses from the food chain occur at each transfer, both within and between organisms. The reasons for the small percentage of sunlight that is converted into chemical energy include:
Whenever energy is transferred from one form, or from one system, to another some is always lost as heat. As energy passes along a food chain large losses from the food chain occur at each transfer, both within and between organisms. The reasons for the small percentage of sunlight that is converted into chemical energy include:
- Some sunlight misses leaves entirely, and falling onto the ground or other non-photosynthesizing surfaces;
- Some sunlight being reflected from the surfaces of leaves;
- Some sunlight passing through leaves, without being trapped by the chlorophyll molecules;
- Only certain wavelengths of light being absorbed by chlorophyll;
- Energy losses as energy absorbed by chlorophyll is transferred to carbohydrates during photosynthesis.
- not all parts of the plants are eatable such as woody tissues and some roots;
- not all of the parts of the plants eaten are digestible, sot that not all of the molecules can be absorbed and used by the primary consumer;
- energy losses as heat within the consumer's digestive system, as food is digested.