Energy is the ability to do work. In organisms, this work can be physical work, like walking or jumping, or it can be the work used to carry out the chemical processes in their cells. Every biochemical reaction that occurs in an organisms cells needs energy. All organisms need a constant supply of energy to stay alive. Some organisms can get the energy directly from the sun. Other organisms get their energy from other organisms. Through predator-prey relationships, the energy of one organism is passed on to another. Energy is constantly flowing through a community. With just a few exceptions, all life on Earth depends on the suns energy for survival. The energy of the sun is first captured by producers ( Figure 1.1), organisms that can make their own food. Many producers make their own food through the process of photosynthesis. The "food" the producers make is the sugar, glucose. Producers make food for the rest of the ecosystem. As energy is not recycled, energy must consistently be captured by producers. This energy is then passed on to the organisms that eat the producers, and then to the organisms that eat those organisms, and so on. Recall that the only required ingredients needed for photosynthesis are sunlight, carbon dioxide (CO2 ), and wa- ter (H2 O). From these simple inorganic ingredients, photosynthetic organisms produce the carbohydrate glucose (C6 H12 O6 ), and other complex organic compounds. Essentially, these producers are changing the energy from the sunlight into a usable form of energy. They are also making the oxygen that we breathe. Oxygen is a waste product of photosynthesis. The survival of every ecosystem is dependent on the producers. Without producers capturing the energy from the sun and turning it into glucose, an ecosystem could not exist. On land, plants are the dominant producers. Phytoplankton, tiny photosynthetic organisms, are the most common producers in the oceans and lakes. Algae, which is the green layer you might see floating on a pond, are an example of phytoplankton. There are also bacteria that use chemical processes to produce food. They get their energy from sources other than the sun, but they are still called producers. This process is known as chemosynthesis, and is common in ecosystems without sunlight, such as certain marine ecosystems. Producers include (a) plants, (b) algae, and (c) diatoms.


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most producers make glucose through photosynthesis.

-->  a. true

b. false

energy is recycled through an ecosystem.

a. true

-->  b. false

what is the chemical formula of glucose?

a) c8h12o8

b) c6h6o6

-->  c) c6h12o6

d) c12h6o12

what are the necessary ingredients for photosynthesis?

a) sunlight, carbon dioxide and oxygen

-->  b) sunlight, carbon dioxide and water

c) sunlight, oxygen and water

d) sunlight only

what are the most common producers in the ocean?

-->  a) phytoplankton

b) seaweed

c) marine plants

d) bacteria

how is food produced in ecosystems without sunlight?

a) by photosynthesis

b) by phytoplankton

-->  c) by chemosynthesis

d) by autosynthesis

essentially, almost all energy on earth originates from

a) plants.

-->  b) the sun.

c) photosynthesis.

d) food.

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