Fundamentally, most eucaryotes produce energy (ATP) through alcoholfermentation (e.g. yeast), lactic acid fermentation (e.g. muscle cells,neutrophils), aerobic respiration (e.g. molds, protozoa, animals) oroxygenicphotosynthesis (e.g. algae, plants). These modes of energy-generatingmetabolismexist among procaryotes, in addition to all the following types ofenergyproductionwhich are virtually non existent in eucaryotes.

productivity comes from algae and the other photosynthetic prokaryotes.

The first step in in all living cells is , which can take place without the presence of molecular oxygen. If oxygen is present in the cell, then the cell can subsequently take advantage of via the to produce much more usable energy in the form of than any anaerobic pathway. Nevertheless, the anaerobic pathways are important and are the sole source of ATP for many anaerobic bacteria. Eukaryotic cells also resort to anaerobic pathways if their oxygen supply is low. For example, when muscle cells are working very hard and exhaust their oxygen supply, they utilize the anaerobic pathway to lactic acid to continue to provide ATP for cell function.

Glossary of Terms: P - Geography : Physical Geography

Introduction Photosynthesis occurs only in the presence of light, and takes place in the chloroplasts of green plant cells....

For photosynthesis to occur, plants need: · Light energy from the sun · Chlorophyll to absorb light energy · Carbon dioxide from the atmosphere and from respiration in plant cells · Water which is absorbed by the roots and transported to the leaves by the xylem tubes....

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Cyanobacteria are,which are known to be the earliest forms of life, throughout time theyhave adapted to the changing earth, and in turn help it evolve. Prokaryotesbelong to the kingdom (Greek for single) and are small celledorganisms that lack membrane-enclosed organelles. They havecell walls, but their composition differs from those of plants, protisitsand fungi. They are similar to , but they have smallerand simpler genomes, and differ in genetic replication, protein synthesis,and recombination. Prokaryotes are photosyntheticand aquatic and can exist in almost any environment, and individually theirimpact may be microscopic, but collectively their impact on the earth isimmense.

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The heterocysts fix nitrogen
into ammonium ions which diffuse to neighbouring vegetative cells via the microplasmodesmata, at least some of
this ammonium combines with the glutamate to form the amino acid glutamine which is then exported to the
vegetative cells (which process the glutamine by removing the nitrogen and turning it back into glutamate).

Only cyanobacteria and some other forms of bacteria can fix nitrogen.