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How Does Life Work?

Biosphere Process

Photosynthesis: How Life Feeds


Photosynthesis is the process of making food, on which all life depends. "Photo" means "light"; "synthesis" means "putting together," so the word means "putting together with light." It all begins with energy. Earth continuously receives two enormous kinds of energy from the sun: Light and Heat (infra-red).

Photosynthesis is life's greatest invention. It began in the ocean. Tiny early bacteria discovered that by using this new process, they could feed themselves instead of having to eat other bacteria.

The food it learned to make is called a carbohydrate, or simple sugar. It uses light for energy plus water plus carbon dioxide. This is the way it's written in chemistry:

12H2O + 12CO2 ---------->>>>>C6H10O5 + O2





water + carbon dioxide sucrose
+ oxygen

That is, water (H2O) plus carbon dioxide (CO2) combined in a chloroplast in the presence of light results in f sugar (C12H22O11) plus oxygen (O2). The oxygen is a by-product, or leftover. Or waste. This 'waste' oxygen, generated by countless billions of photosynthetic bacteria and archaea for millions of years, created the oxygen atmosphere that allows animals to breathe.

This description of photosynthesis is vastly simplified. In truth, it is much more complex. There are dozens of steps or stages in the process, and more subtle chemical changes than are shown above. Mineral nutrients dissolved in water are also necessary. A little of the light energy is used to create proteins and fatty acids in different kinds of photosynthesis.

Plant cells, like other eucaryotes (protists fungi and animals), evolved through symbiosis, that is, two or more organisms combining to make a new kind of cell. They combined by engulfing (swallowing) each other. We know this because chloroplasts and mitochondria have their own bacteria-style DNA, which is quite different from the DNA in the cell nucleus. Animal cells contain two kinds of DNA: nuclear DNA (which contains the genetic heritage of the species) and mitochondrial DNA (mitochondria are the "power generators" in every cell). Plant cells contain three kinds of DNA, the same two that animals have, plus chloroplast DNA. Plant cells, in other words, are the result of two symbiosis events, one to contain mitochondria, and one to contain chloroplasts.

Plant leaves get carbon dioxide from the air by opening tiny pores called stoma. This one is on a corn leaf. The two yellow cells are the guard cells that open and close the hole. Keeping the stoma open requires plentiful water available for transpiration. If stomas close, no carbon dioxide enters and photosynthesis stops.




Here is the basic sequence of  plant photosynthesis: 

  The plant "inhales" carbon dioxide through its leaves.
  The plant "soaks up" sunlight through its leaves.
  The plant pulls in water and dissolved mineral nutrients through its roots and mcorrhizal fungi partner.
  With its sap, the plant circulates carbon dioxide and water and dissolved minerals to every cell
  Each cell then produces food, using carbon dioxide and water 
plus sunlight. Photosynthesis produces oxygen as a by-product or leftover.  
  A little of the leftover oxygen is used by the plant for respiration (energy-making); most of the oxygen is released into the air.

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Biosphere: Introduction
Biosphere as Place: Introduction
Biosphere as Ocean: Life Zones
Biosphere as Ocean Floor: Benthic Biomes One
Biosphere as Ocean Floor: Benthic Biomes Two
Biosphere on Land: Terrestrial Biomes
Biosphere on Land: Anthropogenic Biomes
Biosphere as Process: Introduction
Biosphere Process: Floating Continents, Tectonic Plates
Biosphere Process: Photosynthesis
Biosphere Process: Life Helps Make Earth's Crust
Biosphere Process:
Rock Cycle--Marriage of Water and Rock
Biosphere Process: Marriage of Wind and Water
Biosphere Process: Gas Exchange
Biosphere as An Expression of Spirit
The Ecological Function of Art
The Earth Goddess
The Tree of Life
The Green Man
Earth Art
Biosphere as Community
Biosphere Microcosm: Bacteria and Archaea
The Procaryote Domain
Biosphere Microcosm: Germs
Biosphere Community: The Eucaryote Domain
Biosphere Community: Protists 1: Algae
  Biosphere Community: Protists 2: Protozoa
Biosphere Community: Plants: What's New?
Biosphere Community: Plant Diversity--Major Groups
Biosphere Community: Plant Defense
Biosphere Community: Plant Pollination
Biosphere Community: Plant Seed Dispersal
Biosphere Community: Kingdom Animals
Biosphere Community: Kingdom Fungi
Biosphere Community: Six Great Extinctions
Return to Ecology Index