1. Exit Choose to view chapter section with a click on the section heading. ►The Nature of LifeThe Nature of Life ►How Energy Enters Living SystemsHow Energy Enters Living Systems ►The Ocean’s Primary ProductivityThe Ocean’s Primary Productivity ►Energy Flow Through the BiosphereEnergy Flow Through the Biosphere Chapter Topic Menu

2. MenuPreviousNext 4 - 2 The Nature of Life Theoretical physicist Stephen Hawking: “The laws of science do not distinguish between the past and the future. In order to survive, human beings have to consume food which is an ordered form of energy, and convert it into heat, which is a disordered form of energy… The progress of the human race in understanding the universe has established a small corner of order in an increasingly disordered universe.”  This principle of physics called entropy, or randomness, appears to be the driving force of all life in our universe. nDefining life appears simple if you compare a fish and a rock. From a scientific point of view, it’s not quite so cut-and-dried. Often life and nonlife share the same elements: matter, carbon atoms and energy reactions. nEnergy reactions found in living systems also exist outside of life. For example: fire results when a reaction releases chemical energy within substances. Living systems use energy similarly – by releasing chemical energy for life processes. nAll life uses energy. Therefore it is possible to define “life” based on the characteristics living systems have apart from nonliving systems with respect to energy use. The Nature of Life Chapter 4 Pages 4-2 & 4-3

3. MenuPreviousNext 4 - 3 Elements Essential for Life The Nature of Life Chapter 4 Page 4-3

4. MenuPreviousNext 4 - 4 Matter and Energy nLife requires matter and energy to exist. All living organisms are composed of about 13 of 118 known elements from the periodic table.  Carbon, hydrogen, oxygen, and nitrogen account for 99% of the mass. Nine other elements account for the remaining 1%. These elements, in combinations, account for all biological chemicals. nScientists recognize more than 1.6 million different species, as many as 30 million may exist. nDespite this huge number, all organisms organize matter into biological chemicals and into cells.  A cell is the smallest whole structure that can be defined as a living system.  Organisms can consist of a single cell or billions of codependent cells. nAll life organizes matter into cells. The Nature of Life Chapter 4 Pages 4-3 & 4-4

5. MenuPreviousNext 4 - 5 Matter and Energy (continued) nThe first law of thermodynamics states that energy can be transferred from one system to another in many forms. However, it cannot be created nor destroyed.  Energy is defined as the capacity to do work.  Energy is necessary for life because living systems use it to accomplish the processes of life: reproduction, growth, movement, eating, etc.  Organisms need energy to help break down complex molecules into simple molecules. They need more energy to build distinct complex molecules from simple molecules.  Organisms cannot create energy – but can use it to perform useful work. Living systems must acquire energy from outside sources. The Nature of Life Chapter 4 Pages 4-4 & 4-5

6. MenuPreviousNext 4 - 6 Entropy nThe second law of thermodynamics states that disorder increases with time and eventually all energy and matter will be distributed evenly.  Entropy is the measure of how much unavailable energy exists in a system due to even distribution. High entropy = low organization and low energy potential.  Living systems use energy to create order and to gather and store potential energy. The increased order is local and temporary, and requires more energy to create than it retains. Here, matter exists in a low-entropy (organized) state.  Example: About 85% of the energy required to organize protein into complex muscle tissue is ultimately lost as heat in creating the tissue. The Nature of Life Chapter 4 Pages 4-4 & 4-6

7. MenuPreviousNext 4 - 7 Autotrophy and Heterotrophy nTerrestrial and most marine organisms get their energy directly or indirectly from the sun. nAutotrophy is the process of self-feeding by creating energy-rich compounds called carbohydrates.  Autotrophs obtain energy from the sun or chemical processes.  They do this by converting the energy from sunlight and inorganic compounds into carbohydrates. Plants are autotrophs. nMany organisms, including virtually all animals, cannot produce their own carbohydrates. These organisms get their energy and matter by consuming other organisms. This is called heterotrophy.  Heterotrophs are organisms that rely on other organisms for sources of energy.  We are heterotrophs. Humans rely on photosynthesizing plants, bacteria, and other micro-organisms for life.  This is one reason why the health of the natural environment is a crucial issue. How Matter and Energy Enter Living Systems Chapter 4 Page 4-7

8. MenuPreviousNext 4 - 8 Respiration nWhether an organism is an autotroph or a heterotroph, it must convert carbohydrates into usable energy. nOrganisms use oxygen to engage in cellular respiration. nRespiration is the process of releasing energy from carbohydrates to perform the functions of life. (This is not the same as breathing.)  The chemical process for respiration is: How Matter and Energy Enter Living Systems Chapter 4 Pages 4-7 & 4-8

9. MenuPreviousNext 4 - 9 Photosynthesis nBecause they create energy-rich compounds, autotrophs are also known as primary producers. nPrimary producers combine energy from sunlight with inorganic materials to form energy-right organic compounds.  Conduit through which the biosphere gets almost all its energy.  Organisms with chlorophyll are the majority of primary producers. nChlorophyll allows for the collection of sunlight. nThe process of using light energy to create carbohydrates from inorganic compounds is called photosynthesis.  Because carbon dioxide and water have more oxygen than is needed, the process also releases oxygen.  Without photosynthesis we would not have the oxygen we need to breathe. How Matter and Energy Enter Living Systems Chapter 4 Page 4-9

10. MenuPreviousNext 4 - 10 Photosynthesis (continued) nNote that even organisms with chlorophyll respire. If you look at photosynthesis you can see it is a complementary process to respiration. nThe chemical process for photosynthesis is: nAerobic respiration meaning respiration that uses oxygen. nAnaerobic respiration releases energy through chemical reactions that do not require oxygen.  Anaerobic respiration is not as efficient as aerobic respiration. How Matter and Energy Enter Living Systems Chapter 4 Pages 4-9 & 4-10

11. MenuPreviousNext 4 - 11 Chemosynthesis nChemosynthesis is the process of using chemicals to create energy-rich organic compounds.  It is similar to photosynthesis because it produces carbohydrates.  Chemosynthesis differs from photosynthesis; it does not use sunlight as an energy source, it uses chemical energy within inorganic compounds. nChemosynthetic organisms are primary producers.  Fixation is the process of converting, or fixing, an inorganic compound into an organic compound. nIn 1977, there was an important discovery of a major biological community in the deep ocean relying on chemosynthesis.  These communities use chemical energy from minerals in the hot spring water coming from the hydrothermal vents. How Matter and Energy Enter Living Systems Chapter 4 Pages 4-11 & 4-12

12. MenuPreviousNext 4 - 12 Marine Biomass nThe main “products” of primary production are carbohydrates.  Scientists measure primary productivity in terms of the carbon fixed (bound) into organic materials. nBiomass is the mass of living tissue. The biomass at a given time is called the standing crop.  Example: The average standing crop in the oceans is 1-2 billion metric tons. On land, the average standing crop is 600 to 1,000 billion metric tons. nComparing primary productivity of the seas to that of the land, the land’s primary production is slightly higher.  How is it possible that the total primary production from marine ecosystems is only a bit less than that of terrestrial ecosystems? – marine ecosystems cycle their energy and nutrients much more rapidly. The Ocean’s Primary Productivity Chapter 4 Pages 4-13 to 4-15

13. MenuPreviousNext 4 - 13 Plankton nThe term “plankton” does not describe a kind of organism, but a group of organisms with a common lifestyle and habitat. Plankton include autotrophs, heterotrophs, predators and grazers.  Plankton drift/swim weakly at the mercy of water motion.  Plankton are not a species, but include many species.  Most are very small, some, like the jellyfish, grow several meters long.  Some start life as planktonic larvae and then become nektonic organisms that swim or attach themselves to the bottom as benthic organisms.  Meroplankton live part of their lives as plankton.  Holoplankton remain plankton all their life. nPhytoplankton are primary producers responsible for more than 92% of marine production. nZooplankton are primary and secondary consumers of other plankton. Chapter 4 Pages 4-15 & 4-16 The Ocean’s Primary Productivity

14. MenuPreviousNext 4 - 14 Plankton (continued) nFour most important kinds of phytoplankton:  1. Diatoms are the most dominant and efficient photosynthesizers known. nThey convert more than 50% of the light energy they absorb into carbohydrate chemical energy. They have a rigid cell wall made of silica called a frustule which admits light. This is an ideal cell material for a photosynthesizer.  2. Dinoflagellates are characterized by one or two whip-like flagella which they use to move in water. nMost are autotrophs. They are the most significant primary producers in coral reefs. They are also the principal organisms responsible for plankton blooms.  3. Coccolithophores are single-cell autotrophs characterized by shells of calcium carbonate. nThey live in bright shallow water.  4. Silicoflagellates are micro-organisms with internal support structures made of silica and have one or more flagella. nThey are structurally and chemically more primitive than diatoms. Chapter 4 Pages 4-17 & 4-18 The Ocean’s Primary Productivity

15. MenuPreviousNext 4 - 15 Plankton (continued) nUnderstanding the role of picoplankton has changed the way marine biologists think about tropical region productivity.  Picoplankton are extremely tiny plankton.  May account for up to 79% of the photosynthesis in tropical waters.  Many are cyanophytes, which are bacteria with chlorophyll.  Can also be called cyanobacteria or blue-green algae.  Their role in primary productivity is to be food for heterotrophic bacteria.  They may also play a significant role in producing oxygen and taking up carbon dioxide. Chapter 4 Pages 4-18 The Ocean’s Primary Productivity

16. MenuPreviousNext 4 - 16 Limits on Marine Primary Productivity nLimiting factors are physiological or biological necessities that restrict survival. Too much or too little of a limiting factor will reduce population. nLimiting factors in the ocean include:  Inorganic nutrients such as nitrogen and phosphorus compounds.  Sunlight due to season, depth, or water clarity. nTropical waters have low productivity.  Warm upper water act to trap nutrients in the cold layers that are too deep for photosynthesizing autotrophs. nThe Arctic and Antarctic have little temperature difference allowing nutrients to cycle to shallower water. nTemperate regions, coastal areas, have more primary productivity due to more nutrients from rain runoff.  Shallow water keeps them from sinking too deep. nAreas of highest productivity are in the Antarctic Convergence Zone and near shore temperate regions due to nutrient availability. Chapter 4 Pages 4-19 to 4-21 The Ocean’s Primary Productivity

17. MenuPreviousNext 4 - 17 Limits on Marine Primary Productivity (continued) nLight is an important limiting factor.  The amount of daylight affects photo- synthesis and primary productivity. For example, the Antarctic Convergence Zone has optimum nutrients available, seasonal sunlight limits its productivity. nDepth is a limiting factor too.  Depth affects photosynthesis and primary productivity. Suspended particles and the light’s angle limit how much light penetrates water. Even in very clear water, very little photosynthesis takes place below 100 meters (328 feet).  Too much light can be bad too. Photo- inhibition takes place when too much light overwhelms an autotroph. It cannot photo- synthesize when water is too shallow. The Ocean’s Primary Productivity Chapter 4 Page 4-21

18. MenuPreviousNext 4 - 18 Limits on Marine Primary Productivity (continued) nDifferent phytoplankton species have different optimal depths.  As light conditions change, the advantage shifts from species to species. nAutotrophs produce carbohydrates and oxygen, but they also respire.  They use carbohydrates and some oxygen for respiration. The less light, the less photosynthesis and the less carbohydrates are produced. nAt some point, the amount of carbohydrates produced exactly equals the amount required by the autotrophs for respiration. nThe point of zero net primary production is called the compensation depth.  This is the depth at which about 1% of the surface light penetrates.  If phytoplankton remain below compensation depth, they will die within a few days. The Ocean’s Primary Productivity Chapter 4 Page 4-22

19. MenuPreviousNext 4 - 19 Trophic Relationships nThe hierarchy of what-eats-what can be illustrated with a trophic pyramid.  It is a representation of how energy transfers as they consume each other. nPrimary producers, mainly photosynthesizers, make up the base. Most of these are plants. In the ocean, phytoplankton are primary producers.  Primary consumers, the first level of heterotrophs, eat the primary producers. Most of these are herbivores (animals that eat plants). In the ocean, zooplankton are primary consumers. nSecondary consumers, eat primary consumers. nEach level eats the level below and has significantly less biomass (living matter) than the level it eats. Energy Loss Through Trophic Levels nOnly about 10% of the energy transfers from one level to the next, so each level is about a tenth of the size of the level underneath. 90% of the energy is lost to entropy. Energy Flow Through the Biosphere Chapter 4 Pages 4-24 to 4-26

20. MenuPreviousNext 4 - 20 Food Webs and Decomposition nA food web is a way to illustrate different levels of consumers and energy flow. In real life, organisms consume across levels, not just below. The food web better represents the flow of energy through consumption in nature. nDecomposers break down organic material into inorganic form. They take out the very last usable energy from organic matter to sustain themselves.  Decomposers are primarily bacteria and fungi, their job is to convert dead organisms into the compounds primary producers use.  Bacteria are the most important decomposers.  Decomposition is important because it completes the materials cycle.  Within systems, energy flows and matter cycles. Energy Flow Through the Biosphere Chapter 4 Pages 4-27 & 4-28