Chapter 2 BSCS

LIFE AND ENERGY

See p. 52 table 2.1 add

-made of cells

to #2 add takes energy to maintain high degree of chemical organization...

All chemical bonds contain energy depending on the “energy level” of the shared electrons; some bonds have more energy than others. When bonds are broken, energy is usually released and when bonds are made, energy is usually required.

All cells have enzymes (a type of protein), which can help make (anabolism) or break (catabolism) bonds. Together, the building or anabolic reactions and the breakdown reactions or catabolic ones, are called metabolism.

To get the activation energy for a cell’s reactions, organisms typically break the bonds of a molecule called Adenosine Tri Phosphate (ATP the “energy currency of life”) forming ADP + P. See pg. 65. Cells can store only small amounts of ATP, yet they use HUGE amounts. The answer to this paradox is that cells can also quickly rebuild the ADP + P back into ATP. The energy to do this, is released during the breakdown of organic compounds, while glucose, lipids and proteins are all used it is mainly glucose, some lipids and finally a small percent of proteins. So, cells use ATP for their activation energy but need carbohydrates/glucose for the energy to rebuild ADP + P back into ATP.

This process of using the energy in organic molecules to produce more ATP from ADP and P is called cellular respiration. In an ATP molecule, the last two phosphate groups are held by very special high-energy covalent bonds. Cells usually only break off the last P of ATP, releasing energy. Some of this released energy is useful and causes chemical reactions (activation energy) but most is heat energy. In other words, organisms constantly break down ATP to ADP and P for some activation energy. SLOW DOWN, REREAD THIS! DO YOU HAVE QUESTIONS? ASK ME.

Living cells can only do chemical reactions. No more, no less. All cellular work: growth, repair, cell division, cellular movement, synthesis of macromolecules such as: carbohydrates, proteins, lipids and nucleic acids, are the result of chemical reactions. The activation energy for all these biochemical reactions comes ONLY from the breakdown of ATP.

One characteristic of a living organism is to obtain glucose. This is more or less what your book means with its first entry in Table 2.1 on page 52. Look at this table again.

Two things can happen to any food molecule (carbohydrate/lipid/protein) it will either be broken apart during cellular respiration to make more ATP or it will be used or rearranged, to make the organism’s needed compounds, we are what we eat. Organisms can obtain their glucose in one of two ways:

1. Producers or Autotrophs - As explained above, all organisms break glucose down to remake ATP (cellular respiration). They then break ATP for activation energy. What makes autotrophs different is that they can make or produce their own glucose. All the plants, some protists and some bacteria are producers.

These producers take in the inorganic compounds carbon dioxide and water, then using solar energy and their wonderful enzymes, rearrange the atoms of carbon dioxide and water into the carbohydrate glucose and then they can change glucose along with other molecules from the soil into, the other organic compounds. The reaction that makes glucose using the sun’s energy is called photosynthesis. Producers also need a variety of inorganic nutrients, such as phosphates and nitrates. We can buy these inorganic nutrients: phosphates, nitrates, etc. at the Home Depot. They are called fertilizer! Autotrophs that photosynthesize are also called photoautotrophs.

Most producers are photoautotrophs; a few producers don’t use the sun’s energy to rearrange carbon dioxide and water’s atoms but use chemicals such as hydrogen sulfide (H₂S). They are called chemoautotrophs.

2. Consumers or Heterotrophs - these organisms also of course perform cellular respiration but they can’t make their own glucose like the producers. They go out and “steal” glucose, they eat other organisms. That’s you! Animals, fungi (mushrooms), the other unicellular protists and the non-autotrophic bacteria are all Consumers.

Some types of consumers are also called Decomposers- All the fungi, consumer bacteria and some insects produce waste products which include molecules such as; nitrates and phosphates, that provide the plants (photoautotrophs) with the phosphorus, sulfur, nitrogen, and other trace elements make their other organic and inorganic molecules. These types of consumers are also called Decomposers. See p. 57 figure 2.6

Decomposers make things “rot”. It might look and smell disgusting but the plants and other producers need these decomposer waste products such as those nitrates and phosphates. Consumers (just like you) need the producers!

All the organisms (producer and consumer) in an area (pond, lawn, forest, ocean, etc.) are called biotic. The relationships are called a food web. All consumers rely directly or indirectly on the producers for their organic compounds. Remember the consumed organic compounds (carbohydrates, lipids, proteins, nucleic acids) that are eaten will either be used for cellular respiration (activation energy to drive the reactions of life) or to make the consumer’s compounds. The producers (at least the photoautotrophs) rely on the sun for their original source of energy, and their consumers rely on the producer’s molecules. So...... ultimately most organisms directly or indirectly rely on the SUN. See p. 57 figure 2.6 The producers rely on the decomposers to change the once living organism’s organic material back into the inorganic fertilizers/nutrients.

The materials/matter/atoms, get recycled within an ecosystem’s food web. The decomposers redistribute materials/matter/atoms back to the producers, consumers eat the plants, decomposers “eat” everything and round and round it goes. It is a cycle.

The atoms in all of our molecules are just borrowed. Because of fungi, bacteria and some insects someday you too will decompose. Then a plant or other producer will make its molecules, cells and tissues with those atoms and the cycle will continue. Guess what? Your atoms came from the food you ate and have been in organisms that have lived and died more times than we can count.

Look again at figure 2.6. The atoms eventually just go around and around, from organism to organism, that is what recycled means.

All the nonliving items; soil, water, atmosphere, plant nutrients, temperature, etc. in that area are called abiotic. Together the abiotic and biotic are called the ECOSYSTEM. Together all the ecosystems on this planet are called the BIOSPHERE.

While materials/matter/atoms cycle within the ecosystems, ENERGY does NOT cycle, it flows. Most ecosystems rely on solar energy being converted to chemical energy by photosynthesis’ production of carbohydrates. This energy flows from the sun to the photoautotroph to the consumers. Some of an organism’s available energy ( about 40%) will be used to create the activation energy to cause biochemical reactions; to move, grow, eat, digest, reproduce, heal, stay organized, in other words; to live. But most (about 60%) of its energy is converted to heat.

Let’s be gross and disgusting and say that there is a cute little fox minding its own business and along comes a very hungry and dangerous bunny, which eats the fox. The bunny will only on average gain about 10% of those fox calories/energy units for its own activation energy. What happens to the rest? Well, a rather large amount of the fox was not actually eaten (bones, fur, leftovers) then a good amount of the fox that was eaten was not actually digested but ends up going out pretty much as it went in, what we officially call “bunny poop”, and then about 60% of what did get digested is released as heat, leaving about 10% of the energy in the original fox tissues actually being used by the bunny that eats it. Only 10% of the energy in that first order or primary consumer can be used by the second level or secondary consumer etc. This is called the 10% rule. It is not entirely accurate but is as good of guesstimate as we have.

The sun’s light energy is the ultimate source for most of the biosphere’s biotic members. Remember some ecosystems are dependent on chemoautotrophs and not reliant on sunlight. Regardless if the producers are chemoautotrophs or photoautotrophs the energy within the ecosystem flows, meaning it does not get back to its origin. As an example, the sun’s energy that powers photosynthesis never gets back to the sun, it is NOT recycled. Look again at figure 2.6. That is why we say “energy flows”. Without the sun’s energy photoautotrophs cannot build their organic compounds (glucose, etc.). It is these organic compounds that all life depends on for both cellular respiration and to build other macromolecules. When our sun’s energy runs out in a few billion years, that’s the end of life on our planet.

Look at p. 637, figure 24.4 for a picture of this 10% transfer of energy between different levels of a food web. The different consumer levels are referred to as trophic levels. We call the consumers that eat producers, first order consumers or primary consumers. Those that eat the primary consumers are second order or secondary consumers. Anybody want to guess what the consumer that eats a second order consumer is called? YOU SO SMART- THIRD ORDER OR TERTIARY CONSUMER! What are you being when you eat cows? hmmmmmm....... well, Mr. Johnson, since the cow is the first order consumer and I eat the cow, that makes me a second order consumer! Most land based/terrestrial food chains never go above third order consumer. Not enough of the original energy from the sun left to make enough fourth order consumers. Think about it. Mass (weigh) all the producers (grass, weeds, trees) that are found in the Parker lawn. That would be the producer biomass. Now calculate the biomass of all the bugs, worms, etc. that eat the grass and it would be roughly 10% of the producer biomass. The biomass of the birds, that eat the bugs and worms would only be about 10% of that. So, in this case, the biomass of the birds, which the producers can keep alive/support, is only about 1% of the original biomass of the producers. Grass to bugs was 10%, bugs to birds is 10%. 10% of 10% is 1%! And if you must know, since the oceans are sooooooo darn big, a very small number of its food chains do go higher than third order, but very few and those don’t go far above that.