Biology 100/101
Lecture 5: Ecosystems: Energy and Matter
(Print Version)

Announcements &
Assignments

Lecture Objectives

Web Resources

Matter & Energy

Energy Producing
Reactions

Energy Using
Reactions

Energy Flow

Lecture Activity

Food Webs

Decomposition &
Matter Cycling

Greenhouse
Effect

Lecture Syllabus

IB 100/101 Home Page

Announcements & Assignments

Answers to many of these questions can be found at the Text On-Line Learning Center

You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Ross and Ed" discussion.

Objectives

After studying this material you should be able to:

1. Describe the means by which autotrophs and heterotrophs obtain energy and matter from their environment.
2. Describe the roles of primary producers, herbivores, carnivores, and decomposers in the energy flow and nutrient cycling of an ecosystem.
3. Explain how the concepts in the table below play an integral part in the growth and reproduction of individuals and the energy flow and nutrient cycling of an ecosystem.

Photosynthesis	Respiration
Biosynthesis (Anabolism)	Net Primary Production
Biomass	Decomposition

4. Define and explain the distinction between the terms "energy flow" and "nutrient cycling" in an ecosystem.
5. Apply the terms "energy flow" and "nutrient cycling" to an explanation of the "energy pyramid" or the concept of "the rule of tens."
6. Describe the role of each of the concepts listed in objective #3 in the global carbon cycle.

Web Resources

General overview of the carbon cycle

The World Resources Institute

Life is made up of matter and energy

What are you made of?

Where does your energy come from?

How do you use it?

• Anybody eat Cheerios for breakfast?
• What about a Breakfast burrito??
• Nutrition Facts listing on food labels indicates nutrients that address today's health concerns.
• Overview of Chemical Digestion. Figure: Lewis et al., Life, Fig. 37.11, pg. 742
• METABOLISM: all the biochemical reactions within cells that acquire and use energy.
• Catabolism (degradation) refers to metabolic pathways that break down large molecules into smaller ones, which release energy. That energy which isn't released as heat is stored temporarily in a high energy molecule called ATP (adenosine triphosphate) until it is required. Figure: Lewis et al., Life, Fig. 5.9, pg. 88
• Anabolism (biosynthesis) refers to metabolic reactions that use energy to synthesize new compounds. A typical adult uses 2 billion ATP molecules a minute! Figure: Lewis et al., Life, Fig. 5.9, pg. 88
• Human energy and the dietary Calorie. The energy intake of humans in the form of food is often expressed in dietary Calories (kilocalories).

All life consists of matter (chemicals) and energy (the ability to do work, or the ability to change or move matter).

Reactions that provide the energy and chemical compounds for living organisms

Photosynthesis

CO2 +

H2O +

---

Light Energy

--->

Simple Carbohydrates (Organic Compounds)

+ O2

(Cellular) Respiration

O2 +

Simple Carbohydrates

---->

Heat +

Usable Chemical Energy

+ CO2

+ H2O

These reactions are COUPLED to TRANSFER energy from the sun to chemical form. This energy transformation sustains all life.

In the process CARBON is CYCLED from the abiotic environment to living organisms and back to the abiotic environment.

Figure: Lewis et al., Life, Fig. 5.2, pg. 84

The chemical reactions that transfer energy are inefficient. Only a fraction of the energy stored in nutrients is used by cells; the rest is dissipated as heat.

How do organisms use energy and chemical compounds produced by photosynthesis and respiration?

Biosynthesis

Lewis et al. use the term anabolism; see Figure: Lewis et al., Life, Fig. 5.9, pg. 88

Simple Organic Compounds	+ Minerals +	Chemical Energy (From Respiration)	--->	Complex Organic Compounds
Simple Carbohydrates		------>		Complex Carbohydrates
Fatty Acids & Glycerol		------>		Fats & Lipids
Amino Acids		------>		Proteins
Nucleotides		------>		DNA & RNA

• Energy flow from respiration reactions to biosynthesis permits the structural organization seen within organisms.
• Energy flow among organisms from photosynthesis to respiration results in structure seen within communities.

Energy flow: Community trophic level relationships

• Organisms extract energy from each other (consumers) and, ultimately, the sun (producers).
  Figure: Lewis et al., Life, Fig. 1.3, pg. 4
• Energy flow through four trophic levels.
  Figure: Lewis et al., Life, Fig. 43.11, pg. 865

Lecture activity

1. Get together in small groups.

2. Each person PRINT and SIGN your name in one corner of a piece of paper AND indicate your TA.

3. What did you have for your last meal? (Hopefully, breakfast!)

4. Was it an autotroph or heterotroph?

5. How many linkages are there between you and your ultimate energy source?

6. What limits the number of links in a food chain?

Food webs and efficiency of energy transfer

• Figure of Food Web: Lewis et al., Life, Fig. 43.10, pg. 864
• Food webs describe the relationships between the eaters and the eaten in communities. They represent the pathways that nutrients and energy follow as they move through a succession of plants, grazing herbivores, and carnivorous predators. Producers sit at the bottom of the food web and are in the first trophic level or link in the food chain. Consumers (herbivores) in the second trophic level eat the producers, and consumers in the third trophic level eat the consumers. No organisms prey on the carnivore sitting at the highest trophic level.
• Most food chains only have three links (eg., grass -> cow -> cowboy).

Energy flow through an ecosystem, showing four trophic levels. Figure: Lewis et al., Life, Fig. 43.11, pg. 865

• Organic compounds synthesized by primary producers are stored in the form of biomass (the total dry weight of individual organisms, populations, trophic levels, or entire ecosystems)
• Moving upwards through the trophic levels, the numbers and biomass of organisms decrease and the size of the organisms increase. The larger numbers of small organisms at the lower trophic levels collectively have a much larger biomass than the smaller number of organisms at the upper levels.
• The amount of food energy stored per unit time is greatest at the first trophic level, and subsequently decreases at each successive trophic level.
• The Rule of Tens. Only 10% of the energy in a trophic level is passed on to the next trophic level. The 90% energy loss at each trophic level goes to the metabolic needs of the organisms at that level. These needs include the energy required for motion, breathing, eating, growth, and reproduction. Most energy, however, is lost as heat.
• Energy flow through an ecosystem, showing 10% rule of energy transfer. Figure: Lewis et al., Life, Fig. 43.11, pg. 865
• Energy Pyramid showing inefficiency of energy transfer.

Decomposition and matter cycling

• What if portions of an organism remain uneaten, or if a plant or animal dies naturally?
• Decomposers (e.g., bacteria and fungi) break their tissues down and release the energy stored within the organism's body to the environment as heat.
• Eventually, all stored energy is dissipated as heat. Ecosystems require continual energy input to function indefinitely.
• Decomposers play a critical role in food webs because they break down the organism's organic molecules to nutrients or simple molecules such as carbon dioxide and water. They recycle the finite supply of the essential elements of life (e.g., carbon, nitrogen, phosphorus) making them available for primary producers to take up once more.
• Since no significant amount of new matter comes to the Earth from space, this recycling of matter is vital for the continuation of life on the planet.
• Three biogeochemical cycles:
• The Carbon cycle Figure: Lewis et al., Life, Fig. 43.14, pg. 868
• The Nitrogen cycle Figure: Lewis et al., Life, Fig. 43.15, pg. 869
• The Phosphorus cycle Figure: Lewis et al., Life, Fig. 43.16, pg. 870

The Greenhouse Effect: Consequences of human modification of the Carbon cycle

• Carbon dioxide in the atmosphere acts like a "transparent blanket" around the earth allowing light energy in but preventing some heat energy from leaving the atmosphere. Figure: Lewis et al., Life, Fig. 45.5, pg. 903
• Some other gases have similar effects (e.g., methane) but are less abundant in the atmosphere.
• The US lifestyle is responsible for a large part of CO2 emissions Global CO2 emissions keep rising.
• Combustion of carbon in long-term storage results in elevated carbon dioxide concentrations in the atmosphere.
• There is a correlation between CO2 level and global average temperature.
  Figure: Lewis et al., Life, Fig. 45.6, pg. 904
• Temperatures have increased by about 1.5 degrees C in the last century and may increase by another 3-5 degrees in this century.
• Climate greatly influences the distribution of life on Earth. What will be the physial and biological effects of global warming??

The Global Carbon Cycle from The Woods Hole Research Center

Biomass Burn Images from NASA