Bio 178 Lecture 19Photosynthesis (Cntd.)

Copyright: J. Elson-Riggins

Reading

• Chapters 10 & 11, P 1186, 1220

Quiz Material

• Questions on P 206 & 226

• Chapters 10 & 11 Quizzes on Text Website (www.mhhe.com/raven7)

Outline

• Photosynthesis

Energy Cycle - Importance of Photosynthesis

The Energy Cycle

• Cellular Respiration

Uses the glucose and O2 made by photosynthesis to fuel endergonic reactions.

The energy for life is released, not produced by cellular respiration.

• Photosynthesis

The waste products of cellular respiration are the raw materials for photosynthesis - to make glucose and O2.

The Carbon Cycle

The Carbon Cycle• CO2 UseGlobally, photosynthesis uses ~10% of atmospheric CO2 to produce organic compounds.

All terrestrial heterotrophs obtain their C indirectly from photosynthetic organisms.

• Carbon Acquisition

Decomposers recycle C in dead organisms either into the atmosphere or into aquatic sediments.

• CO2 ReleaseHeterotrophs release C back into the atmosphere through respiration.

Burning fossil fuels releases C into the atmosphere.

The Carbon Cycle (Cntd.)

• Balance Between Carbon Release and Use

Respiration and Photosynthesis are approximately balanced.

Consumption of fossil fuels has shifted this balance.

Deforestation is also shifting this balance.

Deforestation

Copyright: J. Elson-Riggins

DeforestationFacts• ~1/2 the original extent of the world’s tropical rainforests were left by the mid-1990s. From this, an area greater than the size of Indiana is clear-cut every year.

• Destruction of the Amazon rainforest reached its highest level in 10 years from Aug 03 - Aug 04 with 10,000 square miles burned and cut down. 17.3% of the Amazon rainforest has now been destroyed.

• If this rate continues all the tropical rainforests in the world will have gone in ~ 30 years.

Deforestation

http://www.greenpeace.org.uk/forests/media/pressrelease.cfm?ucidparam=20050519110452

http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2005/05/20/wjung20.xml http://www.wwf.org.uk/news/

n_0000001569.asp

Consequences of Deforestation• The Carbon CycleDeforestation decreases global photosynthesis increasing atmospheric CO2.

Burning forest to convert it to pastureland further increases atmospheric CO2.Increasing atmospheric CO2 enhances the greenhouse effect increased global temperatures.

• The Hydrologic Cycle

~1/2 the precipitation that falls in the rainforest is a result of transpiration. This is also responsible for cloud formation and affects global temperatures (reduces evaporative cooling).

Consequences of Deforestation (Cntd.)

• BiodiversityAlthough tropical rainforests cover ~ 7% of terrestrial earth, they hold >1/2 of all the plant and animal species on earth.

It is estimated that 137 species disappear globally every day (http://earthobservatory.nasa.gov/Library/Deforestation/).

• Nutrient LossIn tropical rainforests most of the nutrients are present in the plants, rather than the soil. Removing the trees removes the nutrients required for growth. Any remaining nutrients are washed away when it rains.

Within 3 years the ground will no longer support crops.

Selective Logging(Asner et al. 2005. Science 310: 480-482)

• What is it?Individual trees are removed from the rainforest, rather than clear-cutting the forest.

• How much selective logging occurs?Due to lack of appropriate technology selective logging has been historically underestimated - logged areas of the Brazilian Amazon have been logged 60-123% (per year) more than previously estimated (1999-2002).

• ConsequencesIncreases annual C flow from the Amazon 25% more than previously estimated for deforestation alone.

Thins shady canopy and causes damage to undergrowth forests are drier and more flammable.

The Ceiba tree is an example of a tree that is very important in the Amazon. It is much taller than the other trees and therefore can offer other organisms the opportunity to be exposed to more sunlight. Epiphytes are found on the ceiba tree, including bromeliads. These fill with water and therefore provide habitat for amphibians. Many organisms use the ceiba tree. However, the ceiba tree is also a very valuable resource for humans. It is the source of kapok, which was used historically for filling life jackets. The length of the tree also makes it valuable for making long canoes. Ceiba trees are therefore highly sought after by humans. What might be the effects on the Amazon ecosystem of cutting down a Ceiba tree?

Ceiba Tree

Copyright: J. Elson-Riggins

Ceiba Tree

Copyright: J. Elson-Riggins