CHAPTER 5

PHOTOSYNTHESIS


The Greenhouse Effect

-    Global warming is the progressive increase of Earths average temperature.

-    Effects of global warming:

-   Rise in sea levels

-   Global melting of glaciers

-   Loss of habitat for temperature-sensitive species

-   More severe storms

-    Greenhouse effect is the mixture of carbon dioxide and other greenhouse gases in the atmosphere.

-   Sunlight warms the surface of the Earth.

-    Most of the warmth radiates into space.

-    Some of the warmth is absorbed by gases in the atmosphere, making the Earth warmer.

-    These gases are what keeps the earth a warm plant, but in excess these gases cause global warming.

-    Heat is the total amount of energy in a substance.

-    Temperature measures the intensity of heat how rapidly molecules are moving.

-    Earths water plays a major role in moderating temperatures.

-    Water has a high capacity to absorb and release heat, due to hydrogen bonding between molecules.

 

The Flow of Carbon

-    Carbon cycles between living organisms, the atmosphere, bodies of water, and the soil.

-    Fossil fuels are stored carbon that contribute to increase carbon dioxide release

-    Measurements of carbon dioxide from Antarctic ice cores shows that it has been increasing in the atmosphere over the past 50 years.

-    Data from ice cores show present levels of carbon dioxide are the highest in the last 400,000 years.

-    Temperature and amount of carbon dioxide are correlated

 

Can Photosynthesis Reduce the Risk of Global Warming?

-    Photosynthesis is the process by which plants and other microorganisms trap light energy from the sun.

-    Photosynthesis takes Carbon dioxide and combines it with water, using light energy to produce glucose and oxygen.

-    Photosynthesis is done by plants and some bacteria, but not by animals or fungi.

-    Photosynthesis occurs in organelles called chloroplasts.

-    Stroma: thick fluid inside chloroplasts.

-    Thylakoids: disk-like membrane structures that give the chloroplast more surface area.

-   Surface of thylakoid is covered with chlorophyll pigment molecules

Chlorophyll absorbs light energy from the sun

 

Overview: Photosynthesis

-    Photosynthesis is a chemical reaction

-  6CO2 + 6H2O + light energy -> C6H12O6 + 6O2

-    Photosynthesis takes place in 2 steps, in different areas of the chloroplast.

 

Photosynthesis - The Light Reactions

-    Light reactions (thylakoids):

-    Produces oxygen, ATP and NADPH

 

Photosynthesis - Calvin Cycle

-    Series of reactions that occur in the stroma to produce glucose using ATP AND NADPH

 

How Global Warming Might Reduce Photosynthesis

-    Stomata openings in leaves for entrance of gases

-    Guard cells regulate stomata openings

-    Transpiration: movement of water out of a plant through stomata

-  Stomata open: plenty of carbon dioxide, loss of water

-  Stomata closed: conserves water, limits photosynthesis

-    Higher temperatures can lower the rate of photosynthesis

-    Closing of stomatal openings may counteract photosynthesis through photorespiration.

-    During photorespiration oxygen is used instead of carbon dioxide to react with RuBP.

-    This leads to plants releasing carbon dioxide instead of oxygen.

-    Most plants are C3 plants

-   Close stomata to conserve water when hot

-   Can cause photorespiration to occur

-    C4 plants avoid photorespiration

-   An additional enzyme allows them to make sugars even though stomata are almost closed

-    CAM plants open their stomata only at night

-   Carbon is stored as an acid

-   During the day, acid is broken down to carbon dioxide for use in photosynthesis

-    Table 5.1 gives examples of each type of plant

-    Deforestation: clearing of forests for farming and human settlements

-    25% of carbon dioxide added to the atmosphere comes from cutting and burning forests in the tropics.

-    Replanting helps decrease carbon dioxide levels: young trees have faster net photosynthetic rates than older trees.

 

5.5 Decreasing the Effects of Global Warming

-    Biggest sources of carbon dioxide emissions:

-   Industry

-   Transportation

-   Commercial, residential, agricultural

-    Each of us can work to reduce our own contribution (carbon footprint) to worldwide emissions.

-    Table 5.2 gives examples of ways to reduce global warming