BIOL 1404 HON 2015

Tuesday, March 3, 2015

Pre Test Info for the Second Midterm

This graph plots the rate of photosynthesis as a function of the concentration of carbon dioxide in a growth chamber where scientists were able to hold all variables constant while varying the CO2 concentration.

***********************************

This graph plots the relationship between photosynthetic rate and the density of sugar cane plants in a series of field experiments that varied the plant density.

*************************************

This graph plots how heart rate (shown in the pink line- the one on top) and the cellular lactate concentration depended on cycling speed.

Plant Diversity

Here is a link to a powerpoint presentation about plant diversity.

Do not worry about the life cycles. focus on understanding the major evolutionary advances that have occurred during plant evolution.

http://www.slideshare.net/secret/DBv71wnKTH1YBN

Tuesday, February 24, 2015

Factors Limiting the Rate of Photosynthesis

The graph above shows how the rate of photosynthesis is affected by irradiance (light level) and the concentration of carbon dioxide.

The rate of photosynthesis can be limited by a variety of environmental factors including

1) light
2) concentration of carbon dioxide
3) water
4) soil nutrients

Which factor most limits photosynthesis varies between environments.

Light- Can directly limit the rate of photosythesis by limiting the rate at which ATP and NADPH are produced.

Carbon dioxide- can directly limit the rate of photosynthesis by limiting the rate at which the Calvin Cyle takes place.

Water- can indirectly limit the rate of photosynthesis. When plants are water stressed they close their stomata (long before the concentration of water in the cell becomes too low for water to supply electrons to P680). Thus, the rate of photosynthesis is water stressed plants is directly limited by the amount of carbon dioxide in the leaf.

Soil Nutrients- Sometimes the rate limiting step in photosynthesis is the rate at which carbon dioxide + RuBP ==> PGA. This reaction is catalyzed by the enzyme RuBP carboxylase. Increasing the amount of RuBP carboxlyase in the cell can increase the rate at which this reaction occurs. Fertilizing plants with nitrogen will increase the amount of RuBP Carboxylase produced by the plant.

Expected Learning Outcomes

By the end of this class a fully engaged student should be able to

- discuss the factors that can directly or indirectly limit the rates of photosynthesis
- discuss how the most limiting factors should vary between environments
- discuss how the activities of farmers such as irrigation and fertilization can increase photosynthetic rates
- interpret the graph at the top of the post (irradiance measures light intensity and the three lines represent different concentrations of carbon dioxide)
- explain what why the graph shows that shape

Why Aren't Plants Black?

If I was hired as an engineer to design a machine whose job was to convert light energy into chemical energy I probably would not choose to use a green pigment. Instead, I would choose to use a black pigment because black pigments would absorb more energy because they would absorb all wavelengths of light. If you look at a field of plants you will notice that they are green (OK this doesn't work too well around Lubbock in the winter)and we have learned that chlorophyll, a green pigment, is the dominant photosynthetic pigment. What is going on?

Here is one theory about why chlorophyll is the dominant photosynthetic pigment in plants today. Early on there were photosynthetic bacteria with purple pigments (purple is a combination of red and violet). These aquatic bacteria had a very simple sort of cyclic electron flow that was able to convert light energy into energy in ATP (they didn't have non-cyclic flow or the Calvin Cycle).

Origin of chlorophyll- The purple pigment absorbed all wavelengths of light except for the reds and violets. Thus, any bacteria using purple pigments that lived deeper in the water than the purple bacteria on the surface would have no light to use because it had all been absorbed by the surface bacteris (exploitative competition). Because red and violet wavelengths pass through to deeper water, bacteria that contained a pigment that was able to absorb these wavelengths would be able to coexist with the purple bacteria. This was the origin of chlorophyll.

Competition purple and green photosynthetic pigments. Over time there was competition between organisms with purple photosynthetic pigments and green photosynthetic pigments. Obviously, the green photosynthetic pigments won this competition because chlorophyll is the dominant photosynthetic pigment today (there are still examples of photosynthetic bacteria with purple pigments, but they are limited to very harsh environments). Interestingly, chlorophyll came to dominate, not because it was a better at absorbing light energy, but rather because the cyclic flow machinery associated with chlorophyll was more efficient at producing ATP than the machinery associated with the purple pigment was. Thus, it is an evolutionary accident that modern plants are green.

Black Plants

It would be possible for modern plants to be black if they had enough accessory pigments to allow them to absorb all wavelengths of light. In fact, some red algae that live deep below the surface where light levels are low are basically black. Because the amount of light is not the factor that limits the rate of photosynthesis in most terrestrial plants, it is not worth the cost of producing extra accessory pigments. However, deep in the ocean where light levels are low, plants benefit from being able to absorb all wavelengths of light so deep marine algae have invested in extra accessory pigments.

Expected Learning Outcomes

By the end of this course a fully engaged student should be able to

- discuss why terrestrial plants to not invest in the accessory pigments required to make them black

Leaf Structure

Lecture Video: http://mediacast.ttu.edu/Mediasite/Play/c952faeba33546d3b8910e6e1bbf716c1d?catalog=4dc7289a-d3e0-4ae5-8fdc-5b86c027a06b

In most plants, leaves are the major sites of photosynthesis. Thus, we can think of leaves as "photosynthesis machines" and use our knowledge of natural selection to try to understand aspects of leaf structure.

Further Reading

http://micro.magnet.fsu.edu/cells/leaftissue/leaftissue.html

Expected Learning Outcomes

By the end of this course a fully engaged student should be able to

- discuss important differences between animals and plants in gas uptake
- diagram the cross section of a leaf
- discuss the characteristics and purpose of the cuticle, stomata, spongy mesophyl cells, and the palisade cells.
- explain the adaptive basis of leaf structure

Wednesday, February 18, 2015

Photosynthesis- Light Independent Reactions

Lecture Video- http://mediacast.ttu.edu/Mediasite/Play/842d916401044c20a370989776ea66631d?catalog=4dc7289a-d3e0-4ae5-8fdc-5b86c027a06b

Photosythesis takes place in two steps. In the first step, known as the light dependent reactions, light energy is converted into chemical energy held in the bonds of ATP and NADPH.

Expected Learning Outcomes

By the end of this course a fully engaged student should be able to

- list the parts of a photosystem
- discuss the function of a photosystem
- describe where the light dependent reactions of photosythesis occur and discuss why these reactions occur in this location
- describe cyclc electron flow, be able to explain both the energetic result and what chemcical changes occur
- describe non-cyclic electron flow, be able to explain both the energetic result and what chemical changes occur
- describe the cause and the result of chemiosmosis
- answer the question- "why doesn't photosynthesis stop after the production of ATP and NADPH in the light dependent reactions

Further Reading

A simple introduction to the process of photosynthesis
Photosynthesis- http://www.eoearth.org/article/Photosynthesis

Here is a link to some fairly detailed info about photosynthesis (it contains some very good diagrams).
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html

Powerpoint Presentation

Here is the powerpoint presentation that I will use in class.

http://www.slideshare.net/MarkMcGinley/photosynthesis-light-dependent-reactions

Further Viewing

These videos contain animations that might help you to understand what is happening in the light dependent reactions. I encourage you to watch each of these videos.

1) This video has some great animations of what is going on in the light dependent reactions.

http://www.youtube.com/watch?v=hj_WKgnL6MI

2) This is a video of a woman with a very southern accent talking about photosyntheis with some decent animations.

http://www.youtube.com/watch?v=RFl25vSElaE&feature=related

3)Another explanation of light dependent reactions.

http://www.youtube.com/watch?v=BK_cjd6Evcw