CP Biology Period 6

The end of the School Year is almost upon us!


If you have not submitted any assignments, 


               please see me A.S.A.P.




Please prepare for Final Exams. Use your Review Packets!





Circulatory/Digestive System Travel Brochures are due. 


Alternate assignment for webquest activity due no later than 

Monday, March 16.


Use these PPT notes for additional practice.

 Bio 6 PPT Cellular Respiration.pdf 


Notes from class:

       Photosystem 2                                                              Photosystem 1                                             

 sunlight breaks down H2O                                      sunlight excites electrons again                         

     electrons get excited                                         NADP+ plus electrons = NADPH                          

   electrons move to ETC                              H+ goes through ATP synthase and makes ATP         

    oxygen leaves plant                                                                                                                             


                                              Calvin Cycle                                                                                              

           RUBP plus CO2 makes glucose with help of NADHP and ATP                                             



Photosynthesis Packet Notes with Answers:


Photosynthesis is the process of transferring light energy into organic compounds that are usable by organisms. 6CO2 + 6H2O + energy à C6H12O6 + 6O2

     Autotrophs are organisms that manufacture food from inorganic substances and energy.  This is done by either photosynthesis or chemosynthesis. Autotrophs also perform cellular respiration.

Autotrophs are the sole point of energy into an ecosystem.  Energy moves through an ecosystem via a food web.

Heterotrophs take in food from their environment by consuming nutrients or other organisms.  Heterotrophs only perform cellular respiration.

       **Heterotrophs are classified according to what they eat, plants (herbivores), meat (carnivores), or both (omnivores).

     The products of photosynthesis are the reactants for cellular respiration and the products of cellular respiration are the reactants for photosynthesis.

C6H12O6 + 6O2 à 6CO2 + 6H2O + energy

Light Absorption in Plants

     The first steps of photosynthesis are known as the light reactions.  Light is absorbed by pigments in the chloroplast.  The inner membrane of the chloroplast is known as the thylakoid.  They are interconnected and sometimes stacked in structures calledgrana.  The thylakoids are surrounded by a fluid known as the stroma. 

      The light we see appears white but is actually comprised of a variety of wavelengths referred to as the visible spectrum.  The wavelengths are measured from crest to crest of a wave.  The wavelengths range from about 400nm (violet) to about 700nm (red).

     A substance can absorb various wavelengths of light but the wavelength that is reflected is what we see.  Pigments in thechloroplast absorb various wavelengths of light.

     The thylakoids contain a variety of pigments.  The most important are chlorophylls a and b.  Neither tend to absorb much green light.  Chlorophyll b and other pigments, carotenoids, yellow orange and brown are considered accessory pigments.  They assist chlorophyll a in capturing the light energy used directly in the light reactions.

Electron Transport

     A photosystem is a cluster of pigments.  There are two.  Accessory pigments absorb and pass energy along until chlorophyll a is reached. 

1.  Light causes electrons to enter a higher energy level in two molecules of chlorophyll a in photosystem II.

2.Chlorophyll a becomes oxidized and the electrons are passed to a primary electron acceptor.

3. The electrons are passed along a series of molecules losing energy along the way, the electron transport chain.  The lost energy moves protons into the thylakoid.

4. Light excited electrons from chlorophyll a molecules in photosystem I and passes them along to a primary electron acceptor.  These electrons are replaced by the ones from photosystem II.

5. Electrons from photosystem I move through the electron transport chain bringing them toward the stroma.  The electrons combine with a proton and NADP+ transforming it to NADPH.

     Meanwhile, water molecules are split to replace the lost electrons from photosystem II

          2H2O  à 4H+  +  4e-  +  O2

     The protons remain in the thylakoid, the electrons are available to photosystem II and the oxygen diffuses out of the chloroplast to leave the plant.


     The formation of ATP relies on a concentration gradient of protons across the membrane, higher inside the thylakoid.  Additional protons are pumped in from the stroma.  This concentration gradient is potential energy. ATP utilizes the potential energy to form ATP.  ATP synthase functions as both a carrier protein as well as an enzyme.

The Calvin Cycle:

     The second part of photosynthesis, the light independent reactions, use energy molecules formed in the light reactions to synthesizeorganic compounds.

Step 1

     The required CO2 diffuses into the stroma from the cytosol where it is joined to a 5-C carbohydrate, ribulose 1,5 bisphosphate,RuBP, to form a temporary molecule, rubisco, which splits immediately into 2, 3-C molecules of phosphoglycerate, PGA.

Step 2

     The PGA is converted into another 3-C molecule, PGAL, (glyceraldehyde 3 phosphate, G3P), using the NADPH and some of theATP formed in the light reactions.  A phosphate from ATP joins to each PGA, followed by a proton from NADPH.  The phosphate is then released forming the PGAL.  The ADP, phosphate and NADP+produced go back to be recycled in the light reactions.

Step 3

     Most of the PGAL goes on to reform the RuBP, but some are used by the plant cell to form other organic compounds.

Per Turn of the Cycle

   1 CO2 required

   3 ATP

   2 NADPH


Per Molecule of PGAL (3 turns of the cycle)

   1 PGAL produced

   9 ATP used

   6 NADPH used


     Some of the organic compounds produced from the PGAL include amino acids, lipids and carbohydrates, including glucose, fructose, sucrose, glycogen, starch and cellulose.  Glucose is not directly produced by the pathways of photosynthesis.

Alternative Pathways

     Plants that form PGA during carbon fixation are known as C3 plants.  Some plants live in less favorable climates where the stomata, the pores though which water, CO2 and O2 can enter and leave plants, are usually closed.  Closed stomata raise the levels of oxygen and decrease the levels of carbon dioxide in plants inhibiting carbon fixation.

     C4 plants have a different adaption to deal with different environments.  They partially close their stomata during the hottest part of the day to reduce water loss.  They use a 4-C intermediate.  CO2 is fixed into a 4-C compound used to release CO2 into the Calvin cycle.  Examples include corn, sugarcane and crabgrass.  Such plants lose about half as much water

     CAM plants like cacti and pineapples open their stomata at night, taking in CO2 and fixing it into a variety of compounds to be used during the day. This particular adaptation causes such plants to grow slowly, but lose even less water than C3 or C4 plants.


  Bio 6 Photosynthesis notes.pptx