Photosynthesis Learning Objectives, Enduring Understandings, and Essential Knowledge

Introduction

As with the rest of my curriculum, I’ve gone through the College Board’s Course and Exam Description for AP Biology and extracted the following Learning Objectives, Enduring Understandings, and pieces of Essential Knowledge. I’ve used this to inform the development of my on-line tutorials about photosynthesis, and the instruction I’m delivering to my own students at BHS. I’d love to know what you think.

Photosynthesis related learning objectives

Source: Course and Exam Description

  1. LO 2.4: The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy.
  2. LO 2.5: The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy.
  3. LO 2.41:The student is able to evaluate data to show the relationship between photosynthesis and respiration in the flow of energy through a system. 

Photosynthesis Essential Knowledge and Enduring Understandings

Source: This is a summary of material in the Course and Exam Description. Material in italics is quoted verbatim.

2.A.2: Organisms capture and store free energy for use in the environment

a. Autotrophs capture free energy from physical sources in the environment.

  1. Photosynthetic organisms capture free energy present in sunlight (as opposed to chemosynthetic organism, acquire energy by absorbing inorganic molecules in their environment)

c. Different energy-capturing processes use different types of electron acceptors. NADP+ is listed as an illustrative example of an electron acceptor in photosynthesis.

d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.

Evidence of student learning is a demonstrated understanding of each of the following:

  1. During photosynthesis, chlorophylls absorb free energy from light, boosting electrons to a higher energy level in Photosystems I and II.
  2. Photosystems I and II are embedded in the internal membranes of chloroplasts (thylakoids) and are connected by the transfer of higher free energy electrons through an electron transport chain (ETC). [See also 4.A.2]
  3. When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thykaloid membrane is established.
  4. The formation of the proton gradient is a separate process, but it is linked to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase.
  5. The e energy captured in the light reactions as ATP and NADPH powers the production of carbohydrates from carbon dioxide in the Calvin cycle, which occurs in the stroma of the chloroplast.

? Memorization of the steps in the Calvin cycle, the structure of the molecules and the names of enzymes (with the exception of ATP synthase) are beyond the scope of the course and the AP Exam.

e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.

g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.

Evidence of student learning is a demonstrated by understanding that

  1. Electron transport chain reactions occur in chloroplasts (photosynthesis), mitochondria (cellular respiration) and prokaryotic plasma membranes.
  2. (n/a)
  3. The passage of electrons is accompanied by the formation of a proton gradient across the inner mitochondrial membrane or the thylakoid membrane of chloroplasts, with the membrane(s) separating a region of high proton concentration from a region of low proton concentration. In prokaryotes, the passage of electrons is accompanied by the outward movement of protons across the plasma membrane.

  4. The flow of protons back through membrane-bound ATP synthase by chemiosmosis generates ATP from ADP and inorganic phosphate.

2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization.

a. Molecules and atoms from the environment are necessary to build new molecules. Evidence of student learning is a demonstrated understanding of each of the following:

  1. Carbon moves from the environment to organisms where it is used to build carbohydrates, proteins, lipids or nucleic acids. Carbon is used in storage compounds and cell formation in all organisms.

4.A.2: The structure and function of subcellular components, and their interactions, provide essential cellular processes.

g. Chloroplasts are specialized organelles found in algae and higher plants that capture energy through photosynthesis.
[See also 2.A.2, 2 B.3]

Evidence of student learning is a demonstrated understanding of each of the following:

  1. The structure and function relationship in the chloroplast allows cells to capture the energy available in sunlight and convert it to chemical bond energy via photosynthesis.
  2. Chloroplasts contain chlorophylls, which are responsible for the green color of a plant and are the key light-trapping molecules in photosynthesis. ere are several types of chlorophyll, but the predominant form in plants is chlorophyll a.
    ? The molecular structure of chlorophyll a is beyond the scope of the course and the AP Exam.
  3. Chloroplasts have a double outer membrane that creates a compartmentalized structure, which supports its function. Within the chloroplasts are membrane-bound structures called thylakoids. Energy-capturing reactions housed in the thylakoids are organized in stacks, called “grana,” to produce ATP and NADPH, which fuel carbon- fixing reactions in the Calvin-Benson cycle. Carbon xation occurs in the stroma, where molecules of CO2 are converted to carbohydrates.

Material related to photosynthesis also shows up in

1.B.1: Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.

b. Structural evidence supports the relatedness of all eukaryotes (membrane bound organelles such as chloroplasts are mentioned here)

2.B.3: Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.

b. Membranes and membrane-bound organelles in eukaryotic cells localize (compartmentalize) intracellular metabolic processes and speci c enzymatic reactions. Chloroplasts are listed as a possible illustrative example (along with the Golgi, E.R., mitochondria, etc.

What I Focus on In Teaching and Learning

In my teaching of photosynthesis, I boil this down to

  1. Photosynthesis as the key process that brings energy and matter into the biosphere (photosynthesis as the basis of carbon fixation)
  2. The interdependence/complementarity of photosynthesis and respiration.
  3. The two phases of photosynthesis (light reactions and Calvin cycle)
  4. The structure of chloroplasts: (thylakoids, organized into stacks, with stroma between the thylakoids and the inner membrane. Where, in relationship to this structure, the light reactions and Calvin cycle occur.
  5. How the light dependent reactions work (Z scheme, how ATP and NADPH are produced; ATP production through chemiosmosis). I also cover cyclic electron flow. 
  6. Overview of the Calvin cycle
  7. Evolution of photosynthesis (where it first emerged) and its evolutionary importance (creation of oxygen atmosphere)

I cover a lot of this in my three music videos about the light reactions. I also have a very old song about the Calvin cycle.

Link back to Module 32: Photosynthesis Menu