Introduction

Module 6 – Photosynthesis

Introduction

In the last few modules, we looked at some of the processes that require energy at the cellular level and examined the production of energy through cellular respiration (the stepwise breakdown of the glucose molecule (“food”)). In this module, we will explore the ability that some organisms have to produce their own food.

As you are likely aware, plants produce their own “food” or sugar through a process called photosynthesis . They are autotrophs while we are heterotrophs and cannot produce our own food. While there are other organisms that also produce their own food (and I challenge you to identify a few on your own), we will focus, in this module, on how plants produce their own food through the process of photosynthesis. Think of photosynthesis as the process of building complex molecules (sugar) that will later be broken down through cellular respiration to produce cellular energy (ATP).

As you work through this module, think first about the plant structures that facilitate photosynthesis and then examine the nature of sunlight and the energy used to power this process. Once you have a good general understanding of the structures involved and the nature of sunlight, break down photosynthesis further and explore the two essential stages of photosynthesis:

  • the Light Reactions
  • the Calvin Cycle

Think about how these processes lead to the production of sugar and oxygen as a by-product. Once you feel comfortable with these things, you will look at some of the alternative ways plants “fix” carbon.

One interesting thing to consider as you finish this module are the similarities between cellular respiration and photosynthesis. On the surface they may seem like completely opposite processes, but they have quite a few similarities including the following:

  • both are multi-step processes within the cell
  • both undergo chemiosmosis as part of the process and involve electron carriers
  • both take place in organelles that are thought to have been acquired through endosymbiosis (The Theory of Endosymbiosis) 1 .

Learning Outcomes

This module addresses the following Course Learning Outcomes listed in the Syllabus for this course:

  • Demonstrate knowledge of biological principles.
  • Demonstrate knowledge of scientific method.
  • Communicate scientific ideas through oral or written assignments.
  • Interpret scientific models such as formulas, graphs and tables.
  • Demonstrate problem solving methods in situations that are encountered outside of the classroom 1 .

Module Objectives

Upon completion of this module, the student will be able to:

  • Define autotroph and heterotroph and give examples of each.
  • Identify two organisms outside of plants that undergo photosynthesis.
  • Define the following terms: producer , consumer , chloroplast , chlorophyll , thylakoids , grana , stroma , photosystems I and II , stomata ,guard cells , mesophyl .
  • Describe the overall reaction of photosynthesis, identify the reactants and products, and compare them to the reactants and products of cellular respiration.
  • Answer the questions:
    • Where in the plant body does photosynthesis take place?
    • What structures are involved?
  • Define pigment.
  • Answer the questions:
    • What pigment promotes photosynthesis in the plant?
    • What qualities of light does it preferentially absorb?
    • What qualities will it reflect?
  • Describe the two essential steps of photosynthesis (The light reactions and the Calvin cycle) and where (specifically) they take place in the chloroplast.
  • Describe the properties of light.
  • Answer the question:
    • How does this form of energy promote photosynthesis in the plant?
  • State several similarities between the processes of cellular respiration and photosynthesis.
  • Describe the differences between C3, C4, and CAM plants in terms of the process of photosynthesis 1 .