1. Agenda 9/26 and 9/27 Photosynthesis Overview
Aquatic Plant Lab Planning

2. Warm Up
Plants go through cellular respiration AND photosynthesis. Why do they have to go through both?

3. Cellular Respiration: making energy from glucose
Photosynthesis: making glucose
Plants cannot eat their glucose, so they have to go through this extra step

4. Photosynthesis Part I: Overview & The Light-Dependent Reactions

5. Where does photosynthesis happen?

6. Leaves: The Photosynthetic Organs of Plants
Leaves perform most of the photosynthesis in plants.
cuticle
upper epidermis
palisade mesophyll
spongy mesophyll
- The cuticle is a waxy layer that helps to prevent the leaf from losing too much water through transpiration (don’t forget – lipids, like waxes, are hydrophobic!). This is a great time to emphasize the evolutionary adaptations that some plants possess to thrive in dry environments; a thicker cuticle helps to block the escape of water by osmosis, thus helping the plant maintain homeostasis despite the dry external conditions. The upper and lower epidermis provides a barrier from the external environment (much as our skin does). The palisade and spongy mesophyll are in red because those cells (within a leaf – don’t forget to emphasize scale here!) have many chloroplasts and perform most of the photosynthesis within a plant. The “spaces” between the cells in the spongy mesophyll layer are for gases (CO2 for use during the Calvin Cycle and O2 prior to its release from the leaf. Each stoma (plural, stomata) is surrounded by a pair of guard cells; stomata are pores that allow gases to enter and exit a leaf. The xylem and phloem make up the vascular tissue of a plant, and transport water from roots to shoots in vascular plants (xylem) and transport sugars from sugar sources to sugar sinks (phloem). The xylem provides the water to be used during the light reactions of photosynthesis, and the phloem transports the carbohydrates from the leaves to other parts of the plant after the Calvin Cycle.
lower epidermis
Xylem & phloem
stoma
Bundle-sheath cells

7. Leaves: The Photosynthetic Organs of Plants
Leaves have a LOT of surface area to facilitate absorption of sunlight.
- Although lots of surface area facilitates the absorption of more sunlight (and thus photosynthesis can occur at a faster rate), having lots of surface area also allows more transpiration to take place through the stoma on the underside of leaves in dry environments; this can lead to desiccation. Many species of plants that exist in these environmental conditions have evolutionary adaptations that limit transpiration.
Are there any drawbacks to leaves having a large amount of surface area?

8. Chloroplast Structure: A Review
In eukaryotes, photosynthesis takes place inside chloroplasts inside cells (inside leaves).
Chloroplasts have 3 membranes:
Granum
Outer membrane
Inner membrane
Thylakoid membrane, folded to form thylakoids
Thylakoids are
arranged in stacks
called grana.
-Again, students can get caught up on the scale of where photosynthesis occurs. Emphasize to them that chloroplasts are cellular organelles, found inside cells, which make up tissues, which make up organs (such as leaves). Alternatively, show them the picture on slide 4 and describe that we’re now looking at ONE chloroplast inside one of the cells in the mesophyll.
-Emphasize to students the structure of membranes (phospholipid bilayer with embedded proteins) and the “benefits” of having membranes (able to separate different/incompatible processes into different areas, and the ability to build a concentration gradient by having two distinct and separate areas**).
Chlorophyll and other pigments involved in photosynthesis are embedded in the thylakoid membrane.

9. Photosynthesis: An Overview
The net overall equation for photosynthesis is:
Photosynthesis occurs in 2 “stages”:
The Light Reactions (or Light-Dependent Reactions)
The Calvin Cycle (or Calvin-Benson Cycle or Dark Reactions or Light-Independent Reactions)
6 CO2 + 6 H2O C6H12O6 + 6 O2
light
Photosynthesis is an endergonic reaction because it requires an input of energy to occur; that energy comes in the form of light energy and is dependent solely on the frequency of the incident light.
Though the Calvin Cycle is sometimes referred to as the Dark Reactions, emphasize to students that this is actually a very poor name since these reactions do NOT ever occur in the dark. The Calvin Cycle requires ATP and NADPH from the light reactions. As soon as the light is gone, so is the supply of ATP and NADPH so the Calvin Cycle stops, too. The AP exam is most likely to refer to the Calvin Cycle as “Light-Independent Reactions” but even that is a misleading term. Emphasize to students that even though these reactions do not use light directly, they do stop as soon as the light (think energetic photons) is gone.

10. Photosynthesis: An Overview
Follow the energy in photosynthesis,
light
Light
Reactions
Calvin
Cycle
Organic compounds (carbs)
ATP
NADPH
light
thylakoids
stroma
- It cannot be overemphasized that energy is not MADE, but is instead transformed through the processes of photosynthesis and cellular respiration. Each of the “boxes” (light/ATP & NADPH/organic compounds) contains energy, but in a different form. Photosynthesis is a process that converts energy from an “un-usable form” (light) into a “usable form” (organic compounds), and requires an intermediate step (ATP/NADPH).
Granum

11. Where do plants get their mass?

12. How can we see plants going through photosynthesis?

13. Demo Explanation As I exhale CO2 into the solution it turns yellow
There is bromothymol blue (an indicator) that is blue in a neutral or basic solution but turns yellow when acidic
The CO2 I am exhaling causing the solution to turn yellow
Now…how can we use this to gather evidence that supports the fact that plants consume carbon dioxde?