Phun with Photosynthesis

Chapter Overview

• 7.1: Photosynthetic Organisms• 7.2: Plants as Solar Energy Converters• 7.3: Light Reactions• 7.4: Dark Reactions (Calvin Cycle)• 7.5: Other Types of Photosynthesis

• 7.1: Photosynthetic Organisms– Flowering Plants

• Plant Cell Review– Chloroplasts, stroma, thylakoids, grana, chlorophyll– Stomata

Key Points:Mesophyll vs. Bundle-Sheath

From wiki

Anatomy of a typical leaf (from a C3 plant)

Nomenclature

• Leaves have 3 basic regions:– Epidermis– Mesophyll = “Middle Leaf”.– Veins

PhotosynthesisBasic Idea:

The sun floods the earth with high energy radiation (photons)

Inside the plant cell, inside the chloroplast, located within the thylakoid membrane,Is a biological “antenna” that catches these photons.

The energy is then converted from visible light energy to chemical energy.

This energy conversion, which is a series of REDOX reactions, occurs in the Chloroplast.

The hollow inside is the Stroma,

The stroma contains stacks of coin-shaped objects called thylakoids.Each stack is called a granum (latin for “stack of coins).

Thylakoids are lined by a membrane as well, which contains proteins involved in photosynthesis (including chlorophyll).

Mechanism

• Pigments catch photons– Chlorophyll a and b– Carotenoids

• These compounds act as molecular “light sponges”.

Chlorophyll

Absorbs photons of specific wavelengths

The range of wavelengths a chlorophyll molecule can absorb correpond to its action spectrum.

The “Antennas”

Photosystem II Photosystem I

Complex animation 1 Complex animation 2 Complex animation 3

Simpler Animation 1

• Basic Reaction:– Chlorophyll, located within a “photosystem” complex,

absorbs light energy.• An electron becomes greatly energized, and escapes.• (This escaped electron is replaced by a lower energy

electron from somewhere else)

– The high-energy electron is passed to a molecule that more easily accepts electrons than the photosystem.

– The electron is continually passed down a chain of proteins, until it is considered a ‘low energy’ electron.

• The electron can be seen as performing work on it’s way down the energy gradient.– It’s forcing protons (hydrogen ions!) to be

pumped into the thylakoid space.– This concentration gradient is used by ATP

Synthase to make ATP (a proton ‘water mill’)

• The book’s animation

• 7.2: Plants as Solar Energy Converters

• 7.4: Dark Reactions (Calvin Cycle)– The book’s animation

• 7.5: Other Types of Photosynthesis

• http://photoscience.la.asu.edu/photosyn/education/photointro.html

Carrying electrons through space?

• Unless proteins are sitting right next to each other, and can literally ‘hand off’ high energy electrons, there needs to be a way to transport these high energy electrons around. How?

• NADP, NAD, FAD, FADP, etc….

– Just see these as carriers of the hot potato.– High energy electrons don’t just move through space

on their own; they are always carried. These are the guys with the thick oven mits.

• Fun Facts– There are several hundred chlorophyll

molecules per photosystem