The Big Intro • This is all about the relationship between two chemical processes found in living cells • Autotrophs make nutrient molecules, and • Both Autotrophs and Heterotrophs use these nutrient molecules for their energy needs. This is cellular respiration and comes later.
Photosynthesis in Overview • Process by which plants and other autotrophs store the energy of sunlight into sugars. • Requires sunlight, water, and carbon dioxide. • Overall equation: 6 CO2 + 6 H20 C6H12O6 + 6 O2 • Occurs in the leaves of plants in organelles called chloroplasts.
Leaf Structure • Most photosynthesis occurs in the palisade layer. • Gas exchange of CO2 and O2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface. Palisade Spongy
Chloroplast Structure • Inner membrane called the thylakoid membrane. • Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana) • Stroma is a liquid surrounding the thylakoids.
Pigments • Chlorophyll A is the most important photosynthetic pigment. • Other pigments called antenna or accessory pigments are also present in the leaf. • Chlorophyll B • Carotenoids (orange / red) • Xanthophylls (yellow / brown) • These pigments are embedded in the membranes of the chloroplast in groups called photosystems.
Photosynthesis: The Chemical Process • Occurs in two main phases. • Light reactions • Dark reactions (aka – the Calvin Cycle) • Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. • Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.
Light Reactions • Light-dependent reactions occur on the thylakoid membranes. • Light and water are required for this process. • Energy storage molecules are formed. (ATP and NADPH) • Oxygen gas is made as a waste product.
Dark Reactions • Dark reactions (light-independent) occur in the stroma. • Carbon dioxide is “fixed” into the sugar glucose. • ATP and NADPH molecules created during the light reactions power the production of this glucose.
Photosynthesis Let’s take a closer look Click This Right Arrow Icon to Proceed
How Plants Make Sugars Pay attention; this is the lesson! Click This Right Arrow Icon to Proceed
In this interactive lesson you will learn how plants take carbon from the air to make glucose Have you ever thought about where plants get the energy to grow? Is it from the soil?Is it from the rain?Or is it from the sun? Let’s get started with navigation basics first Click The Right Arrow Icon Again
Navigation – from here on out you: Click this Left Arrow Icon to go back one slide. Click on this Home Icon to go to the Main Menu. Click this Left Arrow Icon to go forward one slide.
Lesson Menu Lessons to learn: 1. ATP – The Energy Currency 2. Chloroplasts 3. Photosynthesis – Light Dependent Reactions 4. Photosynthesis – Light Independent Reactions Assessment
LESSON 1 Have you ever used a rechargeable battery? Well, every living thing uses the same molecule for the short-term storage of energy. It is called ATP. The function of this molecule can be compared to a rechargeable battery. This molecule is called the energy currency of ALL living things! What does this word currency mean? Let’s look to the web for a definition – click here ?
So by calling ATP the energy currency of all cells we mean that different parts of cells exchange this molecule when energy is needed and consumed. Since all living organisms use this same ATP molecule, an analogy to this would be going anywhere in the world and being able to buy goods with dollars, quarters, and nickels and other U.S. currency. So how is this molecule like a re-chargeable battery? Let’s find out!
This is a graphic representation of ATP Notice the three main parts of ATP: • Adenine – a nitrogenous base • Ribose – a sugar • 3. 3 Phosphate molecules
Go back and look at the ATP graphic again. It also has a bond labeled a high-energy bond. Do you remember what this implies? Energy is stored in the bonds of molecules. ATP is unstable. (click on your answer)
That’s right! Energy is stored in the bonds of molecules. Remember from our unit on Biochemistry that whenever chemical bonds are formed or broken energy is exchanged. When bonds are broken energy is released and generally, energy is needed to form bonds. What about the re-chargeable battery analogy?
See if you can deduce the correct answer. 3 phosphates attached to the adenosine molecule represents a fully charged battery, with a maximum number of energy–rich chemical bonds. The adenosine molecule itself is the fully charged battery. (click on your answer)
Excellent! When 3 Phosphates are attached to adenosine this energy currency is at its highest denomination, like a fully charged battery. This molecule is again called adenosine triphosphate or ATP.
The fewer phosphates, the less energy these molecules have because they have fewer bonds from which to release energy. Adenosine diphosphate (Half-charged battery) Adenosine monophosphate (dead battery) This concludes lesson 1.
LESSON 2 Photosynthesis is The absorption of light energy from the sun by specialized organelles. That use this energy to power chemical reactions that use water and “fix” carbon dioxide from the atmosphere into energy storage molecules called glucose. It is the occurrence of two successive series of chemical reactions called: 1. Light dependent reactions 2. Light independent reactions
What was the specialized organelle we studied in the cells unit where photosynthesis occurs? Vacuole Chloroplast
Good job! Chloroplasts are the specialized organelle in plants and some algae where photosynthesis occurs. This view would be through a cross-section of the leaf
The light dependent reactions (subject of lesson 3) occur in the thylakoid membrane . The light independent reactions (subject of lesson 4) occur in the stroma. The thylakoids (as seen in the graphic) are arranged like a stack of coins called a granum, with the side of the granum oriented towards the sun for maximum light exposure. This concludes lesson 2.
LESSON 3 As stated in lesson 2 photosynthesis involves water, CO2, light energy and sugars,but let’s get more specific. Let’s look at the chemical and word formulas for photosynthesis. 6CO2 + 6H20 sunlight C6H12O6 + 6O2 Carbon dioxide + water sunlight glucose + oxygen Next is a concept map of the whole process.
Concept Map Photosynthesis includes Light independent reactions Light dependent reactions occurs in uses uses occur in Light Energy Thylakoid membranes ATP Stroma NADPH to produce to produce of ATP NADPH O2 Chloroplasts Glucose
Here’s a graphic representation of the two series of reactions.
The light dependent reactions capture the energy of the sun. The light-dependent reactions are comprised of two sets of reactions called photosystems. Photosynthesis begins with Photosystem II because it was the first set of reactions discovered.
The chlorophyll molecule is raised to an excited state. The electron lost by the chlorophyll is replaced by the enzymatic splitting of water Photosystem II Begins with absorption of energy (photon) by a chlorophyll molecule (Chl).
This electron is passed down a chain of molecules called the electron transport chain or redox chain. Energy from this transfer of electrons is used to produce ATP, leaving the electron in a low energy state to be recharged by Photosystem I
Energy from this excited electron is exchanged across different molecules (called carriers) ultimately being used to convert NADP+ to NADPH. The low energy electron from photosystem II replaces one that in photosystem I that has become energized and left the chlorophyll Molecule in photosystem II. NADPH stores this electrical energy for use in the light independent reactions.
The Light Dependent Reactions (Overview)
Where did the light dependent reactions take place again? In the stroma In the thylakoid membranes
Correct! This completes lesson 3
LESSON 4 Let’s Review The two series of chemical reactions that comprise Photosynthesis are called? Photosystem I and Photosystem II Light dependent and Light independent
Correct! The two series of chemical reactions that comprise photosynthesis are called the: Light dependent reactions – they require light and therefore occur in the thylakoid membrane Light independent reactions – these don’t require light and occur in the stroma
Light Independent Reactions (also called Calvin Cycle, after man who discovered them) Are a cyclical set of reactions that use the CO2 from the atmosphere to make the high energy sugar glucose Take a look at the overview of photosynthesis again
Here’s an overview of the Calvin Cycle. Next we’ll break it down in stages. The quantities listed are for the production of one glucose molecule which is produced from six turns of the cycle Acronyms we’ll use RuBP - ribulose biphosphate PGA - phosphoglycerate PGAP - diphosphoglycerate PGAL - phosphoglyceraldehyde
The cycle starts when (3) 5-carbon molecules (from the previous cycle) of RuBP combine with (3) CO2.molecules from the atmosphere. This combination of molecules forms six molecules of the 3-carbon compound PGA.
The energy and phosphates from six ATP’s is taken to convert the 6 PGA’s to 6 PGAP’s
Where did these ATP’s come from? The Light dependent reactions The mitochondria
In this next step the energy from 6 NADPH’s is used to remove the phosphate molecules forming 6 PGAL’s You are right!
Where did these NADHP’s come from? The cytoplasm The Light dependent reactions
At this point (after three turns of the cycle) one of these PGAL’s leaves the cycle. You are correct! Six turns of the cycle produces 2 of these PGAL molecules which combine to form a glucose molecules.
The remaining 5 PGAL molecules are converted to (3) 5-carbon intermediates, then back to 3 RuBP molecules to start the cycle again.
ASSESSMENT Question 1 of 5 The energy currency of all cells in all organisms is Adenosine diphosphate Adenosine triphosphate Adenosine monophosphate