Picture Guide to Chapter 8 Photosynthesis

8-1 Energy and Life

Objectives Explain where plants get the energy they need to produce food Describe the role of ATP in cellular activities

Q: Where does energy come from? A: Our food, but originally the energy in food comes from the sun

Autotrophs Make their own food

Heterotrophs Cannot make their own food

Chemical Energy and ATP The principal chemical compounds that cells use to store and release energy is called ATP adenosine triphosphate

Storing Energy ATP stores energy in the third phosphate ATP is like a fully charged battery

Releasing Energy Q: How is the energy in ATP released? A: Break bond between the second and 3rd phosphates 2 ADP

Using Biomechanical Energy Active Transport Movement of organelles throughout cell Synthesis of proteins and nucleic acids Produce light Blink of firefly caused by an enzyme powered by ATP

ATP Availability Most cells only have enough ATP for a few seconds of activity Why? Not good at storing energy over the long term Glucose stores 90 times the chemical energy of ATP Cells generate ATP from ADP as needed by using the energy in foods like glucose

Biology in History 1643 – van Helmont: trees gain most of their mass from water 1771 – Priestly: discovered plants release oxygen 1779 – Ingenhousz: plants need sunlight to make oxygen 1845 – Mayer: proposed plants convert light energy into chemical energy

Bio in History pt. 2 1948 – Calvin: traces chemical path that carbon follows to make glucose 1992 – Marcus: describes electron carrier molecules in electron transport chain 2004 – Iwata & Barber: identify the mechanism for splitting water in photosynthesis

8-2 Photosynthesis: An Overview

Photosynthesis The process in which plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates – sugars and starches – and oxygen as a waste product

Photosynthesis

The Photosynthesis Equation light CO2 + H2O C6H12O6 + O2 (Carbon Dioxide) (Water) (Sun) (Glucose) (Oxygen)

Chlorophyll The plant’s principle pigment, absorbs light energy in the blue-violet and red spectrum of visible light

Chlorophyll a and Chlorophyll b Absorption of Light by V B G Y O R

Because light is a form of energy… Anything that absorbs light also absorbs the energy from that light When chlorophyll absorbs light, much of the energy is transferred to electrons in the chlorophyll molecule, raising the energy level of these electrons These high-energy electrons make photosynthesis work

Thylakoids Sac-like photosynthetic membranes arranged in stacks

Grana Stacks of thylakoids

Stroma The fluid filled region outside the thylakoid

Scientists describe the reactions of photosynthesis in two parts Light – dependent reactions (takes place in the thylakoid membranes) Light – independent reactions (takes place in stroma)

Carrier Molecule Compound that can accept a pair of high energy electrons and transfer them along with most of their energy to another molecule Ex.) NADP+

Q: What does this do? NADP+ NADPH A: this traps sunlight in chemical form

Light Dependent Reactions Uses energy from light to produce Oxygen gas ATP NADPH

8-3 The Reactions of Photosynthesis

Light-Dependent Rxns Function: use energy from sun to make oxygen and convert ADP & NADP+ into ATP and NADPH Thylakoids have clusters of chlorophyll and proteins called photosystems

Steps for L-D Rxns Photosystem II – a. Light energy absorbed & excited electrons b. Water is split to replace electrons, releases Hydrogens (H+) and Oxygen

Steps for L-D Rxns 2. Electron Transport Chain (ETC) – a. High energy electrons move to photosystem I b. Energy from electrons pumps H+ ions into thylakoid space

Steps for L-D Rxns 3. Photosystem I – a. Electrons get reenergized by sunlight b. 2nd ETC transfers electrons to NADP+, makes NADPH

Steps for L-D Rxns 4. ATP Synthase – a. H+ ions build up creating + charge b. Each H+ crosses membrane rotating ATP synthase converting ADP to ATP

The Calvin Cycle The ATP and NADPH formed by the light-dependent reactions contain an abundance of chemical energy Not stable enough to store that energy for more than a few minutes. The Calvin cycle uses ATP and NADPH from light – dependent reactions to produce high energy sugars

The Calvin Cycle These reactions don’t require light, therefore these reactions are called Light – independent reactions

Light Indep. Rxns/The Calvin Cycle

Steps for L-ID Rxns CO2 Enters the Cycle – a. CO2 enters the stroma & combines with 5-Carbon compounds b. Get twelve 3-Carbon compounds from 6 CO2

Steps for L-ID Rxns 2. Sugar Production – a. Midcycle, two of the 3-Carbon compounds removed. i. Used to make sugars, lipids, aminos & etc… b. Remaining ten 3-Carbon compounds go back to six 5-carbon compounds to cycle through again

Steps for L-ID Rxns 3. Summary– a. Calvin Cycle used 6 CO2 to make a single 6-Carbon sugar b. Energy needed to make this sugar comes from light-dependent rxns

Photosynth – End Results Light-dependent rxns trap light & convert it to chemical energy Light-independent rxns use that chem energy to make high energy sugars END RESULT: Plenty of food and oxygen for animals

Factors Affecting Photosynthesis Not enough water Temperature Light intensity

1. Temperature High or low temps can slow or stop it - Enzymes for Photosynth work best between 0°C - 35°C

2. Light Intensity Light intensity - speed it up or slow it down High intensity would naturally increase the rate (to a certain point)

3. Amount of Water Shortage could stop photosynth completely Can also damage plant tissues Desert plants & conifers have waxy coating to protect from moisture loss

Extreme Conditions Photosynth C4 Photosynth CAM Plants

C4 Photosynth Special pathway to gather CO2 in low light to pass to Calvin Cycle - 1st molecule has 4 carbon (C4) Allows photosynth under harsh light and high temps Requires extra ATP to work Ex. Corn, sugar cane, and sorghum

C.A.M. Plant Crassulacean Acid Metabolism (C.A.M.) Named after family of plants Bring in air only at night CO2 combines with other molecules to make organic acids that trap Carbon - During the day, the plants squeeze leaves shut & use trapped Carbon for food. Ex. Pineapple trees & some cacti

Fun Fact C.A.M. plants are often planted along freeways to help “retard” brushfires

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