Cell Energy: Photosynthesis Chapter 8

Energy and life Energy- Ability to do work No energy = no life Laws of thermodynamics First law- energy cannot be created or destroyed, it can only be changed/converted. Second law- entropy in a system is always increasing Entropy: amount of disorder, energy not available to do work Said simply: energy cannot be converted without the loss of useable energy (thermal energy/heat) Example : Food chains

10% Rule Only 10% of energy from a trophic level is passed to next level Caused by 2nd law of thermodynamics

Forms of Energy Energy comes in many forms: Light Heat Electricity . . . Energy can also be stored in the bonds of chemical compounds.

Autotrophs and heterotrophs Autotrophs- organisms that make their own food from energy from the sun or other sources Known as producers Heterotrophs- organisms that need to ingest or consume food to obtain energy Known as consumers ALL organisms have to release the energy in sugars and other compounds to live.

Metabolism- all of the chemical reactions in a cell Anabolism- Synthesis reactions in a cell Example: photosynthesis Catabolism- Decomposition reactions in a cell Example: Cellular respiration

Photosynthesis- light energy from the sun is converted into chemical energy for use by the cell Cellular respiration- Organic molecules are broken down to release energy for use by the cell.

Chemical Energy and atp ATP- Adenosine Triphosphate- Energy for the cell Made of adenosine, ribose and three phosphates ATP releases energy when the bond between the second and third phosphate groups is broken, forming a molecule called adenosine diphosphate (ADP) and a free phosphate ADP + P (or Pi)

CHEMICAL ENERGY AND ATP (Not in notes) Storing energy- when bonds are formed, energy is stored ADP- Adenosine diphosphate is similar to ATP, but with two phosphates instead of three Energy is stored when another phosphate is added to ADP

Energy is released when bonds are broken Releasing energy Energy is released when bonds are broken When a phosphate is removed from ATP, energy is released As many as two phosphates can be removed from ATP Remove one phosphate = ADP Remove two phosphates = AMP (Adenosine Monophosphate)

Using biochemical energy 1. Cells use ATP for active transport, to move organelles in the cell, and to synthesize proteins and nucleic acids 2. Cells do not keep large amounts of ATP in the cell. The cell can regenerate ATP from glucose as needed Cellular Respiration 3. ATP is great for transferring energy, but not for storing it.

Where do trees get their mass from? Veritasium Video Video from: http://www.youtube.com/watch?v=2KZb2_vcNTg

Photosynthesis overview Photosynthesis- The process by which plants use sunlight to convert water and carbon dioxide into sugar The photosynthesis equation: 6 CO2 + 6 H20 + light  C6H12O6 + 6 O2 Carbon dioxide and water and light  sugar and oxygen What are the products and the reactants?

photosynthesis requires light Visible light is a mixture of wavelengths: ROY G BIV Shorter waves: more energy Longer waves: less energy Wavelength corresponds to color

Pigments in photosynthesis Pigments- light absorbing particles There are different types of pigments Chlorophyll- principal pigment that absorbs light in the blue-violet and red regions, but not the green Chlorophyll is found in the chloroplasts of leaves This is why chloroplasts and plants look green There are accessory pigments: like carotenoids (think carrots)

Chlorophyll is best at absorbing ____________ Chlorophyll a & b Chlorophyll is best at absorbing ____________ Does not absorb ______________________ Blue and red Green and yellow

Photosynthesis Reactions Site of photosynthesis Pigment: chlorophyll Organelle: Chloroplast Double membrane Contains Thylakoids, grana, stroma Plant cell: mesophyll Gas exchange: stomata

Organelles of photosynthesis Thylakoids – membranes that form sacs in which pigments are embedded Grana (granum, singular) – The stacks of thylakoids Stroma – the space surrounding the thylakoids Contains enzymes that catalyze the formation of sugar from carbon dioxide and water Also contains the chloroplast’s DNA & RNA

Parts of the Chloroplast Stroma – Liquid inside the chloroplast. Surrounds the thylakoid membranes. Grana – (granum plural) Stacks of thylakoid membranes Thylakoid – Membranes containing photosystems Photosystems – Light capturing systems Parts of the Chloroplast

Two Processes of Photosynthesis 1. Light Dependent Reaction 2. Calvin Cycle (Light Independent Reaction)

The light reaction Overview Takes place in the membrane of the thylakoids Chlorophyll absorb the light, light energy is converted into chemical energy needed to produce sugars Water is split into Hydrogen and Oxygen in the process

Steps to the light reaction: Thylakoid membrane Photons of light strike Photosystem (PS) II, one of two clusters of light absorbing pigments Two electrons from PS II jump to an e- carrier Electrons moves from PS II to PS I (other photosystem) e- get re-excited in PS I

Steps of photosynthesis At the same time, light energy is used to split a molecule of water into 2H+ , O2 and 2e- 2 H2O → 4 H+ + 4 e- + O2 O2 leaves out the stomata (pores) H+ remain in the inside of the thylakoid These e- replace those lost in PS II

Together they convert NADP+ to NADPH The re-excited electrons in PS I combine with H+ from splitting of water Together they convert NADP+ to NADPH NADPH is an electron carrier that will take the electrons into the second phase (dark phase) of photosynthesis

Meanwhile, in the thylakoid The H+ now in HIGH concentration in the thylakoid space travel down their membrane through ATP Synthase to the stroma This energy adds a Pi to ADP to make ATP The ATP and the NADPH now head to the Calvin Cycle to act as the energy to drive the reaction Summary: Reactants- H20 and Light Products – O2 (as waste), ATP and NADPH

Helpful animations http://www.stolaf.edu/people/giannini/flashanimat /metabolism/photosynthesis.swf step by step photosynthesis light reaction

The Calvin Cycle Overview Takes place in the stroma (empty space) ATP and NADPH from the light reaction are used to “fuel “ the Calvin Cycle Saves chemical energy from light reaction in sugar

Steps to the Calvin cycle CO2 enters through the stomata (pores in the leaf) and combines with RuBP Catalyzed by RuBiCO, the most abundant enzyme on earth! Series of reactions convert CO2 into glucose

Steps of Calvin cycle Carbon for Glucose comes from CO2 Hydrogen for Glucose comes from NADPH – from light reaction Oxygen for glucose comes from CO2 Needs energy for reactions to occur – comes from Light reaction

What it really looks like

Summary of the Calvin cycle Reactants- ATP, NADPH , and CO2 Products: Glucose

Summary of photosynthesis Two step process 1. Light Dependent Reaction in the Thylakoid membrane 2. Light Independent Reaction (Calvin Cycle) in the Stroma The reactants : CO2 and H2O The products: C6H12O6 AND O2

What Affects the rate of photosynthesis? Temperature CO2 Light Water