Cell Energy: Photosynthesis

Today’s Agenda Objectives… Define heterotroph and autotroph. Describe the laws of thermodynamics. Explain the importance and role of ATP in living organisms. Identify the organelle of photosynthesis and its part, as well as where the two reactions of photosynthesis occur. GoFormative Energy Notes Kahoot Intro to Photosynthesis Chloroplast Cutout

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.

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) ADP has 2 phosphates

CHEMICAL ENERGY AND ATP Storing energy- when bonds are formed, energy is stored 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 through 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 Location Site of photosynthesis Pigment: chlorophyll Organelle: Chloroplast Double membrane Contains Thylakoids, grana, stroma

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

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

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

Light Dependent reaction in the Thylakoid membrane Photons of light strike chlorophyll in Photosystem (PS) II, one of two clusters of light absorbing pigments In photosystem II: These light photons jump between chlorophyll molecules until they arrive at a specific chlorophyll a, termed the reaction center a. Called pigment 680 (P680)

Light Dependent reaction in the Thylakoid membrane At the reaction center, this energy from the photons is used to excite two of the reaction center’s electrons (e-) These electrons “jump” to an e- carrier, which moves them from PS II to Photosystem I (the second 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- Called photolysis 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

As light strikes PS I, e- arriving at PS I become re-excited The re-excited electrons in PS I combine with H+ from photolysis Together they convert NADP+ to NADPH NADP+ is an electron carrier that will take the electrons into the second phase (dark phase) of photosynthesis

The H+ now in HIGH concentration in the thylakoid space travel down their concentration gradient 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 (fluid-filled space) ATP and NADPH from the light reaction are used to “fuel” the Calvin Cycle stores chemical energy from light reaction in sugar

Steps to the Calvin cycle CO2 enters through the stomata (pores in the leaf) and combines with a 5-carbon sugar, ribulose biphosphate (RuBP), to form 6-carbon sugar Called Carbon fixation because makes CO2 organic Catalyzed by RuBiSCO, the most abundant enzyme on earth! The 6 carbon sugar immediately breaks down into two 3- carbon sugars called PGA This happens because it was unstable

Steps of Calvin cycle Each PGA is converted into a 3 carbon sugar, G3P, in a series of reactions Requires 1 ATP and 1 NADPH per G3P Called Reduction Phase Reduction: add electrons

Steps of calvin cycle NOTE: Happens with 3 C02 at once, so make 6 G3P molecules using 6ATP and 6 NADPH Product f 3 CO2 undergoing the cycle is1 G3P leaves the cycle to make glucose Remaining 5 G3P rearrange into 3 RuBP in a series of reactions that require 3 ATP Called regeneration phase Requires 1 ATP per RuBP

What it really looks like

Summary of the Calvin cycle Reactants- ATP, NADPH , and CO2 Products: Glucose (or G3P)

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