Introduction

 ALL cells need energy and matter for growth and reproduction.  Some organisms (like plants) obtain their energy directly from the Sun.  Other organisms must consume food to obtain energy.

 Autotrophs: self feeders, organisms capable of making their own food  Photoautotrophs: use photosynthesis = makes organic compounds (glucose) from light. Converts sun energy into chemical energy usable by cells.  Chemoautotrophs: use chemosynthesis = makes organic compounds using energy from the oxidation of inorganic chemicals, such as sulfur released from deep hydrothermal vents.

 Energy = Capacity to do work  Potential Energy = Stored energy (the energy must be released for it to do any work e.g. apple hanging by a stem)  Kinetic Energy = The energy of motion (apple falling to the ground)  Chemical Energy = Energy stored in the bonds of molecules. Type of potential energy. Once the chemical bonds are broken, the atoms have extra kinetic energy. The atoms can move, do work, make things happen!

The CARBON CYCLE

1. Photosynthesis = light energy from the Sun is used to transform carbon dioxide and water into energy-rich food molecules. CO 2 + H 2 O C 6 H 12 O 6 + O 2 Carbon Dioxide Water Light Energy GlucoseOxygen

2. Cellular Respiration = all of the chemical reactions needed to break down (metabolize) carbohydrates (and other molecules) to transfer chemical energy to ATP. C 6 H 12 O 6 + 6O 2 6H 2 O + 6CO 2 Carbon Dioxide Water GlucoseOxygen ATPADP

 Involves over 100 chemical reactions.  The overall process happens in two main stages:  1. PHOTO stage: light dependent  2. SYNTHESIS stage: light independent

 Splits water and produces ATP.  Photosystem reactions need light energy.  Stores chemical energy in the bonds of glucose.  Synthesis reactions need chemical energy (ATP) and H + from photo stage.

 Carbon dioxide and water plus light energy are the raw materials of photosynthesis.  Enzymes and chlorophyll are accessories that are needed to make photosynthesis occur

 Visible and Invisible radiation from the Sun and other sources of radiant energy.  Radiowaves, microwaves, x-rays, etc  Visible radiation is usually simply called LIGHT.

 All forms of electromagnetic radiation travel at m/s  Different frequency of light results in different wavelengths, which are perceived as different colours.  The highest frequency of light is violet and the lowest frequency is seen as red.  A combination of all of the frequencies is interpreted as White light.

 Light travels through space in the form of individual energy “packets” called photons.  The amount of energy in a photon depends on the frequency of light. The higher the frequency the more energy the photon is able to deliver.  More energy in a photon of violet than in red.

 To use the energy of light for photosynthesis, a plant must absorb photons of light.  Molecules that absorb light are called Pigments.  Most plant leaves contain chlorophyll pigments which give leaves their green colour.  Absorption is only one of three possible outcomes when light strikes a surface.  The other two are reflection and transmission

 Photosynthesis takes place in chloroplasts  Chloroplasts contain light absorbing pigment molecules (chlorophyll a & b)  Chlorophyll absorbs red, violet, and shades of blue.  The chlorophyll passes the energy onto other molecules that can be used by the synthesis reactions.

 Very small – 40 chloroplasts in 1mm.  Very powerful - perform hundreds of reactions in just 1 second.  Has a double membrane.

 Folded THYLAKOID membranes form stacks known as GRANA. The folding increases the surface area for reactions to occur.  Inside the thylakoid is a space called the LUMEN

 In and around the grana is a watery substance called STROMA  The chloroplast also contains lots of ENZYMES.

 Chlorophyll pigments are packed into clusters called PHOTOSYSTEMS  The photosystems are located in the THYLAKOIDS.

 Light is first received at PHOTOSYSTEM II  The chlorophyll molecules pass the energy to the REACTION CENTER  Chlorophyll in the reaction centre donates excited electrons to an electron acceptor (PLASTOQUINONE).

 The chlorophyll in the reaction centre then splits the nearest WATER molecules.  PHOTOLYSIS forms oxygen, hydrogen ions, and electrons.

 The OXYGEN that is produced is a waste product.  Oxygen molecules pass out the chloroplast membrane into the cell’s CYTOPLASM.  The plant’s own cells use some of the oxygen to carry out cellular RESPIRATION.

 Excited electrons are passed from the primary electron acceptor (plastoquinone) to the ELECTRON TRANSPORT CHAIN  As the electrons pass through the chain, ENERGY is released.  This energy is used to pump protons into the LUMEN (space between thylakoids).

 A CONCENTRATION GRADIENT of protons develops across the thylakoid membrane.  HIGH concentration inside and LOW outside  The protons move back down the gradient through the enzyme ATP Synthase.  This passage is used to make ATP from ADP.

 Adenosine triphosphate  One molecule of ATP contains three PHOSPHATE groups  When removing the THIRD phosphate group, lots of energy is given off  An excellent molecule for shuttling ENERGY around within cells.

 At PHOTOSYSTEM I, chlorophyll molecules absorb more energy from the Sun.  This re-excites ELECTRONS and moves them to a high energy level.  The electrons are used to REDUCE NADP to form NADPH.

 Nicotinamide adenine dinucleotide phosphate  NADPH is the reduced form of NADP.  Reduction is the GAIN of electrons by a molecule, atom, or ion

 Does not require sunlight  Requires 18 ATP's, 12 NADPH's, and CO 2 to produce glucose  Uses the products from the Light Reaction  Occurs in the STROMA of the chloroplast  Three phases of the Dark Reaction  Carbon Fixation  Reduction  Regeneration

 Carbon fixation is a process which involves the conversion of carbon in gas compounds to carbon in solid compounds.  In order for carbon fixation to occur, energy in the form of ATP and NADPH are needed (from the light reactions).  The carbon can be used to make organic compounds.

 The carbon of a CO 2 molecule from the ATMOSPHERE is attached to a 5-carbon sugar called RuBP  This forms an UNSTABLE 6-carbon compound  The 6-carbon compound BREAKSDOWN to form two 3-carbon molecules  called Glycerate 3-phosphate

 The Glycerate 3-phosphate are converted to TRIOSE PHOSPHATE using energy (ATP) and hydrogen (from NADPH) from the Light Reaction  For every 3 molecules of CO 2 there are 6 molecules of triose phosphate produced  Only 1 is net gain  What happens to the other 5?  Regeneration

 Products need to be regenerated to keep the cycle going.  5 of the 6 triose phosphate molecules are regenerated using ATP and produce RuBP molecules which are then ready to receive new CO 2 and continue the cycle  The one triose phosphate molecule COMBINED with another triose phosphate molecule is used to make glucose, fructose, sucrose, starch and cellulose for the plant.

 Describes how much sugar a plant can produce over time  It describes how productive a plant is under various conditions  What things would control the rate of photosynthesis?

1. Light Intensity:  High Intensity Light causes the rate of photosynthesis to increase  The rate will increase until it reaches its saturation point  At the saturation point, the rate of photosynthesis remains constant

2. Temperature:  As temperature increases, so does the rate of photosynthesis  Enzymes function at an optimal temperature: If the temperature is too high or too low, enzymes will not function properly  Rate of photosynthesis will slow down or stop.

3. Water:  Water is one of the raw materials of photosynthesis  A shortage of water can slow or even stop photosynthesis  Water stress causes stomata to close, preventing CO 2 from entering the leaf

4. Carbon Dioxide:  An increase in CO 2 concentration causes the rate of photosynthesis to increase  More CO 2 available means more sugar made in the light independent reaction

 In hot, dry environments plants maximize photosynthesis by limiting water loss.  Leaves of plants contain stomata which are tiny holes in the leaves that release by products and take in raw materials need for photosynthesis

 Most plants will close their stomata to prevent water loss but this limits carbon dioxide intake  Some plants will only open the stomata during night  It is a fine balance between receiving the necessary supplies and preventing water loss.

 If the CO 2 concentration in the cell drops below 50 ppm, the cell begins to undergo PHOTORESPIRATION which results in the fixation of oxygen instead of carbon dioxide.  This is a very wasteful process as it produces a substance that is not useful to the cycle.

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