Photosynthesis Chapter 8 p

Boring Definition Process by which certain groups of organisms capture energy from sunlight and convert that solar energy into chemical energy that is initially stored in a carbohydrate Process by which certain groups of organisms capture energy from sunlight and convert that solar energy into chemical energy that is initially stored in a carbohydrate

Photosynthesis Process by which plants make their own food Process by which plants make their own food Requires carbon dioxide, water, minerals, and sunlight Requires carbon dioxide, water, minerals, and sunlight Gives off oxygen Gives off oxygen All life on earth based on this process All life on earth based on this process

Electromagnetic Spectrum

Why the Spectrum is Relevant Plants absorb some light energy from the sun. Plants absorb some light energy from the sun. Absorption of blues and reds in the visible portion of the spectrum drive photosynthesis Absorption of blues and reds in the visible portion of the spectrum drive photosynthesis Plants are green because they reflect green light, instead of absorbing it. Plants are green because they reflect green light, instead of absorbing it.

Leaf Anatomy What we see Blade- “leafy” part Blade- “leafy” part Petiole- leaf stem Petiole- leaf stem Stomata- pores in the epidermis that allow carbon dioxide in and water out Stomata- pores in the epidermis that allow carbon dioxide in and water outLayers Epidermis on top and bottom Epidermis on top and bottom Mesophyll Mesophyll

Mesophyll Cell Typical plant cells Typical plant cells Contain chloroplasts, from 1 to hundreds per cell Contain chloroplasts, from 1 to hundreds per cell

Chloroplasts Organelles that are the site of photosynthesis Organelles that are the site of photosynthesis Outer membrane Outer membrane Inner membrane Inner membrane Stroma-liquid material Stroma-liquid material Granum- stack of thylakoids Granum- stack of thylakoids Thylakoid Thylakoid

Thylakoids Network of chloroplast membranes Network of chloroplast membranes Specific sites of photosynthesis, along with stroma Specific sites of photosynthesis, along with stroma Include pigments- molecules that absorb sunlight, especially chlorophyll a Include pigments- molecules that absorb sunlight, especially chlorophyll a

Reactions in Photosynthesis Light Reactions Depend directly on sunlight Depend directly on sunlight Occur in thylakoid membranes Occur in thylakoid membranes Dark Reactions Occur in stroma Occur in stroma AKA Calvin Cycle AKA Calvin Cycle

Electron Review ElectronNucleus High energy electrons are farther away from the nucleus High energy electrons are farther away from the nucleus

Light Reactions: Photosystems Organized complex of molecules in thylakoid membranes that takes in solar energy and transforms it into chemical energy Organized complex of molecules in thylakoid membranes that takes in solar energy and transforms it into chemical energy Pigments collect light energy Pigments collect light energy Energy passed on to reaction center in a redox reaction Energy passed on to reaction center in a redox reaction Light energy is converted into chemical energy Light energy is converted into chemical energy Electrons are accepted by reaction center, making it a high energy region Electrons are accepted by reaction center, making it a high energy region

An Example of a Photosystem

Photosystem II Photosystem II collects solar energy Photosystem II collects solar energy Energy converted to chemical energy Energy converted to chemical energy Electrons accepted in reaction center Electrons accepted in reaction center Central chlorophyll loses electrons, becomes oxidizing agent Central chlorophyll loses electrons, becomes oxidizing agent Electrons go on to electron transport chain Electrons go on to electron transport chain Electrons in center chlorophyll replaced with electrons from water in a reaction controlled by an enzyme Electrons in center chlorophyll replaced with electrons from water in a reaction controlled by an enzyme

Photosystem I Accepts low energy electrons from PS II electron transport chain Accepts low energy electrons from PS II electron transport chain Collects solar energy to re-energize electrons Collects solar energy to re-energize electrons Passes electrons through another electron transport chain to electron carrier NADP + to store energy in the reduced form (NADPH) Passes electrons through another electron transport chain to electron carrier NADP + to store energy in the reduced form (NADPH)

How does this affect you? The light reactions split water molecules, allowing plants to give off the O 2 we need to breathe. This reaction uses water. The light reactions split water molecules, allowing plants to give off the O 2 we need to breathe. This reaction uses water. The dark reactions produce carbohydrates for the plant to eat, and we eat them too! These reactions also use carbon dioxide. The dark reactions produce carbohydrates for the plant to eat, and we eat them too! These reactions also use carbon dioxide. Passing electrons using a redox reaction is an efficient enough use of energy to allow for life. Passing electrons using a redox reaction is an efficient enough use of energy to allow for life.

Dark Reactions Function: high energy electrons from the light reactions are combined with CO 2 and a sugar to make a high energy carbohydrate that can serve as food Function: high energy electrons from the light reactions are combined with CO 2 and a sugar to make a high energy carbohydrate that can serve as food Also called the C3 cycle because of the number of Carbons in the first step Also called the C3 cycle because of the number of Carbons in the first step

Steps to the Calvin Cycle 1. Enzyme rubisco combines CO 2 and RuBP (sugar). (This is a fixation process because it incorporates a gas into an organic molecule.) 2. RuBP is energized using ATP and NADPH. 3. The product of step 2 is glyceraldehyde-3- phosphate (G3P), a high energy molecule that can be made into other sugars (i.e. glucose). 4. RuBP is regenerated.

An Alternative Pathway: C 4 Photorespiration- occurs when rubisco binds with oxygen instead of CO 2, making C 3 photosynthesis inefficient Photorespiration- occurs when rubisco binds with oxygen instead of CO 2, making C 3 photosynthesis inefficient Named for 4 carbon product of first reaction Named for 4 carbon product of first reaction Mostly occurs in warm-climate places because stomata are closed to keep water in Mostly occurs in warm-climate places because stomata are closed to keep water in Keeps a higher concentration of CO 2 in cells for photosynthesis Keeps a higher concentration of CO 2 in cells for photosynthesis