Unit TwoUnit Two“Energy Acquisition”“Energy Acquisition”

““Photosynthesis”Photosynthesis”

The Sun and PlantsThe Sun and Plants

What makes life possible on Earth is the What makes life possible on Earth is the presence of a medium sized star, the Sunpresence of a medium sized star, the Sun

Also, just as important is the fact the Earth Also, just as important is the fact the Earth is at a near perfect distance from the sun: is at a near perfect distance from the sun: “not too hot, and not too cold”“not too hot, and not too cold”

However, animals like us humans still However, animals like us humans still could not survive for any length of time could not survive for any length of time without plants to convert light energy into without plants to convert light energy into biomass, i.e. food for us!biomass, i.e. food for us!

The Sun and PlantsThe Sun and Plants Plants are called producers/autotrophs Plants are called producers/autotrophs

because they, in essence, make their own because they, in essence, make their own food by using sunlight and other chemical food by using sunlight and other chemical compounds found in nature (note: some compounds found in nature (note: some algae and bacteria also make their own algae and bacteria also make their own food)food)

The food they make enables them to grow The food they make enables them to grow (addition of biomass)….. and they do not (addition of biomass)….. and they do not ever consume other living organisms in ever consume other living organisms in the processthe process

Because of this food generating ability, Because of this food generating ability, they are placed at the bottom of the food they are placed at the bottom of the food chain….all other species depend on them chain….all other species depend on them for survivalfor survival

PhotosynthesisPhotosynthesis

The process by which plants generate food The process by which plants generate food (Glucose) for their cells is called (Glucose) for their cells is called “Photosynthesis”“Photosynthesis”

There are 3 main stages of There are 3 main stages of Photosynthesis:Photosynthesis:

A) Capturing energy from sunlightA) Capturing energy from sunlightB) Using that energy to make ATP B) Using that energy to make ATP

and NADPH (Light Dependent and NADPH (Light Dependent Reactions)Reactions)C) Using ATP and NADPH to make C) Using ATP and NADPH to make Carbohydrates (Calvin Cycle)Carbohydrates (Calvin Cycle)

Chemical Reaction for PhotosynthesisChemical Reaction for Photosynthesis

carbon dioxide + water + light carbon dioxide + water + light energy ---> glucose + oxygen + energy ---> glucose + oxygen + waterwater

COCO22 + H + H22O + light energy ---> O + light energy ---> CC66HH1212OO66 + O + O22 + H + H22OO

Photosynthetic StructuresPhotosynthetic Structures The Chloroplast is the light The Chloroplast is the light

sequestering organelle, and is also the sequestering organelle, and is also the site of all three stages of site of all three stages of PhotosynthesisPhotosynthesis

The Chloroplast is composed of internal The Chloroplast is composed of internal membranes that are organized into membranes that are organized into flattened sacs called “Thylakoids”flattened sacs called “Thylakoids”

These Thylakoids are stacked on top of These Thylakoids are stacked on top of each other in columns called “Grana”each other in columns called “Grana”

A fluid called the “Stroma” surrounds A fluid called the “Stroma” surrounds the stacks of Thylakoidsthe stacks of Thylakoids

Photosynthetic StructuresPhotosynthetic Structures The light sequestering pigment, The light sequestering pigment,

Chlorophyll, is located within the Chlorophyll, is located within the Thylakoids in groups called Thylakoids in groups called “Photosystems”“Photosystems”

The Photosystem is the starting point of The Photosystem is the starting point of PhotosynthesisPhotosynthesis

The Chlorophyll captures “Photons”, The Chlorophyll captures “Photons”, tiny packets of energy from sunlight, tiny packets of energy from sunlight, which they subsequently transfer to which they subsequently transfer to proteins that assist in the generation of proteins that assist in the generation of ATP and NADPHATP and NADPH

Sunlight’s EnergySunlight’s Energy

It is very fortunate the Chlorophyll in It is very fortunate the Chlorophyll in the Chloroplasts of plants is perfectly the Chloroplasts of plants is perfectly suited to the energy levels found in suited to the energy levels found in visible light that comes from the sunvisible light that comes from the sun

Further, there are many energy Further, there are many energy sources like radio waves, gamma sources like radio waves, gamma rays, microwaves, but each either rays, microwaves, but each either has too little energy or too much has too little energy or too much energy to be compatible with plants energy to be compatible with plants energy harnessing systemenergy harnessing system

The Electromagnetic SpectrumThe Electromagnetic Spectrum

Chlorophyll AbsorptionChlorophyll Absorption

The leaves of plants are usually green due to The leaves of plants are usually green due to the fact Chlorophyll absorbs light in the violet, the fact Chlorophyll absorbs light in the violet, blue, and red range of the spectrumblue, and red range of the spectrum

Chlorophyll reflects the green portion of the Chlorophyll reflects the green portion of the visible spectrum, and therefore the leaves visible spectrum, and therefore the leaves take on a characteristic green appearancetake on a characteristic green appearance

““Carotenoids” are a group of Carotenoids” are a group of accessory pigments that capture accessory pigments that capture violet to blue-green light and violet to blue-green light and reflect yellow, orange, & redreflect yellow, orange, & red

Photosynthesis: Stage 1Photosynthesis: Stage 1

A) Capturing energy from sunlightA) Capturing energy from sunlight– A photon of light in the appropriate A photon of light in the appropriate

wavelength is sequestered by a wavelength is sequestered by a chlorophyll molecule and this energy is chlorophyll molecule and this energy is passed to another chlorophyll moleculepassed to another chlorophyll molecule

Photosynthesis: Stage 2Photosynthesis: Stage 2(exergonic)(exergonic)

B) Using energy to make ATP and B) Using energy to make ATP and NADPH (Light Dependent Reactions)NADPH (Light Dependent Reactions)1. the energy from excited electrons taken 1. the energy from excited electrons taken

from water is used in the “Electron from water is used in the “Electron Transport System” to pump Hydrogen Ions Transport System” to pump Hydrogen Ions (protons) across the Thylakoid membrane (protons) across the Thylakoid membrane

2. Many Hydrogen Ions (protons) 2. Many Hydrogen Ions (protons) accumulate in the Thylakoid serving as accumulate in the Thylakoid serving as the energy source to construct ATP the energy source to construct ATP molecules from ADP moleculesmolecules from ADP molecules

Photosynthesis: Stage 2Photosynthesis: Stage 2(exergonic)(exergonic)

3. The electron from water that had its 3. The electron from water that had its energy used in the Electron Transport energy used in the Electron Transport System is now directed to another System is now directed to another photosystem to be reenergized by the photosystem to be reenergized by the absorption of another photon of lightabsorption of another photon of light

4. This electron enters another Electron 4. This electron enters another Electron Transport System and is transferred to Transport System and is transferred to NADP+NADP+

5. NADP+ bonds with a Hydrogen Ion 5. NADP+ bonds with a Hydrogen Ion (proton) to form NADPH, which is (proton) to form NADPH, which is important in stage 3 production of important in stage 3 production of carbohydratescarbohydrates

Light Dependent ReactionsLight Dependent Reactions

Photosynthesis: Stage 3Photosynthesis: Stage 3(endergonic)(endergonic)

C) Using ATP and NADPH to make C) Using ATP and NADPH to make Carbohydrates (Calvin Cycle)Carbohydrates (Calvin Cycle)

1. ATP generated in Stage 2 (Light 1. ATP generated in Stage 2 (Light Dependent Reactions) is used as Dependent Reactions) is used as

the fuel the fuel for the Calvin Cyclefor the Calvin Cycle2. NADPH generated in Stage 2 2. NADPH generated in Stage 2

provides the Hydrogens needed to provides the Hydrogens needed to build Glucosebuild Glucose

3. Numerous proteins acting as 3. Numerous proteins acting as enzymes drive the production of enzymes drive the production of GlucoseGlucose

Photosynthesis: Stage 3Photosynthesis: Stage 3(endergonic)(endergonic)

4. The Calvin Cycle has to go to completion 4. The Calvin Cycle has to go to completion six times in order to produce one Glucose six times in order to produce one Glucose molecule: each cycle completion adds just molecule: each cycle completion adds just one Carbon atom from COone Carbon atom from CO22 to make the to make the Glucose molecule, which has 6 Carbon Glucose molecule, which has 6 Carbon atomsatoms

5. To keep both Stage 2 and Stage 3 5. To keep both Stage 2 and Stage 3 functioning, used ADP and NADP+ from functioning, used ADP and NADP+ from the Calvin Cycle is returned to the Electron the Calvin Cycle is returned to the Electron Transport System in the photosystemsTransport System in the photosystems

Calvin CycleCalvin Cycle

PhotorespirationPhotorespiration During extreme environmental During extreme environmental

conditions (hot and dry), plants close conditions (hot and dry), plants close their “Stomata” to reduce water losstheir “Stomata” to reduce water loss

Once their stomata are closed they no Once their stomata are closed they no longer absorb Carbon Dioxide, and longer absorb Carbon Dioxide, and therefore the Oxygen that is usually therefore the Oxygen that is usually released as a byproduct of released as a byproduct of photosynthesis, is incorporated into the photosynthesis, is incorporated into the Calvin Cycle causing it to “short circuit”Calvin Cycle causing it to “short circuit”

Some plants use CSome plants use C44 Photosynthesis (use Photosynthesis (use of different cells and chemical of different cells and chemical reactions) during hot, dry days in order reactions) during hot, dry days in order to continue to photosynthesize to continue to photosynthesize

Photosynthesis OverviewPhotosynthesis Overview

http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie.htm

https://www.youtube.com/watch?v=sQK3Yr4Sc_k