Photosynthesis: Life from Light and Air

Energy needs of life  All life needs a constant input of energy  Animals = Heterotrophs  get their energy from “eating others”  eat food = other organisms = organic molecules  make energy through respiration  Plants = Autotrophs  get their energy from “self”  get their energy from sunlight  build organic molecules (food) from CO 2  make energy through photosynthesis

Photosynthesis This is the equation you are used to seeing, but this is not the whole story… + water + energy  glucose + oxygen carbon dioxide 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++

What is the main chemical fuel that most living organisms use to store energy?  ATP – adenosine triphosphate What does an ATP molecule consist of? Adenine, ribose, and three phosphate groups What do the lines between the parts of the molecule represent? Chemical bonds ATP

WHAT IS THE ROLE OF ATP IN CELLULAR ACTIVITIES?  The characteristics of ATP make it an exceptionally useful molecule that is used by all types of cells as their basic energy source

 Even though ATP is very efficient at transferring energy, it is not very good for storing energy over the long term.  Living organisms store large amounts of energy in the form of glucose (90 times more energy than ATP)  Cells can break apart glucose and make ATP molecules very easily to release the energy slowly

How do plants live?  Photosynthesis  Energy building reactions  collect sun energy  make ATP  Sugar building reactions  use ATP for energy  use CO 2 as carbon for new sugars  build sugars  glucose, cellulose, starch  build all other organic molecules  proteins, lipids, carbohydrates, DNA  store energy for future use  starch in seeds & roots

Photosynthesis  Actually 2 separate reactions  Energy building  use sunlight  make energy (ATP)  Sugar building  use ATP  use CO 2  make sugars (C 6 H 12 O 6 ) Energy building reactions Sugar building reactions sun ATP ADP CO 2 sugar

CO 2 Chloroplasts Leaf Chloroplast absorb sunlight & CO 2 make energy & sugar Chloroplasts contain Chlorophyll

Energy Building Reactions O2O2 H2OH2O Energy Building Reactions sunlight ATP H2OH2O O2O2 light energy  ++  makes ATP energy  releases oxygen as a waste product

Sugar Building Reactions sugars C 6 H 12 O 6 CO 2 Sugar Building Reactions ATP CO 2 C 6 H 12 O 6 ADP ATP  ++ ADP  builds sugars  uses ATP  cycles ADP back to make more ATP

Putting it all together sugars C 6 H 12 O 6 CO 2 ATP ADP H2OH2O O2O2 sunlight CO 2 H2OH2O C 6 H 12 O 6 O2O2 light energy  +++ Sugar Building Reactions Energy Building Reactions Plants make both:  ATP  sugars

WHAT IS THE ROLE OF CHLOROPHYLL IN PHOTOSYNTHESIS?  In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts  Sunlight, which your eyes perceive as “white” light, is actually a mixture of different wavelengths of light of various colors

Any compound that absorbs light also absorbs energy from that light. When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These high-energy electrons make photosynthesis work HOW WELL WOULD A PLANT GROW UNDER PURE YELLOW LIGHT? The plant would not grow well because neither chlorophyll a nor b absorbs much light in the yellow region of visible light

8-3 THE REACTIONS OF PHOTOSYNTHESIS  Take a look at the picture of a chloroplast on page 208  Photosynthesis is broken down into two reactions  light-dependent reactions- occur in thylakoid membrane  light-independent reactions (Calvin Cycle) – occur in the stroma

WHAT HAPPENS IN THE LIGHT-DEPENDENT REACTIONS?  The light-dependent reactions produce oxygen gas and convert ADP and NADH+ into the energy carriers ATP and NADPH  NADP+ - a carrier molecule that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule; NADP+ converts to NADPH when it accepts electrons

WHAT IS THE CALVIN CYCLE?  The Calvin Cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars

Factors that can affect photosynthesis  water  temperature  intensity of light

 Bring In  CO 2 H2OH2O  light  Let Out O2O2  Move Around  sugars So what does a plant need? 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ roots shoot leaves

Leaf Structure H2OH2OCO 2 O2O2 H2OH2O phloem (sugar) xylem (water) stomate guard cell palisades layer spongy layer cuticle epidermis  gases in & out  water out  transpiration O2O2

Stomates  Function of stomates  CO 2 in  O 2 out  H 2 O out guard cell stomate

Xylem carry water up from roots

Phloem: food-conducting cells  carry sugars around the plant wherever they are needed  new leaves  fruit  seeds

Putting it all together  Making a living…  sunlight  leaves = solar collectors  photosynthesis  gases: CO 2 in & O 2 out  stomates = gases in & out H2OH2O  roots take in water from soil  pulled up by leaf evaporation  nutrients  roots take in from soil

How are they connected? glucose + oxygen  carbon + water + energy dioxide C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ Respiration + water + energy  glucose + oxygen carbon dioxide 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ Photosynthesis

H2OH2O Energy cycle Photosynthesis Cellular Respiration sun The Great Circle of Life! Where ’ s Mufasa? glucose O2O2 CO 2 plants animals, plants ATP

The poetic perspective  All of the solid material of every plant was built out of thin air  All of the solid material of every animal was built from plant material Then all the cats, dogs, mice, people & elephants… are really strands of air woven together by sunlight! sun air

Any Questions??