Photosynthesis Jaime Crosby CHS

Photosynthesis: Trapping the Sun’s Energy

Trapping Energy From Sunlight To use the energy of the sun’s light, plant cells must trap and store it in a form that is readily usable by cell organelles, ATP

Photosynthesis Photosynthesis is the process plants use to trap the sun’s energy and build carbohydrates, called glucose that store energy

Light Dependent / Independent Reactions Photosynthesis must occur in two phases Light Dep. React. convert light energy into chemical energy, produce ATP Light Ind. React. utilize ATP to produce glucose

Key Plant Cell Components The chloroplast is where photosynthesis occurs Light dep. reactions take place in the membranes of the thylakoid discs in chloroplasts Thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight Chlorophyll is the most common pigment

Light-Dependent Reactions Sunlight strikes chlorophyll, energy is transferred to electrons which become excited or energized Electrons are passed to electron transport chain, a series of proteins embedded in the thylakoid membrane Electron is passed from protein to protein, losing a small amount of energy each time it is passed

Allows small amounts of the absorbed energy to be released at a time This energy can be used to form ATP from ADP After first e-chain, second e-chain is utilized Excited electron is carried to stroma of the chloroplast by NADP+ (becomes NADPH)

NADPH does not utilize the energized electron, stores for later reactions Photolysis occurs, two molecules of water are split to replace the electrons lost from chlorophyll, oxygen and four hydrogen ions released

Light-Independent Reactions Does not require light Calvin cycle, a series of reactions that use carbon dioxide to create carbohydrates, takes place

Calvin Cycle --Carbon fixation –PGA formation –Use of ATP and NADPH –Glucose production –ATP and PGAL replenish RuBP

Photosynthesis Equation 6CO2 + 12H2O  C6H12O6 + 6H20 + 6O2

Respiration Exact opposite equation from PS Occurs in the mitochondria, makes ATP

Phases of respiration Glycolysis: glucose becomes fructose and then 2 pyruvic acid molecules Kreb’s cycle or Citric Acid Cycle: Pyruvic acids become Acetyl CoA. ATPs and CO2 are produced Electron Transport Chain: Oxygen is the final Electron acceptor and 32 ATPs are made

Growth and Plant Hormones 5 major groups of plant hormones –Auxins –Gibberellins –Cytokinins –Abscisic Acid –Ethylene

Auxins Production occurs at meristems and buds, which promotes shoot growth toward sunlight

Gibberellins Intensely increases growth of root and shoot, mostly shoot. Can bring about flowering in some plants, and can encourage plants to propagate at lower temperatures. Also, can increase thickness of stems, size of fruit or length of internodes. EXPENSIVE

Cytokinins Stimulate mitosis to occur, thus are found a the meristems, also differentiate cells to final function. Prolong life of stored vegetables.

Abscisic Acid (ABA) Block the effect of auxin in dormant buds, causing leaves to fall off and is released when a leaf wilts to close stomata

Ethylene Increases ripeness of fruits, production of female flowers (and thus more fruit)

Tropisms Permanent, directed movements resulting from an external stimulus –Phototropism: growing in response to light Stems, petioles of leaf orient to light –Gravitropism: growing in response to gravity Primary root is +, branches or shoot is -