The Basics of Photosynthesis Add Subtitles here

Describe a basic food chain.

The Basics of Photosynthesis Photosynthesis is carried out by a number of different organisms: plants algae some protists cyanobacteria All of which contain CHLOROPHYLL Absorbs light energy and begins the process of photosynthesis There are several types of chlorophyll found in organisms We cover two common types Chlorophyll a Chlorophyll b

The Basics of Photosynthesis Chlorophyll molecules contain PORPHYRIN RINGS Attached to a long hydro-carbon tail (similar to fatty acids) Porphyrin rings are also found in hemoglobin and in the ETC The porphyrin ring contains a Mg atom at its centre surrounded by a hydro-carbon ring of alternating single AND double bonds Chlorophyll a and b differ only at the R group Chlorophyll a contains a -CHO Chlorophyll b contains a –CH3

The Basics of Photosynthesis CYANOBACTERIA! commonly referred to as blue-green algae unicellular (but grow in colonies) live in oceans, lakes, rivers, soil, and rocks areas with high nitrogen and phosphate levels led to rapid growth and into cyanobacteria blooms discolour water may be dangerous to fish, birds, humans, etc produce a toxin, microcystin, which can cause headaches, vomiting, diarrhea, & itchy skin Lichens that you see on rocks, is mix of fungi and cyanobacteria

The Basics of Photosynthesis CYANOBACTERIA! evolved ~ 3 billion years ago probably the first organisms to use sunlight to produce organic compounds from CO2 and H2O considered to be closely related to chloroplasts in plant cells so similar in fact that there is a theory about it... Endosymbiotic Theory proposes that an ancestor of cyanobacteria was engulfed by an early eukaryotic cell – which benefitted both cells! the cyanobacteria was protected from harsh environments the eukaryotic host obtained food produced by the new tenent thus, giving rise to plant cells

The Basics of Photosynthesis Eukaryotic Autotrophs! Algae, some protists, and plant cells contain their chlorophyll within CHLOROPLASTS The chlorophyll is what gives leaves, stems, and unripened fruit their green colors Only the areas containing chloroplasts can photosynthesize Leaves are the primary photosynthetic organ of plants

The Basics of Photosynthesis CHLOROPLAST STRUCTURE Stroma – protein-rich liquid in the interior of the chloroplast Thylakoids – a system of interconnected membrane bound sacs forming a separate compartment within the stroma * Increase surface area for optimum photosynthesis Thylakoid Membrane – photosynthetic membrane that contains chlorophyll and electron transport chain

The Basics of Photosynthesis CHLOROPLAST STRUCTURE Grana / Granum (sing.)– stack of thylakoids Lamella – unstacked thylakoids between grana - connects grana ** CHLOROPLASTS: - Have an inner and outer membrane - Have their own DNA

The Basics of Photosynthesis Leaves May be thin, broad, narrow, etc. Their structure and arrangement on stems/branches has evolved so that maximum surface area is exposed to sunlight Structure/arrangement also limits the distance CO2 has to travel to reach the chloroplasts PRIMARY FUNCTION: (you guessed it) PHOTOSYNTHESIS

The Basics of Photosynthesis STRUCTURE OF THE LEAF! Cuticle – Waxy, water-resistant coating on leaf Epidermis Layer – transparent colorless layer of cells below the cuticle of the leaf, stem, or root Mesophyll Layer – the photosynthetic cells (form bulk of leaf)

The Basics of Photosynthesis STRUCTURE OF THE LEAF! Guard Cells – photosynthetic epidermal cells that form and regulate the size of the stomata Stomata – opening on the surface of the leaf to allow for gas exchange between the leaf and the atmosphere Vascular Bundles – tubes and cells that transport nutrients

The Basics of Photosynthesis TRANSPIRATION The loss of water vapour from plant tissues through stomata Stomata cover only 1-2% of a leaf’s epidermal surface are responsible for 85% of the water lost by a plant Transpiration helps photosynthesis in two ways: Creates ‘transpirational pull’ - helps move water, minerals, etc from roots to leaves Produces evaporative cooling effect (like sweating) - prevents leafs from reaching temps that would denature their enzymes that catalyze photosynthesis

The Basics of Photosynthesis STOMATA Guard cells control the size of stoma in response to the surrounding environment Stomata are open when guard cells are turgid (swollen/full) Stomata are closed when guard cells are flaccid (empty) Size of guard cells control water movement via osmosis Osmosis follows the diffusion of K+ ions Movement of K+ ions coupled with active transport of H+ Thus, changes in the stoma opening are ATP-dependent

The Basics of Photosynthesis STOMATA When K+ ions move into guard cells, water follows by osmosis Thus, causing the guard cells to swell  stoma opens walls start to buckle outwards, increasing size of stoma When K+ ions move out of guard cells, water follows by osmosis Thus, causing the guard cells to sag  stoma closes

The Basics of Photosynthesis STOMATA Generally, stomata are: open during the day closed at night Why? 1. Sunlight (blue light) activates specific receptors on the guard cell membrane (blue-light receptors) 2. This stimulates H+ pumps that drive protons out of cells and allow K+ ions to enter * via electro-chemical gradient 3. When K+ enters cells, water follows via osmosis 4. Cell swells, and stomata opens --- 5. Simultaneously, mesophyll cells are photosynthesizing and using up CO2 6. Reduction in CO2 causes more water to enter cells (thus stoma opens more) Closing: Stomata start to close as [sucrose] drops in guard cells *[Sucrose] is dropping from photosynthesize occuring