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 centresurrounded 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 PhotosynthesisCYANOBACTERIA!• 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 PhotosynthesisCYANOBACTERIA!• evolved ~ 3 billion years ago• probably the first organisms to use sunlight toproduce 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 PhotosynthesisEukaryotic 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 PhotosynthesisCHLOROPLAST STRUCTUREStroma – 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 PhotosynthesisCHLOROPLAST STRUCTUREGrana / 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 PhotosynthesisLeaves

• 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 PhotosynthesisSTRUCTURE 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 PhotosynthesisSTRUCTURE 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 PhotosynthesisTRANSPIRATION 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:

1.Creates ‘transpirational pull’- helps move water, minerals, etc from roots to

leaves2.Produces evaporative cooling effect (like sweating)

- prevents leafs from reaching temps that would denature their enzymes that catalyze photosynthesis

The Basics of PhotosynthesisSTOMATA

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 PhotosynthesisSTOMATA

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 PhotosynthesisSTOMATA

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 gradient3. When K+ enters cells, water follows via osmosis 4. Cell swells, and stomata opens---5. Simultaneously, mesophyll cells are photosynthesizing and using up CO26. 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