1. The Basics of Photosynthesis
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2. Describe a basic food chain.

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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
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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