1. Photosynthesis and Leaves

2. Photosynthesis
process used by plants using light energy to create sugar (glucose, C6H12O6) from carbon dioxide (CO2) and water (H2O)
oxygen gas (O2) is produced as a waste product and the light energy used is stored as chemical energy

3. Investigating Photosynthesis
Jan Van Helmont (1643)
Carefully massed soil, and tree seedling and watered over 5 years.
Determined most of the mass of the tree came from water.

4. Investigating Photosynthesis
Joseph Priestley (1771)
Lit a candle and placed a bell jar over it, watching the flame go out.
Reasoned that there was something in the air necessary to keep the flame going.
When a plant was placed under the bell jar, discovered that the candle could be relit after several days.
Reasoned that the plant released something into the air necessary for the flame.

5. Investigating Photosynthesis
Jan Ingenhousz (1779)
Showed the effect observed by Priestley only occurred when plants were exposed to light.

6. Investigating Photosynthesis
Julius Robert Mayer (1845)
Proposed that plants convert light energy into chemical energy

7. Photosynthesis Equation

8. Chloroplast
oval shaped organelle in plant leaf cells (and some protists’ cells) where photosynthesis takes place

9. Light plants use visible light to power photosynthesis in chloroplasts
visible (white) light is actually ALL visible colors of light
plants absorb energy from many different colors of light

10. Pigment material that changes the color of reflected light
plants gather the sun’s energy with light absorbing pigments

11. Pigment
the primary plant pigment is chlorophyll

12. Chlorophyll
plant pigment that absorbs light energy very well in the blue, violet and red wavelengths of visible light
Why are plants green?
chlorophyll reflects green light

13. Carotenoids secondary pigments absorb different wavelengths of light
produces fall leaf colors as plants break down chlorophyll
produces colors of many fruits and vegetables

14. Leaves organs where photosynthesis takes place
provide a place for gas exchange

15. Stomata pores on the surface of a leaf
allow gases to enter and leave the plant
surrounded by two guard cells

16. Guard Cells
specialized cells that can open and close to control gas exchange
typically closed in time of drought
prevents water from leaving the plant

17. Mesophyll chlorophyll containing leaf tissue
portion of the leaf that conducts photosynthesis

18. Mesophyll
palisade mesophyll
dense area of sugar-producing cells

19. Mesophyll spongy mesophyll
area of sugar-producing cells with many air spaces

20. Cuticle
waxy outside layer of a leaf
helps prevent water loss

21. Epidermis
outside layer of cells

22. Xylem and Phloem
vascular bundle (______) of the plant

23. Xylem and Phloem vascular bundle (veins) of the plant
xylem – moves water and minerals

24. Xylem and Phloem vascular bundle (veins) of the plant
phloem – moves food energy (sugar)

25. Xylem and Phloem

26. Summary Using whiteboards, identify the letter labels below. C B D E
F & G A H I J

27. Summary
Label the following leaf cross section.

28. Factors that affect Photosynthesis
Factors that affect Photosynthesis *think of the “ingredients” necessary for photosynthesis*
characteristics of the ecosystem that a plant grows in can affect how well it can perform photosynthesis
some factors allow plants to make sugar quickly while other factors slow down their ability to make sugar
light
length of exposure, color, intensity or brightness (distance from source)
water amounts
CO2 concentration

29. Photosynthesis and Enzymes
plants use many enzymes to produce their food made in the process of photosynthesis
enzymes are proteins that speed up chemical reactions
enzyme efficiency can be affected by many factors
Temperature, pH
these factors can also speed up (or slow down) photosynthesis

30. Connection to ATP
But what do living things do with the sugar made in photosynthesis?
Eventually…living things will break down sugar and convert the energy into ATP
More on this later when we learn about cellular respiration

31. Summary
Sometimes plants in a community will slow down or stop performing photosynthesis. This can be brought on by drought, human activities, disease, or many other factors. Describe what would happen to other members of the plants’ community.