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PHOTOSYNTHESIS
4.2 Plant Structure
Plant Body
Leaf = blade + petiole
Functions
Exposes surface to sunlight
Major site of photosynthesis
Conserves water
Provides for gas exchange
Blade
Petiole
Stoma =
opening in the leaf
for gas exchange,
water evaporation
Conserves water
Photosynthesis
Structures of the
Leaf
Transports water
and sugar to stem
and roots
The process where organisms
obtain most of their ATP is
called Cellular Respiration
Cellular respiration occurs in the
mitochondria of the cell.
Where does
photosynthesis
take place?
Plants
 Mainly occurs in the leaves:
a. stoma - pores
b.mesophyll cells
Mesophyll
Cell
Chloroplast
Stoma
Mesophyll Cell of Leaf
Nucleus
Cell Wall
Chloroplast
Central Vacuole
Photosynthesis occurs in these cells!
Stomata (stoma)
Pores in a plant’s cuticle through which
water vapor and gases (CO2 & O2)
are exchanged between the plant and
the atmosphere.
Stoma
Carbon Dioxide
(CO2)
Guard Cell
Oxygen
(O2)
Guard Cell
Found on the underside of leaves
Chloroplast
Organelle where photosynthesis takes place.
Stroma
Outer Membrane
Inner Membrane
Thylakoid
Granum
Thylakoid stacks are connected together
Parts
chloroplasts – dbl membrane organelle that
absorbs light energy
Thylakoids – flattened sacs contain pigment chlorophyll
Grana (pl: granum) – layered thylakoids (like
pancakes)
Stroma – solution around thylakoids
Stomata – pore on underside of leaf where O2 is
released and CO2 enters
Stroma : chloroplast :: cytosol : cytoplasm
Thylakoid
Thylakoid Membrane
Granum
Thylakoid Space
Grana make up the inner membrane
 The main form of energy from the sun is
in the form of electromagnetic radiation
 Visible radiation (white light) used for
photosynthesis
 Remember : ROY
G. BIV?
The electromagnetic spectrum
 A Red Object absorbs the blue and green wavelengths
and reflects the red wavelengths
Why are
plants
green?
 pigment a compound that absorbs light
 different pigments absorb different wavelengths of white
light.
 chlorophyll is a pigment that absorbs red & blue
light (photons) so green is reflected or transmitted.
 Chlorophyll is located in the thylakoid membranes
So, Plants are green because the green
wavelength is reflected, not absorbed.
2 types of chlorophyll
 Chlorophyll a – involved in light reactions
 Chlorophyll b – assists in capturing light
energy – accessory pigment
 Carotenoids – accessory pigments –
captures more light energy
 Red, orange & yellow
The electromagnetic wavelengths and the
wavelengths that are absorbed by the chlorophyll
During the fall, what
causes the leaves
to change colors?
Fall Colors
 In addition to the chlorophyll
pigments, there are other pigments
present
 During the fall, the green
chlorophyll pigments are greatly
reduced revealing the other
pigments
 Carotenoids are pigments that are
either red, orange, or yellow