Transcript Photosynthesis and the Leaf

Photosynthesis and the Leaf
Energy
A. The sun is the source of energy
for almost all life on Earth
B. The sun’s energy is transferred
into a useable form through
photosynthesis
C. Photosynthesis uses energy from
the sun to convert water and
carbon dioxide into high-energy
sugar and oxygen
Photosynthesis & Respiration
• 3 Kinds of Respiration
– 1) external respiration- breathing, exchange of
gases between atmosphere and lungs
– 2) internal respiration – exchange of O2
between blood and body cells
– 3) cellular respiration – chemical reaction
where O2 molecules and broken down food
molecules react to produce ATP in the
mitochondria
Formula for Respiration
C6H12O6+ 6O2  6H2O + 6CO2 + energy
Glucose + oxygen = water + carbon dioxide + ATP
• This is the process by which glucose molecules are
broken down to release energy (ATP)
• Occurs inside the mitochondria of cells
The Respiration/Photosynthesis
Cycle
Produced by Respiration
Used in Photosynthesis
CO2 + energy
Glucose + O2
Used in Respiration
Produced by Photosynthesis
Photosynthesis
What kind of organisms carry out photosynthesis?
A. They have pigments =
light absorbing molecules
B. Plants and other green
organisms have
specialized organelles that
help with this process.
This organelle is called
chloroplast
C. Photosynthesis takes place
inside the chloroplast
within leaf cells
Formula for Photosynthesis
What goes in? What goes out?
Start with the equation:
6CO2 + 6H2O C6H12O6+ 6O2
Carbon dioxide + water = glucose + oxygen
Light-dependent
Reactions
• These reactions require
light
• Take place in the
thylakoid membranes
• Produces ATP, NADPH
(electron carrier), and
oxygen
Calvin cycle
• The second cycle of
photosynthesis
• Products from lightdependent reactions are
synthesized into high
energy glucose
• These reactions are also
known as the lightindependent reactions,
because they do not
require light
Leaf Structure
A. Epidermis
• the top and
bottom layers of
the leaf
• Protects the
inner tissue from
injury or drying
out
Leaves
B. Cuticle
• waxy covering on the leaves secreted by the
epidermis cells, prevents water from escaping
• Important because plants need water for
photosynthesis
Leaves
C. Stomata (pl. stoma)
• Pores scattered through the leaf epidermis
• Carbon dioxide enters through stoma and
Oxygen is released through stoma
• Water vapor can also pass in and out of the
stoma (dew)
• Stoma are generally open at night and closed
during the day. Typically on underside of leaf
Leaves
D. Guard Cells
• Crescent shaped cells which guard the stoma
• Responsible for opening and closing the stoma
• Guard cells pull stoma open when they become
turgid (full of water)
Leaves
E. Mesophyll
• Layers of cells inside the epidermis
• Most photosynthesis takes place inside this part
of the leaf where the cells contain chloroplasts.
Leaves
F. Leaf veins
• Vascular tissue in the leaves that contain xylem
and phloem
• Evaporation from the leaves (transpiration)
produces the suction that pulls water up the
xylem delivering nutrients to other parts of the
plant.
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