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Chapter 15
Plant Processes
15.1 Photosynthesis &
Respiration
Gas Exchange in Plants
• Humans:
• Plants:
INHALE
EXHALE
N
N
O2
CO2
CO2
H2O
vapor
O2
CO2
H2O
• Plants need water and CO2 to survive
• ROOTS absorb most of the water &
move it up through the plant
• Stomata: small openings on leaves
where water and gases enter & leave
plants (**CO2)
• Guard Cells: structures that swell &
shrink to regulate the opening & closing
of the stomata
Stomata
• When guard cells lose water, they shrink
and close the stomata.
– Less CO2 enters and less H2O leaves
• Stomata are usually closed at night or
when the plant lacks water.
Open & Closed Stomata
Transpiration:
• Loss of water
vapor through
the stomata of
a leaf
Photosynthesis:
• The process by which plants use CO2,
water, and sunlight to produce food
Chlorophyll
• 6CO2 + 6H2O + light energy
C6H12O6 + 6O2
Chlorophyll:
• A pigment that traps light energy from the
sun and gives leaves and stems in plants
their green color
Steps of Photosynthesis
• 1. CO2 & H2O are the “ingredients”
• 2. These atoms are rearranged to form a
new molecule (C6H12O6), a simple sugar
called glucose
• The energy in the chemical bonds of
glucose is used by the plant for growth &
reproduction
Photosynthesis Table
Ingredients
Products
6 CO2 (carbon
dioxide)
6 H2O (water)
C6H12O6 (glucose)
Light energy
6 O2 (oxygen)
Products of Photosynthesis
• O2 most is released through stomata
• C6H12O6  main form of food for plant
cells
Importance of Photosynthesis
• 1. provides food for nearly all other
organisms on Earth
• 2. removes carbon dioxide from the
atmosphere and replaces it with oxygen
Respiration:
• Series of chemical reactions by which all
organisms break down food to release
energy
• Occurs in the mitochondria of a cell
Respiration Equation
• C6H12O6 + 6O2
energy
6CO2 + 6H2O +
• This equation is the exact reverse of
photosynthesis!
2 Types of Respiration
• 1. Aerobic: occurs in the presence of O2
• 2. Anaerobic: occurs without O2
• Aerobic respiration combines oxygen and
food to release the energy in the chemical
bonds of food.
Cellular Respiration Table
Ingredients
Products
C6H12O6 (glucose)
6 CO2 (carbon
dioxide)
6 O2 (oxygen)
6 H2O (water)
Energy
Importance of Respiration
• Energy in food is in a form that CANNOT
be used by cells.
• During respiration, food energy is
converted into a form that all cells can use
• Aerobic respiration returns CO2 to the
atmosphere where it can be used again by
photosynthetic organisms
15.2 Plant Responses
• Stimulus: anything in the environment
that causes a change in the behavior of an
organism
• Response: change in behavior as a result
of the stimulus
2 Types of Stimuli
• 1. Outside (phone ringing)
• 2. Inside (chemical reactions & hormones)
ALL living organisms, including plants,
respond to stimuli.
Hormones:
• Substances made by cells for use
somewhere else in the organism
Tropisms:
• Response of a plant to an outside stimulus
• Can be positive or negative (toward or
away from the stimulus)
• Thigmotropism:
– plant response to touch
• Gravitropism:
– plant response to gravity
• Phototropism:
– plant response to light