HortBotany
Lesson Plan 5
Photosynthesis & Respiration
- Photosynthesis (A Food Production Reaction)
Photosynthesis comes from the root words “photo”, meaning light, and
“synthesis” meaning to build or make. So, photosynthesis is a reaction that occurs
in plants in the presence of light where light energy is used to make food.
Photosynthesis is probably the most important chemical reaction on the planet.
Photosynthesis occurs in cell organelles called chloroplasts. Chloroplasts are
found primarily in the cells of leaves, but may also be found in the cells of some
stems. Generally speaking, any part of the plant that is green in color is made up
of cells containing chloroplasts. This is true because choroplasts contain a greencolored pigment called chlorophyll. Some plants, like Coleus for example, have
highly variegated leaves containing many colors. Even though you may not see
much “green” in a Coleus leaf, chloroplasts containing chlorophyll are still
present. Other, more dominant pigments, such as reds, pinks, yellows, and purples
hide the presence of chorophyll.
In the food chain plants are considered primary producers. Many small animals
feed upon plants and are, in turn, eaten by larger animals and so on. In this way
all animals are dependent upon plants at some point in the food chain.
The rate of photosynthesis is affected by the availability of inputs and by
temperature.
Using the diagram on page 3 called “An Outline of Plant Metabolism” write, in
the spaces provided, the inputs and outputs of the reaction:
INPUTS:
_____________________
OUTPUTS: __________________
_____________________
__________________
_____________________
_____________________
Now write out the reaction, using the inputs and outputs above, on a single line:
PHOTOSYNTHESIS:
________ + ________ + ________ + _________
________ + ________
page 2
- Respiration (A Food Consuming Reaction That Produces ATP)
Respiration takes place in the mitochondria of plant cells. Remember that
mitochondria are found in all living plant cells. While photosynthesis
is a reaction that requires light and occurs during the daytime, respiration
occurs in plant cells 24 hrs a day. Respiration is essentially the reverse
reaction of photosynthesis.
ATP is a chemical. Think or ATP as being stored “chemical energy”.
Respiration then, is that process in plants that allows them to convert food
(glucose, carbohydrates) into a more useable product (ATP). ATP then
provides the chemical energy necessary convert sugar and soil minerals
into various products that plants require for growth and maintenance.
Some of those products are listed on the right hand side of the diagram on
page 3.
The rate of respiration is affected by the availability of inputs and by
temperature.
Using the diagram on page 3 called “An Outline of Plant Metabolism” write, in
the spaces provided, the inputs and outputs of the reaction:
INPUTS:
_____________________
OUTPUTS: __________________
_____________________
__________________
__________________
__________________
Now write out the reaction, using the inputs and outputs above, on a single line:
RESPIRATION:
________ + ________
________ + ________ + ________ + ________
page 3
page 4
An Outline of Plant Metabolism
Light and chlorophyll
Water
Carbon
dioxide
PHOTOSYNTHESIS
Sugars
Starch
Pectin
Cellulose
Lignin
Fats
Oxygen
Proteins
Soil Minerals
Enzymes
Pigments
Carbon
dioxide
RESPIRATION
Hormones
Vitamins
Water
HEAT
ATP
-
page 5
Sources of the inputs and fates of outputs:
PHOTOSYNTHESIS INPUTS:
Water: absorbed by the roots; transported throughout the plant in the xylem.
Light: provided by the sun or some artificial light source. Plants primarily use red and
blue wavelengths of light for photosynthesis.
Chlorophyll: located in the chloroplasts of leaf or stem cells.
Carbon dioxide: found in our atmosphere. Carbon dioxide enters the leaves through the
stomata.
PHOTOSYNTHESIS OUTPUTS:
Oxygen: most of the oxygen produced during photosynthesis exits the plant through the
leaf stomata. Some oxygen is dissolved in the cell cytoplasm.
Sugar: the sugars made during photosynthesis are distributed throughout the plant in a
special tissue called phloem. During the day, sugars move to the actively growing shoot
tips of plants. During the evening, sugars are moved down into the stems and roots for
storage.
RESPIRATION INPUTS:
Oxygen: oxygen is abundant in our atmosphere and can enter the plant through the leaf
stomata where it is dissolved in the cell cytoplasm. Soil pore spaces can hold air, which
contains oxygen, and this oxygen can diffuse directly across the epidermis of root hairs.
Sugar: created in the leaves and transported in phloem.
RESPIRATION OUTPUTS:
Carbon dioxide: in the leaves, carbon dioxide can exit the plant through the leaf stomata
or be dissolved in the cell cytoplasm. In stems and roots it is dissolved in the cell
cytoplasm and eventually diffuses across epidermis and into the atmosphere.
Heat: is radiated out of the plant.
Water: is dissolved in the cell cytoplasm.
ATP: is dissolved in the cell cytoplasm until it is needed to convert sugars and soil
minerals into useful plant products.
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