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Plant Science

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Title: Plant Science

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Unit

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Problem Area

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Lesson

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Student Learning Objectives

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Terms

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Terms cont.

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Why is photosynthesis important?

Photosynthesis is the process in which carbon
dioxide and water are transformed, in the
presence of light, into carbon-containing,
energy-rich, organic compounds.
A. Photosynthesis provides the fundamental energy
foundation for all organisms. Photosynthesis
occurs in green plants, seaweed, and algae.
Plants can produce millions of glucose molecules
per second. Excess glucose produced is converted
into starch and carbohydrates and stored in the
plants roots, stems, and leaves. Stored glucose
can be converted to energy when required by the
plant.

B. Humans and animals are unable to manufacture
glucose for energy. The animal kingdom relies on
plant material for glucose. Glucose is a
significant energy source for humans and animals.
C. Oxygen breathed by humans and animals is the
oxygen produced through the photosynthetic
reaction. Without the photosynthetic reaction,
oxygen would not be replenished in the
atmosphere.
D. Humanity is reliant on the earliest products
of photosynthesis. Fossil fuels such as natural
gas, coal, and petroleum are composed of complex
hydrocarbons. These hydrocarbons are the remnants
of organisms that relied on photosynthesis
millions of years in the past.

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What is the structural unit in which
photosynthesis takes place?

B. Chlorophyll is found in two forms. Chlorophyll
a is bright green and is responsible for
absorbing energy from the violet-blue to red,
red-orange light wavelengths. Chlorophyll b is
yellow-green and absorbs different wavelengths of
light.
Carotenoids are supplementary yellow and orange
pigments that absorb energy from
green-yellow-orange wavelengths. The energy
absorbed by carotenoids can be transferred to
chlorophyll a.

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What are the photosynthetic processes?

Plants convert light energy into chemical energy
of sugar molecules through the process of
photosynthesis.
A. Using light energy from sunlight, chlorophyll
manufactures ATP and NADPH. Plants use the energy
held in the ATP and NADPH molecules to make
carbohydrates. Examples of carbohydrates are
sugars, starches, and cellulose. While sugars and
starches are used for energy, cellulose is a
building block for the cell walls of plants.
B. Photosynthesis is a very complex process and
is divided into two stages.

When the energy reaches the chlorophyll molecule
P700, the P700 molecules uses the energy to boost
its electrons. The electrons are then passed from
one carrier to another, called an electron
transport chain.
Nicotine adenine dinucleotide (NADP) lies at the
end of the electron transport chain. Using the
energy released by the electrons, two electrons
from the chain combine with a hydrogen ion and
NADP to form NADPH. NADPH can then be used to
make carbohydrates.

D. The light-dependent reaction continues with
Photosystem II. Light energy activates electrons
in the Photosystem II pigments. These pigments
transfer their energy from excited electrons to
the chlorophyll molecule, P680.
Energy is used to transfer electrons through a
different electron transport chain. As the
electrons pass through the chain, some of the
energy is used to fuel the production of ATP.

ATP is formed by the addition of one phosphorus
atom to adenosine diphosphate (ADP). The electron
transport chain will eventually deliver the
Photosystem II electrons to Photosystem I and the
P700 electrons.
The P680 electron is replenished by water
absorbed from the plants roots. The oxygen from
the water will diffuse out of the chloroplast and
is released into the air through the stoma on the
leaf.

E. The light-independent reaction does not
require light. In this reaction ATP and NADPH are
used to make high-energy carbohydrates. Termed
the Calvin cycle, the light-independent reactions
use the electrons and hydrogen ions associate
with NADPH and the phosphorus associated with ATP
to produce glucose.
These reactions occur in the fluid surrounding
the thylakoids. The light-independent reactions
begins when carbon dioxide links to sugar
molecules called ribulose bisphosphate (RuBP) in
the process known as carbon fixation.

Initially a six-carbon molecule is formed.
Instantly, the molecule splits into 2
three-carbon molecules. The three-carbon
molecules join to form simple sugars, glucose,
and fructose.
It takes six turns of the Calvin cycle, involving
the input of six CO2 molecules and hydrogen from
NADPH and ATP, to result in one molecule of
glucose. Most plants are referred to as C3 plants
because the first product of carbon fixation is a
three-carbon compound.

F. Many plants have the ability to fix carbon
dioxide into four-carbon compounds. C4 plants
originated in areas of high temperatures, high
light intensities, and limited amounts of water.
Corn, sugar cane, and crabgrass are C4 plants.
C4 plants have specialized cells known as bundle
sheath cells. Reactions of the C4 pathway take
place in the mesophyll cells. In the process, the
plants fix CO2 into four-carbon compounds. A
result of the C4 pathway is an increased
concentration of carbon dioxide in bundle sheath
cells.

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What factors affect photosynthesis?

A. The first requirement for photosynthesis is a
healthy, living plant. Healthy plants contain
chlorophyll and the pigments necessary for
photosynthesis.
B. Carbon dioxide must be in ample supply. The
higher the concentration of CO2 , the higher the
rate of growth.
C. Water must be available for the plant to use.
Stomata may close to conserve water, decreasing
the absorption of CO2, shutting down
photosynthesis.
D. Light or radiant energy drives photosynthesis.
Light must be present for photosynthesis to occur.