Topic 14.2 - Plant Nutrition
Biology 1001 - November 16, 2005
1. Introduction
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Nutrition involves obtaining energy, carbon, and
other essential organic and inorganic compounds
for metabolism
Plants require sunlight, CO2, water and certain
minerals
Sunlight & CO2 are obtained from the aerial
environment through the shoot, especially leaves
Water & minerals are obtained from the
subterranean environment, through the roots
Plants perform photosynthesis to synthesize
organic molecules
They perform cellular respiration to derive
energy from these organic molecules
Photoautotrophs
2. Chloroplasts: The Sites of Photosynthesis
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Figure 10.3!!
Chloroplasts are located in mesophyll cells
of the leaf (30-40 chloroplasts per cell)
Chloroplast internal structure includes a
dense fluid called stroma and stacks of
thylakoid sacs called grana
Chlorophyll in the thylakoid membrane
absorbs the light energy necessary for
photosynthesis
Green wavelength light is reflected, which
is why chloroplasts & leaves are green
Stomata on the leaf surface allow CO2 to
enter, O2 & H2O to leave the leaf
Vascular veins transport water & minerals
to the leaf and the organic products of
photosynthesis away from the leaf
3. Overview of Photosynthesis
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Overall equation of photosynthesis
 An
anabolic pathway of endergonic reactions
 6CO2 + 12H2O + light energy  C6H12O6 + 6O2 6H2O
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About the process
 Water
is consumed and new molecules of water are formed
 Water is split during photosynthesis, not carbon dioxide
 The enzymes required for photosynthesis are located in the
stroma or embedded in the thylakoid membrane
 Photosynthesis does not occur as the reverse of cellular
respiration, but as two sets of many reactions each
The Two Stages of Photosynthesis
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The Light Reactions
 The
“photo” part of photosynthesis, these reactions occur
in the thylakoid membrane
 Light energy drives a transfer of electrons and hydrogen
from water to NADP+, producing NADPH
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H2O  2H+ + 2e- + 1/2O2
NADP+ + H+ + 2e-  NADPH
This is reducing power
 Light
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energy also phosphorylates ADP to ATP
ADP + P  ATP
This is chemical energy
 Water
is split and oxygen released during these reactions
 ATP and NADPH are used in Calvin cycle
The Two Stages of Photosynthesis
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The Calvin Cycle
 The
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“synthesis” part of photosynthesis, occurs in the stroma
The reactions of the Calvin Cycle do not directly require light, but
they require the products of the light reactions, so they generally
occur in the light
 Carbon
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enters the Calvin Cycle as CO2 and leaves as sugar
It first gets added to already existing organic molecules, a process
called carbon fixation
It then gets reduced to a carbohydrate using the reducing power of
NADPH and the chemical energy of ATP
The carbohydrate produced by photosynthesis is actually the three
carbon sugar glyceraldehyde-3-phosphate, not glucose
NADP+ released from the Calvin Cycle are
returned to the thylakoid membrane and used again in the
light reactions
 ADP and
The cooperation of the light reactions and the
Calvin cycle - Figure 10.5!,!!
4. The Relationship of Photosynthesis to
Cellular Respiration
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Energy enters the ecosystem as sunlight
and gets stored as chemical energy in the
organic products of photosynthesis which
also releases oxygen as a by-product
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During cellular respiration the organic
molecules react with oxygen and are
broken down to release the energy that
phosphorylates ATP and powers cellular
work - some of the energy dissipates as
heat
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The products of cellular respiration are
used as the reactants of photosynthesis
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Note the recycling of molecules but the
flow of energy through the ecosystem
Figure 9.2!
An Overview of Cellular Respiration
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A catabolic pathway of exergonic reactions
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Mostly occurs in the mitochondria; enzymes for cellular
respiration are embedded in the mitochondrial membranes
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Cellular respiration is the combustion of organic compounds by
oxygen
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Fermentation is a partial degradation of organic compounds that
does not involve oxygen
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Organic compounds + oxygen  carbon dioxide + water + energy
C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP & heat)
Glucose  carbon dioxide + ethanol + energy (ATP & heat)
The three stages of cellular respiration are glycolysis, the citric
acid cycle and oxidative phosphorylation
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ATP is produced at each stage, but mostly by oxidative phosphorylation
An Overview of Cellular Respiration
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Glycolysis, which occurs in
the cytosol, converts
glucose to pyruvate
Pyruvate is converted to
CO2 during the citric acid
cycle which occurs in the
matrix of the mitochondria
Also during the citric acid
cycle, electrons are added to
NAD and FAD converting
them to NADH and FADH2
These carry electrons to the
inner membrane where they
are added to oxygen to
release energy during
oxidative phosphorylation
O2
H2O
Figure 9.6!
Link to Video
Comparing Photosynthesis & Cellular Respiration
Compare and contrast photosynthesis and cellular respiration for each of
the following characteristics
Feature
Photosynthesis
Cellular Respiration
Water
Used
Produced
Oxygen
Produced
Used
Carbon dioxide
Used
Produced
Energy
Used
Produced
Organic molecules
Produced
Used
When does it occurs In the light
Anytime
Organelle involved
Chloroplast
Mitochondrion
Which organisms
use it?
Photoautotrophs
Most (all?) eukaryotes
including plants and Certain prokaryotes
algae