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Cell Energy
Part 6
Plants and Cell Respiration
• Plants use cell respiration to generate
more ATP
• Why does a plant need so much ATP?
• Active transport
• Cell division
• Cell respiration requires oxygen
• Roots get oxygen from the oxygen in air
pockets in the soil
• Drowning plants
• Leaves gave plenty from photosynthesis
• Leaves take in carbon dioxide
• Not possible if leaves are submerged in
water
• Gas diffuses more slowly in water than air
Plant Adaptations for Cell Respiration
• Conditions to grow Rice
• Wet or Dry
• Rice grows in “paddies”
• Fields where soil is purposefully flooded
• Water-tolerant plant
• Weeds cannot compete b/c they are not water
tolerant
• Rice paddies are muddy
• Contain microorganisms that use aerobic
respiration and take up all available oxygen
• Rice needs to adapt to survive in wet
conditions
Rice Adaptations to Flooding
1. Growing taller
• Top parts of leaves
and flower spikes
above water
• Oxygen and carbon
dioxide exchanged
through stomata
Rice Adaptations to Flooding
2. Aerenchyma Tissue
• Tissue in stems made of loosely
packed cells
• Air space AND cells of the cortex
• Enable gas to diffuse through it
to other parts of plant, even
underwater parts
• Supplemented by air trapped in
between ridges of underwater
leaves
• Leaves Hydrophobic &
corrugated
• Holds thin layer of air in contact
with leaf surface
Rice Adaptations to Flooding
3. Alcohol Fermentation
• Used by cells of
submerged roots
• Part of the time
• Ethanol= toxic to plant
• Rice plants have more of
the enzyme ALCOHOL
DEHYDROGENASE
(breaks down ethanol)
• Rice plants have high
tolerance for ethanol
• Rice can actively grown
when oxygen is scarce
using ATP from Glycolysis
and alcohol fermentation
Measuring Oxygen Uptake
• Use respirometer
• Measures oxygen uptake
• Suitable for measuring the rate of oxygen
consumption of seeds or small terrestrial
invertebrates
• We only want to measure decrease in oxygen
consumption…
• Carbon dioxide is produced during respiration so
that will increase the gas in the chamber so….
• Use chemical to absorb carbon dioxide
produced
•
•
•
•
Soda-lime
Potassium-hydroxide solution
Sodium Hydroxide
Use cotton or wool to prevent contact between
this chemical and organisms
• Now we are only measuring decreasing in
volume of oxygen in the tube (which is
because of the oxygen consumption of
organism)
• To measure the rate of oxygen consumption,
use a MANOMETER
• Fluid filled scale
• No air bubbles
• Same quantity of fluid in both manometers
(important!)
Other Variables to Monitor
• Both of the following alter air volume in apparatus:
• Changes in Temperature
• Changes in Pressure
• Ensure temperature is kept constant throughout use of respirometer
• Use water bath maintained at stable temp (thermostatically controlled warm
water bath ideal)
• Use a control tube
• Place in a dead organism or object of same mass (but not respiring)
• Helps compensate for changes in atmospheric pressure
• Subtract the distance moved in the control tube (without respiring organism)
from the distance moved and recorded in the experimental manometer
Converting Distance Moved to Volume
• Must know
diameter of the
capillary tube
• Volume of liquid in
tube = length x ∏r2
• Answer will be the
value for the
volume of oxygen
absorbed by the
organism
Using a respirometer to investigate temperature
• Place respirometers in water baths of different
temperatures
• 2 options:
• Use same respirometer throughout whole experiment
• Use different respirometers during each experiment
(think about variables to control)
• Each temperature would require a control
respirometer
• Compare rates of respiration at different
temperatures by simply measuring the distance
the fluid moves in the manometer at various times
during the experiment (this will give you the rate)
Using a Respirometer to Measure RQ
• Two things to determine:
• Oxygen consumed
• Carbon Dioxide given off
• Set up 2 respirometers (see figure)
• First respirometer: living organism at bottom,
cotton wool, carbon dioxide absorbing material
(soda lime)
• Second respirometer: should also contain mass of
living organism but should NOT contain chemical
to absorb carbon dioxide (like our previous control
tubes)
• Maintain a controlled experiment by putting
unreactive, inert material, like glass beads, where
the chemical used to be (same mass and volume of
carbon dioxide absorbing material)
• 2nd tube identical to 1st tube minus the soda
lime/carbon dioxide absorbing chemical
Using a Respirometer to Measure RQ
• The difference between the distance moved by the
manometer fluid in the experimental tube and the distance
moved in the control tube is therefore due to the carbon
dioxide output
• When more carbon dioxide is produced than
oxygen….the volume of air in the
respirometer will increase (by y cm3 min-1)
• If the respiratory substrate is carbohydrate:
• the amount of carbon dioxide given out will equal
the amount of oxygen taken in. The fluid in the
control tube will not move, so y=O.
When Less Carbon Dioxide is Produced….
• Less CO2 produced than O2 absorbed = volume of air in respirometer
will decrease (by z cm3 min-1)
• Calculation will be:
• RQ = CO2 = x - z
X
O2
This will lead to a
respiratory quotient
LESS than 1
(possibly a lipid or
protein as a substrate)
Alternate ways of Measuring Rate of Respiration
• Use redox dye ( act as NAD or NADP)
• DCPIP (dichlorophenolindophenol)
• Methylene Blue
• DO not damage cells
• When reduced (accepting electrons and hydrogen
ions), they change from blue to colorless
• Rate of change from blue  colorless = rate of
respiration
• Use to investigate various factors influencing
respiration
• Temperature
• Concentration
• substrates