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 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 O2 X 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