2.8 cell respiration

Question 1

why does reduction in volume in a respirometer correspond to use of oxygen?

Answer 1

• alkali is used to absorb CO2

- reductions in volume are due to use of oxygen

Question 2

what is cellular respiration?

Answer 2

• conversion of energy from one form to another (not in type of energy but rather nature of energy storage form in terms of molecules)
• cell metabolises variety of organic compounds to produce atp as source of energy
• e.g. C6H12O6 + 6O2 –> 6CO2 + 6H2O + atp + heat (lost in the process; important for thermoregulation and caused by 2nd law of thermodynamics: all things tend to go into a state of entropy (disorder / chaos) –> when energy is converted from 1 form to another, some energy is always lost as “waste energy” in the form of heat)
• metabolic pathways involve enzymes

Question 3

how is energy released from atp? (atp = adenosine triphosphate)

Answer 3

made up of:

• adenine nitrogenous base
• 5 carbon sugar ribose
• 3 phosphate groups
• energy released from atp when HYDROLYSIS occurs and 1 phosphate molecule is used to phosphorylate another molecule, transferring phosphate molecule in process
• atp is used as a form of energy currency
• vs glucose, used as storage molecule for energy and not directly used

Question 4

how does aerobic respiration in a cell work?

Answer 4

conducted in 3 phases:
1. glycolysis: occurs in cell cytoplasm; glucose molecule converted into 2 pyruvate molecules [PRODUCES NET 2 ATP MOLECULES]
- glucose (6 carbon sugar) –> 2 pyruvate (2 X 3 carbon sugar) + 2 atp
2. (a) conversion of pyruvate into a 2-C compound (link reaction)
(b) 2-C compound used in cycle (kreb’s cycle / tri-carboxylic acid cycle) to produce atp and other high energy compounds [tca –> NET 2 ATP MOLECULES]
3. oxidative phosphorylation: high energy compounds from tri-carboxylic acid cycle (tca cycle) is used to phosphorylate adp (adenosine diphosphate) into atp [NET 34 ATP MOLECULES]
STEPS 2 AND 3 IN MITOCHONDRIA

THUS TOTAL 38 ATP MOLECULES FROM FULL METABOLISM OF 1 GLUCOSE MOLECULE

Question 5

how does anaerobic respiration in a cell work?

Answer 5

• everything in cytoplasm
• cell can undergo glycolysis [glucose –> 2 pyruvate]
• other reactions cannot proceed due to lack of oxygen
• only small amount (NET 2 ATP) produced when 1 glucose molecule is metabolised
• pyruvate formed converted into lactate (salt form of lactic acid) by enzyme lactate dehydrogenase
• in humans: pyruvate –> lactate
• in yeast: pyruvate –> ethanol + carbon dioxide

Question 6

what is the use of anaerobic respiration in yeast?

Answer 6

• use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking
• microorganisms like yeast can undergo anaerobic respiration and carry out glycolysis to produce small amount of energy
• pyruvate formed is converted into alcohol instead of lactic acid
• used in the fermenting processes and bio-ethanol as a biofuel
• baking: yeast is used as a source of carbon dioxide
• carbon dioxide released during anaerobic respiration when the yeast consumes carbohydrates found in flour
• aerobic respiration will initially take place, but the oxygen will run out quickly and the yeast cells will switch over to anaerobic respiration
• tiny CO2 bubbles stretch the protein fibers within the dough -> dough rises

Question 7

why and how is there anaerobic respiration during intense exercise for humans?

Answer 7

• glucose + enzymes = carbon dioxide + ethanol / lactic acid (in humans)
• intense exercise: oxygen used up rapidly due to high rate of aerobic respiration
• anaerobic respiration used to supplement aerobic respiration, RAPIDLY supplying additional small amounts of atp w/o need for oxygen
• more atp produced and available -> power of muscle contractions increased
• lactic acid (lactate) produced decreases pH within cell cytoplasm and disrupt other cellular reactions
• hence threshold of lactic acid that can be tolerated
• lactate must be broken down into CO2 and H2O in presence of O2