Which one of the following statements is correct ?
- A.Glucose breaks down to CO₂, H₂O and energy in all organisms
- B.Glucose breaks down into ethanol, CO₂ and energy in our muscle cells
- C.Glucose breaks down into CO₂, H₂O and energy in all aerobic tissues
- D.Glucose breaks down into lactate and energy in yeast
Correct answer
Explanation
The correct answer is C. In aerobic tissues, where oxygen is available, glucose is broken down completely into carbon dioxide, water and energy.
Aerobic respiration begins with glycolysis in the cytoplasm, which gives pyruvate. With oxygen, pyruvate enters the mitochondria, passes through the Krebs cycle and the electron transport chain, and is fully oxidised to CO₂ and H₂O, releasing about 30 to 38 ATP per glucose. Without oxygen the breakdown stops partway: yeast ferments pyruvate into ethanol and carbon dioxide, and our muscles, during hard exercise, turn it into lactic acid (lactate), which causes cramps.
A is wrong: anaerobic organisms such as yeast and many bacteria do not break glucose down to CO₂ and H₂O.
B is wrong: our muscle cells make lactate, not ethanol, when oxygen runs short.
D is wrong: yeast makes ethanol and CO₂, not lactate.
Exam tip: Yeast → ethanol + CO₂; muscle → lactic acid; aerobic → CO₂ + H₂O.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →