Cellular Respiration & Scientific Investigations Notes

Cellular Respiration

Cellular respiration is the chemical process where glucose is broken down to release energy, either in the presence of oxygen (aerobic respiration) or absence of oxygen (anaerobic respiration).

1. Aerobic Respiration (Needs Oxygen)

• Aerobic respiration takes place in the presence of oxygen, inside the cytoplasm and mitochondria of cells.
• Requirements: Oxygen and glucose.
• By-products: Carbon dioxide, water, and ATP energy.
• Word Equation: $Glucose + Oxygen \rightarrow Carbon Dioxide + Water + ATP$
• Aerobic respiration occurs in three stages:
  • Glycolysis:
    • Takes place in the cytoplasm, outside the mitochondrion.
    • No oxygen is required.
    • Glucose is broken down into smaller molecules, releasing a small amount of energy stored in ATP molecules.
    • Releases high-energy hydrogen ions (H) used in oxidative phosphorylation.
  • Krebs Cycle:
    • Can only take place if oxygen is present.
    • Occurs inside the mitochondrion.
    • Releases carbon dioxide and high-energy hydrogen ions (H).
    • Transports hydrogen atoms to oxidative phosphorylation via hydrogen carrier enzymes.
  • Oxidative Phosphorylation:
    • Takes place inside the mitochondrion and requires oxygen.
    • Passes high-energy hydrogen atoms from one hydrogen carrier enzyme to the next, releasing energy.
    • Uses released energy to combine a phosphate molecule to an ADP (Adenosine Di-phosphate) molecule to form ATP (phosphorylation).
    • Formula: $ADP + P \rightarrow ATP$
    • Oxygen acts as the final hydrogen acceptor, binding with hydrogen to form water, which is released as a waste product.

2. Anaerobic Respiration

• Anaerobic respiration takes place without oxygen.
• Occurs for short periods, mainly during physical exercise.
• Occurs differently in plants and animals.
• Produces less ATP than aerobic respiration.
• In animals: Lactic acid fermentation occurs in muscles during intense exercise.
• In plants: Alcoholic fermentation occurs.

Uses of Anaerobic Respiration in Industry

• Yeast and other fungi respire anaerobically and are used to produce alcoholic beverages like beer and wine.
• Yeast cells are also used to cause bread to rise during baking.
• The fermentation process is also used to produce cheese.

Differences Between Aerobic and Anaerobic Respiration

Scientific Investigations

Hypothesis:

A hypothesis is an attempt to explain an event or observation using available information. It is a testable statement.

A hypothesis must:

• Have two variables (dependent and independent).
• State the relationship between the two variables.
• Be testable.
• State the independent variable first (cause) and then the dependent variable (effect).

Variables:

• Controlled/Fixed Variable: Factors kept constant to ensure the results are valid.
• Independent Variable: The factor being investigated, manipulated by the investigator. It is represented on the X-axis of a graph.
• Dependent Variable: The effect of the independent variable, usually measured.

Reliability:

Reliability means that investigation results must be repeatable.

• To improve reliability: Repeat the investigation or increase the sample size.

Validity:

Validity relates to how the experiment/investigation was carried out. All factors/variables must be controlled/fixed except the one being tested.

• To address factors decreasing validity: Identify factors/variables that weren't fixed/controlled.

Investigation: $CO_2$ is Produced by Living Organisms During Respiration

Living organisms produce carbon dioxide as a by-product of aerobic respiration. The presence of carbon dioxide can be tested using clear lime water, which turns milky in its presence.

• Soda lime removes carbon dioxide from the atmosphere.

• Sodium hydroxide removes carbon dioxide from a liquid.

• These ensure no carbon dioxide enters the experiment, proving it's a result of organism respiration.

• Hypothesis: Carbon dioxide is produced by living organisms during respiration.

• Aim: To prove that carbon dioxide is produced by living organisms during respiration

Materials:

• Small organism (e.g., snail).
• Alcohol.
• Large jar.
• Test tubes.
• Rubber stoppers with holes.
• Glass tubes.
• Electric pump.
• Soda lime.
• Sodium hydroxide solution.
• Lime water.

Method:

1. Use a small organism (e.g., snail).
2. Sterilize the equipment to prevent micro-organisms from influencing the result.
3. Place the snail in a large jar.
4. Set up the apparatus ensuring tight seals.

Experimental Set-up:

• Test tube A: Soda lime
• Test tube B: Sodium Hydroxide solution
• Test tube C: Lime water
• Test tube D: Snail in Jar with Lime water

Results:

• Test tube B: Lime water remains clear (Carbon dioxide removed by soda lime and sodium hydroxide).
• Test tube D: Lime water turns milky (Carbon dioxide produced by the snail).

Conclusion:

Carbon dioxide is produced during respiration by living organisms (the snail).

Questions from Text:

• 1.1 What would be the hypothesis for the experiment shown above?
• 1.2 What is the significance of sterilizing the seeds before they are used?
• 1.3 Give one controlled variable in this investigation.
• 1.4 Explain how you would set up a control for this experiment.
• 1.5 What would be the purpose of setting up a control experiment?
• 1.6 Explain why germinating seeds were used in this investigation.

Experiment on Aerobic Respiration:

• Seeds of the same kind were used.
• The Seeds and the apparatus were sterilized before the investigation.
• Apparatus was placed in a dark cupboard at $35°C$
• A control was set up with 10% formulin solution
• Sterilize the beans so cellular respiration cannot take place.