Respiration: anaerobic respiration — KCSE Biology

KCSE Biology · 61 practice questions · 3 syllabus objectives · 3 revision lessons

27 easy29 medium5 hard

Last updated · Aligned to the KNEC KCSE syllabus

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Write the equation for anaerobic respiration in plants and animals

Compare aerobic and anaerobic respiration

Respiration: anaerobic respiration

Revision Notes

Concise lesson notes for Respiration: anaerobic respiration, written to the KCSE Biology marking standard. Read the first lesson free below.

Anaerobic Respiration Equations

Anaerobic respiration occurs in the absence of oxygen and is crucial for energy production in both plants and animals. The equations for anaerobic respiration differ slightly between these two groups.

In animals, anaerobic respiration primarily occurs during intense exercise when oxygen is limited. The equation is:

Glucose → Lactic Acid + Energy (ATP)

In plants and some microorganisms, the process results in ethanol and carbon dioxide. The equation is:

Glucose → Ethanol + Carbon Dioxide + Energy (ATP)

Key points to remember:

  • Anaerobic respiration is less efficient than aerobic respiration.
  • It produces less energy (ATP) per glucose molecule.
  • Lactic acid can cause muscle fatigue in animals.
  • Ethanol and carbon dioxide are useful byproducts in fermentation processes for plants.

Understanding these equations helps in grasping how organisms adapt their metabolic processes to different environmental conditions.

Key points to remember

  • Anaerobic respiration occurs without oxygen.
  • Animals produce lactic acid; plants produce ethanol.
  • Both processes yield energy (ATP) from glucose.
  • Lactic acid causes fatigue; ethanol is used in fermentation.
  • Anaerobic respiration is less efficient than aerobic respiration.

Worked example

Write the equation for anaerobic respiration in animals.

Answer: Glucose → Lactic Acid + Energy (ATP)

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More lessons in this topic

Lesson 2: Aerobic vs. Anaerobic Respiration

Objective: Compare aerobic and anaerobic respiration

Respiration is vital for energy production in living organisms. There are two main types: aerobic and anaerobic respiration.

Aerobic respiration occurs in the presence of oxygen and is more efficient in energy production. The general equation is:
Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
This process takes place in the mitochondria of cells.

Anaerobic respiration, on the other hand, occurs in the absence of oxygen and produces less energy. The general equation for anaerobic respiration in animals is:
Glucose → Lactic Acid + Energy (ATP)
In yeast, it is:
Glucose → Ethanol + Carbon Dioxide + Energy (ATP)
This process occurs in the cytoplasm.

Key differences:

  • Oxygen requirement: Aerobic requires oxygen; anaerobic does not.
  • Energy yield: Aerobic produces more ATP (approximately 36-38 ATP); anaerobic produces only 2 ATP.
  • End products: Aerobic produces CO₂ and H₂O; anaerobic produces lactic acid or ethanol and CO₂.

Understanding these differences helps explain why organisms choose one method over the other based on environmental conditions.

  • Aerobic respiration requires oxygen; anaerobic does not.
  • Aerobic produces more ATP than anaerobic.
  • End products differ: CO₂ and H₂O vs lactic acid or ethanol.

Compare aerobic and anaerobic respiration in terms of oxygen requirement and energy yield.

  • Oxygen requirement: Aerobic needs oxygen; anaerobic does not.
  • Energy yield: Aerobic yields 36-38 ATP; anaerobic yields only 2 ATP.
Lesson 3: Understanding Anaerobic Respiration

Objective: Respiration: anaerobic respiration

Anaerobic respiration is a type of respiration that occurs without oxygen. It mainly takes place in certain microorganisms and muscle cells during intense exercise. The process allows organisms to produce energy when oxygen is scarce.

Key points of anaerobic respiration:

  • Location: Occurs in the cytoplasm of cells.
  • Energy yield: Produces less energy compared to aerobic respiration.
  • End products: In animals, it produces lactic acid; in yeast, it produces ethanol and carbon dioxide.

Importance of anaerobic respiration:

  • Enables survival in low-oxygen environments.
  • Provides quick energy during short bursts of activity.

In summary, anaerobic respiration is crucial for energy production in the absence of oxygen, allowing organisms to adapt to various environmental conditions.

  • Occurs without oxygen in the cytoplasm of cells.
  • Produces less energy than aerobic respiration.
  • End products include lactic acid or ethanol and carbon dioxide.
  • Enables quick energy production during intense exercise.
  • Essential for survival in low-oxygen environments.

Explain anaerobic respiration in yeast.

  • Yeast undergoes anaerobic respiration in the absence of oxygen.
  • It produces ethanol and carbon dioxide as by-products.
  • This process is used in brewing and baking.

Sample Questions

Read 3 questions and answers free. Sign up to access all 61 questions with full KNEC-style marking schemes and a personalised study plan.

1
easySHORT ANSWER2 marks

Name two end products of anaerobic respiration in yeast. (2 marks)

Answer & marking scheme

Part (a) — 2 marks
Ethanol / alcohol (1 mk)
Carbon dioxide (1 mk)
2
easySHORT ANSWER4 marks

Write the equation for anaerobic respiration in (a) yeast and (b) human muscle cells.

Answer & marking scheme

Part (a) — 4 marks
Yeast (alcoholic fermentation): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + small amount of energy (ATP). (2 marks for fully correct; 1 mark for correct reactant and products but missing/wrong energy) (2 mks)
3
easySHORT ANSWER4 marks

Write the equation for anaerobic respiration in (a) yeast and (b) human muscle cells.

Answer & marking scheme

Part (a) — 4 marks
Yeast (alcoholic fermentation): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + small amount of energy (ATP). (2 marks for fully correct; 1 mark for correct reactant and products but missing/wrong energy) (2 mks)
4

Write the equation for anaerobic respiration in (a) yeast and (b) human muscle cells.

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Frequently asked questions

What does the KCSE Biology topic "Respiration: anaerobic respiration" cover?

Respiration: anaerobic respiration covers Write the equation for anaerobic respiration in plants and animals; Compare aerobic and anaerobic respiration; Respiration: anaerobic respiration, all aligned to the official KNEC KCSE Biology syllabus.

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HighMarks has 61 Respiration: anaerobic respiration practice questions for KCSE Biology, each with a full marking scheme. The first 3 are free; sign up to access the rest, plus all KCSE mock exams and past papers.

Are these aligned with the KNEC KCSE syllabus?

Yes. Every objective on this page is taken directly from the official KNEC KCSE Biology syllabus. Practice questions match the KCSE exam format and are graded against the standard KNEC marking scheme.

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