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16 Jan 2026

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4 pages

Nat 5 and A-Level Biology Notes: Respiration, Fermentation, and More

Chloé Merson

@chlomerson_7

Respiration is a vital process in living organisms that breaks... Show more

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# Respiration

Cell respiration
of glucose

し

energy

What is respiration?

ATP

ADP+P

energy

muscle
_contraction,
sperm
movement,
photos

Stages of Aerobic Respiration

Aerobic respiration occurs in two main stages: glycolysis and pyruvic acid breakdown. These stages are crucial for understanding the stages of aerobic respiration a level Biology curriculum.

Stage 1: Glycolysis

Takes place in the cytoplasm
Oxygen is not needed
Glucose is broken down into pyruvic acid using enzymes
Produces 2 ATP molecules

Stage 2: Pyruvic Acid Breakdown

Occurs in the mitochondria
Oxygen is required
Pyruvic acid is completely broken down into carbon dioxide and water
Generates 36 ATP molecules

Highlight: The total ATP production in aerobic respiration is 38 molecules (2 from glycolysis and 36 from pyruvic acid breakdown).

Vocabulary: Glycolysis is the first stage of respiration where glucose is broken down into pyruvic acid in the cytoplasm.

The aerobic respiration diagram illustrates the process, showing how glucose is broken down in the presence of oxygen to produce ATP, carbon dioxide, and water. This visual representation is essential for students studying cellular respiration and the aerobic respiration equation.

Fermentation: Anaerobic Respiration

Fermentation is a type of anaerobic respiration that occurs when an organism cannot take in enough oxygen to meet its energy demands. This process is important for understanding fermentation GCSE Biology and fermentation bbc bitesize ks3 topics.

Key features of fermentation:

Glucose is only partially broken down
Fewer ATP molecules are produced compared to aerobic respiration
The entire process takes place in the cytoplasm
Only 2 ATP molecules are produced

Definition: Fermentation is a type of respiration where glucose is partially broken down without oxygen, producing different end products in animal and plant cells.

Highlight: The products of fermentation differ between animal and plant cells. Plant and fungal cells undergo alcoholic fermentation, while animal cells undergo lactic acid fermentation.

Fermentation equations:

Plant and Fungal cells: Glucose → Ethanol + Carbon dioxide + ATP
Animal cells: Glucose → Lactate + ATP

Like aerobic respiration, fermentation also occurs in two stages:

Stage 1: Glycolysis (same for animals and plants)

Glucose is broken down into pyruvic acid
2 ATP molecules are formed

Vocabulary: Pyruvic acid is also known as pyruvate.

Differences in Fermentation Between Cell Types

The second stage of fermentation differs between plant/fungal cells and animal cells. This distinction is crucial for answering Nat 5 Biology respiration questions and understanding the word equation for fermentation in animal cells.

Plant and Fungal Cells (Alcoholic Fermentation):

Pyruvic acid is broken down into ethanol and carbon dioxide
The process is irreversible
No additional ATP is produced

Animal Cells (Lactic Acid Fermentation):

Pyruvic acid is broken down into lactate (lactic acid)
The process is reversible
No additional ATP is produced

Highlight: In animal cells, once enough oxygen becomes available, lactate can be converted back to pyruvic acid for aerobic respiration.

Example: The fermentation equation for plant cells is: Glucose → Ethanol + Carbon dioxide + ATP

Example: The word equation for fermentation of yeast (a fungal cell) is the same as for plant cells.

Understanding the structure of ATP is essential for comprehending how energy is stored and utilized in cells. ATP consists of an adenosine molecule bonded to three phosphate groups. When energy is needed, the bond between the second and third phosphate groups is broken, releasing energy and converting ATP to ADP (adenosine diphosphate).

This detailed explanation of respiration and fermentation provides a comprehensive overview for students studying enzymes used in respiration a level Biology and helps answer Nat 5 Biology respiration questions. It also clarifies the differences between aerobic and anaerobic respiration, which is crucial for understanding cellular energy production in various organisms and conditions.

Respiration Overview

Respiration is the enzyme-controlled process of breaking down glucose to produce energy for cells. This energy is stored in the form of ATP (adenosine triphosphate) molecules.

Key points:

Two types of respiration: aerobic and anaerobic (fermentation)
Glucose is the main energy source
Energy is released when glucose is broken down
ATP is stored in muscle cells and throughout the body
Cells with high energy demands have more mitochondria

Vocabulary: Mitochondria are organelles that function as the site of stage 2 (pyruvic acid breakdown) in aerobic respiration.

Definition: Aerobic respiration is the enzyme-controlled process where glucose is broken down in the presence of oxygen to release energy in the form of ATP, producing carbon dioxide and water as byproducts.

Highlight: The aerobic respiration equation is: Glucose + Oxygen → Carbon dioxide + Water + ATP

Example: Aerobic respiration provides energy for various cellular processes such as muscle contraction, sperm movement, photosynthesis, and protein synthesis.

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4 pages

Nat 5 and A-Level Biology Notes: Respiration, Fermentation, and More

Chloé Merson

@chlomerson_7

Respiration is a vital process in living organisms that breaks down glucose to produce energy in the form of ATP. This process occurs in two main types: aerobic respiration and anaerobic respiration(fermentation). Aerobic respiration requires oxygen and produces more... Show more

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Stages of Aerobic Respiration

Aerobic respiration occurs in two main stages: glycolysis and pyruvic acid breakdown. These stages are crucial for understanding the stages of aerobic respiration a level Biology curriculum.

Stage 1: Glycolysis

Takes place in the cytoplasm
Oxygen is not needed
Glucose is broken down into pyruvic acid using enzymes
Produces 2 ATP molecules

Stage 2: Pyruvic Acid Breakdown

Occurs in the mitochondria
Oxygen is required
Pyruvic acid is completely broken down into carbon dioxide and water
Generates 36 ATP molecules

Highlight: The total ATP production in aerobic respiration is 38 molecules (2 from glycolysis and 36 from pyruvic acid breakdown).

Vocabulary: Glycolysis is the first stage of respiration where glucose is broken down into pyruvic acid in the cytoplasm.

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Fermentation: Anaerobic Respiration

Key features of fermentation:

Glucose is only partially broken down
Fewer ATP molecules are produced compared to aerobic respiration
The entire process takes place in the cytoplasm
Only 2 ATP molecules are produced

Definition: Fermentation is a type of respiration where glucose is partially broken down without oxygen, producing different end products in animal and plant cells.

Highlight: The products of fermentation differ between animal and plant cells. Plant and fungal cells undergo alcoholic fermentation, while animal cells undergo lactic acid fermentation.

Fermentation equations:

Plant and Fungal cells: Glucose → Ethanol + Carbon dioxide + ATP
Animal cells: Glucose → Lactate + ATP

Like aerobic respiration, fermentation also occurs in two stages:

Stage 1: Glycolysis (same for animals and plants)

Glucose is broken down into pyruvic acid
2 ATP molecules are formed

Vocabulary: Pyruvic acid is also known as pyruvate.

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Differences in Fermentation Between Cell Types

Plant and Fungal Cells (Alcoholic Fermentation):

Pyruvic acid is broken down into ethanol and carbon dioxide
The process is irreversible
No additional ATP is produced

Animal Cells (Lactic Acid Fermentation):

Pyruvic acid is broken down into lactate (lactic acid)
The process is reversible
No additional ATP is produced

Highlight: In animal cells, once enough oxygen becomes available, lactate can be converted back to pyruvic acid for aerobic respiration.

Example: The fermentation equation for plant cells is: Glucose → Ethanol + Carbon dioxide + ATP

Example: The word equation for fermentation of yeast (a fungal cell) is the same as for plant cells.

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Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Respiration Overview

Respiration is the enzyme-controlled process of breaking down glucose to produce energy for cells. This energy is stored in the form of ATP (adenosine triphosphate) molecules.

Key points:

Two types of respiration: aerobic and anaerobic (fermentation)
Glucose is the main energy source
Energy is released when glucose is broken down
ATP is stored in muscle cells and throughout the body
Cells with high energy demands have more mitochondria

Vocabulary: Mitochondria are organelles that function as the site of stage 2 (pyruvic acid breakdown) in aerobic respiration.

Definition: Aerobic respiration is the enzyme-controlled process where glucose is broken down in the presence of oxygen to release energy in the form of ATP, producing carbon dioxide and water as byproducts.

Highlight: The aerobic respiration equation is: Glucose + Oxygen → Carbon dioxide + Water + ATP

Example: Aerobic respiration provides energy for various cellular processes such as muscle contraction, sperm movement, photosynthesis, and protein synthesis.