IB MYP 4-5 Biology-Cell Respiration- Study Notes - New Syllabus
IB MYP 4-5 Biology-Cell Respiration- Study Notes – New syllabus
IB MYP 4-5 Biology-Cell Respiration- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Aerobic vs anaerobic respiration
- Mitochondria structure and function
- ATP production and energy transfer
Cellular Respiration
What is Cell Respiration?
Cellular respiration is the process by which cells break down glucose to release energy in the form of ATP (adenosine triphosphate). It occurs in all living cells and is essential for powering biological functions like movement, growth, and repair.
There are two main types:
- Aerobic respiration (requires oxygen)
- Anaerobic respiration (does not require oxygen)
1. Aerobic Respiration
Definition: Breakdown of glucose in the presence of oxygen to produce a large amount of ATP.
Location: Occurs in the mitochondria of eukaryotic cells.
Overall Equation: \[ \mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + 36\text{–}38\ ATP} \]
Key Stages
- Glycolysis (in cytoplasm): Glucose is broken into 2 pyruvate molecules, producing 2 ATP.
- Link Reaction & Krebs Cycle (in mitochondria): Produces CO₂, NADH, FADH₂, and 2 ATP.
- Electron Transport Chain (inner mitochondrial membrane): Uses oxygen to produce the majority of ATP (up to 34 ATP).
Features:
- High energy yield (36–38 ATP per glucose)
- Produces carbon dioxide and water as waste
- Requires continuous oxygen supply
2. Anaerobic Respiration
Definition: Breakdown of glucose without oxygen, producing less ATP.
Location: Occurs in the cytoplasm
- In animals (e.g., muscle cells during intense activity):
Glucose → Lactic Acid + 2 ATP - In yeast and some bacteria (fermentation):
Glucose → Ethanol + CO₂ + 2 ATP
Features:
- Very little ATP (only 2 per glucose)
- Useful when oxygen is limited (e.g., sprinting)
- By-products like lactic acid can cause muscle fatigue
- Ethanol fermentation is used in baking and alcohol production
Comparison: Aerobic vs. Anaerobic Respiration
Why Do Cells Use Anaerobic Respiration at All?
When oxygen is scarce, such as during intense exercise, cells must continue to produce energy.
Anaerobic respiration allows temporary energy production, though it is much less efficient. Lactic acid buildup is reversible when oxygen is restored.Summary
- Cell respiration is essential for providing ATP to support life processes.
- Aerobic respiration is more efficient and preferred when oxygen is available.
Anaerobic respiration serves as a backup when oxygen is limited.
Mitochondria: Structure and Function
What Are Mitochondria?
Mitochondria are membrane-bound organelles found in most eukaryotic cells. They are responsible for producing ATP (adenosine triphosphate) through the process of aerobic respiration.
Often called the powerhouses of the cell, mitochondria convert chemical energy from glucose into a usable form of energy for all cellular activities.
Basic Functions of Mitochondria
- Perform aerobic respiration (oxidative phosphorylation)
- Produce ATP from glucose and oxygen
- Generate heat in some specialized cells (thermogenesis)
- Help regulate cell metabolism, calcium storage, and apoptosis
- Contain their own DNA, allowing them to produce some of their own proteins
Structure of Mitochondria
Mitochondria have a double membrane system and a highly specialized internal structure that supports energy production.
1. Outer Membrane
- Smooth and permeable to small molecules and ions
- Contains proteins called porins that form channels
2. Inner Membrane
- Highly folded into structures called cristae
- Selectively permeable
- Contains electron transport chain proteins and ATP synthase
- Site of oxidative phosphorylation
3. Cristae
- Increase the surface area for ATP production
- Hold the enzymes needed for the final steps of respiration
4. Intermembrane Space
- Space between outer and inner membranes
- Plays a role in proton gradient formation for ATP production
5. Matrix
- Gel-like interior enclosed by the inner membrane
- Contains:
- Enzymes for the Krebs cycle
- Mitochondrial DNA and ribosomes
- Substrates like NADH, FADH₂
Mitochondrial DNA and Ribosomes
Mitochondria contain their own circular DNA and have 70S ribosomes, similar to bacteria. This enables them to replicate, transcribe, and translate some of their own proteins.
These features support the endosymbiotic theory, which suggests mitochondria evolved from ancient bacteria that were engulfed by primitive eukaryotic cells.
Summary Table: Structure and Function
| Structure | Function |
|---|---|
| Outer Membrane | Allows passage of small molecules and ions |
| Inner Membrane | Houses proteins for electron transport and ATP synthesis |
| Cristae | Increase surface area for energy production |
| Matrix | Site of Krebs cycle, contains enzymes, DNA, and ribosomes |
| Intermembrane Space | Helps build the proton gradient for ATP formation |
| Mitochondrial DNA | Codes for some proteins, allows partial self-replication |
| Ribosomes | Synthesizes mitochondrial proteins |
Key Point
The number of mitochondria varies by cell type. Cells with high energy demands, such as muscle cells and neurons, have more mitochondria to meet their ATP requirements.
ATP Production and Energy Transfer
What is ATP?
Structure of ATP
- One adenine (a nitrogenous base)
- One ribose (a five-carbon sugar)
- Three phosphate groups (linked by high-energy bonds)
How Does ATP Work?
The energy is stored in the bonds between phosphate groups, especially the last two bonds.
When the terminal phosphate bond is broken (hydrolyzed), ATP becomes ADP (adenosine diphosphate) and releases energy:
ATP → ADP + Pi + energy
This released energy is used by the cell for:
- Active transport
- Muscle contraction
- Biosynthesis (building macromolecules)
- Nerve impulse transmission
- Cell division
ATP Production: Overview
ATP is mainly produced during cellular respiration. The process involves several steps:
1. Glycolysis (in cytoplasm)
- Glucose is split into 2 pyruvate molecules
- Produces 2 ATP (net) and 2 NADH
2. Krebs Cycle (in mitochondrial matrix)
- Pyruvate is broken down, releasing carbon dioxide
- Produces 2 ATP, NADH, and FADH₂
3. Electron Transport Chain (inner mitochondrial membrane)
- Uses NADH and FADH₂ to pump protons and form a proton gradient
- Protons flow through ATP synthase, generating ~34 ATP
Anaerobic ATP Production
- Occurs in the absence of oxygen
- Only glycolysis occurs
- Yields 2 ATP per glucose
- End products: lactic acid (in animals) or ethanol + CO₂ (in yeast)
ATP Regeneration
ATP is not stored in large quantities. It is constantly regenerated from ADP and inorganic phosphate using energy from food.
This regeneration happens rapidly and continuously, especially in active cells like muscle or nerve cells.
Energy Transfer in Cells
| Biological Process | Energy Use From ATP |
|---|---|
| Active Transport | Moving ions/molecules across membranes |
| Muscle Contraction | Interactions between actin and myosin |
| Biosynthesis | Building proteins, DNA, and other macromolecules |
| Cell Division | Chromosome movement and spindle formation |
| Signal Transmission | Nerve impulses and synaptic activity |
Summary
- ATP is a high-energy molecule crucial for all life functions
- It is produced primarily via aerobic respiration, with the highest yield from the electron transport chain
- ATP provides energy by releasing a phosphate group and is rapidly recycled in cells