📌Definition Table

Term	Definition
Cristae	Folds of the inner mitochondrial membrane that increase surface area for ATP production.
Matrix	Fluid-filled space inside mitochondria containing enzymes, ribosomes, and mitochondrial DNA.
Thylakoid	Flattened membrane-bound sac in chloroplasts where light-dependent reactions occur.
Stroma	Fluid-filled space in chloroplasts containing enzymes, ribosomes, and DNA.
Photosystem	Protein-pigment complex in thylakoid membranes that captures light energy.

📌Introduction

Mitochondria and chloroplasts are double-membrane organelles responsible for ATP production through respiration and photosynthesis respectively. Their structures are highly adapted to maximise efficiency in energy conversion.

❤️ CAS Link: Create an interactive 3D model of mitochondria and chloroplasts for a school science fair, explaining how each adaptation aids energy production.

📌 Structure and Adaptations of Mitochondria

• Double membrane: Outer membrane allows molecule entry; inner membrane is highly selective and folded into cristae.
• Cristae: Increase surface area for the electron transport chain and ATP synthase.
• Matrix: Contains enzymes for the Krebs cycle, ribosomes for protein synthesis, and mitochondrial DNA for enzyme production.
• Intermembrane space: Allows accumulation of protons for chemiosmosis.
• Small size: Increases surface area-to-volume ratio for faster diffusion of substrates and products.
• Dynamic nature: Can change shape and number to meet cell energy demands.

🧠 Examiner Tip: Always link the structure of cristae to increased ATP production capacity in mitochondria-related questions.

📌 Structure and Adaptations of Chloroplasts

• Double membrane: Controls exchange of substances with cytoplasm.
• Thylakoids: Contain photosystems, electron carriers, and ATP synthase for the light-dependent stage of photosynthesis.
• Grana: Stacks of thylakoids increase surface area for light absorption.
• Stroma: Contains enzymes for the Calvin cycle, ribosomes, and chloroplast DNA.
• Pigments: Chlorophyll a, chlorophyll b, and carotenoids absorb different wavelengths of light.
• Interconnected thylakoid membranes: Efficient transport of energy and products between light-dependent and light-independent reactions.

🌍 Real-World Connection: Chloroplast adaptation research has been used in developing high-efficiency crop plants through genetic modification.

📌 Shared Features of Mitochondria and Chloroplasts

• Both have double membranes, DNA, and 70S ribosomes — enabling production of some proteins independently of the nucleus.
• Both generate ATP through chemiosmosis using electron transport chains.
• Both maintain proton gradients across internal membranes.
• Endosymbiotic theory explains their origin from free-living prokaryotes.
• Presence of multiple copies of DNA and ribosomes allows rapid synthesis of proteins for energy conversion.