Advanced: Organelle Detail for Grade 7-9
Part of Cell Organelles · GCSE GCSE Biology revision
This higher tier covers Advanced: Organelle Detail for Grade 7-9 within Cell Organelles for GCSE Biology. Revise Cell Organelles in Cell Biology for GCSE Biology with 12 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 10 of 13 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
Topic position
Section 10 of 13
Practice
12 questions
Recall
15 flashcards
Advanced: Organelle Detail for Grade 7-9
Grade 7-9 Only
Mitochondria Structure
Mitochondria have a double membrane. The inner membrane is highly folded into projections called cristae, which massively increase the surface area for the enzymes and proteins involved in aerobic respiration. The central fluid-filled space is called the matrix, where the Krebs cycle reactions occur.
Chloroplast Structure
Chloroplasts also have a double outer membrane. Inside, they contain flattened membrane sacs called thylakoids which are stacked into columns called grana. Chlorophyll is found in the thylakoid membranes. The fluid-filled space between the grana is called the stroma, where the Calvin cycle (carbon fixation) occurs.
Why Both Have Their Own DNA
Both mitochondria and chloroplasts contain their own circular DNA and 70S ribosomes — the same type as bacteria. This is strong evidence for the endosymbiotic theory: ancient eukaryotic cells engulfed free-living bacteria, which then evolved into these organelles rather than being digested. This is why both organelles have a double membrane — the inner membrane is the original bacterial membrane.
Quick Check: Insulin is a protein hormone made by cells in the pancreas. Which three organelles would be most active in a pancreatic cell making large amounts of insulin? Explain why for each.
1. Ribosomes (on rough ER) — protein synthesis: the mRNA code for insulin is translated into a polypeptide chain here. 2. Rough endoplasmic reticulum — the newly made insulin polypeptide is folded into its correct 3D shape inside the rough ER, then transported to the Golgi. 3. Golgi apparatus — modifies and packages the insulin into secretory vesicles, which fuse with the cell membrane and release insulin into the bloodstream (exocytosis). Mitochondria would also be very active, providing ATP energy for all of these processes.