Lesson 5 of 6 / Cell structure and organisation
Mitochondria and ribosomes
Which organelle releases energy, and which makes protein?
I can identify mitochondria and ribosomes in diagrams and electron micrographs and state their functions.
I can identify mitochondria and ribosomes and state their functions.Syllabus
Syllabus K327 / K328, Topic 1(b). Identify mitochondria and ribosomes and state their functions.
About 5 min
Make a guess. You are not marked.
A muscle cell contracts again and again all day. Which organelle would you expect it to have lots of?
Show the answer
Mitochondria, to release energy by aerobic respiration.
Repeated contraction needs a steady energy supply. Aerobic respiration in mitochondria releases it.
The key idea
Mitochondria are sites of aerobic respiration; ribosomes synthesise proteins. A cell needs both processes to function.
Electron micrographs show finer detail than light micrographs. These images are sections through cells, so the same structure can look different at different angles.
Explore the idea
Energy release or protein synthesis?
Use the micrograph below. Find the enclosing boundary and the internal folds.
The original diagrams and micrographs have different illustrative scales. A diagram is a model, while a micrograph records a specimen.
Explanation
Mitochondria are organelles in which aerobic respiration occurs. This releases energy from food molecules for cell activities. Cells that have high energy demands, such as contracting muscle cells, commonly contain many mitochondria.
In an electron micrograph, look for an enclosing boundary with an inner membrane folded inside it. The folds are useful evidence for a mitochondrion. An oval outline alone is not enough: different organelles can have similar overall shapes.
Ribosomes are much smaller structures that synthesise proteins from amino acids. In electron micrographs they appear as small dense dots, either in the cytoplasm or on membranes. They are not normally resolved individually using a school light microscope.
A cell making protein needs ribosomes for synthesis and energy released in respiration for its activities. Do not swap these functions: a mitochondrion does not manufacture all the proteins a cell needs, and a ribosome is not the site of aerobic respiration.
Step by step
- 1
Inspect the image
Look for internal folds or a repeated pattern of small dense dots.
- 2
Name the structure
Distinguish the mitochondrion from the much smaller ribosomes.
- 3
State its job
Connect respiration to energy release and ribosomes to protein synthesis.
Worked example
An active muscle cell
A muscle cell has many organelles with folded inner membranes. Identify them and explain why they are useful.
One way to explain it
They are mitochondria. They provide a large capacity for aerobic respiration, releasing energy for repeated muscle contraction.
Why this answer works
- Use the internal folds as identification evidence.
- Connect the named organelle to respiration.
- Link energy release to the specific activity: contraction.
Watch out for this
A student says: "Ribosomes release energy while mitochondria make proteins." What is wrong with this?
Show the answer
Ribosomes synthesise proteins. Mitochondria are sites of aerobic respiration, releasing energy for cell activities.
Check your understanding
Which statement correctly interprets an electron micrograph?
Show the answer
An organelle with a folded inner membrane is consistent with a mitochondrion, a site of aerobic respiration.
The internal pattern supports the identification and is linked to the correct function.
Exam-style questions
Check your understanding
A gland cell makes and secretes large amounts of an enzyme. Which pair of structures would you expect to find in large numbers?
Show the answer
Ribosomes and mitochondria
Ribosomes make the protein, and mitochondria release energy for making and secreting it.
Quick recall
Which organelle releases energy, and which makes protein?