Cell Types with Abundant Mitochondria—Identify the Best Example Mitochondria are expected to be especially numerous in which of the following cell types due to high aerobic ATP demand?

Introduction / Context:
Cells with sustained energy requirements rely on oxidative phosphorylation and therefore accumulate more mitochondria. Understanding which tissues fit this profile helps connect cell structure to function.

Given Data / Assumptions:

• Muscle cells (especially slow-twitch skeletal and cardiac) continually require ATP.
• Red blood cells of mammals lack mitochondria.
• Green leaf cells possess mitochondria but also chloroplasts; photosynthesis does not replace mitochondrial ATP supplies in the dark, yet mitochondria density is typically less than in endurance muscle.

Concept / Approach:
Muscle’s contractile activity demands large, steady ATP flux. Cardiac myocytes are exemplars of extreme mitochondrial density. Although all eukaryotic cells have mitochondria (except mammalian RBCs), the relative abundance is greatest in tissues with constant oxidative workloads.

Step-by-Step Solution:

Verification / Alternative check:
Quantitative morphometry shows mitochondria occupy a large fraction of cardiac cell volume; oxidative enzyme staining confirms high activity.

Why Other Options Are Wrong:

• Green cells: have mitochondria, but not as densely packed as heart/slow-twitch muscle.
• RBCs: zero mitochondria.
• Keratinocytes: comparatively low sustained ATP demand.
• “None of these”: incorrect since muscle is a clear example.

Common Pitfalls:
Overgeneralizing photosynthesis to imply fewer mitochondria needs; plants still use mitochondria, but muscle remains the archetype for abundance.

Final Answer:
Muscle cells (highly active skeletal/cardiac)