Animal and plant cells: mitochondria

The idea

Mitochondria are organelles found in the cytoplasm of eukaryotic cells, including animal, plant, algal and fungal cells. They are the site of aerobic respiration, where glucose and oxygen are used to release energy that the cell needs for processes such as growth, movement and active transport. Cells that demand a lot of energy, such as muscle cells, sperm cells and liver cells, contain many mitochondria, whereas less active cells contain fewer. A useful method in exams is to observe the number of mitochondria on an electron micrograph and relate this number to the cell's energy demand.

For example: A sperm cell has many mitochondria to release energy for swimming.

What earns the marks

• Identifies mitochondria as organelles in the cytoplasm of eukaryotic cells.
• States that mitochondria are the site of aerobic respiration.
• Explains that respiration releases energy for the cell's activities.
• Links a high number of mitochondria to cells with high energy demands, such as muscle cells or sperm cells.

Common mistakes and how to put them right

• Saying mitochondria make energy.

  Put it right by stating they release energy from glucose during respiration, since energy cannot be created.

• Confusing mitochondria with chloroplasts.

  Put it right by noting chloroplasts carry out photosynthesis and are found only in plant and algal cells.

• Claiming mitochondria are found in bacterial cells.

  Put it right by stating bacteria are prokaryotes and have no membrane-bound organelles.

Exam tips

• Write that mitochondria are the site of aerobic respiration, not simply where respiration happens.
• Use cell examples such as muscle or sperm cells to justify a high mitochondrial count.