Eukaryotes and prokaryotes: Plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus.

The idea

Eukaryotic cells include all plant and animal cells. Whatever their shape or size, they share three features: a cell membrane, cytoplasm and genetic material enclosed in a nucleus. The cell membrane is a partially permeable barrier that controls what enters and leaves the cell. The cytoplasm is the jelly-like fluid where most chemical reactions of the cell take place, and it holds the cell's organelles. The nucleus contains the genetic material, DNA, arranged in chromosomes, and it controls the activities of the cell. Plant and animal cells also contain mitochondria for respiration and ribosomes for protein synthesis, while plant cells additionally have a cell wall, a permanent vacuole and often chloroplasts. Prokaryotic cells, such as bacteria, are much smaller and have no nucleus: their genetic material is a single loop of DNA free in the cytoplasm.

What earns the marks

• Eukaryotic cells are plant and animal cells, and they all possess a cell membrane, cytoplasm and genetic material enclosed in a nucleus.
• The cell membrane controls the movement of substances into and out of the cell and is partially permeable.
• The cytoplasm is where most of the cell's chemical reactions occur and where the organelles are found.
• The nucleus encloses the genetic material, which is DNA organised into chromosomes, and it controls the cell's activities.
• Prokaryotic cells such as bacteria lack a nucleus, so their genetic material lies free in the cytoplasm, usually as a single DNA loop.

Common mistakes and how to put them right

• Saying that plant cells have no cell membrane because they have a cell wall.

  Put it right: Plant cells have both a cell membrane and a cell wall outside it.

• Stating that prokaryotic cells have a small nucleus.

  Put it right: Prokaryotic cells have no nucleus at all and their DNA is free in the cytoplasm.

• Describing the cytoplasm as empty space.

  Put it right: The cytoplasm is where most chemical reactions take place and where organelles are located.

Exam tips

• When listing the shared features of eukaryotic cells, name all three: cell membrane, cytoplasm and genetic material enclosed in a nucleus.
• If asked to compare plant and animal cells, start with the features they share and then give the plant-only structures such as the cell wall and permanent vacuole.
• Use the term partially permeable when describing the cell membrane, and link it to controlling what enters and leaves the cell.