Prokaryotes and eukaryotes, one cell or many
Bacteria are prokaryotes. Their cells are simple and very small, and their genetic material lies in the cytoplasm, not inside a nucleus with a membrane. Eukaryotes have a true nucleus surrounded by a membrane, and their cells are more complex. Some eukaryotes are unicellular, such as Euglena, amoeba, Paramecium and yeast: one cell does all the jobs of life, and we need a microscope to see it. Others are multicellular, such as plants, animals and mushrooms, with specialised cells. All three kinds of cell, animal, plant and bacterial, have a cell membrane, cytoplasm and ribosomes. Animal and plant cells have a nucleus and mitochondria, and bacterial cells do not. Plant and bacterial cells have a cell wall. Only plant cells have chloroplasts and a large vacuole. Only animal cells have a centrosome. So it is wrong to say all cells have a nucleus or a cell wall.
| Part | Animal cell | Plant cell | Bacterial cell |
|---|---|---|---|
| membrane | yes | yes | yes |
| cytoplasm | yes | yes | yes |
| ribosomes | yes | yes | yes |
| nucleus with a membrane | yes | yes | no |
| mitochondria | yes | yes | no |
| cell wall | no | yes | yes |
| chloroplasts | no | yes | no |
| large vacuole | no | yes | no |
| centrosome | yes | no | no |
Sort and compare. Write twelve names on cards: amoeba, camel, yeast, date palm, Paramecium, mushroom, Euglena, bacterium, honeybee, wheat, rabbit and mint. Sort them into unicellular and multicellular. Then draw a Venn diagram for animal and plant cells with the parts from the lesson. A microscope picture or a school microscope with your teacher can help.