Living things or organisms are made up of cells. Some organisms may be made up of just a single cell (unicellular), like bacteria, whereas others are made up of loads of cells, like a plant.
With the invention of the electron microscope in the 20th century, scientists were able to see structures inside of cells more clearly. These structures are called organelles. It was noticed that organisms in the animal, plant, fungi and protist kingdoms all had a cell membrane, cytoplasm and a visible nucleus that contained the genetic material. These are called eukaryotic cells.
Organisms like bacteria are much smaller than eukaryotic cells. The genetic material in a bacteria isn't in a nucleus - these are said to be prokaryotic cells. The genetic material is usually a single loop of DNA, and there may be one or more rings of DNA called a plasmid. Prokaryotic cells have cytoplasm and a cell membrane surrounded by a cell wall. Many (but not all) have a capsule surrounding the cell wall. Some prokaryotic cells may also have flagella to help with movement.
The organelles in eukaryotic and prokaryotic cells differ and have various jobs. Let's look at these organelles a little more closely:
Nucleus- Contains the genetic material which the cell uses to make proteins. Cell activities are controlled here. Kind of like the control centre of a cell.
Cytoplasm - Jelly-like substance that contains the organelles. Many chemical reactions happen here.
Cell membrane - Controls the substances which enter and leave the cell. A bit like the gates at the Houses of Parliament!
Mitochondria - Very small structures in the cytoplasm where respiration takes place, releasing energy for the cell.
Ribosomes - Makes all the proteins needed for the cell via gene translation.
Some organelles are only found in plant cells, such as chloroplasts, cell wall and vacuoles. Let's look at their jobs below:
Chloroplasts - contain a green pigment called chlorophyll which absorbs sunlight for photosynthesis, the process plants use to make glucose.
Vacuole - sometimes called the permanent vacuole. It's a space in the middle of the cell filled with cell sap, it keeps the plant rigid to support the plant.
Cell wall - made of long cellulose fibres to make the cell stronger, and supports the plant.
Prokaryotic cells have some similar features to eukaryotic cells, like the cytoplasm, cell membrane and cell walls. However, the cell wall in prokaryotes is made of a different substance than in plants and its role is to maintain the cell's shape and protect the cell. The cytoplasm and cell membrane do similar roles as in eukaryotic cells.
In the following activity, you will compare eukaryotic and prokaryotic cell features and functions.