All living beings have two characteristics in common: they are made of cells and they carry out three vital functions.
The cells
All living beings, humans included, are made up of microscopic units called cells.
Cells are different shapes and sizes. All cells have three parts: a membrane , cytoplasm and genetic material .
The cell membrane surrounds the cell. It protects it and keeps the cytoplasm and the other contents of the cell inside.
The cytoplasm is a thick liquid found inside the cell membrane. It is home to different organelles , which are the parts of the cell that produce substances, obtain energy...
The genetic material controls the cell’s activity.
–Most living beings have eukaryotic cells (their genetic material is inside an organelle called a nucleus ).
–Bacteria have prokaryotic cells with no nucleus. Their genetic material is in the cytoplasm.
Complete the sentences with the correct word.
1 The surrounds and protects the cell.
2 The controls the cell’s activity.
3 is a gel-like substance within the cell membrane.
4 The cytoplasm is home to different .
5 Eukaryotic cells have their genetic material inside a .
What does a eukaryotic cell have that a prokaryotic cell does not?
Cells and organisation
Unicellular organisms. Some organisms like bacteria, protozoa or yeast are made up of only one cell. Some of them can group together into colonies but they are not organised or coordinated.
Multicellular organisms. Living beings like plants or animals are made up of lots of cells.
Some multicellular organisms, such as humans, have various groups of cells organised and coordinated into tissues , organs and systems .
Tissues are groups of similar cells specialised in doing a specific activity. These cells work together in teams. For example, muscular tissue is made up of elongated cells called muscular cells.
Organs are made up of different tissues. Organs carry out a task. The heart is an organ, made of muscular tissue as well as other different tissues. The heart pumps blood.
Systems are made up of different organs that work together. Systems complete a function. For example, the circulatory system contains different organs, one of which is the heart. The circulatory system distributes nutrients and carries waste.
In your own words define tissues, organs and systems and explain what they do.
Complete the sentences with the correct word.
1 Cells come in different shapes and .
2 Living beings are made up of .
3 Living beings can be unicellular or .
4 Some cells group together to form .
5 An is made up of various tissues.
6 A is made up of various organs.