Libro digital

All living beings have two characteristics in common: they are made of cells and they carry out three vital functions.

Cells are microscopic units, which have got different shapes and sizes. All cells have three parts:

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 and obtain energy, etc.

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.

Cells and organisation

Unicellular organisms are made up of only one cell. Some of them can group together into colonies but they are not organised or coordinated. Bacteria are unicellular organisms.

Multicellular organisms are made up of a lot of different cells and they are all different shapes and sizes. Each cell has got a special function. The cells are organised and they work together as a team.

Plants and animals are multicellular organisms.
In many multicellular organisms, the cells are organised into tissues, organs and systems.

Tissues are groups of cells specialised in doing a specific activity. For example, muscle cells form muscle tissue.

Organs are made up of different tissues. 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 to complete a function. The circulatory system, for example, distributes nutrients and carries waste. It contains different types of organs, one of which is the heart.

Copy and complete the sentences with the correct word.

1 The surrounds and protects the cell.

2 The is the control centre of a eukaryotic cell.

3 is thick liquid inside the cell membrane.

4 The perform essential tasks.

What has a eukaryotic cell got that a prokaryotic cell hasn't got?

Copy and complete the sentences with the correct word from the box.

cells multicellular organ sizes system tissues

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.

The vital functions

All living beings carry out three vital functions: nutrition, interaction and reproduction.

The nutrition function is the process in which living beings obtain oxygen and the nutrients they need, use substances in their bodies and eliminate waste.

Living beings obtain nutrients in two main ways:

Heterotrophic nutrition. Living beings, like animals, obtain nutrients by feeding on other living beings or their remains.

Autotrophic nutrition. Living beings, like plants, produce their nutrients from water and carbon dioxide.

The interaction function. Through the interaction function, living beings react to changes in their environment.

Living beings like animals have sense organs like eyes to detect changes and react to them.

Living beings like plants haven´t got sense organs. They react to changes by growing or modifying their bodies.

The reproduction function allows living beings to produce offspring.

Asexual. Living beings produce new individuals from parts of their body.

Sexual. Two different types of individuals are needed: a male and a female. Each one has different reproductive cells, called gametes. They join together to produce offspring.