- Make sure you understand cell specialisation and know that many cells have a specific functions.
- Understand that cells develop into different subcellular structures as they differentiate into an organism and that is how they become specialised.
- Understand that cells can have different functions depending on their structure.
- Know that many animal cells lose the ability to differentiate at an early stage, but many plant cells never lose this capability.
- Mature animals usually use cell division as the main way to replace and repair cells.
- The cell structure of a sperm cell, nerve cell and muscle cells is different in animals. The root hair cells, xylem and phloem cells in plants also have different structures.
Cell Differentiation and Specialisation
Not all cells in an organism do the same job. The cell's structure is related to the job it does, so cell structures vary from one another. This differentiation in structure leads to many cell types with different shapes and functions. When cells express specific genes that characterise a certain type of cell we say that a cell has become differentiated.
Specialised cells
Specialised cells are cells in the body that do just a few specific things. They help break down food, they help fight infection, and they make hormones. The majority of cells in an organism are specialised and have a designated function. Depending on its responsibility, a cell can look different to suit its specific purpose. For example, certain cells may have evolved different structures mainly due to their function more so than other parts of the body.
Cell differentiation
When a cell expresses specific genes that characterise a certain type of cell, it is said to have differentiated. Once cells differentiate, they only produce the proteins characteristic for that type of cell.
Specialised cells are important for the differentiation of living organisms. They differentiate into a cell that performs a particular function in the body and lead to more efficient functioning. Specialisation does come at a cost.
When a cell becomes different or specialised for a process such as reproduction, it loses the ability to produce copies of itself. Multicellular organisms require cells able to do this task, so they maintain some unspecialised cells that can replenish the others. These are called stem cells.
The cell differentiation process is illustrated in the diagram below. It is a simplified diagram of a complex process. Differentiation is not a simple, linear process of cells getting more and more specialised but instead involves changes in subcellular structures and the development of different types of cells.
Most forms of differentiation only happen during the development of an organism. Animals usually lose this ability once they become specialised, but plant cells never lose it.
Mature animals have cells that serve very specialized and defined functions. They mainly produce other cells to repair and replace damaged ones, such as skin or blood cells.
Examples of specialised cells
Sperm cells
To make a complex organism, such as a mouse or mushroom, we need many different types of cells. Similar to how a building requires many different materials to be assembled in order to construct it properly.
To start things off, for animals life begins when two sex cells come together and fuse. These two cells are highly specialised, meaning they have specific sizes, as well as shapes and sub-celular structures to help them fulfil their functions.
For example, the sperm cell is very small as it only needs to transport DNA from the father. However, it does have lots of mitochondria which provide energy for its tail. The egg cell, meanwhile, is much larger as it needs to hold information such as a map and other essential building blocks important for life.
Below, you can see a simplified diagram of a sperm cell. As you can see, there are also lots of mitochondria in the cell to provide the energy it needs to do this. It also carries enzymes in its head to digest through the egg cell membrane.
Muscle cells
Muscle cells are specialised for contraction. The function of a muscle cell is to contract quickly and they have a lot of mitochondria, so that there is enough energy to do this. These cells are long, so that they have space to contract and be able to contract quickly.
Nerve cells
Nerve cells are specialised for rapid signalling. They are the smallest and most numerous type of cell in the human body and, unlike other cells, their main function is to communicate with other cells through electrical and chemical signals. Nerve cells are long and branch out to connect other nerve cells together. They work by carrying electric signals from one part of the body to another.
Root hair cells in plants
Root hair cells are cells on the surface of plants that are specialised for absorbing water and minerals. They grow into long "hairs" that stick out into the soil and gives plants a big surface area to absorb water and ion. The root hairs are where most water absorption happens. They are long and thin so they can penetrate between soil particles and they have a large surface area for absorption of water.
Phloem and xylem cells in plants
Phloem and xylem are specialised cells that transport substances. These cells form the phloem and xylem tubes, which carry food & water around plants.
The cells of plants are classified as either xylem or phloem cells. The xylem cells are responsible for transporting water and nutrients up the plant, while phloem cells transport food throughout the plant. Plants need both types of cell to survive. The two types of cell work together in a process called vascular tissue.
The tubes in plant cells are formed by long, continuous cells as opposed to the more familiar animal cells. Xylem & phloem both have a similar structure. Xylem cells are hollow in the centre and phloem cells have very few subcellular structures, so that substances can flow through them. This allows them to serve different but equally important functions.
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