Cells - Cell Specialisation and Organisation Flashcards
Why are cells specialised?
In multicellular organisms, cells are specialised to perform specific functions. Similar cells are then grouped together into tissues, tissues into organs and organs into systems for increased efficiency.
What function do cells get specialised to perform?
To stay alive, all cells of a multicellular organism perform certain basic functions. However, no one cell can provide the best conditions for all functions. Therefore the cells of multicellular organisms are each specialised in different ways to perform a particular role. Each specialised cell has evolved more or fewer of certain organelles and structures to suit the role it carries out.
What are stem cells?
Stem cells are the first group of cells in an embryo that are all initially identical (undifferentiated). As it matures, each cell takes on its own individual characteristics that suit it to the function that it will perform when it is mature. In other words, each cell becomes specialised in structure to suit the role that it will carry out.
How does a cell become specialised?
All the cells in an organism are produced by mitotic divisions from the fertilised egg. It follows that they all contain exactly the same genes.
Every cell contains the genes needed for it to develop into any one of the many different cells in an organism. But only some of these genes are switched on (expressed) in any one cell, at any one time. Different genes are switched on in each type of specialised cell. The rest of the genes are switched off.
What changes when a cell becomes specialised?
It is not just the shape of different cells that varies, but also the numbers of each of their organelles.
For example, a muscle or sperm cell will have many mitochondria, while a bone cell has very few. White blood cells have many lysosomes while a muscle cell has very few.
How has evolution helped cells to become more specialised?
The cells of a multicellular organism have therefore evolved to become more and more suited to one specialised function. These cells are adapted to their own particular function and perform it more effectively. As a result, the whole organism functions efficiently.
What are tissues?
For working efficiency, cells are normally aggregated together. Such a collection of similar cells that perform a specific function is known as a tissue.
What are epithelial tissues?
Epithelial tissues are found in animals and consist of sheets of cells. They line the surfaces of organs and often have a protective or secretory function. There are many similar types, including those made up of thin, flat cells that line organs where diffusion takes place, for example the alveoli of the lungs, and ciliated epithelium that lines a duct such as the trachea. The cilia are used to move mucus over the epithelial surface.
What are xylem tissues?
The xylem occurs in plants and is made up of a number of similar cell types. It is used to transport water and mineral ions throughout the plant and also gives mechanical support.
What is an organ?
Just as cells are aggregated into tissues, so tissues are aggregated into organs. An organ is a combination of tissues that are coordinated to perform a variety of functions, although they often have one predominant major function.
What tissues is the stomach in animals made up of?
In animals, the stomach is an organ that is involved in the digestion of certain types of food. It is made up of tissues such as:
- muscle to churn and mix the stomach contents
- epithelium to protect the stomach wall and produce secretions
- connective tissue to hold together the other tissues
What tissues is the leaf in plants made up of?
In plants, a leaf is an organ made up of the following tissues:
- palisade mesophyll made up of leaf palisade cells that carry out photosynthesis
- spongy mesophyll adapted for gaseous diffusion
- epidermis to protect the leaf and allow gaseous diffusion
- phloem to transport organic materials away from the leaf
- xylem to transport water and ions in the leaf
Are capillaries, arteries and veins organs?
Blood capillaries are not organs whereas arteries and veins are. All three structures have the same major function, namely the transport of blood. However, capillaries are made up of just one tissue - epithelium - whereas arteries and veins are made up of many tissues (e.g. epithelial, muscle and other tissues).
What is an organ system?
Organs work together as a single unit known as an organ system. These systems may be grouped together to perform particular functions more efficiently. There are a number of organ systems in humans.
What is the digestive system?
The digestive system digests and processes food. It is made up of organs that include the salivary glands, oesophagus, stomach, duodenum, ileum, pancreas and liver.
