WHAT IS A CELL?
By definition, a cell means 'the smallest functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.' A cell, whether it be a plant or animal cell, has special, specific tasks that they carry out. Red bloods cells, for example, have the job of carrying oxygen around the body, and have a special shape to enhance the amount of haemoglobin (which carries the blood). WHO DISCOVERED CELLS AND WHEN? The person who discovered cells is Robert Hooke. He was a British scientist born in 1635. Hooke made the discovery in 1665, and although he actually saw the dead cell walls of plant cells, he was the first person to notice these structures. He thought that the cells looked similar to cells or small rooms which monks lived in, which is where the name 'cell' was derived from. The first person to witness a live cell under a microscope was Anton van Leeuwenhoek, who saw and described the algae Spirogyra and bacteria. UNICELLULAR vs MULTICELLULAR A unicellular organism is one that consists of only one cell. This means that the organism is usually a bacteria or a very simple organism. A multicellular organism is one that, like us humans, consist of many cells. These types of organisms are more complex and can carry out more roles. Some other examples of multicellular organisms are many types of plants, dogs, fish, etc. SPECIALISED CELLS Multicellular organisms have specialised cells, meaning that groups of cells carry out certain tasks. Some examples of this are red blood cells, whose outer membrane allows oxygen to diffuse through it easily. The hollow shape enables there to be more surface area for oxygen to be absorbed in to. There is no nucleus in this cell once it has matured, meaning that the entire cell is full of haemogloblin, which is the substance that carries oxygen. Another example is a leaf cell, which is packed with chloroplasts to enable photosynthesis to occur. Cell specialisation is so important in multicellular organisms because it gives the organism order and structure. Without each cell having a certain job, there would be complete chaos. Much like a group project at school, different people do different jobs to get a task done more quickly and efficiently. With all the cells working together, separarately but ultimately in unison, the organsim can live and work with ease. (See below for three examples of specialised cells.) ORGANELLES The defintion of an organelle is a structrural and functional unit, such as a mitochondrion, in a cell or unicellular organism. Some organelles known are the nucleus, endoplasmic reticulum, golgi apparatus, ribosomes, cytoplam, cell membrane etc. 3 EXAMPLES OF SPECIALISED CELLS: |
Robert Hooke-discovered cells
Plant cell under a microscope
Cheek cell under a microscope
PROKARYOTIC CELLS vs EUKARYOTIC CELLS The definition of a prokaryotic organism is 'a single-celled organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelles.' The definition of a eukaryotic organism is 'any organism whose cells contain a nucleus and other organelles enclosed within membranes.' The main difference between prokaryotic and eukaryotic cells is that eukaryotic cells have many organelles within them, whereas prokaryotic cells do not. Prokaryotic cells have been around since the beginning of Earth, however eukaryotic were created during evolution. Prokaryotic cells have no nucleus, only one chromosome, and hardly any other organelles. They are usually unicellular. A typical prokaryotic cell is bacteria and archaea, whereas a eukaryotic cell could be a red blood cell. |
Root Hair Cell
Sperm Cell
Red Blood Cell