What is a Cell?
All living things are made up of tiny building blocks known as cells. There are many different types of cells, but each of them has a responsibility in keeping the internal mechanisms of a living organism functioning smoothly. Within a cell, there are specialized organelles, each with its own unique function. Some organelles are only present in animal cells while others are only present in plant cells, but several organelles are common in both.
- Cytoplasm - jelly-like fluid that fills the cell and holds organelles in place
- Cytoskeleton - provides structure for the cell
- Cell Membrane - directs the movement of materials into and out of a cell
- Nucleus - controls the activities of a cell
- Smooth Endoplasmic Reticulum - creates fats and lipids for transport out of the cell
- Rough Endoplasmic Reticulum - creates proteins for transport out of the cell
- Golgi Apparatus (Golgi Bodies) - package proteins for transport
- Mitochondria - break down sugar molecules to create energy
- Ribosomes - creates proteins
- Vacuole - storage of water and nutrients
Functions of Cell
There are many various functions that a cell has within an organism.
1. Structure and Support
Cells such as skin cells provide structure for organisms, while plants contain cells that form specialized tissues to keep their structure rigid.
2. Growth and Repair
Cells replicate using a process called mitosis to generate new cells. This repairs injuries and also enables an organism to grow.
3. Transport of Materials
Cells enable the import of nutrients such as water and oxygen and the export of waste.
4. Produce Energy
An organism needs energy to function, so the cell plays a key role in producing ATP energy for the organism. In animals, this occurs via cellular respiration, and in plants, this occurs via photosynthesis.
Asexual reproduction takes place when cells replicate themselves, creating identical cells and offspring. Sexual reproduction involves the combining of sex cells to mix genetic information.
Types of Cells
Prokaryotic cells are simple in structure and were believed to be the first cells to evolve. The domains of Bacteria and Archaea are the only two to contain prokaryotic cells, although this makes up a large majority of Earth's biomass. Prokaryotic cells do not have a true nucleus or many of the membrane bound organelles found in eukaryotic cells. However, a prokaryotic cell does contain the following:
- Cell wall
- Cell membrane
Prokaryotic cells also have a third outer layer called a capsule. This capsule provides even more protection for a bacterial cell and allows it to stick to other surfaces.
Eukaryotic cells are larger and more complex than prokaryotic cells. Plant and animal cells are both eukaryotic and contain several diverse organelles that are not found in prokaryotic cells. These organelles include an endoplasmic reticulum, vacuoles, mitochondria, golgi apparatus, lysosomes, and chloroplasts. Eukaryotic cells contain a membrane bound nucleus in which the DNA of the organism is held, unlike a prokaryotic cell where the DNA is coiled in the middle of the cell itself.