Cells are the simplest basic building blocks of life. Many chemical reactions occur inside our cells to keep us alive.
Examples of cells:
Brain cell (Neuron)
All cells takes in raw materials, process these raw materials to make new molecules and make use of these new molecules in the cell or transported to the other parts of the body for other body functions.
Most cells are too small to be seen with our eyes and we use a light microscope to help see these cells and their parts. A light microscope is able to magnify objects to more than 1000x its original size. For anything much smaller than a cell, it can be observed using a electron microscope, which is able to magnify objects up to 200,000x its original size. The diagram below shows the size of an animal cell with respect to a normal adult human (female).
The different types of cells in our body and in plants may not look the same, but they all have similar parts. Each living cell consist of 2 major components, namely the cell surface (or plasma) membrane and the protoplasm.
- The cell surface membrane is partially permeable membrane that encloses the protoplasm of a cell. A partially permeable membrane is a barrier of the cell which allows only some substances to cross and enter or exit the cell.
- The protoplasm is a living material in a cell which consists of the cytoplasm and the cell nucleus. Its composition is unique to each type of cell and suited for the cell function.
The cytoplasm is the part of the protoplasm found between the cell surface membrane and the nucleus, where most of the cell activities occurs.
- Consists of specialised structures known as the organelles such as the ribosome, along with many enzymes which carry out specific functions in the cell. These organelles are often much smaller in size compared to the cell as a whole, and require an electron microscope to see them. Listed below are the organelle functions.
- Can exist can exist either in the sol (liquid) or gel (semi-solid) state, dependent on the composition of substances and organelles in the cells.
The nucleus is an organelle within the cell which is essential for cell division and controls cell activities such as repairing of worn out parts in the body. It consists of 4 major components – nuclear envelope, nucleoplasm, nucleolus and chromatin.
- Nuclear envelope is the two-layered membrane of the nucleus which separates the contents of the nucleus from the rest of the cytoplasm
- Nucleoplasm is the dense material within the nucleus which acts similarly like the “protoplasm” of a nucleus
- Nucleolus (plural: -li) plays a part in making of proteins in the cell
- Chromatin is a network of long thread like structures, made up of deoxyribonucleic acid (DNA) which stores hereditary information and instructions a cell needs to carry out the chemical reactions within itself.
In addition to the above mentioned parts of a living cell, a plant cell have two distinct components absent in the animal cell – cell wall and chloroplast (Marked by a red rectangular box in the diagram above.
- Cell wall is a non-living part which surrounds the cell surface membrane, protecting the plant cell from injury and give the plant cell its fixed shape. It is made up of cellulose and is fully permeable.
- Chloroplast organelle with green pigment, chlorophyll, essential for photosynthesis (process by which plants make food)
Each animal cell carries a pair of centriole (also known as basal bodies) which is absent in the plant cell. Centrioles are small structure found outside of the body which helps in cell division (in mitosis) and the formation of flagella and cilia, through making microtubules. In addition, vacuoles may or may not be present in animal cells. If present, it is likely to be small and numerous (Plant: large, central vacuole).
Depending on the location in our body, our cell have different cell structures which allows them to perform specific cellular function. However, our cells do not start off this way.
All our cells originated from a single parent known as the embryonic stem cell, which have the capability to differentiate into the different types of cells we see in our body. Differentiation is a process which occur during development, when cells with general function develops to become one with specific function. Cells may acquire special structured or lose certain structures during differentiation.
When the same type of cells combine to serve a particular set of functions, they are collectively known as a simple tissue (e.g. muscle tissue). Complex tissues on the other hand are made up of different types of cells (e.g. Blood, xylem tissue). Different tissues may combine to form organs (e.g. stomach, leaf). When the different organs work together for a common purpose, they form a organ system. The organism is made up of numerous organ systems working together to support the basic survival needs.