There’s no such
thing as a typical cell. Cells are the
building blocks of life, and all living things are made from them. Each cell has internal organelles they are all based
in the cytoplasm of the cell which has the texture of sloppy jelly. It contains
many dissolved substances such as proteins. This post explores the different cell types and the structures within cells.
Biology - Cells and organisms
An Organelle is a small structure within a cell, meaning that all cells are made of organelles. The nucleus is probably the most important organelle because it contains DNA coiled up as chromosomes. The DNA contains all of the information about which proteins to make inside the cell, which reactions should happen and (in a broader context) what the organism as a whole will look like.
The cytoplasm is the structure in which most of the reactions take place - as a general rule, it is found around the outside of the vacuole in plant cells or everywhere within the cell membrane in animal cells. Most of the other structures can be found outside of the cytoplasm, for example the chloroplasts, which contain chlorophyll to allow them to generate energy from sunlight (photosynthesis, only found in plant cells), or the mitochondria which carry out the respiration reactions in the cell.
The vacuole is the structure that is usually found in the centre of a plant cell. They are filled with cell sap, a solution of sugars. Some specialised animal cells have temporary vacuoles which store food and water, but this is not common.
Around the outside of the cytoplasm will be a cell membrane. All cells have a cell membranes but it is very hard to see in plants because it is against the cell wall. A cell membrane is a very thin layer of protein and fat which controls what goes in and out of the cell. We describe it as a partially permeable; this means it lets some things through but prevents others from entry to the cell.
Around the outside of the cytoplasm will be a cell membrane. All cells have a cell membranes but it is very hard to see in plants because it is against the cell wall. A cell membrane is a very thin layer of protein and fat which controls what goes in and out of the cell. We describe it as a partially permeable; this means it lets some things through but prevents others from entry to the cell.
Cell walls can only be found in plants, and are made of a polymer called cellulose. A cell wall is a very strong covering for the cell. It protects and supports the cell. It can withstand the internal pressures of turgor (when the cell has become stiff because it has absorbed so much water through osmosis. Turgor keeps plants stiff so that they can grow tall and compete for light). Spaces between the cellulose fibres allow even large molecules to pass through; it is described as fully permeable.
There are a few interesting exceptions to the rules. Xylem vessels in plant stems do not have nuclei because they are technically dead cells. Red blood cells have no nuclei because they need to conserve room in the nucleus to carry as much haemoglobin as possible.
Remember - there are many exceptions. This is just an accurate generalisation that can be applied for most GCSE purposes.
There are a few interesting exceptions to the rules. Xylem vessels in plant stems do not have nuclei because they are technically dead cells. Red blood cells have no nuclei because they need to conserve room in the nucleus to carry as much haemoglobin as possible.
Remember - there are many exceptions. This is just an accurate generalisation that can be applied for most GCSE purposes.
