Looking around we see living things as well as non-living things. We’ve always thought and told ourselves – what makes an organism work, or what doesn’t an inanimate entity have what it has?
Well, the solution to this is the existence of all living beings of the fundamental unit of life – the cell. All species are made up of cells. Some are made up of a single cell and are considered unicellular organisms, while some are considered multicellular organisms, like humans, consisting of several cells. Read more Life Science topics here
What is Cell? The Fundamental Unit of Life
The cell is the fundamental unit of structure, function, and physiology of all recognized organisms. The smallest unit of life is a cell. Cells are also referred to as ‘the building blocks’ of creation. Cell is a term derived from the Latin word cella, Which means ‘small room’. All species are made up of cells. Some are made up of a single cell and are considered unicellular organisms, while some are considered multicellular organisms, like humans, consisting of several cells.
Unicellular species are capable of performing
- autonomous development and
- the basic functions of life.
Anything that is less than a full cell structure does not guarantee an independent life. The cell is the essential structural and functional unit of all living organisms. Anton Von Leeuwenhoek first saw a live cell and identified it. The nucleus was later identified by Robert Brown. The microscope’s invention and its development which led to the electron microscope revealed all of the cell’s structural details.
What is Cell Theory
In 1838, a German botanist, Matthias Schleiden, studied a vast variety of plants and found that all plants are composed of various kinds of cells that make up the plant’s tissues. At around the same time, the British zoologist Theodore Schwann studied various forms of animal cells in 1839 and confirmed that cells had a thin outer layer known today as the plasma membrane. Based on his observations of plant tissues, he also concluded that the appearance of the cell wall is a special feature of plant cells.
Based on this, Schwann suggested the theory that animal and plant bodies are made of cells and cell components. The cell theory was conceived jointly by Schleiden and Schwann. However, this hypothesis hasn’t clarified how new cells were created. Rudolf Virchow first stated in 1855 that cells were separated and new cells were created from pre-existing cells (cellula-e omnis). He updated the Schleiden and Schwann hypotheses to give a final structure to the cell theory. Cell theory as it is currently known is:
- Every living organism consists of cells and products of cells.
- All cells have their roots in pre-existing cells.
Important Characteristics of Cells or Facts about Cells
- Standard plant cells, its outer border has a distinct cell wall and its cell membrane is just within.
- Human cheek cells have an outer membrane as the cell’s boundary layer. Within each cell is a dense fused membrane layer called the nucleus.
- The nucleus comprises the chromosomes that in turn comprise the content of the genome, DNA.
- Cells with membrane-binding nuclei are considered Eukaryotic cells whereas cells without a membrane-binding nucleus are Prokaryotic cells.
- For all prokaryotic and eukaryotic cells, the cell volume is filled by a semi-fluid layer called cytoplasm.
- The cytoplasm is the primary area of cellular development in plant and animal cells. This involves a number of chemical reactions to hold the cells in ‘working condition.’
- Besides the nucleus, the eukaryotic cells, including the endoplasmic reticulum (ER), do have other membrane-bound distinct structures called organelles. Complex golgi, lysosomes, mitochondria, microbodies, vacuoles, etc.
- The prokaryotic cells lack these organelles attached to the membrane.
- Ribosomes are non-membrane attached organelles present in both eukaryotic and prokaryotic cells of both plants and animals. Within the cells, ribosomes are located not just in the cytoplasm, but even in the chloroplasts in plants and mitochondria of the two organelles, and on rough ER.
- Animal cells contain another non-membrane bound organelle called centriole that helps to separate the cells.
- The scale, form, and functions of the cells vary greatly. For example, the smallest cells, Mycoplasmas, are just 0.3 µm in length while the bacteria maybe 3 to 5 µm.
- The largest single cell isolated, is an ostrich’s egg.
- Human red blood cells are around 7.0 µm in diameter, for multicellular species.
- The nerve cells are among the longest. Cells vary differently in shape, too. such as disc-like, polygonal, columnar, cuboid, threadlike, or even irregular
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