Cell Shape and Size: Learn about Different Cell Structures, Types

Why are cells so tiny if they are an organism’s fundamental structural and functional unit? Cells are the smallest units of life on Earth, that emerged at least 3.5 billion years ago. What is the shape of neurons? Is it round like cocci? Cell Shape and Size play a very important role in describing a particular organism or its cells structural and functional properties. This article covers the definition of cells, their shape and much more. To know more about Cell Shape and Size, scroll down the article.

What is a Cell?

The cell is defined or referred to as the basic structural, functional, and biological unit of all known living organisms. The smallest unit of life is the cell, which is self-replicating and autonomous, which is also referred to as “life’s building blocks“.

The word ‘cell’ is derived from the Latin word called ‘cella,’ which refers to a ‘small room‘.

Cell biology, cellular biology, or cytology is a field of biology that studies cells.

Diversity of Cell

Within the same organism, different cells might be in different sizes and shapes. They may not be particularly large, but their forms can be rather diverse. These cells, on the other hand, all have similar capacities, including collecting and utilising dietary energy, reacting to their surroundings, and reproducing. The form of a cell influences its function in part.

Cell Number

Each living organism is made up of cells, which are the smallest units of the organisation. An organism’s cell count can range from one to millions or trillions. Organisms are categorised as Unicellular or Multicellular based on the number of cells they contain.
1. Unicellular Organisms – Organisms made up of only one cell are known as unicellular organisms. A single cell conducts all of the essential functions for life, including growth, reproduction, movement, and excretion. Amoeba, Chlamydomonas, Paramecium, and other organisms are examples.
2. Multicellular Organisms – Organisms made up of more than one cell and are known as multicellular organisms. The cells of these organisms are generally dedicated to certain functions—plants, animals, fungus, etc.

What Determines the Size and Shape of a Cell?

Cells rarely remain in a spherical form within an organism. They are flattened (epithelial cells), spindle-shaped (muscle cells), spider-shaped (nerve cells), and other shapes. A cell’s size and shape are determined by four factors:
1. Surface-volume ratio
2. Nucleocytoplasmic ratio
3. Rate of cellular activity
4. Cell associations.

Surface-Volume Ratio
i. The interior content of the cell is separated from the external environment by the cell membrane. This distinction, however, does not imply isolation.
ii. The membrane allows a variety of chemicals to flow through it. These chemicals are required for the cell’s functions to perform.
iii. A cell’s entire surface area is just enough to hold its internal contents. Any increase in surface area causes a massive rise in cell volume, which throws the balance off.
iv. As a result, the ratio of surface area to interior volume determines the specific form and size of a cell.

Nucleo-Cytoplasmic Ratio
i. The coordinated activity of the cell’s many components allows it to operate. The coordination between the nucleus and the cytoplasm is the most crucial.
ii. The nucleus generates chemicals that enter the cytoplasm and regulate its activities. A cell’s cytoplasmic region is just large enough for a nucleus to regulate.
iii. The nucleus will be unable to control its activity if the cytoplasmic region becomes too large.
iv. As a result, a cell’s nucleo-cytoplasmic ratio never exceeds one-seventh to one-twelfth of its total size.
v. In certain circumstances, the presence of many nuclei in a big cell overcomes this issue.

Rate of Cellular Activity
i. Despite the fact that all cells in a live organism are vital, some are metabolically more active than others.
ii. The more active cells are generally smaller, with a higher surface-volume ratio and nucleo-cytoplasmic ratio than the bigger cells, allowing them to function more actively.

Cell Association
i. In multicellular forms that exhibit some rigidity, cell-to-cell attachment is critical.
ii. The degree of attachment has a significant impact on the structure of the cell and its functional properties.

All four variables listed above are clearly connected, with the surface-volume ratio and nucleo-cytoplasmic ratio playing the most significant roles in determining the cell’s size, shape, and characteristics.

Cell Size

i. Micrometres are used to measuring the size of cells in live organisms.
ii. The majority of cells are 5-15 micrometres in size.
iii. Some multicellular species, such as Amoeba, may be smaller than numerous unicellular forms.
iv. In bacteria, the smallest cell is 0.1 to 0.5 mm.
v. Some single cells, such as those seen in bird and reptile eggs, are extremely big.
vi. The ostrich egg is the largest cell, measuring 170mm by 130mm.
vii. Nerve cells are the longest cells in humans (1-2m). A nerve cell can grow to be many metres long.
viii. The diameter of red blood cells is just 5-8 µ.
xi. The size of cells is unrelated to the size of an organism, although it is determined by their function.

Cell Shape

The activities of each cell are reflected in the range of cell shapes observed in prokaryotes and eukaryotes, supporting the structure-function connection prevalent throughout life. Each cell type has developed a form that is most closely associated with its function.

Depending on the purpose, the cell takes on a number of forms. Cells come in a variety of forms, including:

Skin cells
i. These skin cells have a flat surface.
ii. They are a protective body cover with a flat form that allows them to cover a large area.

Fig: Skin cells

Muscle cells
i. Muscle cells are long, thin, and elongated.
ii. Muscle cells expand and contract, and their long and thin structure aids in this process.

Fig: Muscle cells

Nerve cells
i. These nerve cells have a lengthy fibrous structure.
ii. Long, thin extensions (axons and dendrites) connect these nerve cells to other nerve cells.
iii. The extensions aid the neuron in swiftly transmitting chemical and electrical information throughout the body.
iv. Nerve cells can contain fibres that are over a metre long.
v. Messages are transmitted down these fibres from one nerve cell to the next.

Fig: Nerve cell – Neuron

Blood cells
i. White blood cells are disc-shaped but have the ability to alter form.
ii. WBC in the blood alters their form to kill bacteria or any pathogens that are disease-causing organisms.
iii. The structure of red blood cells (erythrocytes) allows them to pass through capillaries with ease.

Fig: Blood cells

Study about Eukaryotic Cell here

Plant cells
i. Depending on their purpose, plant cells might be rectangular, circular, oval, or elongated. Plant cells on the outside of the stem give the plant its strength.
ii. For support, these cells have strong cell walls. Food is stored in specific cells in plants, and these cells are bigger than other cells.

Fig: Plant cell

Do You Know!!

Some organisms do not have a proper shape!

Amoeba is one of the well-known organisms which do not possess a proper shape. It is a single-celled species with no distinct form, which uses pseudopodia to move and feed on prey.

 Fig: Amoeba

Summary

Within the same organism, different cells might be of different sizes and shapes. They may not be particularly large, but their forms can be rather diverse. The surface area to volume ratio of a cell determines its size. A smaller cell transports substances more efficiently, including waste products than a bigger cell.
Through this article, we understood that the cells come in many different shapes. Everything, however, is dependent on the functions to be performed. Various types of folding enhance the surface area of numerous cells. The risk of inner volume change has decreased as a result of this elevation.

Frequently Asked Questions (FAQs) on Cell Shape and Size

The most frequently asked questions about cell shape and size are answered here: