There is something unique about our planet. Though all planets are made up of the same matter, somehow, life managed to flourish on our planet. There are many reasons responsible for this that play an important part in our survival. First is the development of animal and plant cells from hydrocarbons and other elements. The presence of oxygen and water. The distance of the planet from a red hot ball of fire called Sun. The existence of the Moon that churns our oceans. The presence of a protective envelope of the atmosphere around us that saves us from radiation and regulates the weather. All these factors are essential, but surprisingly life did not start in this environment.
How Did Cell Formation Begin?
Fossils found in recent times show that the first signs of life emerged in the deep dark depth of our oceans. A place where lava was bubbling out of seafloor cracks and with tonnes of water above it. This soup of chemicals created first cells that would have never survived in the condition we call favorable. A cell consists of elements like hydrogen, carbon, oxygen, nitrogen, and other elements in trace amounts.
These were simple cells with just a membrane and nucleus. Their only function was to reproduce and swallow the stuff. The evolution and changing conditions slowly allowed them to branch out into more complex cells. These complex cells allowed the existence of life as we see it today. Complex life can be differentiated based on animals and plant cells. Though the start was from the same point, along the evolution road, some structural changes on conditions forced them to diverge. This resulted in the development of properties that are polar apart from each other.
This difference in properties can be understood only when we first learn about the components of both types of cells. Let’s start from cells present in animals.
Basic Structure of an Animal Cell
These are a class of eukaryotic cells, which are made up of several components like the nucleus, organelles, and mitochondria bound by a plasma membrane. The development of the animal kingdom was only possible because of one component that this cell lost millions of years ago. This type of cell does not have a rigid cell wall. This allows these cells to develop into specialized blocks for different organs. They acquire different functions according to the organ that they are part of. The ability of movement is the single biggest defining feature of animals, which wouldn't have been possible otherwise.
Do you know the largest cell in the animal kingdom? It is the egg of an Ostrich. Generally, the size of an animal cell ranges from 1 to 100 microns. For example, the largest cells in the human body are neurons present in our brain. It is not possible to see them without the use of a microscope.
The structure of an animal cell is important to understand because it led to the development of features that are important for animal life. These abilities came because we have specialized brain cells. We have limbs for movement, nerves, and tissues that are specified to perform certain tasks, and bones to provide a core structure that is flexible enough to allow motion. Let’s understand the components.
Cell Membrane: It is a protective covering around the cell, which is made up of plasma. It allows the absorption of nutrients because it is partially permeable. It is elastic in structure, thus allowing flexibility and stretching.
Cytosome: It is the fluid present around the nucleus inside a cell membrane. There are several organelles present in it that are necessary for the functioning of the cell. It consists of water (90%), and the rest are enzymes, proteins, vitamins, RNAs, nucleotides, sugar residues, amino acids, and other organic and inorganic substances.
Mitochondria: These are the rod-like structure which is the largest cytoplasmic organelle. Mitochondria are uniformly distributed throughout the cytoplasm. In some cells, they are found in certain zones. They are the powerhouse of the cell.
Ribosomes: These are minute, granular bodies found scattered throughout the cytoplasm either singly or in groups. These are made up of RNA and protein, and ribonucleoprotein in nature. They are the protein production houses of the body.
Lysosomes: These are spherical and bag-like structure. They are important cytoplasmic organelle, which is found only in animal cells. The cells of the liver spleen, thyroid gland, and brain are particularly rich in lysosomes. Under certain conditions, the lysosomes may digest their own cellular content because of digestive enzymes.
Golgi Apparatus: Its main function is the packaging and secretion of proteins. It receives proteins from Endoplasmic Reticulum. It packages it into membrane-bound vesicles, which are then transported to various destinations, such as lysosomes, plasma membrane, or secretion.
Nucleus - It is a highly specialized organelle that serves as the information processing and administrative center of the cell. This organelle has two major functions: it stores the cell's hereditary material or DNA, and it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division).
Now, you have understood the basic structural features of an animal cell. It will be fascinating to learn about the components of a plant cell to understand the contrasts and similarities.
Basic Structure of a Plant Cell
Plants are unique among the eukaryotes, organisms whose cells have membrane-enclosed nuclei and organelles because they can manufacture their own food. Chlorophyll, which gives plants their green color, enables them to use sunlight to convert water and carbon dioxide into sugars and carbohydrates, chemicals the cell uses for fuel.
The plant cell is rectangular and comparatively larger than the animal cell. Even though plant and animal cells are eukaryotic and share a few cell organelles, plant cells are quite distinct when compared to animal cells as they perform different functions. Some of these differences can be clearly understood when the cells are examined under an electron microscope.
Some animals, such as cows, sheep, and goats, can digest cellulose with the help of bacteria in their stomachs. Humans cannot digest cellulose, better known as dietary fiber, which passes through our bodies, and is something that we should eat to keep our waste moving. Lignin fills in the spaces between cellulose and other molecules in the cell wall. It also helps water molecules move from one side of the cell wall to the other – an important function in plants. Here are a few important components of a plant cell.
Chloroplasts: It is an elongated organelle enclosed by a phospholipid membrane. The chloroplast is shaped like a disc, and the stroma is the fluid within the chloroplast that comprises a circular DNA. Each chloroplast contains a green-colored pigment called chlorophyll required for the process of photosynthesis.
Cell Wall:Like their prokaryotic ancestors, plant cells have a rigid wall surrounding the plasma membrane. It is a far more complex structure, however, and serves a variety of functions, from protecting the cell to regulating the life cycle of the plant organism.
Endoplasmic Reticulum: The ER is a membrane system of folded sacs and tunnels. The ER helps move proteins within the cell as well as export them outside of the cell. There are two types of endoplasmic reticulum. First is, Rough Endoplasmic Reticulum. It is covered with ribosomes,and the other is, Smooth endoplasmic reticulum (no ribosomes).
Golgi Apparatus: The Golgi apparatus is the distribution and shipping department for the cell's chemical products. It modifies proteins and fats built in the endoplasmic reticulum and prepares them for export as outside of the cell.
Vacuoles: Plant cells additionally possess large, fluid-filled vesicles called vacuoles within their cytoplasm. Vacuoles typically comprise about 30 percent of a cell's volume, but they can fill as much as 90 percent of the intracellular space. Plant cells use vacuoles to adjust their size and turgor pressure.
Nucleus: The nucleus is a membrane-bound structure that is present only in eukaryotic cells. The vital function of a nucleus is to store DNA or hereditary information required for cell division, metabolism, and growth. It manufactures the cell’s protein-producing structures and ribosomes. The nuclear membrane is perforated with holes called nucleopore that allows proteins and nucleic acids to pass through.
Plant cells have certain distinguishing features, including chloroplasts, cell walls, and intracellular vacuoles. Photosynthesis takes place in chloroplasts; cell walls allow plants to have strong, upright structures, and vacuoles help regulate how cells handle water and storage of other molecules.
Both types of cells have some common components, as we learned above. It is important to look at the differences in either functioning of these parts or their existence in cells.
What Are the Main Differences Between Animal and Plant Cells?
Shape: Animal cells are either irregular or round, as there is no rigid cell wall to prevent them from flexing. When the pressure inside the cell is balanced, and there is no motion,the shape becomes round. Plant cells are either square or rectangular, depending on the vertical extension of the plant. As they generally grow upright, they tend to be elongated towards the growing end.
Membrane vs. Wall: Animal cells don’t have a rigid wall, but they have a plasma membrane around the cell. It allows the absorption and waste secretion process. Plants have to grow rigid to balance with forces of nature, so they have walls that protect them. When these cells die, they convert into a protective coating around the branch or stem to give it physical and structural strength.
Nucleus: It is present in the center of an animal cell as it carries the most important information regarding DNA and genes. These are starting points of the diverse evolution that happened in animals. The nucleus of a plant cell is located on one side of the cell as space is mostly taken over by vacuoles.
Lysosomes: In animal cells, they have a significant presence, but in plant cells, they are rare to find. Their function is related to digestion, and there is no such process in plants, generally.
Vacuoles: Animal cells have a large number of small vacuoles spread across the volume of the cell. They do not play any significant role in the overall functioning of the unit. Plant cells have a single but large vacuoles in the center of the cell. They are important to regulate the pressure inside a cell.
Cilia: Theyhave a frequent occurrence in animal cells but are absent from the greener branch of the evolution. They are small, slender, and hair-like structures present on the surface of all mammalian cells. They are primitive and could be single or many. Cilia play a major role in locomotion.
Mitochondria: They are the energy-producing units of the cell. As you can guess, they are present in large numbers in animal cells as the energy requirement is high. In plant cells, the energy is stored in the form of raw materials,and there are no such components to start a chemical reaction. But there are few plants that use external sources for energy like the pitcher plant, which requires these components to convert food into energy.
Nutrition: Animal cells survive on other organisms as they can not produce food on their own. They are dependent on plants and smaller animals for it and are heterotroph. Plants cells can use solar energy and chemicals present in them to create their food. They also store the excess food in different forms to supply it to non-autotroph species.
The differences in both types of cells are justified because of their role in the existence of a particular species. But some components feature in both kinds, and it is important to learn about them too.
What Are the Main Similarities Between Animal and Plant Cells?
As we have already learned about all the important features in cells, we present basic components that are similar in both cells. Their functions are also similar and related to the internal functioning of the cells.
Endoplasmic Reticulum (Smooth and Rough)
These components are not related to locomotion or diversification of cells based on organ functions. They are inherited from the primitive structure in both types of cells. Some of these components may have mutated over the years to suit the characteristics of a certain species.
Nobody can deny that life has become more complex with evolution. There are new features added with every passing generation. It is hard for students to grasp all this information at once. They require help when they are asked to write complex biology coursework by their professors. Help was never far, but you need to find the best to achieve the grades that you deserve.
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