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As you might already know, cells are the smallest living unit and can be found in every living thing found on the planet. There are many different types of cells depending on what organism they are found in. These cells are all built for different tasks and functions so they will have different parts. For example, plants that perform photosynthesis will have a different cell structure than animal cells. There are two main classifications of cells, prokaryotic and eukaryotic cells.
Prokaryotic cells are single-celled organisms and they do not have a nucleus or organelles. These organisms belong to the domains of Bacteria and Archaea. Also, they only reproduce asexually.
Archaea used to be classified in the same domain as Bacteria, but it was discovered that Archaea are different. Archaea are only found in some of the harshest environments such as salt lakes, oceans, hot springs, and the guts of humans and ruminants. Bacteria are instead found pretty much everywhere on the planet including radioactive wastewater. Also, during asexual reproduction, Bacteria can do many things Archaea can, but Archaea can not form spores as Bacteria can.
As mentioned previously, prokaryotic cells do not have a nucleus or organelles. Although they lack those two parts, they still have other parts:
Capsule: the outermost layer of the cell. Keeps everything contained.
Cell wall: keeps the cell's shape.
Plasma membrane: manages the entry and exit of substances within the cell.
Cytoplasm: gel substance that holds all of the inner parts of the cell.
Ribosomes: create the proteins the prokaryote needs.
Nucleoid: contains the DNA.
Pilus: helps attach the cell to different surfaces. They can also help cells move.
Flagellum: helps the cell move.
Figure 1 shows a labeled example of a prokaryotic cell.
Figure 1. Prokaryotic cell diagram. Source: Ali Zifan via commons.wikimedia.org
Depending on the type of prokaryote, they can perform different tasks. Some prokaryotes are able to decompose dead material like plants and animals and turn it into nutrients. These nutrients can then go back to cycles like the carbon cycle or nitrogen cycle. Cyanobacteria, a type of prokaryote, can actually create oxygen. Scientists are also currently trying to figure out how to use bacteria to consume plastic.
In the carbon cycle, prokaryotes are decomposers. This means when they break down dead matter, they return the carbon from the bodies back into the atmosphere as carbon dioxide. Plants will then be able to use this carbon dioxide during photosynthesis.
In the nitrogen cycle, prokaryotes help by taking nitrogen from the atmosphere and converting it into usable forms for plants and animals.
Eukaryotic cells are more complex cells than prokaryotic cells because they have more parts such as a nucleus. They are found in plants, animals, and fungi and they belong to the domain Eukaryota. They can have different parts depending on which organism they belong to. For example, plant cells will have chloroplasts, but animal cells will not. Figure 2 shows an example diagram of an animal cell.
Figure 2. Eukaryotic Animal Cell Diagram. Source: Mariana Ruiz via commons.wikimedia.org
The classification of species is a system classifying every species on Earth based on their similar qualities to one another. The Domain Eukaryota splits up into three Kingdoms. These Kingdoms are Plants, Animals, and Fungi. All fungi belong to the Fungi Kingdom, all plants belong to the Plant Kingdom, and all animals belong to the Animal Kingdom. Figure 3 shows an example of how the classification of species works for humans.
Figure 3. Classification of Species. Source: L-Pengo PD-User via commons.wikimedia.org
As the diagram above shows, animal cells have many more parts than prokaryote cells. These extra parts help with specific tasks animal cells need to do to keep the overall body of an organism alive:
Plasma membrane: manages the entry and exit of substances into the cell.
Golgi apparatus: helps with managing proteins and potentially preparing them to be transported out of the cell.
Lysosomes: contain digestive enzymes and help break down parts of the cell that need to be replaced.
Secretory vesicles: help transport or store materials within the cell.
Smooth endoplasmic reticulum: helps create lipids.
Ribosomes: make proteins.
Nucleus: carries the organism's DNA.
Nuclear pore: proteins that allow smaller molecules and ions in or out of the nucleus.
Nuclear envelope: creates nucleus structure and separates the nucleus from the cytoplasm.
Rough endoplasmic reticulum: uses attached ribosomes to help create proteins.
Animal cells have many different functions:
Produce energy
Store energy
Make proteins
Transports other molecules
DNA replication
Depending on where they are in the human body, different cells can have different functions or shapes. There are around two hundred different types of cells in the human body! These are different types of cells such as blood cells, stem cells, and muscle cells.
The cell membrane works to manage what can enter and exit the cell. It is a semipermeable membrane made up of phospholipids. The hydrophobic tails of the phospholipids are on the inside while the hydrophilic heads face the outside of the cell. You can see an example of this in Figure 4 below.
Figure 4. Structure of cell membrane. Source: Mariana Ruiz via commons.wikimedia.org
Figure 5. Plant Cell Diagram. Source: Mariana Ruiz via commons.wikimedia.org
As you can see above in Figure 5, the structure of a plant cell varies from the structure of an animal cell.
These organelles help assist with functions the animal cell does not need.
The different organelles for a plant cell are:
Nucleus: carries the organism's DNA.
Nuclear pore: controls what can and can not enter the nucleus.
Nuclear envelope: creates nucleus structure and separates the nucleus from the cytoplasm.
Nucleolus: produces ribosomes.
Rough endoplasmic reticulum: uses ribosomes to help make proteins.
Golgi apparatus: processes proteins made by rough ER and determines where to send them.
Golgi vesicles: attached to Golgi apparatus and also aid in the transport of proteins.
Cytoplasm: manages entry and exit of molecules in the cell.
Peroxisome: helps with the synthesis of membrane lipids.
Mitochondria: help produce energy and cellular metabolism.
Vacuole: helps maintain water balance.
Tonoplast: membrane surrounding the vacuole.
Chloroplast: helps with photosynthesis.
Thylakoid membrane: helps absorb light energy.
Starch grain: store food for the plant.
Cell wall: provide strength and structure for the plant cell.
Plasmodesmata: found along cell walls and help multiple plant cells exchange molecules.
Smooth endoplasmic reticulum: make lipids.
Ribosomes: make proteins.
There are many different functions performed by plant cells, but the most important is photosynthesis. Photosynthesis is the creation of glucose and oxygen using sunlight, water, and carbon dioxide. Some cells also help transport molecules around the plant.
Nerve cells, also known as neurons, are only found in animals. This is because they are mostly found in the brain, but neurons are also spread throughout the body. They help with receiving information, sending information, and determining where to help send this information such as different parts of the bodies.
Neurons are able to do those tasks due to their structure. They have a large cell body with outstretched nerve fibers. They use axons to send information and dendrites are for receiving information. You can see a diagram of this structure below in Figure 6.
Figure 6. Neuron diagram Source: BrunelloN via commons.wikimedia.org
Prokaryotic cells do not have organelles or a nucleus. They have different tasks such as decomposing dead matter or creating oxygen.
Eukaryotic cells have organelles and a nucleus. They help produce and store energy, make proteins, molecule transportation, and DNA replication.
We can use our knowledge of cells to help create better medicines, vaccines, and develop better plants
It is the organelles found in the cell and the overall function of the cell.
Neurons (nerve cells) send and receive signals. They do this by having a large cell body then having elongated branches sticking off of it. These branches are what send or receive the nerve signals
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