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Cell Structure and Function

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Cell Structure and Function

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.

What are prokaryotic 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.

What is the structure and function of prokaryotic cells?

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.

Cell Structure and Function Prokaryote Diagram StudySmarterFigure 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.

What is the structure and function of eukaryotic cells?

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.

Cell Structure and Function Eukaryotic Cell Diagram StudySmarterFigure 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.

Cell Structure and Function Classification of Species StudySmarterFigure 3. Classification of Species. Source: L-Pengo PD-User via commons.wikimedia.org

Animal cell structure and function

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.

Structure and function of a cell membrane

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.

Cell Structure and Function Cell Membrane StudySmarterFigure 4. Structure of cell membrane. Source: Mariana Ruiz via commons.wikimedia.org

Structure and function of a plant cell

Cell Structure and Function Plant Cell Diagram StudySmarterFigure 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.

Structure and function of nerve cells

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.

Cell Structure and Function Neuron Diagram StudySmarterFigure 6. Neuron diagram Source: BrunelloN via commons.wikimedia.org

Cell Structure and Function - Key takeaways

  • Two main classifications of cells: Prokaryotic and Eukaryotic
  • Prokaryotic cells are simple and are normally bacteria that can function on their own
  • Eukaryotic cells are more complicated and are cells found in plants and animals
  • Plant and animal cells have different organelles because they have different functions
  • Cell membranes are phospholipids that help control what can enter and exit the cell

Frequently Asked Questions about Cell Structure and Function

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

Final Cell Structure and Function Quiz

Question

What are the main differences in structure between prokaryotic and eukaryotic cells? 

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Answer

Eukaryotic cells have a membrane-bounded nucleus, membrane-bounded organelles, and several linear chromosomes. These organelles and membranes compartmentalize the interior of the cell. Prokaryotic cells lack organelles and a nucleus delimited by a membrane, and they have a singular circular chromosome. 

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Question

How can you differentiate an animal cell from a plant cell? 

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Answer

Animal cells characterize by having lysosomes and centrioles. On the other hand, plant cells have vacuoles, chloroplasts, and cell walls.

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Question

Which organelles compose the endomembrane system? 


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Answer

The endoplasmic reticulum, the Golgi apparatus, the nucleus membrane, lysosomes, vacuoles, and the plasma membrane.

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Question

The plasma membrane is found in: 

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Answer

all cells 

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Question

Which of the following components is not found in prokaryotic cells?

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Answer

nucleus

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Question

Which of the following is found both in eukaryotic and prokaryotic cells?

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Answer

ribosomes

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Question

Which of the following structures is not found in prokaryotic cells?

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Answer

chloroplast 

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You are looking at a cell in the microscope. The cell has a cell wall but no chloroplasts, what type of cell is it?

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Answer

a prokaryotic cell 

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You are looking at a cell in the microscope. The cell has a cell wall and chloroplasts, what type of cell is it?

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Answer

a plant cell 

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Question

Why do eukaryotic cells can attain larger sizes than prokaryotic ones? 


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Answer

The membrane-bounded organelles help in the transport of molecules and ions in the interior of the cell. 

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Question

We can find eukaryotic cells only in multicellular organisms like animals and plants. 


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Answer

False. Some eukaryote organisms are unicellular, like the commonly called protists.

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Question

Which of these organisms can have cell walls?

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Answer

fungi 

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Question

Prokaryotic cells do not have genetic material because there is no nucleus to enclose it. 


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Answer

False. Not all cells have a nucleus, prokaryotic cells have their genetic material concentrated in a region called nucleoid.

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Question

Which structure can be found in both animal and plant cells?

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Answer

mitochondrion

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Which of the following are examples of eukaryotic cells?

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Answer

skin cell 

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Which of the nucleus components is continuous with the endoplasmic reticulum?

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Answer

outer membrane of the nuclear envelope

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We can find two bilayered membranes surrounding the:

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Answer

nucleus 

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The structure responsible for ribosome assembly is the:

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Answer

nucleolus

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We can find a single bilayered membrane surrounding the:

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Answer

cell

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Which one of the following sentences is true?

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Answer

Enzymes and other proteins move from the cytoplasm to the nucleus

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Which structure controls the passage of molecules and larger components between the cytoplasm and the nucleus?

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Answer

pore complexes 

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Question

Molecules of rRNA are synthesized in the ____, while mRNA molecules are synthesized in the____. 

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Answer

nucleolus, nucleus

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Question

What are the main functions of the cell nucleus?

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Answer

Duplication of the genetic material (chromosomes); and transcription of protein synthesis’ specifications from DNA to RNA. 

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Question

Protein synthesis is completed within the nucleus.

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Answer

False

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Question

Which of the following is the correct sequence for ribosome synthesis:

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Answer

DNA transcription into rRNA (in the nucleolus), assembly of subunits (in the nucleolus), complete assembly of ribosomes (in the cytoplasm)

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How does having membrane-bounded organelles facilitate cellular metabolism?

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Answer

The versatility of bilayered membranes facilitates the movement of molecules among the system’s components through vesicles splitting off and fusing to the different organelles’ membranes.

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Question

Which cellular structure is involved in detoxification?

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Answer

Golgi apparatus

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Question

Cellular digestion in animal cells occurs in:

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Answer

lysosome

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Cellular digestion in plant cells occurs in the:

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Answer

vacuole

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Question

Where does the synthesis of membrane proteins occur?

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Answer

rough endoplasmic reticulum

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Question

Lysosomes are formed through:

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Answer

vesicles splitted from the Golgi apparatus

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Question

Which organelle is directly involved in intracellular nutrition?

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Answer

Lysosomes

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The smooth endoplasmic reticulum is composed of ____ and its function is _____:

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Answer

tubular interconnected membranous sacs, lipid synthesis and detoxification

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Question

Organize the following steps that describe the sequence that a protein would follow to be secreted. What is the correct order of the letters? 

(a) proteins are further modified and tagged

(b) transport vesicles carry proteins to the plasma membrane

(c) transport vesicles carry proteins to the Golgi apparatus

(d) modified proteins exit the RER

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Answer

d, c, a, b 

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Question

Which of the following functions are performed by the rough endoplasmic reticulum?

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Answer

protein modification

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Which of the following functions are performed by the smooth endoplasmic reticulum?

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Answer

storage of calcium ions

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Which cell would be best for studying lysosomes?

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Answer

phagocytic white blood cell

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Which cell would have an abundance of rough endoplasmic reticulum, Golgi apparatus and transport vesicles?

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Answer

digestive cell

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Question

Which organelle is involved in recycling degraded organelles and components in an animal cell?

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Answer

lysosome

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Question

You are looking at a cell under a microscope, and you see a group of flattened membranous sacs that are not interconnected to each other, and they are surrounded by abundant small vesicles. Which organelle is this?

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Answer

Golgi apparatus

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Question

Mitochondria are present in:

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Answer

all eukaryotic cells

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Question

Where can we find chlorophyll in a chloroplast?

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Answer

thylakoids membrane 

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Question

Photoautotrophic organisms obtain energy from ______ while heterotrophic organisms obtain it from _____. 

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Answer

light; other organisms

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Question

Which of these organelles evolved through endosymbiosis?

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Answer

mitochondrion

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Question

Where do most membrane proteins for chloroplasts and mitochondria come from?

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Answer

free ribosomes (cytoplasm)

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Question

Which process is performed by mitochondria?

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Answer

cellular respiration

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Question

Grana are found in:

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Answer

chloroplasts

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Question

Which of these is not found in mitochondria?

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Answer

stroma

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Question

The process of transferring energy from glucose or lipids into ATP (adenosine triphosphate) is called______ and is performed by______.

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Answer

cellular respiration, mitochondria

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Question

The process of transferring energy from the sunlight into ATP and then using it to synthesize glucose is called______ and is performed by______.

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Answer

photosynthesis, chloroplasts

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