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What Is Cell Structure And Function In Biology

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Functions Of Cell Wall

Cell Biology | Cell Structure & Function
  • It freely allows the movement of water and other chemicals into and out of the cells
  • There are breaks in the primary wall of the adjacent cells through which the cytoplasm of one cell is connected with the other.
  • These cytoplasmic strands which connect one cell to the other one are termed plasmodesmata.

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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.

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

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.

Figure 4. Structure of cell membrane. Source: Mariana Ruiz via commons.wikimedia.org

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Origin Of The First Cell

There are several theories about the origin of small molecules that led to life on the early Earth. They may have been carried to Earth on meteorites , created at deep-sea vents, or synthesized by lightning in a reducing atmosphere . There is little experimental data defining what the first self-replicating forms were. RNA is thought to be the earliest self-replicating molecule, as it is capable of both storing genetic information and catalyzing chemical reactions , but some other entity with the potential to self-replicate could have preceded RNA, such as clay or peptide nucleic acid.

Cells emerged at least 3.5 billion years ago. The current belief is that these cells were heterotrophs. The early cell membranes were probably more simple and permeable than modern ones, with only a single fatty acid chain per lipid. Lipids are known to spontaneously form bilayered vesicles in water, and could have preceded RNA, but the first cell membranes could also have been produced by catalytic RNA, or even have required structural proteins before they could form.

Structure And Function Of A Plant Cell


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.

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What Is The Structure Of Cells

All eukaryotic cells consist of three basic parts. These are the cell membrane, the nucleus, and the cytoplasm. The cell membrane surrounds the outside of the cell, the nucleus is found in the middle of the cell, and the cytoplasm fills the gap between the two. Buried in the cytoplasm are hundreds or thousands of subcellular structures called organelles.

The fluid inside cells is known as the intracellular fluid , while the environment outside of the cell is referred to as the extracellular fluid .

Criteria For Life In Cells And Organisms

  • Order: Cells and parts of cells have a specific order every time. The organelles in a cell are always organised in a similar way. For instance, skin cells are organised in rows.

  • Reproduction: Cells can produce offspring or new cells, sexually or asexually. In eukaryotes, new cells are formed through mitosis. Prokaryotes usually reproduce through binary fission. On a larger scale, animals reproduce and produce young.

  • Growth: For example, the growth of a plant from a seed to a tree.

  • Use of energy: An organism produces energy sources such as ATP, which is needed for various reactions, for example, muscle movement.

  • Homeostasis: Maintaining stable conditions within a body or cell. The inside of a cell always has a specific pH so that reactions can take place at optimal conditions.

  • Response to stimuli: Movement and enzyme production. For example, when plants grow in the direction of sunlight, the plant responds to sunlights stimuli. The same happens with unicellular organisms. When a prokaryote encounters a different environment, it responds to those environmental changes by, for example, producing enzymes.

  • Ability to adapt: Bacteria have not always been resistant to antibiotics this has come through their ability to adapt through genetic mutation.

Cells are considered the building blocks of life because they are the smallest unit to meet these criteria. Even a single-celled prokaryote is considered a living organism.

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Origin Of Eukaryotic Cells

The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearing organelles like the mitochondria and the chloroplasts are descended from ancient symbiotic oxygen-breathing Alphaproteobacteria and “Cyanobacteria“, respectively, which were endosymbiosed by an ancestral archaean prokaryote.

There is still considerable debate about whether organelles like the hydrogenosome predated the origin of mitochondria, or vice versa: see the hydrogen hypothesis for the origin of eukaryotic cells.

Plant Cell Structure And Function

Endosymbiosis theory | Cell structure and function | AP Biology | Khan Academy

In spite of the differences in size and complexity, all cells are mostly composed of the same substances and they all carry out similar life functions. These include growth and metabolism and reproduction by cell division.

Cells are made up of subcellular structures that are responsible for different and specific functions. These structures are known as organelles. A number of these organelles are common to both animal and plant cells. This section will focus on those parts which plants have.

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Frequently Asked Questions On Cell Organelles:

  • Which cell organelle is called the Powerhouse of the cell?

Mitochondria is the cell organelle and is called the Powerhouse of the cell as they carry out the cellular respiration and generate the energy molecules called ATP or Adenosine Triphosphate.

  • Where do we find Chloroplasts and Chromoplast pigments in plants?

Chloroplasts and Chromoplasts are the plastids present in all plant cells. Chloroplasts contain the green colour pigments, present in the leaves, green-coloured stems, etc. Chromoplasts contain thee colourful pigments present in all colourful parts of the plant like flowers and fruits, etc.

  • Why Lysosomes are known as suicide bags?

Lysosomes are called the suicidal bags because they are capable of breaking down or digesting all the wastes, dead and damaged cells.

  • What is Nucleoid?

Nucleoid is a non-membrane, irregular-shaped cell organelle present in all prokaryotic cells. They are the carriers of the genetic material of a cell.

  • The largest membrane-bound organelle in a eukaryotic cell is?

Organelles are special and organized structures seen in living cells. Some of the membrane-bound organelles are vacuoles, nucleus, chloroplasts, lysosomes etc. The nucleus is the largest organelle in the cell.

Stay tuned with BYJUS to learn more about the different types of Cell Organelles, their functions and other related topics at

Read A Brief Summary Of This Topic

cell, in biology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete organism in itself, such as a bacterium or yeast. Other cells acquire specialized functions as they mature. These cells cooperate with other specialized cells and become the building blocks of large multicellular organisms, such as humans and other animals. Although cells are much larger than atoms, they are still very small. The smallest known cells are a group of tiny bacteria called mycoplasmas some of these single-celled organisms are spheres as small as 0.2 m in diameter , with a total mass of 1014 gramequal to that of 8,000,000,000 hydrogen atoms. Cells of humans typically have a mass 400,000 times larger than the mass of a single mycoplasma bacterium, but even human cells are only about 20 m across. It would require a sheet of about 10,000 human cells to cover the head of a pin, and each human organism is composed of more than 30,000,000,000,000 cells.

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Structures Outside The Cell Membrane

Many cells also have structures which exist wholly or partially outside the cell membrane. These structures are notable because they are not protected from the external environment by the semipermeable cell membrane. In order to assemble these structures, their components must be carried across the cell membrane by export processes.

The Cell Membrane And Cell Wall

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A cell is surrounded by a cell membrane or plasma membrane. The cell membrane has fine pores through which it allows selective substances to pass through.The cell wall is found in plant cells and surrounds the cell membrane. It is made up of cellulose. This cell wall gives shape and makes it rigid, it also allows the free flow of substances.

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What Are Microorganisms

Answer: Bacteria are defined as unicellular microorganisms that belong to the prokaryotic group. Bacterial cells are devoid of organelles bound by a membrane.

Answer: The binomial nomenclature was given by the International Committee on Systematic Bacteriology. According to the nomenclature, the name of a bacteria contains two parts- a genus name and a species name. For example, in the name of the bacteria Escherichia coli, Escherichia is the name of the genus, whereas coli is the name of the species.


How Did Cells Originate

Researchers hypothesize that all organisms on Earth today originated from a single cell that existed some 3.5 to 3.8 billion years ago. This original cell was likely little more than a sac of small organic molecules and RNA-like material that had both informational and catalytic functions. Over time, the more stable DNA molecule evolved to take over the information storage function, whereas proteins, with a greater variety of structures than nucleic acids, took over the catalytic functions.

As described in the previous section, the absence or presence of a nucleus and indeed, of all membrane-bound organelles is important enough to be a defining feature by which cells are categorized as either prokaryotes or eukaryotes. Scientists believe that the appearance of self-contained nuclei and other organelles represents a major advance in the evolution of cells. But where did these structures come from? More than one billion years ago, some cells “ate” by engulfing objects that floated in the liquid environment in which they existed. Then, according to some theories of cellular evolution, one of the early eukaryotic cells engulfed a prokaryote, and together the two cells formed a symbiotic relationship. In particular, the engulfed cell began to function as an organelle within the larger eukaryotic cell that consumed it. Both chloroplasts and mitochondria, which exist in modern eukaryotic cells and still retain their own genomes, are thought to have arisen in this manner .

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Cell Structure And Function Kits

Explore hands-on lab kits that cover cell structure and function below.

Students easily compare animal and plant cells, single-celled organisms, and specialized cells using this set of 10 slides and helpful poster. They can explore the cell membrane, cytoplasm, and nucleus within a typical animal cell and look at the structure of typical plant cells, identifying the cell wall, chloroplasts, and vacuoles. Students can also observe examples of specialized cells, including blood, skin, and nerve cells. The laminated poster provides full-color, labeled images and descriptive insight into cellular structure.

BeginningEasy to perform requires little or no prior knowledge.

This kit demonstrates the typical similarities and differences between animal and plant cells. Students prepare slides of their own cheek cells and an onion bulb epidermis.

IntermediateEasy to perform requires some background knowledge.

Introduces the cell, its basic structure, and general concept. Includes Amoeba, Euglena, onion, elodea tips, cork, microscope slides, coverslips, forceps, razor knives, toothpicks, pipets, Protoslo®, stain, and teachers manual with reproducible student guide.

IntermediateEasy to perform requires some background knowledge.

IntermediateEasy to perform requires some background knowledge.

What Other Components Do Cells Have

Structure and Function of a Cell | Cell Organelles | Biology

As previously mentioned, a cell’s cytoplasm is home to numerous functional and structural elements. These elements exist in the form of molecules and organelles picture them as the tools, appliances, and inner rooms of the cell. Major classes of intracellular organic molecules include nucleic acids, proteins, carbohydrates, and lipids, all of which are essential to the cell’s functions.

Nucleic acids are the molecules that contain and help express a cell’s genetic code. There are two major classes of nucleic acids: deoxyribonucleic acid and ribonucleic acid . DNA is the molecule that contains all of the information required to build and maintain the cell RNA has several roles associated with expression of the information stored in DNA. Of course, nucleic acids alone aren’t responsible for the preservation and expression of genetic material: Cells also use proteins to help replicate the genome and accomplish the profound structural changes that underlie cell division.

Proteins are a second type of intracellular organic molecule. These substances are made from chains of smaller molecules called amino acids, and they serve a variety of functions in the cell, both catalytic and structural. For example, proteins called enzymes convert cellular molecules into other forms that might help a cell meet its energy needs, build support structures, or pump out wastes.

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What Defines A Cell

Nature Educationcell membraneplasma membrane

Cell membranes are based on a framework of fat-based molecules called phospholipids, which physically prevent water-loving, or hydrophilic, substances from entering or escaping the cell. These membranes are also studded with proteins that serve various functions. Some of these proteins act as gatekeepers, determining what substances can and cannot cross the membrane. Others function as markers, identifying the cell as part of the same organism or as foreign. Still others work like fasteners, binding cells together so they can function as a unit. Yet other membrane proteins serve as communicators, sending and receiving signals from neighboring cells and the environment whether friendly or alarming .

Within this membrane, a cell’s interior environment is water based. Called cytoplasm, this liquid environment is packed full of cellular machinery and structural elements. In fact, the concentrations of proteins inside a cell far outnumber those on the outside whether the outside is ocean water or blood serum . Although cell membranes form natural barriers in watery environments, a cell must nonetheless expend quite a bit of energy to maintain the high concentrations of intracellular constituents necessary for its survival. Indeed, cells may use as much as 30 percent of their energy just to maintain the composition of their cytoplasm.

Allows Transport Of Substances

Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical processes is eliminated from the cells by active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol diffuse across the cell membrane along the concentration gradient. This is known as passive transport. The larger molecules diffuse across the cell membrane through active transport where the cells require a lot of energy to transport the substances.

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Cell Structure And Function Overview

This section dives further into organelles and divides them into two functional groups organelles that maintain and repair the cell, and organelles that function to collect and distribute the energy needed for biochemical reactions. Lets start with organelles that maintain and repair cellular components.

Whether it is a prokaryotic organism or a eukaryotic organism, there is an ever-changing laundry list of tasks that must be completed in order for an organism to survive, grow, and reproduce. Before cells can replicate their DNA, they first need to collect and digest an energy source. This means the cell may need to move around, grow in size, fight off predators, or change environmental conditions. In a multicellular organism, even more functions are needed to prepare the organism for reproduction.

If we look at the cell membrane alone, we can start to understand the types of repair and maintenance tasks that need to be conducted. For instance, the phospholipids that create a cell membrane are constantly breaking down. These need to be replaced, and many more need to be created as a cell grows. Further, the many proteins embedded within the membrane and the other molecules that cells use to recognize each other, attach to surfaces, and communicate, also need to be created, repaired, or replaced almost constantly!

Together, these two organelles provide energy for almost all of the life on Earth in one way or another!


A Collaborative Oer For Biology

What is a cell?
  • State the components of the cell theory.
  • State the importance of multicellularity.
  • Distinguish the domains under Prokarya and differentiate them from Eukarya
  • Identify the components and describe the function of cellular components in plant cells
  • Identify the components and describe the function of cellular components in animal cells
  • Identify the components and describe the function of cellular components of Amoeba
  • Cell Membrane, Contractile vacuole, cytoplasm, food vacuole, nucleus, nucleolus, pseudopod, ribosome
  • Identify the components and describe the function of cellular components of Euglena
  • Cell Membrane, Chloroplast, Contractile vacuole, cytoplasm, flagellum, nucleus, nucleolus, pseudopod, ribosome, stigma
  • Name the three main layers of the plant cell wall, and list the chemical components of each layer.
  • Describe the general structure and function of the nucleus.
  • Describe the basic structure and function of each of the following cell components: cytoplasm, vacuole, ribosome, endoplasmic reticulum, Golgi complex, lysozome, peroxisome, chloroplast and mitochondrion.
  • Describe the origins of Chloroplasts and Mitochondria
  • List the components of the cytoskeleton, and describe its general role in the cell.
  • The Study of Cells

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