Definition, structure and function of cell organelles

Organisms are composed of cells. Even each organism has cells. Something is said to be alive when composed of at least one cell. That is because, in cells, individuals can see a function or activity as a living creature.

Examples such as looking at the function of motion, respiration, reproduction, and others – others. Therefore, the cell is the smallest and functional structural unit of living things.

The first cell inventor, Robert Hooke . This finding was in 1665. Hooke observed a cork incision using a microscope. Then, Hooke observed the empty spaces that make up the cork.

The empty space is then called a cell. Cell comes from the word selula. Selula means room. Brown (1831) states that the cell is a small room. This room is limited by a membrane and contains fluid cells or protoplasm.

Then, in 1838, Mathias J. Schleiden and Theodor Schwann stated a cell theory. They claim that each organism is composed of one or more cells. Furthermore, these cells originate from previous cells.

Thus the discussion about the inventor and definition of cells. The next discussion will explain about prokaryotic and eukaryotic cells.

Prokaryotic and Eukaryotic Cells

Based on the existence of the nucleus membrane, cells are divided into two, namely prokaryotic and eukaryotic.

As for the difference between the two cells, in terms of cell size, cell nucleus, double-membrane organelles, flagella, cell walls, plasma membrane, cytoplasm, ribosomes, cell division, and groups of organisms, can be explained as follows.

Prokaryotic cells

Prokaryotic cells have the following characteristics.

  1. Cell size is 0.2 – 2.0 µm.
  2. Judging from the cell nucleus, this cell has no nucleus membrane, forms a nucleid, and there are no daughter nuclei or nucleoli.
  3. It does not have a double membrane organelle.
  4. Flagella are composed of two constituent proteins.
  5. Usually have a cell wall, a type of bacterial cell wall, generally composed of peptidoglycan.
  6. The plasma membrane has no carbohydrates and generally has a small amount of steroids.
  7. Judging from the cytoplasm, it does not have a cytoskeleton.
  8. Ribosome size is small, 70s.
  9. Binary cell division.
  10. Prokaryotic cell organism group namely monera (Please read: Understanding Monera).

Eukaryotic cells

The characteristics possessed by this cell are as follows.

  1. Cell size is 10-100 µm.
  2. It has a nucleus membrane and there are daughter cell nuclei or nuclei.
  3. Having a double membrane organelle. This double membrane organelle consists of lysosomes, golgi bodies, reticulum, endoplasm, mitochondria, and chloroplasts.
  4. Flagella are formed from various microtubules. Fifth, it has cell walls in some cells, such as in plant cells which are pricked from cellulose.
  5. Inside the plasma membrane are carbohydrates and steroids.
  6. Have a cytoskeleton.
  7. Ribosome size is small and large. For small sizes, 70S and 80S large.
  8. Cell division is done by mitosis and meiosis.
  9. Eukaryotic cell organism groups are animalia, plantae, fungi, and protists.

After understanding about the nine differences between prokaryotic and eukaryotic cells. Next will be explained about cell structure.

Cell Structure

Cells are divided into three main parts. Parts of the cell, namely the cell membrane, cytoplasm, and cell nucleus. The explanation of the parts of the cell are as follows.

Cell membrane

In animal cells, the cell membrane is an outer sheath of the cytoplasm. Meanwhile, in plant cells, the cell membrane is a cytoplasmic envelope that is inside the cell wall.

Cell wall is an outer layer of cells in plant cells. This cell wall gives a rigid shape to plant cells. This cell wall is useful for protecting cells from mechanical stress.

The cell membrane or plasma membrane is a double phospholipid layer or phospoholipid bilayer. This cell membrane is liquid and fluid. The function of cell membranes, can be described as follows,

  1. Cell membrane as a receptor or excitatory recipient from the outside. These stimuli are both chemical, such as hormones or mechanics such as pressure or touch.
  2. Cell membranes give shape to animal cells.
  3. Cell membranes play a role in the transport of substances that want to enter or exit the cell.
  4. Cell membranes separate cells and protect cells from the outside environment, and maintain the cell nucleus.
  5. Cell membranes are selectively permeable. This property is not accessible to just any ion or molecule so that it can control the movement of ions or molecules that enter and exit the cell.

Furthermore, the cell membrane is composed of lipid molecules, proteins, and carbohydrates. These lipid molecules form compounds with phosphate to phospholipids. Phospholipids are a major component that makes up the cell membrane.

Lipid tail in this phospholipid has hydrophobic properties. While this phosphate head has hydrophilic properties. Therefore, when forming a double phospholipid layer, the head side of the phospholipid faces outward or to the plasma or external environment. Meanwhile, the tail side is inside.

Proteins contained in cell membranes can be divided into integral and peripheral proteins. The explanation of each protein is as follows.

Integral protein. It is a protein that interjects in a double phospholipid layer. This integral protein is useful for the entry and exit of certain substances into or from cells.

Peripheral Protein. Is a protein that attaches to the surface of phospholipids. The nature of this protein is easily separated and only sticks within a certain period.

The function of peripheral proteins play a role in metabolizing membrane components, such as lipids and cell wall oligosaccharides. Then, play a role in the electron transport chain, and transport hydrophobic molecules that have a small size.

Carbohydrates attached to the head of phospholipids form a glycolipid complex or proteins form glycoproteins. This glycolipid functions as an identification signal for intercellular interactions. These glycoproteins can bind to proteins from neighboring cell membranes or other cells to form an intercellular bond.


Cytoplasm is a liquid that is inside the plasma membrane in addition to the cell nucleus. The cytoplasm is composed of cytosols or gel-shaped or colloidal. Then, it is composed of a cytoskeleton or finally cell organelles.

Cytosol is a liquid part that fills 70% of cell volume. This cytosol is formed from the composition of water, salt, and organic molecules. The cytoskeleton is a cellular skeleton in the form of active microfilaments, intermediate filaments, and microtubules.

These microtubules have the largest size and are composed of polymers, alpha tubules and beta. Microfilament is a small filament that forms the cytoskeleton and is composed of G-actin polyemers.

Intermediate filaments have a larger size than microfilament and are more stable. The constituent sub units of the intermediate filament are vimentin, neurofilament, or keratin.

Then, the function of the cytoskeleton, among others, as follows.

  1. The cytoskeleton forms the spindle threads in the division of mitosis.
  2. The cytoskeleton gives and maintains cell shape.
  3. This cytoskeleton regulates cell movements or movements within cells or intracellular transport.

Cell nucleus

Cell nucleus is only owned by eukaryotic cells. The cell nucleus is the most striking part of the cell and is bounded by a nuclear membrane.

In this cell nucleus there is a daughter cell nucleus or nucleus which is a place for ribosomal RNA formation and maturation. The function of the cell nucleus is as follows,

  • Regulates the process of gene expression.
  • Is a place of DNA replication and transcription.
  • Control the process of cell metabolism.
  • Store genetic or DNA information.

After learning about cell structure that consists of cell membranes, cytoplasm, and cell nuclei. Next will be explained about cell organelles.

Also learn:  Characteristics, Structure, Way of Life, Reproduction, and Mushroom Classification

Organelles – Cell organelles

Cell organelles consist of the cell nucleus or nucleus, ribosomes, endoplasmic reticulum, golgi body, mitochondria, lysosomes, periksisomes, centrosomes, plasma membranes, cell walls, plastids, vacuoles, and vesicles. Each organelle can be explained as follows.

Cell nucleus or nucleus. The cell nucleus is enveloped by a membrane with a double membrane and is porous. Pores in the nucleus function as the entry of large size molecules. The nucleus has a daughter cell nucleus or nucleus that produces DNA and ribosomes.

In the cell nucleus there is DNA in the form of chromosomes or chromatin. Therefore, this cell nucleus is useful as a carrier of genetic material. Where this is the place of DNA replication and DNA transcription and cell work regulator.


This ribosome has a round shape. Ribosomes are composed of RNA and protein. Ribosomes form two subunits which do not have membranes. There are ribosomes that are free in cells, but there are also those that bind to RE.

Ribosomes have a function. The function of the ribosome is mRNA translation into protein or protein synthesis.

Endoplasmic reticulum

The edoplasmic reticulum (RE) is made of flat membranes with a single membrane called the cysterna. RE is connected with the cell nucleus membrane.

RE plays a role in the transport of substances. RE can be divided into two, namely coarse RE and fine RE. Rough RE associated with ribosomes. This crude RE acts to transport proteins synthesized in the ribosome. Refined RE plays a role in lipid sitensis, such as phospholipids, steroids, and hormones.

Golgi body

This golgi body is in the form of piles of flat membranes which have a single membrane. Golgi bodies have a protein receptor from crude RE. The protein received in the cis portion of the Golgi will then be modified before it is finally released via the trance portion in the Golgi. Then, this protein is sent to all parts of the cell using vesicles.


Mitochondria are double-membrane organelles that play a role in cellular respiration. The inner membrane of the mitochondria curves to form the crest.

This membrane in the mitochondria produces ATP. ATP is cellular energy so it is often called The Power House. Mitochondrial matrix part functions for fatty acid oxidation and acetyl coenzyme catabolism. This mitochondrial matrix also contains DNA.


Lysosomes are a single membrane round sac. This lysosome contains the enzyme hydrolase which is useful for digesting substances. The function of lysosomes includes digesting old cells and digesting large size food molecules.


This peroxisome has the shape of a round membrane with a single membrane. This peroxisome contains oxidative enzymes, such as catalase. This peroxisome has a role in the oxidation process of fatty acids, ethanol, and other senyama.


The centrosome consists of two cetriols formed from microtubule proteins. This centriol plays a role in forming spindle threads during cell division. These spindle threads have a role to regulate the movement and separation of chromosomes during cell division.

Plasma membrane

This plasma membrane consists of two layers of phospholipids with proteins and carbohydrate chains. This plasma membrane has a role as a supporter of the shape of cells, protectors, regulating the movement of substances in or out of cells. In addition, it also has a role to maintain cell homeostasis.

Cell wall

The cell wall is the outermost coating after cell membranes in some bacteria, plant cells, and fungi. This cell wall has a rigid, hard shape. In plants, the main composition of cell walls is cellulose.

Then, the fungi in the form of chitin cells. In bacteria, cell walls are peptidoglycan. The function of the cell wall is to protect cells, maintain cell shape, and diffusion of various molecules in or out of cells.


Plastids are commonly found in plant and algae cells. This plastide acts as a maker and storage of various chemical compounds needed by cells. Plastids also contain pigments.

This pigment is needed by plants, such as for photosynthesis. The presence of this pigment makes plants appear colorful. In general, plastids are grouped into two types, namely chromoplast and leukoplast.

This chromoplast contains various pigments. While this leukoplas does not contain pigment. Chromoplast can be further divided into three namely chloroplast, faeoplas, and rodoplas.

Chloroplast or chlorophyll pigment, green color. Phaeoplas or fucocantin pigment, dark brown in color. Rodoplasts or phicoeracrine pigments, red in color.

Chloroplast is an organelle that plays a role in the process of photosynthesis. Chloroplast has an oval shape and is covered by a double membrane. Inside this chloroplast there is a collapsed thylakoid membrane called grana (singular called granum).

On the inside of this chloroplast there is a matrix that is the stroma. This chloroplast plays a role in the process of photosynthesis. Leukoplas can be divided into amyloplas, proteinoplas, and elaioplas.

Amyloplast is the part that stores starch. While elaioplas is the part that stores fat. Then, this proteinoplast is the part that stores protein.


A vacuole is a single membrane. This vacuole is filled with liquid. In plants, vacuoles are large in size and stand out.

The function of vacuoles in plants is storing water, food, metabolic waste, and toxins. This vacuole has a membrane or tonoplast whose role is to maintain water pressure or turgor pressure in the cell.


A vesicle is a single membrane that is useful as a storage or transport of substances in cells.

Such is the explanation of the organelles in the cell. Next will be explained about the differences between animal cells and plant cells.

Difference between Animal Cells and Plant Cells

Animal cells or plant cells are both included in eukaryotic cells. Nevertheless, the two have differences. The difference between animal cells and plant cells can be explained as follows.

Animal cell

Cell form is not fixed. Does not have cell walls. Do not have plastids. In general, vacuoles do not have, if any, vacuoles are small in size and are temporary. Having centrosomes and lysosomes.

Plant cells

Cell form is fixed. Has cell walls. Have plastids. Having a vacuole with a large size. Lack of centrosomes and lysosomes.

After understanding about the differences from animal cells and plant cells (if still lacking, please read 12 lists of differences in animal cells and plant cells ) reviewed among others from cell walls, cell shape, vacuoles, centrosomes and lysosomes. Next, it is explained about cell transport.

Cell Transport

Substances – substances that enter or enter the cell through the cell transport mechanism. The movement of this substance through cell membranes has permeable selective properties. This property means that the cell transport mechanism only passes certain substances according to the needs of cell metabolism.

This cell transport takes place in two ways namely actively or passively. The explanation is as follows.

Passive tranpos

Passive transport is the transfer of substances through cell membranes without the need for energy. This transfer occurs due to moving substances in accordance with the concentration gradient. This concentration gradient from high to low.

Passive transport can be divided into two, namely osmosis and diffusion which can be explained as follows. Osmosis is a solvent transfer through a permeable selective membrane from a high solvent or hypotonic concentration to a low or hypertonic solvent concentration.

Diffusion is the transfer of solutes from high concentrations to low concentrations. This diffusion event can be seen in the dissolution of sugar when making sweet tea. Sugar diffusion can make overall tea water sweet.

Molecules and ions which are large enough and polar in nature do not easily enter cells by diffusion alone. molecules and ions such as glucose, Na + ions, and Cl-ions enter cells through a facilitated diffusion process.

That is because it cannot pass through the phospholipid tail which has hydrophobic properties. This facilitated diffusion takes place through protein channels and carrier proteins. This facilitated diffusion takes place spontaneously without the need for chemical energy from ATP hydraulics. Substance transfer that occurs in accordance with the concentration gradient.

Active transport

Active transport is a movement of substances against the concentration gradient that is from low concentration to high concentration through the cell membrane. Active transport requires chemical energy.

This active transport can take place through the mechanism of ion pumps, transport, and endocytosis and exocytosis. The explanation of each mechanism is as follows.

An ion pump is a transfer of ions through a cell membrane against its concentration gradient. An example of an ion pump is the Na-K ion pump which is useful for maintaining differences in the concentration of Na and K inside and outside the cell and generating negative charges inside the cell.

Transport is a movement of two substances that occur simultaneously through a membrane protein or a complex protein without direct energy from ATP. Transport occurs because of a molecule that moves according to its concentration gradient.

Therefore, other molecules can move against the concentration gradient. Transport can be divided into simports, namely the two substances move in the same direction and the antiport is the two substances that move in the opposite direction.

Endocytosis and exocytosis

Endocytosis is a process of entry of substances in the form of liquid or molecules that have a large size into the cell by swallowing these substances. During this process, the cell membrane will bend and surround the substance as if making a sac.

Inside the cell, these sacs form vesicles which will be joined in the enzyme lysosomes or other vesicles. Endocytosis can be divided into phagocytosis which is a molecular endocytosis that has a large size or pinocytosis is a liquid endocytosis.

Meanwhile, exocytosis is a release of substances from the cell by fusion or a combination of vesicles and cell membranes.

Thus the explanation of the structure and function of cells. Hopefully this material can help friends of science in understanding about the structure and function of cells. Happy learning and always successful.


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