Understanding Cell Organelles and Comparing Plant and Animal Cell

June 12, 2020

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In General Science, Biology is one of the most important topic for competitive exams. It is the scoring subject for competitive exams like SSC, UPSC, Bank exams, IAS, PSU, BSSC, IES, NTPC, RRB, BHEL, IOCL, etc. Though Biology is a very vast subject, by understanding its basic concept you can increase your performance level and grab good marks.

Also read – Competitive Exams After 12th

Here, in this article I have described a very basic and important topic of Biology in an elaborated way to get cleared with the concept.

The topics which are covered in this article are:

What are Cell Organelles?
Cell Organelles: Its structure and function
Cell Wall
Cell Membrane
Cytoplasm
Mitochondria
Ribosomes
Plastids
Vacuole
Cytoskeleton
Endoplasmic Reticulum
Golgi Bodies
Lysosmes
Nucleus
Comparison chart of Cell Organelles: Plant Cell and Animal Cell

Before jumping to the Cell Organelles, you must understand what a cell is.

Cell is fundamental, functional and structural unit of an organism. Within a selective permeable membrane, it contains a set of different kind of units, that helps in the growth and reproduction of cell by converting simple nutrients. These different kind of collective units are known as Cell Organelles.

What Are Cell Organelles?

Cell Organelles are the functional unit within the cell, having specialized role in the cell growth.

If the term Organelle is split then,

Organ: the structure has specific vital function in organism

elle: is the suffix, express the term of diminutive, means smallness of any object.

Some organelles are membrane bound organelles and some are non-membrane organelles.
Membrane bound organelles are having membrane of one or two lipid bi-layers.
Most of the organelles located inside the cell but some organelles extended out of the cell structure for the purpose of movement or to engulf nutrients / food. e.g.: Cilia or Flagella

Organelles in Eukaryotic cells include: Cell wall, Cell membrane, cytoplasm, Nucleus, mitochondria, plastids, etc. lets learn their structure and functions individually.

Cell Wall

Cell wall is the structural and protective layer of the Cell, which is located outside of the cell, surrounding the cell membrane.
According to its structural unit, it can be flexible, rigid or tough.
Cell wall is a 2 layered structure: Primary cell wall and secondary cell wall. Both the layers are separated by middle lamina, that contains polysaccharides.
In many organisms, secondary is not always present.
Cell wall is present in three main kinds of organisms: Plant, Fungi and some Prokaryotes.
It is made up of Polysaccharides. Plant Cell Wall is made up of complex polysaccharides such as, Cellulose, Hemicellulose and Pectin.
Fungal cell is made up of Chitin.
Animal Cell does not have cell wall.

Functions of Cell Wall

Major function of cell wall is to give strength and structure to the cell.
It acts as a pressure vessel, to avoid over expansion of water in the cell.
Due to its characteristics of semi permeability, it also have filtering mechanism.

Cell Membrane

It is also known as Plasma Membrane or cytoplasmic membrane or Plasmalemma.
It is located outside of the cell, as biological membrane.
It is made up of lipids and proteins. It consists lipid bi-layer and proteins.
The lipid bilayer contains phospholipids, which has polar head connected to the hydrophobic tails. Polar head are hydrophilic by nature.
According to the functions, there are three types of protein: Integral protein or transmembrane protein, Lipid anchored protein and Peripheral protein.
It is available in both Animal Cell and Plant Cell.

Functions of Cell Membrane

Cell membrane is surrounded to the cytoplasm of the cell, separates intracellular components from the extracellular ones.
It is a semi permeable membrane, which allows selective substances to transport inside the cell, for the purpose of nutritional growth of cell.
Proteins which are available in the structure acts as a transporter or form channels for the transportation of nutrient molecules like: sugar and amino acids.
It also plays a role of diffusion for the transportation of small molecules like carbon dioxide or oxygen. It is a passive transport process.
It also supports the process of endocytocis, in which it engulfs the nutrient molecule by invagination.
In the similar way to endocytosis, it supports the process of exocytosis, where it helps to remove undigestive substances from the cell and to secrete substances like hormone and enzymes.

Cytoplasm

The term Cytoplasm itself explains the meaning:

Cyto is cell
Plasm is fluid

Cytoplasm is the material of the cell covered by Cell membrane, except Nucleus.
There are two main components of cytoplasm: cytosol and organelles.
Cytosol is a colorless, colloidal, gel like solution, which has 80% water and nutrient molecules required for cell.
It is available in both Animal Cell and Plant Cell.

Functions of Cytoplasm

It has elasticity property, by which it can help the movement of material inside the cell by the process known as cytoplasmic streaming.
Due to its fluidity nature, it helps in the cellular and enzymatic reactions by the process of diffusion.
It acts as buffer to protect organelles from damage due to collision or change in pH of the cytosol. It also protects genetic material with the same property.

Mitochondria

It is a round to oval shaped organelle, present in eukaryotic cells.
It is a semiautonomous double layered organelle, contains outer and inner membrane made up of phospholipids and proteins.

Due to presence of double membrane organization, mitochondria has 5 distinct structural parts:

Outer membrane
Inner membrane
Inter membrane space (space between outer membrane and inter membrane)
Cristae (formed due to infolding of inner membrane)
Matrix (space within the inner membrane)

It is available in both Animal Cell and Plant Cell.

Functions of Mitochondria

The most prominent role of mitochondria is energy generation.
It converts oxygen and nutrients into Adenosine Triphosphate (ATP), which is the chemical energy required for the metabolic process of cell. Therefore, Mitochondria is known as Power Generator.
It regulates cellular metabolism.
It acts as digestive system that take nutrients, break them and generate energy for the cell, this biochemical process is also known as cellular respiration.
The main set of biochemical process to generate energy or ATP production are collectively known as Kreb’s cycle or Citric Acid Cycle.
Mitochondria are sensitive to hormones, therefore they easily response to the hormonal signals.
They also regulate membrane potential.

Ribosomes

Ribosomes are found in prokaryotes and eukaryotes. They are also present in mitochondria, chloroplasts and bacteria.
It is a sphere shaped structure in the cytoplasm of cell, mostly available in all living organisms.
They are made up of proteins and Ribonucleic Acid (RNA).
It has two 2 subunits : smaller unit binds to mRNA to decode it and also binds to larger subunit, whereas larger subunit binds to aminoactyl tRNA and the larger subunit.
RNA is obtained from the nucleolus, at the point where ribosomes are arranged in a cell.
It is present in both plant cell and animal cell, some are bounded to membrane of Endoplasmic Reticulum and some are free floating in cytosol.

Functions of Ribosomes

They are the main units for the protein synthesis.
They Convert genetic code into amino acids and those amino acids attached with each other and form a chain like structure known as Protein. This process is known as mRNA translation.
Ribosomes are also act as catalyst to the some biological process like, peptidyl transfer and peptidyl hydolysis.

Plastids

Plastids are membrane-bound organelles found in all types of plant cells and algae. It is absent in animal cells.
It is a group of phylogenetically and physiologically active organelles, those are responsible for biological activities in cell.

There are three types of plastids:

Chloroplasts
Chromoplasts
Leucoplasts

Functions of Plastids

The main role of plastids is manufacturing and storage of food in cell

According to their functions they are divided into some types:

Chloroplasts: plays a major role in photosynthesis. It contains thylakoids and chlorophyll.
Chromoplasts: plays a major role in pigmentation. It is present in flowering plants, fruits and aging leaves. It contains carotenoid pigments. Main purpose of color is to attract pollinators to promote pollination process, which is the important process of plant reproduction.
Leucoplasts: plays a major role in the storage of starch (Amyloplasts), protein (Proteinoplast) and lipid (Elaioplast). They are colourless organelles, mainly utilizes in the synthesis of amino acids and fatty acids.

Vacuole

It is the membrane bound organelle present in plant cell and fungal cell. It is present in some of protist, bacteria and animal cells. Mostly they are absent in animal cells.
It is formed by the fusion of numerous membrane bound vesicles.
It’s structure varies according to the requirements of the functions of the cell.

Function of Vacuole

Main function of the organelle is to maintain fluidity, hydrostatic pressure or turgor within the cell.
It also maintain acidic internal pH in the cell.
It helps to excrete unwanted material or substance from the cell.
In mature plant cells, vacuoles are large in size, which supports the plant cell growth and also provide protection.

Cytoskeleton

It is a complex network of interlinked protein filaments and tubules in the cytoplasm of the cell.
Its present in both Plant cell and animal cell.

It is composed of three types of filaments:

Microfilaments

Size of these filaments are 7nm, thinnest filament of cytoskeleton.
They are composed of protein named actin.

Intermediate filaments

Size of these filaments are about 8 – 12 nm.
They are made up of proteins like keratin, vimentin, desmin and lamin.
They are located between microfilaments and microtubules.

Microtubules

They are the largest fiber of 23nm.
Made up of alpha and beta tubulin.
Most of the microtubules in an animal cell produces from an organelle called centrosome, which is also known as Microtubule Organizing Center (MTOC).
The network of proteins varies according to the organisms and their structures.

Functions of Cytoskeleton

The primary function of cytoskeleton is to give shape to the cells and it also stabilize the collection of cell, that is known as tissues.
It helps the cell to migrate by the process of contraction.
It also takes part in cell division for the segregation of chromosomes and also during cytokinesis.
Microfilaments are also known as “Actin Filaments”, that supports cytokinesis, muscle contraction, cell motility and also takes part in cytoplasmic streaming.( flowing of cytosol throughout the cell)
Intermediate filaments are made up of keratin and its main function is to provide structural support and maintain shape of cell. It also supports the cell to bear tension.
Microtubules forms the spindle apparatus, which helps in the separation of sister chromatid during cell division. It also helps in the movement of molecules within the cell and also helps in the formation of cell wall in plant cells.

Endoplasmic Reticulum

This organelle consists a network of membrane known as cisternae, may be present in continuation with the cell membrane of nucleus in eukaryotic organisms.
The sac like structures of this organelle are held together by cytoskeleton.
Endoplasmic reticulum is present in all kind of cells except red blood cells or spermatozoa.
It is available in both Animal Cell and Plant Cell.

According to the structure, it has been divided into 2 types:

Rough Endoplasmic Reticulum (RER)

It is located immediately adjacent to the cell nucleus.
It is named for its rough appearance, that is due to presence of ribosomes on its surface.
The binding site of ribosomes on the surface of endoplasmic reticulum is known as ‘translocon’.

Smooth Endoplasmic Reticulum (SER)

This organelle do not have ribosomes as the part of its structure. Hence, it has a smooth structure known as Smooth Endoplasmic Reticulum.
Smooth ER found in myocytes are known as Sarcoplasmic Reticulum.
In some areas of ER, it may contain both types together in a layer: partly RER and partly SER, this kind of its structure is known as ‘Transitional ER’.
Transitional ER has exit sites for ER, lipid and proteins which are manufactured in ER, that transport towards Golgi Body.

Functions of ER

The main function of ER is to synthesize, folding, modification and transportation of Protein.
It transports synthesized protein in vesicles towards Golgi apparatus.
RER plays a major role in protein synthesis, which can be done with the help of ribosomes. This process is called as ‘Translation’ or ‘Protein Synthesis’.
SER involves in the synthesis of lipids including, cholesterol and phospholipids, that are responsible for the production for new cell membrane.
In some cells, SER plays a role in the synthesis of steroid hormones from cholesterol.
In liver cells, it helps to detoxify drugs and harmful chemicals.
Sarcoplasmic Reticulum regulates calcium ion concentration in straited muscles.

Golgi Bodies

It is also known as Golgi Apparatus or Golgi Complex.
It is a membrane bound organelle found in eukaryotic cells.
It is made up of flattened stacked pouches known as cisternae.
It is located next to the ER and nucleus into cytoplasm of the cell.
It contains 4 to 8 cisternaes, which are connected by matrix proteins..
This organelle structure has been supported by cytoplasmic microtubules.

It has 3 compartments:

cis: nearest to ER
medial: central layer of cisternae
trans: is far from ER

Animal cells have fewer and larger Golgi apparatus, whereas Plant cells can contain as many as several hundred smaller versions.

Functions of Golgi Bodies

It plays a major role in packaging, modifying and transportation of proteins into vesicles to deliver to the target destinations.
It is also involved in lipid transportation and lysosome formation.
It is also responsible for the formation of proteoglycans (proteins which are glycozylated).
It helps in enzyme formation
In endocrine cells, golgi body helps in hormone production.
During maturation of sperm, it forms acrosome in sperm cells.
In plant cells, all polysaccharides, which are responsible for cell wall production, are synthesized by golgi bodies.
During mitotic cell division, it forms a cell plate at the center of spindle.
Glycoproteins are synthesized in the Golgi complex by the attachment of carbohydrate to the protein products of the endoplasmic reticulum.

Lysosomes

It is a membrane bound organelle, present in all type of eukaryotic cells.
It is a spherical vesicle, that contains digestive enzymes.
They are formed from Golgi Apparatus by the budding process.
It is surrounded by a membrane which helps in maintaining acidic environment in the interior via proton pump.
It is present in both Animal cell and Plant cells. (But rare in plant cells )

Functions of Lysosomes

It helps in the digestion of macromolecules and microorganisms.
It also helps in removal of dead cells.
It also has a role in metamorphosis process of frog.
During interaction between sperms and ovum, lysosomes helps to rupture membrane of ovum and helps in the process of fertilization.
Phagocytosis and pinocytosis are the main process of lysosomes.

Nucleus

It is a membrane bound organelle, present in all type of eukaryotic cells.
It has double layered membrane called as nuclear membrane, which has continuation with ER to permit the entrance of macromolecules.
All the cells have single nucleus, whereas red blood cells have no nucleus.
It is present in the middle of the cell, take about 10% of the cell volume.
There are small bodies often seen in nucleus as known as ‘Nucleoli’ and the gel like matrix contains all nuclear components are known as ‘Nucleoplasm’.
It contains genetic material (DNA)
It is located at the center of cell in animal cell whereas in plant cell it is located at the periphery of the cell.

Functions of Nucleus

It controls growth and reproduction of cell, as it has genetic material.
It helps in the formation of chromosomes, that is combination of DNA and proteins.
It supports the process of genetic transcription.
It maintains cellular metabolism by controlling synthesis of particular enzymes.
It is responsible for protein synthesis, cell division, growth and differentiation.

Comparison of Cell Organelles of Plant Cell and Animal Cell

Plant and animal cells are both eukaryotic cells, thus are structurally very similar . They both contain membrane-bound organelles such as mitochondria, nucleus, golgi apparatus, endoplasmic reticulum, peroxisomes and lysosomes. However, Plant cells can be larger than animal cells.

ORGANELLES	PLANT CELLS	ANIMAL CELLS
Cell Wall	present formed of cellulose	absent
Cell Membrane	present with cell wall	only cell membrane
Cytoplasm	less granular and thin	more granular and dense
Mitochondria	less in number	more in number
Ribosomes	YES	YES
Plastids	present	absent
Vacuole	Large: takes 90% of cell volume	small or absent
Centrosomes	absent	present
Endoplasmic Reticulum	present	present
Golgi Bodies	hundreds in number	fewer and large in size
Lysosmes	rare	always present
Nucleus	located one side of periphery	located in the center

Wrapping Up

Cell and cell organelles is an important topic for competitive exams, to help you score good in this section, I have discussed it in detail, along with a comparison chart of plant and animal cell organelles.

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