[Biology Class Notes] on Organelle Pdf for Exam [2024]

In this article, we are going to discuss the Organelles meaning.

Organelles can be defined as small structures within the cytoplasm that carry out functions necessary to maintain homeostasis in the cell.
Organelles are involved in many processes, for example, energy production, building proteins, secretions, destroying toxins, and are also involved in responding to external signals.

Two Categories of Organelles

Organelles are considered either membranous or nonmembranous.

Membranous Organelles possess their own plasma membrane which is used to create a lumen separate from the cytoplasm.
Organelles may be the location of hormone synthesis or they may be the location of degradation of macromolecules.
Non-membranous Organelles are not surrounded by a plasma membrane and most non-membranous Organelles are part of the cytoskeleton, which is the major support structure of the cell.
These include filaments, microtubules, and centrioles.

Examples of Organelles

In eukaryotic organisms, nearly every cell has a nucleus though there are exceptions. The other common Organelles seen are listed below-

Some special cells or Organelles like neurons also contain synaptic vesicles. All of these structures are membrane-bound. Macromolecular complexes like ribosomes, spliceosomes, centrioles, as well as centrosomes are not surrounded by a membrane, but are important Organelles in most cells, performing vital functions like organizing the cytoskeleton, synthesizing proteins, and processing RNA.

Functions of Organelle

Nutrition – The function of the unicellular organisms ingest food as large particles from the environment and then undergo intracellular digestion. This process needs the presence of Organelles such as food vacuoles or it needs the presence of phagosomes and lysosomes which carry digestive enzymes.
Transport – Intracellular transport is often managed through crisscrossing cytoskeletal filaments and these act like corridors. These filaments form a series of pathways that position Organelles as well these filaments transport materials. In this activity, filaments are aided by motor proteins that usually contain two domains – one which is used to interact with the cargo and the other to navigate the cytoskeletal filament.

Cell Organelles Meaning

Let’s know what is meant by cell Organelles! The cellular components are known as Cell Organelles. These cell Organelles include both membrane-bound Organelles and non-membrane-bound Organelles, present within the cells and are distinct in their structures and functions. These cell Organelles are responsible to coordinate and function efficiently for the normal functioning of the cell. A few of them function by providing shape as well as support, whereas some are involved in the locomotion and reproduction of a cell. There are various Organelles that are present within the cell. They are classified into three categories based on the presence or absence of a membrane.

Organelles Without Membrane: Cell wall, Ribosomes, Cytoskeleton

Single membrane-bound Organelles: Vacuole, Lysosome, Golgi Apparatus, Endoplasmic Reticulum are some single membrane-bound Organelles.

Double Membrane-Bound Organelles: Nucleus, mitochondria and chloroplast.

The difference between Organs and Organelles

Organ, as well as Organelle, are two structural units, which are specialized to perform a unique function in the body of animals.

The Main Difference between an Organ and an Organelle is That –

An organ is a large part of an organism, composed of tissues that perform similar functions.
An Organelle is a specialized structure found inside cells that carry out a specific life process.
Organelles from cells.
Cells form tissues, and tissues form organs. Organelles occur in all eukaryotes. They are microscopic.
But, organs are macroscopic and can only be found in animals and plants. Here are some Organelles -Mitochondria, chloroplast, Golgi apparatus, endoplasmic reticulum, and the nucleus.
The kidney, heart, liver, lungs, and brain are the organs in humans. Flowers, seeds, as well as spores, are the reproductive organs in angiosperms.

Different Cell Organelles and Their Functions

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A jelly-like substance, which consists of water, dissolved nutrients, as well as waste products of the cell.

Cell Organelles	Structure of Cell Organelles	Functions	What Do These Look Like?
Cell Membrane	A double membrane composed of lipids and proteins. Present both in plant and animal cells.	Cell membrane provides a shape that protects the inner Organelle of the cell and acts as a selectively permeable membrane.
Centrosomes	Composed of Centrioles and found only in animal cells.	Centrosomes play a major role in organizing the microtubule and Cell division.
Chloroplasts	Present only in plant cells and contains a green-colored pigment known as chlorophyll.	Sites of photosynthesis.
Cytoplasm	Responsible for the cell’s metabolic activities.
Endoplasmic Reticulum	A network of membranous tubules. It is present within the cytoplasm of a cell.	Forms the skeletal framework of the cell, and is also involved in the Detoxification, production of Lipids and proteins.
Golgi Apparatus	Membrane-bound, sac-like Organelles, and it is present within the cytoplasm of the eukaryotic cells.	It is mainly involved in secretion as well as involved in intracellular transport.
Lysosomes	A tiny, circular-shaped, single membrane-bound Organelles, which is filled with digestive enzymes.	Helps in digestion as well as is responsible for removing wastes and digests dead and damaged cells. Therefore, it is also called the “suicidal bags”.
Mitochondria	An oval-shaped, membrane-bound Organelle, also called the “PowerHouse of The Cell”.	The mitochondria are main sites of cellular respiration. They are also involved in storing energy in the form of ATP molecules.
Nucleus	The largest, double membrane-bound Organelles, which contain all the cell’s genetic information.	Controls the activity of the cell and controls the hereditary characters.
Plastids	Double membrane-bound Organelles. There are 3 types of plastids: Leucoplast –Colorless plastids. Chromoplast–Blue, Red, and Yellow color plastids. Chloroplast – Green coloured plastids.	Helps in the process of photosynthesis and pollination, Imparts color for leaves, flowers, and fruits, and stores starch, proteins, and fats.
Vacuoles	A membrane-bound, fluid-filled Organelle found within the cytoplasm.	Provides shape as well as rigidity to the plant cell and helps in digestion, excretion, and storage of substances.

More about Organelles

Organelles are the cellular subunits. There are a slew of them, each with its unique purpose. These are given as follows:

Plasma Membrane

It is a cellular Organelle that surrounds and protects the contents of the cell. In addition to enclosing cell contents, the plasma membrane regulates the movement of substances into and out of the cell.

As a result, it participates actively in both passive and active transport to and from the cell. These activities also aid in the maintenance of balance even when external conditions change.

Two layers of phospholipids make up the plasma membrane (phospholipids bilayer).

Nucleus/DNA

The chromatic nucleoplasm/nuclear sap, and nucleolus are some of the primary components of the nucleus.

DNA (hereditary material), as well as different proteins and the nucleolus, are all housed in the nucleus.

The center of the eukaryotic cell is enclosed by a nuclear membrane. It is the Organelle that directs behaviors such as protein synthesis and cell division, among others, to govern an organism’s genetic traits.

The DNA of prokaryotes does not have a nuclear membrane. As a result, the genetic material is bonded in the nucleotide region.

Ribosome

Ribosomes are small organelles found in the cytoplasm that carry RNA and particular proteins. Ribosomes engage directly in the creation of proteins within the cell by using their RNA and amino acids.

This procedure entails decoding the information contained in the RNA and producing the needed proteins utilizing amino acids.

Mitochondria

Mitochondria are the biggest Organelles in the cell. Mitochondria, unlike some other Organelles, contain DNA, allowing them to function independently. Mitochondria feature a double-membrane structure with cristae on the inner membrane.

In the presence of oxygen, mitochondria, also known as the powerhouse, are involved in respiration and create ATP (adenosine triphosphate) from substrates. Mitochondria can use their DNA to encode some of the components they need to do their activities.

Vacuoles

A vacuole is a cell compartment that has no cytoplasm and is empty. It holds fluid and is encased in a membrane. Vacuoles are engaged in the export of waste from the cell in circumstances where the cell’s waste products are present, therefore protecting the cell from toxicity.

Cytoskeleton

Microtubules and microfilaments make up the cytoskeleton. The cytoskeleton helps preserve the form of the cell while also ensuring its flexibility by spreading throughout the cell (in the cytoplasm).

Plastids

Plant cells and algae contain plastids, which are a type of Organelle. Plastids, like mitochondria, are membrane-bound Organelles that house nucleoids. They are hence semi-autonomous organ cells.

Chloroplasts, chromoplasts, protoplasts, and leucoplasts are some of the different forms of plastids.

Endoplasmic Reticulum (ER)

The endoplasmic reticulum (ER) is a flattened sac Organelle found in eukaryotic cells that creates an interconnected network (cisternae). The ER, like many other Organelles found in eukaryotes, is surrounded by a membrane. The ER is split into two sections, each with its structure and function.

Centriole

Most eukaryotic cells contain centrioles, which are cylindrical Organelles. They contain microtubules, which are tube-shaped molecules that assist the splitting and moving of chromosomes during
cell division.

Lysosome

A collection of enzyme-filled sacs is referred to as a “lysosome.” They’re acidic enzymes (hydrolase enzymes) that assist the cell to break down macromolecules like lipids and nucleic acids.

Acidic conditions have been discovered inside lysosomes. The lysosome membrane maintains these conditions, allowing the enzymes to perform their jobs in a suitable environment. Acidocalcisomes are lysosome-related Organelles found in eukaryotes.

Golgi Apparatus

In humans, the Golgi apparatus is extensively folded into cisternae (flattened sacs). They’re protected by a membrane that varies in thickness depending on their location. The Golgi apparatus in the cell is involved in the production, storage, and transit of ER products.