Organelles of the cell explained with their characteristics

len Alfred Ajibola - 13th July, 2023 @ 03:50 PM

Topics in Biology

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Academic Questions in Biology

Please click here to see all Questions and Answers

Male Reproductive System - Len Academy

From the above diagram, which of the organ below isn't a requirement for the male reproductive system?

  • A. Bladder

  • B. Ureter

  • C. Glans Penis

  • D. Testis

  • E. Bulbourethral Gland

  • F. Epididymis

A walnut shaped male accessory sex organ located between the bladder and penis is the _____.

  • A. Ductus Ejaculatorii

  • B. Bulbourethral Gland

  • C. Prostate Gland

  • D. Ductus Deferens

  • E. Seminal Vesicles

  • F. Epididymis

In a food chain, the primary consumers are classified under trophic level  _____.

  • A. Zero

  • B. One

  • C. Two

  • D. Three

  • E. Four

  • F. Five

Cold blooded animals are referred to as _____.

  • A. Homeotherms

  • B. Endotherms

  • C. Poilokitherms

  • D. Ectotherms

  • E. Thermotherms

  • F. None of the above

All reptiles are vertebrates.

  • A. True

  • B. False

_____ cells are responsible for the formation of osteoblasts.

  • A. Osteocytes
  • B. Chondrocytes
  • C. Chondroblasts
  • D. Osteoclasts
  • E. Osteoprogenitor cells
  • F. Osteoblastic

_____ is a bone that constitute the axial skeleton.

  • A. Clavicle
  • B. Scapula
  • C. Patella
  • D. Radius
  • E. Sternum
  • F. Femur

Which of the following is false concerning cartilages and bones?

  • A. Cartilage does not have a direct blood supply while bones have direct blood supply
  • B. The process of ossification replaces a cartilage to bone
  • C. The protein that makes up cartilage is called chondrin while that that makes up bone is called ossein
  • D. Cartilage grows from both ends while bones grow from one of its epiphysis
  • E. They both have living cells within them
  • F. Haversian system is absent in cartilage but present in bones

What are Organelles?

Organelles refer to biological structures making up a cell, with each performing one or more distinct role towards the cell's proper functioning. In simple terms, they are subcellular structures with one or more function. Meanwhile, understand that some of these organelles are suspended within the cell's fluidy environment termed cytoplasm.

Please read an introduction to cell here.


Generally, you can think of organelles as departments that carry out specific functions in a factory (called cell). These functions are geared towards achieving a common objective with regards to that cell.

You can read on cell theory here.


Just as various organs in the body perform different functions, the organelles may be likened to 'little organs' carrying their respective roles within the cell. 

To achieve the cell's purpose, most organelles are compartmentalized, and bounded by a membrane. This is what separates the function of one organelle from another. It is noteworthy to state that certain organelles are non-membrane-bound. In this regard, organelles are defined in two ways:


  1. An organelle refers to any membrane-bound biological structure or compartment performing one or more specific functions within cell. Organelles that fall within this category are termed as membranous. Examples of membranous organelles include the mitochondrion and nucleus.
    Please read on the nucleus as an organelle here.

  2. An organelle refers to any biological structure constituting the cell, be it membrane-bound or not, but must carry out specific functions within the cell. Organelles that aren't membrane-bound are often referred to as non-membraneous.


Non-membranous organelles will often consistute a part of the cell's cytoskeleton. You can think of the cytoskeleton as a cell's supporting system (just as the skeleton supports the human body).

Please read on the bones of the human skeleton here.

Examples of such non-membranous organelle include the centrioles, microtubules, centrosome, cell wall and filaments.


The diagram below shows the structure of a cell with its various organelles.

Cell Organelles - Len Academy

You can read on cell theory here.


Organelles are living components within the cell. They may also be called vesicles, which actually refer to 'small organelles' within the cell. These vesicles are membrane-bound, and will typically store various substances, while also transporting them from one part of the cell to another, or from one cell to another.

Understand that organelles are biological and functional components of the cell, and are quite different from intrusions.

Intrusions are non-living materials within the cell, and as such do not carry out biological (or life) activities in themselves. They are not bound by membranes. Examples of cell inclusions include fat droplets, oil globules, glycogen and pigment granules like melanin, hemosiderin and lipofuscin.

You can read keypoints in biology here.


The organelles constitute the structural parts of an eukaryotic cell. A cell is said to be eukaryotic if it has a well-defined nucleus. Such cells (eukaryotes) are found in protists, fungi, plants and animals respectively.

Please read on eukaryotic cell explained with its characteristics here.

It is worthy of note to state that most organelles function within the cell. However, certain organelles may extend their functions outside the cell, and these are often locomotory. Such locomotory organelle include cilia, flagella, archaellum, and trichocyst.


Most organelles are present within the cytoplasm while others are located outside it. Below are organelles present in the cell.

  • Nucleus 

  • Nucleolus (A nuclear organelle)

  • Cell Membrane

  • Cell Wall

  • Mitochondrion

  • Rough Endoplasmic Reticulum

  • Smooth Endoplasmic Reticulum 

  •  Lysosomes 

  • Golgi Apparatus

  • Centrosome (Centrioles)

  • Ribosomes

  • Cytoskeleton

  • Peroxisome

  • Vesicles

  • Vacuoles

  • Chloroplast (Plastid)

  • Cilia

  • Flagella

    You can attempt Len Academy questions for JSS1 here.


Characteristics of Organelles

  1. Organelles are subcellular structures. This implies that they make up the cell.

  2. They are present in eukaryotic cells.
    You can read on prokaryotes here.

  3. They perform one or more specific function.

  4. Specifically, organelles are non-living, and cannot carry out the basic characteristics of life alone.
    Please read on the basic characteristics of life here.

  5. Organelles may be membrane-bound. In this regard, membrane-bound organelles are usually semipermeable.

  6. Most organelles are suspended within the cell's cytoplasm.
    You can read interesting facts for students here.

  7. Kingdom of organisms may have certain organelles exclusive to them. For instance, plant cells have chloroplast and cell wall, while an animal cell lack these specific organelles.
    Please read on protists here.

  8. The functions of the cell organelles are coordinated by the nucleus.

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Amazing facts in Biology

Russia is home to the largest area of forest in our world with a land mass of 815 million hectares

Giant Squid - Len Academy

Giant squid lives deep in the ocean and they have the largest eyes in the world

The movements of the fingers are controlled by muscles of the palms and forehands

Platypus - Len Academy

Platypus (sometimes referred to as the duck-billed platypus) is an egg-laying, semiaquatic mammal found in eastern Australia. It has no stomach and as such, its food goes from the mouth through the esophagus and directly to their intestines.

Pufferfish - Len Academy

Pufferfish contain a toxin called tetrodotoxin. This makes them foul tasting and poisonous to predators. Tetrodotoxin is about 1,200 times more poisonous than cyanide, and there is enough toxin in one pufferfish to kill 30 adult humans. Unfortunately, there isn't any known antidote to this poison.

Interestingly, a delicacy in Japan (called fugu) is made from pufferfish. This meal is very expensive, and must be prepared by trained and licensed chefs. An improper preparation of fugu may lead to the customer's death. Sadly, such deaths are recorded annually

Wombat - Len Academy ​​​​​​

Wombats are the only animal with a cube-shaped poo. They can stack up these cube-shaped poo, marking their territory with it

Robert Waldow - Len Academy

Robert Wadlow (1918–1940) remains the tallest man ever recorded in the Guinness World Records. He was an American who stood at 8 feet, 11 inches.

An abnormally enlarged pituitary gland had resulted into Robert Wadlow's giant size.

Cockroach is the fastest land animal on six legs

Laughing ape - Len Academy

Like humans, all apes laugh when tickled

Ostrich eye and brain - Len Academy

An ostrich's eye is bigger than its brain

Notable points in Biology

Layers of an Artery - Len Academy

An artery is composed of three layers:

  • The outermost layer is termed tunica adventitia (or tunica external). It consist mainly of collagen fibres and connective tissues that anchors the arteries to other nearby tissues.

  • The middle layer is named tunica media. It is made up of smooth muscles and elastic fibres that supports the artery in conveying blood at high pressures.

  • The inner layer is called tunica intima (or tunica internal). It is lined by a smooth tissue called endothelium, and is made up of a fine network of connective tissues.

Please read on the layers of an artery here

All living organisms possess various features in order to survive in their environment. This is the concept of adaptation. As an instance, a fish is able to live in water because it has gills and fins.

Also, a camel is able to survive in the desert because it has large feet to aid walking on sand without sinking. It also has long eyelashes to help protect it from the blowing sand and wind.

Plants are also able to live in different habitats because they have the required adaptive features towards that habitat. For instance:

  • Plants that live in/on water are termed hydrophytes.

  • Plants that live on land with moderate amount of water are termed mesophytes.

  • Plants that live on deserts or arid lands are termed xerophytes.

The point is:

All organisms have various features on them that enables them adapt in their habitat

For a thing to be considered living, it must possess all the basic characteristics of life. These include:

  1. Movement

  2. Respiration

  3. Nutrition

  4. Irritability or Sensitivity

  5. Growth

  6. Excretion

  7. Reproduction

  8. Death

  9. Adaptation

  10. Competition

Please read the explanations on all the basic characteristics of life here

During strenuous exercises like sprinting or running, your body may actually work in the shortage of oxygen. During this time, your body owes oxygen (called oxygen debt) and it must be replenished or repayed after the exercise is stopped. This is why you breathe excess of oxygen after you stopped the exercise.

This is the concept of anaerobic respiration

Food Chain - Len Academy

A food chain is a diagram that shows the relationship between plants and animals within a habitat on the basis of how they rely on each other for food.

Note: Habitat is a place where an organism live. It is of three types:

  • Terrestrial (Land)
  • Aquatic (Water)
  • Arboreal (Treetops)

You can read on food chain here