Cell theory in biology

len Alfred Ajibola - 26th June, 2023 @ 01:56 PM

Topics in Biology

Difference between plant cell and animal cell Nucleus explained with its structures Nucleus explained with its types and functions Organelles of the cell explained with their characteristics Eukaryotic cell explained with its characteristics Prokaryotic cell explained with its structure Characteristics of prokaryotic cell Concept of cell Cell theory in biology Importance and limitations of ecological pyramid Protists explained with their characteristics Contents of the scrotum: Epididymis, vas deferens, spermatic cord and cremaster muscle Tropical savanna explained with its characteristics Concept of ecological pyramid Hindbrain: Medulla Oblongata and its features Food web explained with examples Biology Scheme of Work, SS1, First Term Biology Scheme of Work, SS1, 2nd Term Biology Scheme of Work, SS1, 3rd Term Male accessory sex organs: Seminal vesicles and bulbourethral glands

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

Cell Theory:

The cell theory was first formulated around the eighteenth and nineteenth century by Matthias Schleiden (1804 – 1881), Theodor Schwann (1810 – 1882), and Rudolph Virchow (1821 – 1902). These theories were basically put into three principles or tenets at that time. They are:

  1. All living things are composed of one or more cells.

  2. The cell is the basic structural unit in all organisms.

  3. New cells arise from pre-existing cells.

  4. Please read the concept of cell here.


The first discovery of cell was made in 1665 by Robert Hooke, an English physicist and a natural philosopher. He described this in his book 'Micrographia'.

With the help of a coarse compound microscope, Hooke discovered a multitude of tiny pores from a thin slice of cork. He named these tiny pores 'cells' (from the Latin word 'cella', meaning 'a small room'). However, Hooke did not understand their structure and function since the microscope which he worked with had low magnification. As a result, he couldn't observe the cell's nucleus and organelles.

Robert Hooke - Len Academy
Robert Hooke

He carried out a similar experiment on moulds, and yet did not observe much. However, the moulds kept reproducing asexually, and this made Hooke conclude that their growth was spontaneous, (spontaneous generation, also called abiogenesis), resulting from the presence of heat around their environment.

Please read asexual reproduction in plants here.


Anton van Leeuwenhoek is a Dutch microbiologist and microscopist born in Delft, Netherlands in 1632. He was very skilled with the use of microscope, and as such was able to discover a variety of microscopic organisms. While working on cells, he utilized a compound microscope with improved magnifying lens.

Anton van Leeuwenhoek - Len Academy
Anton van Leeuwenhoek

During his experiment, Leeuwenhoek observed motility (movement and locomotion) in the cells, thus concluding that they were living organisms. He further observed and described other forms of unicellular organisms (bacteria, protozoa and protists), which he generally referred to as 'animalcules' or 'little animals'.

Note: These organisms are termed microorganisms because they can only be seen with the aid of a microscope. In this regard, Anton van Leeuwenhoek is described as the father of microorganisms.

Please read on microorganisms causing food, water and air borne diseases here.


It was Leeuwenhoek who first identified the red blood cells in 1674. Also, he made the first observation on sperm cells (spermatozoa) and egg cell (ovum) respectively. He also discovered that fertilization requires the fusion of spermatozoa and ovum, thereby bringing an end to Robert Hooke's theory of spontaneous generation.

Please read more on scrotum and its contents here.


In 1838, a German botanist and zoologist, Matthias J. Schleiden further worked on cells, and was the first to categorically state that cells are the building blocks of all plants. Following his footsteps within that year, another German botanist, Theodor Schwann stated that cells are also the building blocks (fundamental units) of animals, bringing to rest the debate that plants and animals have fundamental differences in their building blocks.

Matthias J. Schleiden and Theodor Schwann - Len Academy

You can read on the differences between plants and crops here.


Together,  Matthias Schleiden and Theodor Schwann proposed a unified cell theory. It is stated below:

  • All living things are composed of one or more cells.

  • The cell is the basic structural unit in all organisms.

Note: Matthias Schleiden and Theodor Schwann still held onto the theory of spontaneous generation (abiogenesis) as the basis for cell origination.

Please read on sexual propagation in plants here.


The above cell theory failed to explain the production of new cells. In this regard, Rudolf Virchow, another German physiologist, biologist and doctor stated in 1855 that 'all cells come from pre-existing cells', which is interpreted as ‘Omnis cellula e cellula’ in German language.

Rudolf Virchow - Len Academy
Rudolf Virchow

Please read interesting facts for students here.

  • Meanwhile, understand that parts of the cell theory that has nothing to do with the origin of cells were generally accepted by scientists.


In 1883, Scottish botanist named Robert Brown made the first observation into the cell structure of archids. He discovered the function of a cell's nucleus, and came to a conclusion that all activities of the cell are controlled by the nucleus.


Leveraging on the works of Robert Hooke, Anton van Leeuwenhoek, Matthias Schleiden, Theodor Schwann, Rudolph Virchow, and Robert Brown as a foundation of cell research, various scientists further worked in this knowledge towards presenting a modern version of the cell theory. Below is a summary of the modern cell theory:

  1. All living things are made up of one or more cells.

  2. The cell is the basic, structural and functional unit of all living things.

  3. Cells come from pre-existing cells through the process of division.

  4. All cells are the same in regard to their basic chemical composition.

  5. All energy flow (that is, breakdown and build up of molecules) of life occurs within the cell.

  6. Genetic (or hereditary) information (DNA) is passed on from one cell to the other.

  7. Please read key points for students on various subjects here.

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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

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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

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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