Cellular respiration in biology

len Alfred Ajibola - 12th March, 2024 @ 10:57 AM

Topics in Biology

Cellular respiration in biology Len Academy biology mock questions for waec Len Academy biology midterm questions for SS1, 2nd Term Characteristics of saltwater habitat Aquatic habitat explained with its types Types of habitat: Terrestrial habitat explained with examples What is habitat? 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

Academic Questions in Biology

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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

Understanding Cellular Respiration:

Cellular respiration is one of the crucial biological processes that occurs in the cells of living organisms.

Recall that living organisms are composed of one or more cells as their basic and fundamental unit of life. These cells require energy to carry out their metabolic activities (or breaking down and building up functions), which are critical to their survival.

Please read on the concept of a cell here


Cellular respiration covers the process through which cells transform the chemical energy stored in digested food (glucose), typically in the presence of oxygen into Adenosine triphosphate (ATP).

Respiration is defined the oxidation of glucose into ATP. In fact, ATP is the energy currency which the cells utilize to carry out their various functions.

You can read on autotrophic nutrition here.


It is noteworthy to state that respiration is an entirely different process from photosynthesis. In this regard, both plant and animal cells carry out respiration in order to generate energy (ATP), a molecule that powers cellular metabolism. In simple terms, ATP is the molecule (or energy) utilized for the cell's metabolic activities. Without the process of respiration, life ceases.

You can read on the differences between plants and animal cell

The intricate process of cellular respiration involves the breakdown of glucose, or other organic molecules in the presence of oxygen to produce ATP (energy), alongside carbon dioxide (CO2), and water (H2O) as byproducts.


It is noteworthy to state that during vigorous exercise (in human), the muscle cells may break down glucose in the absence of oxygen, releasing lactic acid (lactate) in the process. However, this generates only 2 molecules of ATP; and this is far less compared to the 38 molecules released in the presence of oxygen. In this regard, respiration is put into two types:


  1. Aerobic respiration: Glucose is oxidized to generate ATP. It involves the TCA cycle, and occurs within the mitochondria of the cell. Often regarded as oxidative phosphorylation, it therefore requires oxygen to facilitate the electron transport chain. This chain is responsible for generating a large amount of ATP through a process called chemiosmosis. 38 ATP molecules are generated through this process.

  2. Anaerobic respiration: It occurs in the absence of oxygen, and always produces lesser amount of ATP. Importantly, it takes place in the cytoplasm, and not the mitochondria of cells. Lower organisms such as bacteria and yeast use this respiration type. In humans, it occurs in the muscle cells during heavy activities like exercises, producing only 2 ATP molecules and lactate.

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Note: Aerobic cellular respiration takes place in the bean-shaped mitochondria of all cells. They house the machinery responsible for generating ATP, the currency of cellular energy. For this reason, the mitochondria is termed the power house of the cell.


Glucose is a molecule derived from the digestion of carbohydrates. It serves as the primary source of energy for the cells to carry out their essential functions. In this light, it is a crucial player in kick-starting the energy (or ATP) production within cells.

Upon entering the cell, glucose is subjected to a series of enzymatic reactions in a process known as glycolysis. This initial step involves breaking down glucose into smaller molecules, ultimately yielding pyruvate and a modest amount of ATP. The pyruvate molecules then enter the next stage of cellular respiration, the citric acid cycle, where they undergo further oxidation to release more ATP and high-energy electrons.

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The process of respiration unfolds in three main stages These are:

  1. Glycolysis

  2. Krebs Cycle (Citric Acid Cycle)

  3. Electron Transport Chain.

Glycolysis serves as the initial step in cellular respiration, taking place in the cytoplasm of the cell. During this stage, one glucose molecule is broken down into two molecules of pyruvate through a series of enzymatic reactions, leading to the release of energy in the form of ATP and NADH. Glycolysis therefore acts as the starting point for extracting energy from glucose, and setting the stage for further energy production.

Glycolysis- Len Academy

Please red on the concept of food here.

The Kreb's Cycle (TCA Cycle) occurs within the mitochondria of the cell, and is a crucial stage in cellular respiration. This intricate process of Kreb's cycle involves a series of chemical reactions that further break down the pyruvate molecules from glycolysis. The Krebs cycle generates high-energy molecules such as NADH and FADH2, which carry electrons to the next stage of cellular respiration, that is, the electron transport chain.

Citric Acid Cycle - Len Academy

You can read key points in biology here.

The electron transport chain is the final stage of cellular respiration, taking place in the inner mitochondrial membrane. Here, the high-energy molecules produced in glycolysis and the Krebs cycle donate their electrons to a series of protein complexes. As electrons move through the chain, energy is harnessed to pump protons across the membrane, creating an electrochemical gradient. This gradient drives the production of ATP, the primary energy currency of cells.

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The significance of cellular respiration cannot be overstated, as it is essential for the survival and functioning of all living organisms. By harnessing the energy stored in nutrients, cells are able to carry out vital processes such as growth, repair, and reproduction.

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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