Introduction to Biology


The content provides the following objectives to students;
o   Explain the term biology.
o   List some of the branches/fields of biology.
o   Describe the methods of science used to solve problems.
o    Explain the term Body Symmetry.
o   Distinguish among the various types of sectioning in biology.
o   Take measurements with compound light microscope.
o   Draw specimens and apply all the rule in biological drawing.

Biology as a Science of Life        

Biology is study of form and function of living organisms and how they interact with each other and their environment. It examines the structure, function, growth, origin, evolution, and distribution of living things. (2023) . 

Life Processes

Living things can be distinguished from non-living things by seven basic characteristics. These characteristics are referred to as life processes. Life processes are nutrition, respiration, movement, excretion, reproduction, sensitivity or irritability and growth. Other characteristics of living organism include competition, adaptation and life span or death.

Some examples of Living thigs
Examples of Some living organisms


The process by which living organisms make or obtain food and utilizing it for growth maintenance. Food is the material from which organisms obtain the energy required to sustain life through respiration and carry out all the other processes of life.

Types of Nutrition

1. Autotrophic (or Holophytic) Nutrition: It is type of feeding in which living organisms synthesize or manufacture their own food using simple inorganic substances.  Organisms that make their own food from simple raw materials are referred to as autotroph. There are two kinds of Autotrophic organisms.

a. Photoautotroph or PhotosyntheticThese are organisms that make their own food using energy from sunlight. E.g., green plants.

b. ChemosyntheticThese are organisms that make food using energy from inorganic chemicals. E.g., sulphur bacteria (Thiobacteria). Sulphur bacteria uses hydrogen sulphide to synthesize organic food.

2. Heterotrophic Nutrition: It is form of nutrition in which living organisms obtain their food from the bodies of other organisms. Heterotrophs are organisms that depend directly or indirectly on other organisms for ready-made food.  

Types of Heterotrophic Nutrition

1. Holozoic Nutrition: It is type of feeding in which the living organisms take in solid ready-made food. E.g., herbivores, carnivores and omnivores.

o Herbivores: organisms that feed directly on plants. E.g., cattle, goat and grasshopper

o Carnivores: organisms that feed on flesh of other animals. E.g., dogs, sharks and lions

o   Omnivores: organisms that feed on both plants and animals. E.g., human

2. Saprophytic Nutrition: it is type of nutrition in which the living organism feed on dead organic material. Saprophytes such as fungi and some bacteria, release enzymes to digest their food outside and then absorb the digested food.

3. Parasitic Nutrition: it is form of nutrition in which living organism (the parasite) depend on another living organism (called the host) for its food. E.g., tapeworms and tick.

Difference between Autotroph and Holozoic Mode of Nutrition

Autotrophic Nutrition

Heterotrophic Nutrition

Found in plants

Found in animals

Involves intake of simple inorganic substances

Involves intake of complex organic substances

Manufacture its own food

Depend on other organisms for food

Requires sunlight

sunlight is not required

Involves an anabolic process

Involves catabolic

Involves (chlorophyll for) photosynthesis

Does not involve photosynthesis

Some forms of food capture
Examples of Nutrition in Living Organisms 

Example of nutrition in Living organisms
Some forms of food capture


Respiration is a sum total of chemical reactions which result in the breakdown of food substance to release energy with or without the use of oxygen.

Respiration involves gaseous exchange (external respiration) and internal (tissue respiration).

External Respiration: is the uptake of oxygen and simultaneous elimination of carbon dioxide and water. This is commonly referred to as breathing.

Internal Respiration (also known as cellular or tissue respiration): is a series of chemical reactions within the cell in which organic molecules are oxidized to release energy. 

 Types of cellular respiration

1. Aerobic Respiration: This is the breakdown of glucose in living cells to provide energy in the presence of oxygen. The by-products of the reaction are water and carbon dioxide.  

2. Anaerobic Respiration: This occurs when glucose is broken down to release energy in absence oxygen. In humans, muscle cells respire anaerobically and the by-product is lactic acid. Plant and yeast cells respire anaerobically, producing carbon dioxide and alcohol as a by-product.

Types of cellular respiration


Movement is the change in position of the whole body or parts of the body, from one place to another, in search for food, shelter, mates, etc. Living things move on their own. Non-living things only move if they are pushed or pulled by something else. Animals usually move their whole body from place to place, supported by specialized organs called locomotory organs e.g., fins, wings and legs. Plant movement is not locomotory and does not involve moving the whole body. Leaves turning towards the light or roots growing towards moisture are examples of how plants move.


Excretion is the removal of waste metabolic products from the body. Waste products such as carbon dioxide, ammonia, urea etc. are poisonous and slows down vital chemical reactions, if allowed to accumulate. Plants do not have special excretory organs. Sometimes they store certain substances in harmless form in leaves or stems. E.g., wax, alkaloid, tanin etc.


Excretory Organs

Single-celled organism (e.g., amoeba, euglena etc)

Body surface, contractile vacuole


Malpighian tubules


Flame cells






Growth is irreversible or permanent increase in measurable features such as size, weight and length of an organism. Most animals grow until they reach maturity and then remain at a constant size while plants usually continue to increase in size throughout their life span.  Cells increase in number by dividing in a process called mitosis.

Sensitivity or Irritability

It is the process by which living things respond to stimuli (singular: stimulus). A stimulus is any environmental factor that triggers an action. Examples of stimulus are sound, heat, touch chemicals, taste, smell, temperature, nutrients, water level etc. Living things are sensitive to changes in their internal and external environment. This means that they detect and respond to events in order to maintain a stable and a healthy environment. In higher animals’ sensory organs are developed for the purpose of detecting stimuli. Plants do not have sensory organs and the response is slow but there are certain regions of their bodies such as the shoot tip that are sensitive to light, gravity, water and various chemicals. Only a few can respond rapidly to stimuli, such as the sensitive plant Mimosa.

Sensitive in Plants
The sensitive plant Mimosa


Reproduction is the process by which living organisms give rise to new individuals of their own kind. This ensures the continual existence of the species of an organism. There are two fundamental types of reproduction:

1. Asexual Reproduction: Asexual reproduction involves only one plant or individual to produce a new organism. The process involves no fertilization or exchange of genetic material.  Offspring are identical to the parent. E.g., plants such as potatoes or onion, grow from tubers or bulbs.

2.  Sexual Reproduction: Sexual reproduction involves the fusion of male and female gametes or sex cells to form single cell called a zygote, which develop into new organism. The offspring display some characteristics of both parents. Sexual reproduction ensures high degree of variation among organisms.

Forms of Sexual Reproduction

1. Conjugation involves gametes of similar shape and size e.g., Spirogyra

2. Fertilization involves gametes of different mating types.

Types of Fertilization

1. External Fertilization: a feature of reproduction in which fertilization takes place outside the parent’s body. E.g., frog

2.  Internal Fertilization: a feature of sexual reproduction in which fertilization takes place inside the parent’s body.  This type fertilization necessary for organisms that produce smaller number of sex cells. E.g., reptiles, birds and mammals.


Advantages of Internal Fertilization

1.   No chance of fertilized eggs being eaten by predators

2.   Embryo is protected from shock by the amniotic fluid 

3.   Zygote obtain oxygen or nutrients from the mother

4.   Fertilized eggs are protected inside the parent from harsh environmental condition like temperature

5.   Excretory products of embryo are removed by mother’s circulation

6.   Chance of fertilization is high  

Disadvantages of External Fertilization 

1.   Chance of eggs being fertilized by sperms is low 

2.   No or very low degree of parental care 

3.   Chance of embryo developing to maturity is low

4.  Embryo is exposed to harsh environmental conditions like drought.

Competition: The ability of living organisms to struggle for all necessity of life to survive in their environment.
Adaptation: The ability of organisms to adjust to changes in environment for survival.

Life Span/Death: All living organisms have definite period of existence. All organisms die.

Difference between Plants and Animals



Do not move from place to place

Move from place to place

Presence of cellulose cell wall

Absence of cell wall

No respiratory organs

Respiratory organs present

Autotrophic mode of nutrition

Heterotrophic mode of nutrition

No special excretory organs

Has special excretory organs

Chlorophyll/Chloroplast present

Chlorophyll/Chloroplast absent

Sense organs present

Sense organs absent

Carbohydrates are stored as starch

Carbohydrates are stored as glycogen

Response very slowly to stimuli/long termed

Response quickly to stimuli/short termed

Growth is unlimited / indefinite/growth is apical terminal

Growth is limited/definite/growth in all parts of the body

Branches of Biology

The main branches of biology include: 

Botany:  the study of plants
Zoology: the study of animals
Microbiology: the study of microscopic organisms (microorganisms) and their interactions with other living things
Virology: the study of viruses
Bacteriology: the study of bacteria
Mycology: the study of fungi
Parasitology:  the study of parasites and parasitism
Physiology: the study of functions of organs and parts of living organisms
Genetics: the study of genes and heredity
Histology: the study of cells and tissues
Anatomy: the study of form and function in plants, animals, and other organisms
Entomology: the study of insects etc.
Embryology: the study of the development of embryo of organism. 
Ecology: is the study of plants and animals in relation with their environment.

How Biologist  Work 

Scientific Methods of Research

The scientific method is a process for forming and testing solutions to problems, or analyzing how or why things work. It is the techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge.

The steps of the scientific method

1.  State the Problem - Create a short, meaningful title of your project. Write out a statement of purpose that describes what you want to do.

2.  Form a Hypothesis - This is a possible solution to the problem formed after gathering information about the problem. The term "research" is properly applied here.

3.  Prediction - This step involves determining the logical consequences of the hypothesis. What you expect to happen if the hypothesis is true.

4.  Test the Hypothesis - An experiment is performed to determine if the hypothesis solves the problem or not. Experiments are done to gather data. It is very important that good observations and records are made during an experiment.

5. Collect the Data - This is where you record your observations, measurements, or information from experiment. Make and record accurate measurements.

6.  Analyze the Data - Just what does all that data indicate about answering the problem you are solving?

7.  Draw Conclusions - After examining the data from the experiment, conclusions can be drawn. In its simplest form, the conclusion will be "yes" the hypothesis was correct, or "no" the hypothesis was not correct.

How to Write Biology Lab Report

Laboratory reports are an essential part of all laboratory courses. A lab report is how you explain  what you did in experiment, what you learned, and what the results meant. The order of the report is:

1. Title: This should be brief and describe the main point of the experiment or investigation. An example of a title would be: "Effects of Ultraviolet Light on Borax Crystal Growth Rate".

2.  Introduction / Purpose: Usually the introduction is one paragraph that explains the objectives or purpose of the lab. In one sentence, state the hypothesis. Briefly summarize how the experiment was performed, findings of the experiment, and list the conclusions of the investigation.

3.   Materials: List everything needed to complete your experiment.

4.   Methods: Describe the steps you completed during your investigation. This is your procedure. It may be helpful to provide a Figure to diagram of your experimental setup.

5.   Data/results: Numerical data obtained from your procedure usually is presented as a table. Data encompasses what you recorded when you conducted the experiment. Sometimes the Results section is combined with the Discussion.

6.  Discussion or Analysis: The Data section contains numbers. The Analysis section contains any calculations you made based on those numbers. This is where you interpret the data and determine whether or not a hypothesis was accepted. This is also where you would discuss any mistakes you might have made while conducting the investigation.

7.  Conclusions: Is a single paragraph that sums up what happened in the experiment, whether your hypothesis was accepted or rejected, and what this means.

8.  References: If your research was based on someone else's work or if you cited facts that require documentation then you should list these references.

Importance of Biology 

The study of biology is important in diverse ways which include the following:

□ It helps us to know and appreciate the complexity of living processes.
□ It helps to understand how diseases affect the body and ways to control disease.
□ It helps maintain health ecology for human, animals and plant life.
□ It enables the use of forensics to trace and arrest errant members of society.
□ It also allows agriculturalist to rear unique breeds of plants and animals.
□ It helps in creating solutions to the challenges many living organisms face.
□ It paves the way for inventions and discoveries that improves quality of life.

Careers Associated with the Study of Biology

Knowledge of biology is required for entry into fields such as
1.   Public Health
2.   Medicine
3.   Pharmaceutical
4.   Pathology
5.    Zoology and Botany
6.    Farming and agricultural engineering
7.    Physiotherapy
8.    Microbiology and Biotechnology industries etc

Anatomical Terms 

Biologist in studying living organisms must understand the following terminologies relating to the body 

symmetry, sections and orientation.

Body Symmetry

Body Symmetry Symmetry is the balanced arrangement of body parts around a central point or axis. It shows how a body can be divided into two equal parts. There are three basic kinds of symmetry: radial, bilateral or spherical.

1. Radial Symmetry: Radial symmetry is the regular arrangement of body parts around a central axis. That is body of the organism can be cut along more than one plane to produce identical halves. Animals that exhibit radial symmetry tend to be sessile (immobile). Radial symmetry allows them to reach out in all directions. E.g., sea anemones, jelly fish, star fish, hydra.

2. Bilateral Symmetry: This is where the body of the organism can be cut along only one plane to produce identical halves. Bilateral symmetry is best for motile animals. E.g., Lizards, fishes, toads, butterflies, birds, crabs etc.           

3.  Spherical symmetry: This is where any plane or cut that passes through the center of the object produce two identical halves. Such objects are shaped like spheres or globes. Spherical symmetry is exhibited by colonial algae, such a Volvox.

4.  Asymmetry: Asymmetrical animals have no pattern of symmetry. E.g., Amoeba and Sponges


Orientation describes the position of an organism or viewed when being drawn.

1.     Anterior view – head end of an organism.
2.     Posterior view - caudal or tail end of an organism.
3.     Dorsal view – the upper part or back of the organism.
4.     Ventral view – the underside or belly of an organism.
5.     Lateral view -the left side and right side of the organism.
6.     Pectoral - toward the forelimbs
7.     Pelvic - toward the rear limbs
8.     Distal - far from, farther from the origin
10    Proximal - near, closer to the origin.

Body orientation of organisms
Anatomical directions of organism


A section is a cut made through an organism to see internal features. Biological specimen can be sectioned or cut in three forms:

1. Transverse Section (T.S): is a cut that runs crosswise through the whole or part of an organism.

2. Longitudinal Section (L.S): is a section that runs through the length of the organism (from top to bottom).

3.  Vertical Section (V.S): is a section that runs through whole or part of an organism which has no distinct length or breadth.

Biological Section through objects
Types of Sections


A microscope is an instrument used to observe objects that are too small for the naked eye. Robert Hooke invented the first microscope. The science of investigating small objects using microscope is called microscopy. Microscopic means invisible to the eye unless aided by a microscope. There are many types of microscopes, the most common are:

a.  Optical microscope 

b.  Electron microscope

Optical Microscope

The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscope is the most common type and the first invented microscope. There are two kinds of optical microscope: the simple (single lens) and the compound (many lenses).

1.   Simple microscope (magnifying glass or hand lens): It consist of one convex lens mounted in a metal or plastic frame. It is good to about ten times (10X) magnification.

2.   Compound microscope: has two systems of lenses for greater magnification, the eyepiece lens and the objective lens. Compound microscopes are heavier, larger and more expensive than simple microscopes.

Optical microscope is used in biotechnology, pharmaceutical research, medical diagnosis, mineralogy and microbiology.

Microscope and Hand lens or simple nicroscope
The Microscope versus the Magnifying Glass (Image from Brown University)

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 Components of Compound Microscope

1.  Diaphragm or Iris: is a rotating disk under the stage. This diaphragm is used to adjust or control the intensity of light that is projected into the slide.
2.  Eyepiece Lens or Ocular:  the lens at the top that you look through.  They are usually 10X or 15X power.
3.  Objective Lenses:  Usually 3 or 4 objective lenses are found on a microscope.  They are used to magnify the first image of the specimen.
4.  Tube:  Connects the eyepiece to the objective lenses
5.  Stage:  is the flat platform where slide is placed.  Stage clips hold the slide firmly onto the stage.
6.  Arm/ handle:  supports the tube and connects it to the base
7.  Coarse adjustment knob: is used to bring objects into focus, that is, to locate or see an image of the specimen.
8.  Fine adjustment knob: is used to view fine details of the specimen.
9.  Nose-piece: holds the objective lens. It can be rotate to change the power of the objective lens

image of compound microscope
Drawing of Compound Microscope

Precaution of Using the Light Microscope

1. It must be carried with both hands; one hand holds the limb and the other placed under the base to provide support
2. It should be kept on levelled surface.
3. Before removing the slide from the stage, it is better to change to the low power objective lens to avoid breaking the slide.
4. The lens must be cleaned by wiping them with a special soft tissue moisture ethanol.
5. Lens should not be touched with bare fingers as they leave greasy finger prints on the lens.
6. The stage of microscope must be kept clean and dry. 
7. To avoid wetting the lens the specimen on the slide must be covered with a cover slip.


Electron Microscope

An electron microscope is a type of microscope that uses an electron beam to produce a magnified image. An electron microscope has greater resolving power than a light microscope. It can reveal the structure of smaller objects because electrons have wavelengths about 100,000 times shorter than visible light. There are two kinds of electron microscope. These are the transmission electron microscopes (TEM) and scanning electron microscope (SEM). The TEM is used to examine thin sections whilst SEM is used to see three-dimensional view of specimen.  


Preparation of Wet-mount or Temporal Slide

1.   Take a clean, dry microscope slide and cover slip

2.   Place a drop of water using dropper in the center of the slide

3.   Place the object or specimen to be observed into the liquid without trapping any air bubbles

4.   Place the cover slip at one end of the slide and at 45o and carefully lower the slip on the specimen using needle

5.   Wipe off any excess liquid around the cover-slip

Microscope slides preparation
Preparing microscope slide

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Principles of Biological Drawings

1. Drawings, labels, label lines/guidelines, title, and underlining must be done using HB pencil only on unlined paper, graph, or colored paper.

2. To avoid dirty work, the outline of drawings should be made with sharp HB pencils.

3.   Drawings should be large covering at least 75% of the given drawing space. Be sure to leave space at the sides for labels, at the top for the title, and at the bottom for calculations and other information.

4.  An underlined title must be centered at the top middle of the page or below the drawing. The specimen’s name, special characteristics (e.g., special staining), real size, and diagram magnification must be written below the drawing.

5.  All labels must be presented horizontally beside the sketch. The label lines must be drawn using a ruler and must not cross. Do not use arrows. Make sure your label lines touch the structure being labeled. Students must always write horizontally.

6.  Erase completely all uncompleted lines and rule a new one if it becomes necessary to do so.

7.  Avoid use of double lines

8.  Avoid the use of strokes, broken lines or zig-zag lines when making guidelines.

9.  Do not shade your drawing. Coloring is totally forbidden!

10.  Your drawing must be neat. Do not draw sketchy lines. If you erase, erase completely. Do not draw broken lines.  

11.  A drawing is a pictorial representation of what you see; therefore, it must resemble the specimen in front of you. Draw from your specimen not from the textbook.

N/B: Characteristics of Good Biological drawing

In order to produce very good biological drawings, one must pay attention to the following above characteristics.

a. The heading/Tittle
b. Magnification
c. Outlines
d. Labeling
e. Guidelines

Biological Drawing
Drawing illustrating Biological Drawing

N/B Magnification of a compound microscope = eyepiece lens X objective lens 

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