Introduction to Biology

Biology can be simply defined as the study of life. The word "Biology" comes from two Greek words: "Bios," which means life, and "logos," which means study. A biologist is a scientist who studies living things. They make use of common processes and attributes of science.

Branches of Biology

Biology has several branches, including:

1. Zoology: The study of animals
2. Botany: The study of plants
3. Genetics: The study of how living things inherit characteristics from their parents
4. Ecology: The study of relationships between living things and their environment
5. Physiology: The study of how living things function
6. Morphology: The study of the external features of living things
7. Anatomy: The study of the internal structure of living things

Relevance of Biology

Biology plays a significant role in various aspects of human life, including:

1. Agriculture: Production of hybrids (crops and animals with desired qualities), and use of biological pesticides to control agricultural pests.
2. Medicine: Production of drugs and vaccines for preventing and curing diseases (e.g., penicillin), organ transplants (e.g., kidney transplants), and in-vitro fertilization in infertile couples.
3. Bioremediation: Using naturally occurring bacteria to clean up oil spills and toxic chemicals.
4. Food Production: Production of single-cell proteins (SCP) to combat protein deficiency, as well as advancements in food storage and preservation.
5. Biotechnology: Use of genetic engineering to address genetic diseases.

Methods of Science

Scientific methods involve a sequence of steps followed in conducting research or inquiries. The scientific methods include:

1. Observation: Careful examination of the subject of study.
2. Hypothesis: A scientific guess or prediction regarding the probable outcome of an experiment.
3. Experimental Procedure: The sequential steps followed in conducting the experiment.
4. Results/Analysis: The outcome of the experiment and its documentation.
5. Conclusion: Drawing an outcome based on the results of the experiment or inquiry.

Experimental Patterns

Experiments are designed to eliminate bias and avoid drawing false conclusions. To achieve this, only the factor being tested is varied, while all other factors that might affect the results are kept constant. These experiments are called controlled experiments. In biology, experiments often involve living organisms, which may not always be identical. To minimize this issue, large test samples are used, and experiments are repeated multiple times.

Characteristics of Living Things

Everything in the world can be classified as either living or non-living. Living things include plants and animals (organisms that possess life), such as humans, monkeys, earthworms, flies, mangoes, and hibiscus plants. Non-living things, on the other hand, do not have life, such as stones, water, air, and tables.

1. Movement: The ability to move part or all of the body using energy produced by the organism.
2. Nutrition: Assimilation of food substances needed for respiration and growth.
3. Respiration: Breakdown of food substances to release energy.
4. Reproduction: The production of new individuals of the same species for the continuation of life.
5. Irritability: Ability to respond to stimuli from the environment.
6. Adaptation: Possession of features that enable an organism to live successfully in its environment.
7. Growth: Irreversible increase in body size, weight, and complexity due to the synthesis of new protoplasm.
8. Excretion: Removal of waste products of metabolism produced by chemical processes in the body.
9. Competition: Interaction between organisms or species for food, water, and territory, with the dominant ones surviving.
10. Death: Living things cannot live forever; they eventually die or cease to live.

Differences Between Plants and Animals

Classification of Living Things

Classification involves organizing living organisms into categories or groups based on similarities and shared characteristics.

Binomial System of Nomenclature

This system of naming organisms is based on their genus and species. It was introduced by the Swiss scientist Carl Linnaeus. The first name is the genus and is capitalized, while the second name is the species and begins with a lowercase letter. Examples include:

1. Man: Homo sapiens
2. Domestic Dog: Canis familiaris

Classification starts with the largest group, the kingdom, and progresses to the smallest group, the species:

1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species

Mnemonic: Kanye Prefers Coke Over Flat Grape Soda

Species is the smallest unit of classification. Members of the same species can interbreed, but they cannot breed with members of other species.

Scientists and Classification Methods

1. Linnaeus: 2 kingdoms (plants and animals)
2. Whittaker: 5 kingdoms (animals, plants, fungi, prokaryotes, and protoctists)
3. Woese: 6 kingdoms (animals, plants, fungi, eubacteria, archaebacteria, and protoctists)
4. Woese: 3 domains based on RNA structures (eubacteria, archaea, and eukarya)

Five Kingdoms Classification

All living organisms are classified into five kingdoms:

1. Kingdom Prokaryote (Monera)
2. Kingdom Protista (Protoctista)
3. Kingdom Fungi
4. Kingdom Plantae (all plants)
5. Kingdom Animalia (all animals)

Prokaryotes/ Monera

This group consists of the simplest living organisms, such as bacteria and blue-green algae.

Credit: Parashuram Bannigidad on Researchgate.net

Characteristics:

1. They are single-celled microscopic organisms.
2. They reproduce asexually by binary fission.
3. They possess cell walls made of sugar, protein, and lipids, but not cellulose.
4. They are prokaryotic, meaning they lack a definite nucleus and nuclear membrane, but have chromosomes with a circular strand of DNA.

Protista

Protists can be broadly divided into four groups:

• Protozoa (e.g., Amoeba):
  • They are microscopic organisms.
  • They are unicellular.
  • They move using different organelles: Amoeba uses pseudopodia, while Paramecium uses cilia for locomotion.
  • Most are aquatic, while some are parasitic.
  • They reproduce asexually by binary fission.
Credit: Maristep on Freepik
• Euglenophyta:
  • They possess a flagellum for movement.
  • They have a contractile vacuole for osmoregulation.
  • They possess an eyespot for detecting light.
  • They have the ability to carry out holozoic nutrition.
Credit: EdrawMax
• Chrysophyta
• Pyrrophyta

Characteristics:

• They are unicellular organisms.
• Most protists are aquatic organisms.
• Some are free-living, while a few are parasitic.
• They move by cilia, flagella, or pseudopodia.
• They are eukaryotes, meaning their cells have a definite nucleus.

Fungi

Multicellular fungi have filamentous bodies made up of a network of fine, branching filaments called hyphae (singular: hypha). This mass of hyphae is known as mycelium (plural: mycelia).

Characteristics:

• Fungi, along with bacteria, are the primary decomposers in the biosphere.
• They have a rigid cell wall made of chitin and polysaccharides.
• They are non-green organisms that do not photosynthesize because they lack chlorophyll.
• They reproduce both asexually (by producing spores) and sexually.
• Most fungi are non-motile, except for slime molds.
• They are heterotrophic organisms: some are saprophytic, some are parasitic, and others are symbiotic.
• They lack true roots, stems, and leaves.

Plants

Plants consist of organisms with a cellulose cell wall and chlorophyll for manufacturing their own food. The kingdom Plantae is made up of three major phyla: Thallophyta, Bryophyta, and Tracheophyta.

Phyla of Kingdom Plantae:

• Thallophyta (Algae):
  • Examples include Spirogyra, Volvox, Sargassum, and Kelp.
  • They are simple aquatic photosynthetic plants.
  • They lack true roots, stems, and leaves.
  • They can be unicellular or multicellular and may be green, brown, or red.
  • They reproduce asexually (via cell division, fragmentation, spores) or sexually.
  • They exhibit alternation of generations.
• Bryophyta:
  • They are multicellular green plants.
  • Their cells are differentiated into tissues.
  • They lack true roots, stems, and leaves but have stem-like and leaf-like structures.
  • They are non-vascular plants.
  • They may reproduce sexually or asexually.
  • Examples include Moss and Liverwort.
• Tracheophyta:

  This division is made up of vascular plants and is divided into two subdivisions: Pteridophyta and Spermatophyta.

Pteridophyta

• They are multicellular plants.
• They have true roots (rhizome and adventitious), stems, and leaves.
• They lack well-developed supporting tissues.
• They reproduce using special gametes and spores but do not produce seeds.
• They are non-flowering plants.
• They are mainly terrestrial, though a few are aquatic.
• They reproduce asexually.
• Examples include Dryopteris and Ferns.

Spermatophyta

• They are multicellular, seed-producing plants.
• They have well-developed vascular tissues.
• They have true roots, stems, and leaves.
• They reproduce sexually and do not require water for reproduction.
• They are mainly terrestrial green plants.
• Spermatophytes are divided into two main classes: Gymnospermae and Angiospermae.

Gymnospermae

Characteristics of gymnosperms:

• They are plants with naked seeds.
• They have true roots, stems, and leaves.
• They do not bear flowers.
• Their seeds are borne on cones.
• They are vascular green plants.
• Examples include Pinus, Cycads, Ginkgos, and Conifers.

Angiospermae

Characteristics of angiosperms:

• They are mainly terrestrial plants.
• They are vascular plants.
• They are flowering plants.
• Their seeds are enclosed in fruits.
• They are the most complex green flowering plants.
• Angiosperms are divided into two classes based on the number of cotyledons:
  • Monocotyledonous plants
  • Dicotyledonous plants

Monocotyledonous Plants

Characteristics:

• They bear seeds with only one seed leaf (cotyledon).
• Their vascular bundles are scattered.
• Their floral parts exist in groups of three or multiples of three.
• They have parallel venation.
• They have a fibrous root system.
• They do not undergo secondary growth.
• Examples include Maize, Rice, Palm trees, and Guinea grass.

Dicotyledonous Plants

Characteristics:

• They have net venation.
• They bear seeds with two seed leaves (cotyledons).
• They have a tap root system.
• They usually undergo secondary growth.
• Their vascular bundles are arranged in a regular pattern.
• Their floral parts exist in groups of four or five.
• Examples include Mango, Cowpea, Cashew, and Groundnut.

Animals

Animals consist of multicellular organisms with no cell wall; they lack chloroplasts in their cells and, therefore, feed heterotrophically. Animals can be classified into two main groups:

• Invertebrates – animals without backbones.
• Vertebrates – animals with backbones.

Invertebrates

• Phylum Porifera (sponges)
  • They are primitive multicellular, aquatic animals (colonies of cells).
  • Reproduce asexually and sexually.
  • They lack true tissues and a nervous system.
  • They are attached to rocks, shells, or corals.
  • They live in colonies.
  • Most are hermaphrodites (possessing both male and female sex organs).
Credit: brgfx on Freepik
• Phylum Coelenterata (Cnidaria: Hydra, jellyfish, sea anemones)
  • They are multicellular organisms.
  • Their body is made up of two layers (ectoderm and endoderm).
  • They are mainly aquatic organisms.
  • Their bodies possess radial symmetry.
  • They have soft jelly-like bodies.
  • They have tentacles and stinging cells for capturing prey.
  • They reproduce asexually by budding.
• Phylum Platyhelminthes (Flatworms)
  • They are multicellular flatworms.
  • They are bilaterally symmetrical.
  • They do not have a body cavity (Acoelomate).
  • Their body is made up of three layers: ectoderm, mesoderm, and endoderm.
  • They are mainly parasites in humans and other animals.
  • They are mostly hermaphrodites and reproduce sexually.
  • Examples: Tapeworm, planaria, liver fluke, blood fluke, etc.
• Phylum Nematoda (Roundworms)
  • They have round and cylindrical bodies.
  • They are pointed at both ends.
  • Their bodies are not segmented.
  • They have a partial body cavity (pseudo-coelomate).
  • They are bilaterally symmetrical.
  • Some are parasites, while others are free-living.
  • Examples: Roundworms (Ascaris), hookworms, guinea worms, thread worms, filarial worms.
• Phylum Annelida (Earthworms, leeches)
  • They have internally and externally segmented bodies which are long and cylindrical.
  • They are coelomates, meaning they have a true body cavity.
  • Some are aquatic, while others are terrestrial.
  • They are hermaphrodites and reproduce sexually.
  • They have both mouth and anus.
  • Examples: Earthworms, leeches, tubeworms.
• Phylum Mollusca (Snail, squid, octopus)
  • They have soft unsegmented bodies.
  • They have tentacles on their heads.
  • They have muscular feet adapted for crawling or burrowing.
  • Some have shells, while others do not.
  • Examples: Snails, octopus, oysters, periwinkles, mussels.
• Echinodermata
  • They have radially symmetrical bodies.
  • They are slow-moving marine animals living on seashores and seabeds.
  • They lack a head and brain.
  • They are spiny-skinned animals.
  • They have tube feet used for movement.
  • Examples: Sea urchins, sea cucumber, starfish.
• They have segmented bodies
• They have hard, rigid exoskeleton made of chitin
• Some are aquatic, while others are terrestria
• Their appendages are jointed.
• They are bilaterally symmetrical.
• Arthropods

  This is the largest phylum in the animal kingdom. It is divided into the following classes:

  • Crustacea e.g. Crab, crayfish, shrimps, prawns
  • They are mainly aquatic.
  • They have two body parts cephalothorax and abdomen
  • Their body is protected by a carapace
  • They have two pairs of antennae.
  • They have simple eyes
  • Examples are: crab, crayfish, prawns, shrimps, barnacles, lobsters, etc
  • Insecta e.g. Cockroach, butterfly
  
  • Their body is divided into three parts/ segments namely head thorax and abdomen.
  • They have three pairs of jointed legs.
  • They have two pairs of membranous wings.
  • They have a pair of antennae
  • They have a pair of compound eyes.
  • Myriapoda e.g. Centipedes and millipedes
  • They have long bodies with many segments
  • They have many legs.
  • They have two sub classes namely:
    (i) Chilopoda e.g. Centipedes.
    (ii) Diplopoda e.g. Millipedes.
  • Arachnida e.g. Spider, scorpion, mite, ticks
  • They are mainly terrestrial but a few are aquatic
  • They have two body parts namely cephalothorax and abdomen.
  • They have no antenna.
  • They have four pairs of walking legs.
  • They have simple eyes.

Vertebrates

• Pisces (FISHES)
• These are fishes which are aquatic, cold blooded (poikilothermic) i.e. the body temperature varies with that of the surrounding.
• Their bodies are covered with scales.
• They breathe through their gills
• They have lateral line system for detecting vibration in water
• Reproduction is sexual and fertilization is external
• They have fins which are used for movement
• They show parental care for their young ones
• Aves (Birds)
• They are homoiothermic or warm-blooded animals
• Their body is covered with feathers
• They have toothless beak for feeding.
• They have two pairs of limbs
• They have wings for flight
• They show parental care for their young ones
• Reproduction is sexual and fertilization is internal
• Amphibia
  • Cold-blooded animals that spend part of their life in water.
  • Gaseous exchange through gills, lungs, or skin.
  • Fertilization is external, and they do not show parental care.
  • Examples: Frogs, toads, salamanders.
• Reptilia (Reptiles)
  • Cold-blooded, their skin is covered with dry scales that prevent water loss.
  • They reproduce sexually, and fertilization is internal.
  • Examples: Lizards, snakes, crocodiles.
• Mammalia (Mammals)
  • Warm-blooded (homoiothermic) animals.
  • Their bodies are covered with hair.
  • They have lungs for gaseous exchange.
  • They reproduce sexually, and fertilization is internal.
  • They show parental care and have a well-developed brain.
  • Examples: Humans, cats, dogs, rats, lions, giraffes, goats, cows, elephants.

Viruses

Viruses are non-cellular particles made up of DNA or RNA surrounded by a protein coat. They are harmful parasites that need a host to reproduce. They do not respond to antibiotics and are constantly evolving into new strains.

Living Characteristics of Viruses

• Can reproduce when placed in a living cell.
• Possess characteristics that can be transmitted from generation to generation.

Non-living Characteristics of Viruses

• Form crystals when outside a living cell and become inactive.
• Cannot respire, excrete, feed, or respond to stimuli.