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Biology Chapter:2 Classification
Compiled By Ubeda Mansoor
How Organisms are Classified: Basics
• There are millions of species of organisms on Earth
• A species is defined as a group of organisms that can reproduce to produce fertile offspring
• These species ( smallest group) can be classified into groups by the features that they share . This is a useful way of classifying things, because it helps us to understand how organisms ‘work’.
The Binomial System
• Organisms were first classified by a Swedish naturalist called Linnaeus in a way that allows the subdivision of living organisms into smaller and more specialised groups
• He named organisms in Latin using the binomial system where the scientific name of an organism is made up of two parts starting with the genus (always given a capital letter) and followed by the species (starting with a lower case letter)
• When typed binomial names are always in italics (which indicates they are Latin) e.g. Homo sapiens
• The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species
How Organisms are Classified
• Organisms share features because they originally descend from a common ancestor
• Example: all mammals have bodies covered in hair, feed young from mammary glands and have external ears (pinnas)
• Originally, organisms were classified using morphology (the overall form and shape of the organism, e.g. whether it had wings or legs) and anatomy (the detailed body structure as determined by dissection)
• ( This point is not included in syllabus )As technology advanced, microscopes, knowledge of biochemistry and eventually DNA sequencing allowed us to classify organisms using a more scientific approach
• Studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more recent in time their common ancestor is)
• This means that the base sequences in a mammal’s DNA are more closely related to all other mammals than to any other vertebrate groups
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Kingdoms
1. Animal kingdom 2. Plant kingdom 3. Fungus kingdom 4. Prokaryote kingdom 5. Protoctist kingdom
1. Characteristics of Animal kingdom
They are multicellular, have nucleus (eukaryotic), lack cell wall and chloroplast.
They are heterotrophs (feed on organic substances made by other living organisms).
They have sensory organs, ability to move and internal digestion.
2. Characteristics of Plant kingdom
They are multicellular, have nucleus (eukaryotic), have cell wall made of cellulose and often contain chloroplast.
They are autotrophs ( make their food by photosynthesis) Have leaves, stems, roots and flowers except ferns and mosses.
3. Characteristics of Fungus kingdom
For a long time , fungi were classified as plants . Mushrooms and toadstools are fungi and can be colourful and easy to spot. Main body is made up of microscopic threads called hyphae. These are made up of many cells joined end to end. They do not have chlorophyll so they feed saprophytically or
parasitically on organic matter such as faeces, human food and dead plants and animals.
Many are decomposers, breaking down waste material from other organism. This helps to return nutrients to the soil.
They reproduce by spores.(can spread by wind or animals like seeds)
There are many uses e.g we eat mushroom, use yeast to make ethanol and bread, we obtain antibiotics.
Some are harmful causes food decay and diseases.
Important features
They are usually multicellular but can be unicellular They reproduce by spores
They have nuclei and cell wall made of chitin not cellulose.
They do not contain chlorophyll -no photosynthesis.
They feed by digesting waste organic material and absorbing it into their cells (heterotrophic)
Fig: 1.14. two examples of fungi
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They have mixed collection of organism. Some have plant-like cells with chloroplast and cellulose cell wall while others have animal-like cells.
Most are unicellular but some like seaweed are multicellular.
They feed by photosynthesis and others feed on organic substances made by other organisms
5. Characteristics of Prokaryote kingdom
Bacteria belong to this kingdom. They have cells that are very different from the cells of organism in other four kingdoms. There are useful as well as harmful bacteria, some carry photosynthesis.
The oldest fossils belong to this kingdom- so we think they were the first kind of organism to appear on Earth- biologist have discovered bacteria living in rocks more than 3km beneath the Earth’s surface.
Important features
They are usually unicellular
They have no nucleus ( nuclear material is not bounded by membrane) They have cell walls, not made of cellulose.
They have no mitochondria (cannot respire)
They have circular loop of DNA, which is free in the cytoplasm.
They often have plasmids (smaller loops)
Fig 1.16: Two examples of protoctists. Paramecium has anima-like cells. Chlamydomonas has plant-like cells.
Fig 1.18: The structure of a prokaryotic cell
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Fig 1.19: Photograph taken by electron microscope of a bacteria, that can live in the alimentary canal, and can make you feel ill X10 000
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Groups within the animal and plant kingdom Classifying Animal Kingdom
Vertebrates All vertebrates have a backbone. There are 5 classes of vertebrates:
Classes Main features Examples
1.Fish Loose, wet scales on skin Gills to breathe
Lay eggs without shell in water Have fins
white shark, grouper
2.Amphibians Smooth moist skin with no scales Lay eggs without shell in water The tadpoles live in water,(have gills) Adults live on land(so have lungs)
Frogs, toad and salamander, newt
3.Reptiles Dry, fixed scales on skin
Lay eggs with rubbery shells on land(waterproof)
Crocodiles, lizard, snakes, turtle 4.Birds Skin covered with feathers( they sometimes have scales on their
legs)
They have a beak
They have 2 legs and 2 wings Lay eggs with hard shells on land
Control body temperature (warm-blooded)
Birds evolved from dinosaurs so some biologist consider them dinosaur with feathers e.g Parrot, bluetit, eagle.
Both mammals and bird have a heart with four chambers
5.Mammals Fur/hair on skin
Their young develop in a uterus, attached to the mother by placenta.
Young feed on milk from the mammary gland External ears (ear flap, pinna)
They have different kinds of teeth( incisors, canine, premolars and molars)
They have sweat glands and a diaphragm.
Control body temperature( warm-blooded)
Horse, dog, human, pangolin
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Invertebrates
All invertebrates do not have a backbone. There are 5 classes of vertebrates:
One of the morphological characteristics used to classify invertebrates is whether they have legs or not
Characteristic features of all arthropods
• All invertebrates with jointed legs are part of the phylum Arthropods. They have a waterproof exoskeleton which allows them to live on land without drying out.
• They are classified further into the following four classes:
Breathe through tubes called trachea
Crabs and lobster
Spider, ticks and scorpion
Butterfly, dragonfly and locust Centipede
and
millipede
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Arthropod classification
Ferns & Flowering Plants
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At least some parts of any plant are green, caused by the presence of the
pigment chlorophyll which absorbs energy from sunlight for the process of photosynthesis
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The plant kingdom includes organisms such as ferns and flowering plants Characteristic features of Ferns:
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They are plants with roots, stems and leaves called fronds
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Do not produce flowers but instead reproduce by spores produced on the underside of fronds
Ferns
Ferns reproduce by spores found in the underside of their fronds Characteristic features of Flowering plants:
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They are plants with roots, stems and leaves.
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Reproduce sexually by means of flowers and seeds
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Seeds are produced inside the ovary found at the base of the flower
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Can be divided into two groups – monocotyledons and dicotyledons
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Wheat plants are monocotyledons Sunflowers are dicotyledons
How to distinguish between monocotyledons and dicotyledons:
Network
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Virus
• Virus cause common diseases such as colds and influenza, and also more serious ones such as Aids.
They are not considered to be living orgnisms because they cannot do anything other than just exist until they get inside a living cell. They then take over the cell’s machinery to make multiple copies of themselves. These new virus burst out of the cell and invade others, where the process is repeated.
The host cell is usually killed when this happens.
• They cannot move, excrete, feed, show sensitivity, grow or reproduce. They do not display the seven characteristics of living things.
• This figure shows a virus it is not made of a cell, but is simply a piece of genetic material surrounded by a protein coat. It is highly magnified. The scale bar represent a length of 10 nanometer.
• One nanometer is 1x 10
-9meter. ( you can line up more than 15000 of these virus between 2mm)
Dichotomous Keys
Constructing & Using a Key
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We can match with a picture in the book for identifying an organism . if picture is not available we use a
dichotomous key.•
Keys are used to identify organisms based on a series of questions about their features
• Dichotomous means ‘branching into two’ and it leads you through to the name of the organism by giving two
descriptions at a time and asking you to choose between them.
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Each choice leads to another pair of descriptions
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In order to successfully navigate a key, you need to pick a single organism to start with and follow the statements from the beginning until you find the name
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You then pick another organism and start at the beginning of the key again, repeating until all organisms are
named
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Example of a dichotomous key #1
Example of a dichotomous key #2
