Topic 1- Characteristics and classification of living organisms
Topic 1- Characteristics and classification of living organisms
1.1 Characteristics of living organisms
1.1.1 –Describe the characteristics of living organisms
Use a mnemonic to remember a list, e.g. MRS GREN stands for the first letters of the seven characteristics of living organisms.
– movement as an action by an organism or part of an organism causing a change of
position or place
– respiration is the chemical reaction in cells that breaks down nutrient molecules and releases energy for metabolism
– sensitivity is the ability to detect or sense stimuli in the internal or external
environment and to make appropriate responses
– growth as a permanent increase in size and dry mass by an increase in cell number or cell size or both
– reproduction is the processes that make more of the same kind of organism
– excretion as removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements
– nutrition as taking in materials for energy, growth and development; plants require light, carbon dioxide, water and ions; animals need organic compounds and ions and usually need water.
1.2 Concept and uses of a classification system
1.2.1 Define species
They are a group of organisms that can reproduce to produce fertile offspring
1.2.2 Define and describe the binomial system of naming species
The Binomial System of scientifically naming organisms was developed by Carolus Linnaeus of Sweden;
It is an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species.
Now, let’s take up a simple example: Humans
Genus- Homo
Species- sapiens
Rules for writing scientific names:
The first letter of the genus is ALWAYS capitalised
The first letter of the species is NEVER capitalised
Scientific names of organisms are always italicized or underlined
Homo sapiens
Homo sapiens
1.2.3 State that organisms can be classified into groups by the features that they share
1.2.4 Explain that classification is traditionally based on studies of morphology and anatomy
Classification means sorting organisms into groups according to the features they have in common;
It makes the identification of living organisms easier as there are more than 1 million different species already identified;
The biggest group is called a kingdom;
Each kingdom is divided into smaller groups which include genus and species;
There are many possible ways in which we could group living organisms;
Classification is traditionally based on studies of morphology (the study of the outward appearance) and anatomy (the study of their internal structure);
The sequences of DNA and amino acids are used as a more accurate means of classification than studying morphology and anatomy.
1.2.5 Explain that classification systems aim to reflect evolutionary relationships
By studying the morphology and anatomy of different groups of vertebrates, it is possible to gain insight into their evolution
For example, we put humans, dogs, horses and mice into one group (the mammals) because they share certain features (for example, having hair) that are not found in other groups;
We think that all mammals share these features because they have all descended from the same ancestor that lived long ago;
The ancestor that they all share is called a common ancestor;
Organisms that share a more recent ancestor have DNA base sequences that are more similar than those that share only a distant ancestor.
Thus classification systems aim to reflect evolutionary relationships
1.2.6 Explain that the sequences of bases in DNA and of amino acids in proteins are used as a more accurate means of classification.
1.2.7 Explain that organisms which share a more recent ancestor (are more closely related) have base sequences in DNA that are more similar than those that share only a distant ancestor.
Sequences of bases in DNA and of amino acids in proteins are used as a more accurate means of classification
The sequence of bases in the DNA molecule determines the sequence of amino acids in the proteins made by the organism.
Thus, a mutation in an organism’s DNA leads to a change in its protein structure.
The longer ago the two different organisms separated from a common ancestor, the larger the number of mutations will have occurred, and the greater the differences in the sequence of bases there will be in these organisms’ DNA and RNA. This, in turn, leads to a greater difference in the amino acid sequence in their proteins.
Groups of organisms which share a more recent ancestor (are more closely related) have base sequences in DNA that are more similar than those that share only a distant ancestor.
1.2.8 Construct and use simple dichotomous keys based on easily identifiable features.
Keys are used by biologists in the process of identifying organisms.
A dichotomous key consists of a series of questions.
Each question has two alternative answers.
Depending on which answer is chosen, the user is directed to the next question.
Thus, by starting at the first question, and then by a process of elimination, a specimen may be identified.
E.g.
How to design the key?
Start by putting things in groups;
Identify the characteristics which make up each group;
Then invent statements which divide things up into the groups you created.
1.3 Features of organisms
1.3.1 List the features in the cells of all living organisms.
a. Cytoplasm is jelly-like and contains all the cell organelles
b. Cell membrane is semi permeable and controls what enters and leaves the cell
c. DNA is the genetic material
d. Ribosomes used for protein synthesis
e. Enzymes are involved in respiration
1.3.2 List the main features used to place animals and plants into the appropriate kingdoms
1.3.3 List the main features used to place all organisms into one of the five kingdoms: Animal, Plant, Fungus, Prokaryote, Protoctist
Classification makes the identification of living organisms easier;
It involves sorting animals into groups according to the features they have in common;
The biggest group is a kingdom;
There are 5 kingdoms;
Animal kingdom is divided into phylum a.Invertebrates ( Arthropoda) and vertebrates.
Arthropoda phylum is divided into classes: Myriapods, insects, arachnids, crustaceans,
Vertebrate phylum is divided into classes: Fish, amphibians, reptiles, birds, mammals
The plant kingdom is divided into phylum ferns and flowering plants
a. Prokaryote eg. Bacteria
often unicellular (single-celled)
have no nucleus
have cell walls, not made of cellulose
have no mitochondria.
Loop of naked DNA
They are killed by antibiotics
The cell wall of bacteria contains peptidoglycan
They have smaller ribosomes
b. Protoctists eg. Paramecium, Amoeba
They are mostly unicellular but some are multicellular.
Microscopic
Some have chloroplasts and are similar to plant cells.
Others more like animal cells or fungal cells.
Examples: Amoeba & paramecium
c. Fungi: eg. Yeast, bread mould
usually multicellular (many-celled)
have nuclei
have cell walls made of chitin not made of cellulose
do not have chlorophyll
feed by saprophytic or parasitic nutrition.
Many have a structure called mycelium made of hyphae (tubular threads)
Store carbohydrates as glycogen
Reproduce by producing spores
d. Plants: Eg. Pine, fern
Plants are multicellular
Have chloroplasts for photosynthesis.
Cells have cell walls made of cellulose
Store carbohydrates as starch
Can reproduce asexually and sexually
may have roots, stems and leaves.
e. Animals: eg. Birds, earthworm
multicellular
Don’t have chloroplast and cell wall.
They respond rapidly to changes in their environment.
They can move around.
They often store carbohydrate as glycogen
Most animals reproduce sexually
1.3.4 List the main features used to place organisms into groups within the animal kingdom, limited to: –– the main groups of vertebrates: mammals, birds, reptiles, amphibians, fish –– the main groups of arthropods: myriapods, insects, arachnids, crustaceans
Vertebrates are animals with a backbone;
They are divided into 5 groups
a. Class-Fish eg. perch, shark
Live in water and have fins to swim with.
Have skeletons made of bone & cartilage.
Most have scales.
Have gills for breathing
Are cold-blooded.
Most lay eggs, which are fertilized externally
b. Class-Amphibians eg. frog, toad
• A moist, permeable skin through which they breathe.
• Live or can survive on land but always return to water to lay eggs
• Adults have lungs to breathe air
• Eggs hatch into larvae called tadpoles that live in water
• Tadpoles breathe using gills
• Are cold -blooded.
Most lay eggs in water to be fertilised externally
c. Class-Reptiles e.g salamanders
A tough, dry, scaly skin.
Lay eggs with leathery shells on land
Have lungs for breathing air.
Are cold blooded
Most live on land
d. Class-Birds eg. penguin
Have feathers and wings
Have scaly feet.
Have beaks for feeding.
Have lungs for breathing.
Are warm blooded.
Lay eggs to produce offspring
e. Class-mammals e.g rat, rabbits
Have hair or fur on their bodies.
Have sweat glands
Have lungs for breathing and external ears.
Are warm-blooded.
Most give birth to their young but few species lay eggs.
Females produce milk from mammary glands to feed their young
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II. Invertebrates
These are the animals that do not have vertebral columns.
Like the vertebrates, they are divided into phyla
The largest group (phylum) of invertebrates, by far, is the arthropods.
Phylum: The Arthropods
• They have segmented bodies.
• They have limbs with clearly visible joints.
• They have an exoskeleton (i.e. a skeleton on the outside of the body). (Muscles are attached internally to the exoskeleton – the opposite of ourselves, where muscles are attached externally to our endoskeleton.)
• The exoskeleton is composed of the chemical chitin.
A. Class- Insects ( Butterflies, housefly)
The body is divided into three parts – head, thorax and abdomen. The head, thorax and abdomen are not segments.
They have three pairs of (jointed) legs – attached to the thorax.
They usually have wings – one or two pairs attached to the thorax.
They have one pair of antennae – attached to the head.
Examples: Beetles, ants, butterflies, bees
B. Class - Crustaceans (crabs and lobsters)
Mostly live in water
Two pairs of antennae are attached to the head.
Five or more pairs of legs
The body is divided into cephalothorax and abdomen
No wings
Examples: Crabs, lobsters, shrimps
C. Class- Arachnids (spiders, scorpions)
The body is divided into two parts cephalothorax and abdomen
Four pairs of jointed legs joined to the cephalothorax.
No antennae or wings.
Examples: Spiders and scorpions
D. Class- myriapods (centipedes and millipedes).
One pair of antennae.
Ten or more pairs of legs with one or two pairs of legs attached to every segment.
The body is not divided into thorax and abdomen.
e.g Centipedes
& Millipedes
1.3.5 List the main features used to place organisms into groups within the plant kingdom, limited to ferns and flowering plants (dicotyledons and monocotyledons)
Two major divisions of plants are the ferns and the flowering plants.
A. Ferns
They are green photosynthesising plants.
They do not produce flowers.
Instead, they produce spores that are light and easily carried away by the wind.
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B- Flowering plants (Angiosperm)
Are multicellular organisms
Cells have cellulose cell walls and sap vacuoles
Have root, stem and leaves
Have xylem and phloem
Reproduce by seed production although asexual reproduction is also possible.
Seeds are produced inside the ovary of the flower
Phloem: Transports sugar
Xylem: Transports water and minerals
Flowering plants are subdivided into two groups
(i) Monocotyledons (ii) Dicotyledons
1.3.6 List the features of viruses
X-Protein coat ( capsid)
Y-Genetic material (DNA or RNA)
Viruses are particles rather than cells
They are less than 300 nm in size – around 100 times smaller than a bacterium.
They can be seen only with an electron microscope.
They contain a strand of genetic material (DNA or RNA).
The genetic material is surrounded by a protein coat known as the capsid.
They can reproduce only inside living (host) cells.
Since they are parasites, they cause disease (i.e. they are pathogenic). Examples of diseases caused by viruses are influenza, measles and AIDS.
Viruses are not affected by antibiotics.