Table of Contents
- Topic 1.1.1 – Characteristics of Living Organisms
- Topic 1.1.2 – Concept & Uses of Classification Systems
- 1.1.3 Concept & Uses of Classification Systems: Extended
- 1.1.4 Features of Organisms
- 1.1.5 Features of Organisms: Extended
Topic 1.1.1 – Characteristics of Living Organisms
REMEMBER THE MNEMONIC MRS GREN!
Movement: an action by an or part of an organism causing a change of position or place
Respiration: the chemical reactions that break down nutrient molecules in living cells to release energy for metabolism
Sensitivity: the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses
Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both
Reproduction: the processes that make more of the same kind
Excretion: the removal of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements
Nutrition: the taking in of materials for energy, growth and development
Topic 1.1.2 – Concept & Uses of Classification Systems
How Organisms are Classified
- There are millions different species of organisms on Earth
- A species is defined as a group of organisms that can reproduce to produce fertile offspring
- These species can be classified into groups by the features that they share e.g. all mammals have bodies covered in hair, feed young from mammary glands and have external ears (pinnas)
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
- The species in these groups have more and more features in common the more subdivided they get
- He named organisms in Latin using the binomial system where the scientific name 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
Dichotomous Keys
- Keys are used to identify organisms based on a series of questions about their features
- Dichotomous means ‘branching into two’ and it leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose
- Each choice leads the user onto another two descriptions
- 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
- You then pick another one and start at the beginning of the key again, repeating until all of them are named.
1.1.3 Concept & Uses of Classification Systems: Extended
Reflecting Evolutionary Relationships: Extended
- Classification systems aim to reflect evolutionary relationships between species.
- Traditional biological classification systems grouped organisms based on the features that they shared
- If they shared more similar features then they were said to be more closely related
- In the past, scientists have encountered many difficulties when trying to determine the evolutionary relationships of species based on this method.
- Using the physical features of species (such as color/shape/size) has many limitations and can often lead to the wrong classification of species.
Using DNA to Classify Organisms: Extended
- Organisms share features because they originally descend from a common ancestor.
- 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.
- As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can also be used to determine how closely related organisms are.
1.1.4 Features of Organisms
The Five Kingdoms
- The first division of living things in the classification system is to put them into one of five kingdoms. They are:
- Animals
- Plants
- Fungi
- Protoctists
- Prokaryotes
- Main features of all animals:
- they are multicellular
- their cells contain a nucleus but no cell walls or chloroplasts
- they feed on organic substances made by other living things
- Main features of all plants:
- they are multicellular
- their cells contain a nucleus, chloroplasts and cellulose cell walls
- they all feed by photosynthesis
The Animal Kingdom
Table from Save my Exams:
Vertebrate
| Class | Main Features | Examples |
| Mammals | – Fur/hair on skin – Has a placenta – The young feed on milk from mammary glands – Endothermic | Horse, dog, squirrel, human |
| Birds | – Skin is covered in feathers – Possesses two legs and two wings – Lays eggs on land – Has a beak – Endothermic | Parrot, eagle |
| Reptiles | – Dry, fixed scales on skin – Lay eggs with rubbery shells on land | Snake, turtle, iguana |
| Amphibians | – Smooth, moist skin – Adults usually live on land, but larvae live in the water – Can lay eggs without shells in water | Frog, toad |
| Fish | – Loose, wet scales – Gills to breathe – Lay eggs without shells in water | Flounder, grouper |
Invertebrate
- Invertebrates do not possess a backbone
- One of the morphological characteristics used to classify invertebrates is whether they have legs or not
- All invertebrates with jointed legs are part of the phylum Arthropods
| Class | Main features | Examples |
| Myriapods | – Body consists of many segments – Each segment has at least 1 pair of jointed legs | A millipede |
| Insects | – 3 part body (head, thorax, and abdomen) – 3 pairs of jointed legs – 2 pairs of wings – 1 pair of antennae | A bee |
| Arachnids | – 2 part body (cephalothorax and abdomen) – 4 pairs of jointed legs – No antennae | A scorpion |
| Crustaceans | – More than 4 pairs of jointed legs – Breathe through gills – 2 pairs of antennae | A lobster |
1.1.5 Features of Organisms: Extended
The Five Kingdoms: Extended
- The first division of living things in the classification system is to put them into one of five kingdoms:
- They are:
- Animals
- Plants
- Fungi
- Protoctists
- Prokaryotes
- Main features of all fungi (e.g. moulds, mushrooms, yeast)
- multicellular
- have nuclei and cell walls not made from cellulose
- feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition
- Main features of all Protoctists (e.g. Amoeba, Paramecium, Plasmodium)
- most are unicellular but some are multicellular
- all have a nucleus, some may have cell walls and chloroplasts
- meaning some protoctists photosynthesise and some feed on organic substances made by other living things
- Main features of all Prokaryotes (bacteria, blue-green algae)
- often unicellular
- cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria
The Plant Kingdom: Extended
- The plant kingdom includes organisms such as ferns and flowering plants.
- Because of the presences of chlorophyll, some parts of the plants are green, which absorbs sunlight so they can photosynthesize.
Ferns
- Have leaves called fronds
- Do not produce flowers but instead reproduce by spores produced on the underside of fronds
Flowering plants
- Sexually reproduce through flowers and seeds
- Can be divided into two groups: monocotyledons and dicotyledons
How can I distinguish between monocotyledons and dicotyledons?
- Flowers
- Flowers from monocotyledons contain petals in multiples of 3
- Flowers from dicotyledons contain petals in multiples of 4 or 5
- Leaves
- Leaves from monocotyledons have parallel leaf veins
- Leaves from dicotyledons possess veins that are interconnected and form a web-like shape throughout the leaf
Viruses: Extended
- Viruses are not considered living things, therefore they are not part of any classification system.
- They do not carry out the seven fundamental life processes for themselves, instead they take over a host cell’s metabolic pathways in order to make multiple copies of themselves.
- Virus structure is simply genetic material (either RNA or DNA) inside a protein coat.
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