Chapter 1 : CHARACTERISTICS AND CLASSIFICATION OF LIVING ORGANISMS
Characteristics of living organisms:
- All organisms, whether they are unicellular or multicolour have certain common characteristics. They can be shown by the acronym MRS GREN
- M-movement-action by an organism causing a change of position or place.
- R-respiration- describes the chemical reactions in cells that break down nutrient molecules to release energy
- S-sensitivity-the ability to detect and respond to changes in the environment(stimulus)
- G-growth-permanent increase in size
- R-reproduction-process of making more of the same type of organism
- E- excretion -removal from organisms of toxic materials and other substances in excess of requirements
- N- nutrition- taking in of materials for energy, growth and development
Concept and use of a classification system
- There are two types of classification- Artificial and Natural
- The Artificial system involves classifying organisms according to their colour, habitat, etc . This however, is an inefficient method and therefore organisms cannot be classified correctly in this method
- The Natural system of classification involves classifying organisms on the basis of shared features. This is a much more efficient method than Artificial classification
- Species: A group of organisms that can reproduce to produce fertile offspring
- Closely related species are grouped into a genus
Binomial nomenclature
- This is a way of grouping organisms in two names- the genus name and the species name
- The binomial system of naming organisms is an internationally agreed system of classification where organisms are given Latin names for universal recognition
- Eg: the stoat is Mustella erminea and the the weasel is Mustella nivalis. Both these organisms belong to the same genus(Mustella) but are of different species(erminea and nivalis respectively)
- The first letter of the generic name is always given in capital and the the specific name always starts with a small letter. Both the names are in italics
Types of classification
- Morphology is the study of the form, or outward appearances of organisms
- Anatomy is the study of the internal structure of the organism, as revealed by dissection
- Cladistics is the classification of organisms based on whether or it they have one or more shared unique characteristics derived from the group’s last common ancestor, which are not present in more distant ancestors. Organisms which share a more recent ancestor(and are, therefore, more closely related) have DNA base sequences that are more similar than those that share only a distant ancestor
The Five Kingdom Classification
- Animals
- Plants
- Fungi
- Prokaryotes
- Protoctists
The Animal Kingdom
- Animals are classified into two groups: the arthropods and the vertebrates
Arthropods
- There are four classes of Arthropods
- They have a segmented body with a waterproof exoskeleton and are invertebrates(they have no backbone or spinal cord). They have jointed legs as their exoskeleton prevents movement
- Insects
Insects are the class of Arthropods that have their body divided into three parts, mainly the head, thorax and abdomen. The breathe through trachea, they have 1 or 2 pairs of wings and 3 pairs of jointed legs. They also have 1 pair of antenna and compound eyes
Eg: cockroach, other insects
- Crustaceans
They breathe through gills and live in very wet places, hence many of them are aquatic.
Eg: crabs, woodlice
- Myriapods
They are the centipedes and millipedes. They have a long, thin body with many segments and their bodies are not obviously divided into a thorax and abdomen. They have simple eyes and one pair of antennae.
- Arachnides
These are land dwelling organisms. They have four pairs of legs and their body is divided into a cephalothorax and abdomen. They have no wings and several pairs of simple eyes. They all have piercing jaws and chelicerae(poison fangs). They also have pedipalps to aid in reproduction.
Eg: Spiders and Scorpions
Vertebrates:
- This is the class of beings with a backbone
- They are either poikilothermic (they have a variable body temperature) or homeothermic ( they have a constant body temperature)
- They are divided into five classes:
- Fish
They are poikilothermic organisms. They have eyes. They have external fertilisation and they produce jelly covered eggs in water. They have scales and a lateral line on their body to detect vibrations in the water. They breathe through gills.
- Reptiles
They are poikilothermic organisms. They lay soft shelled eggs on land and have internal fertilisation. They have dry skin and scales and have four limbs( except for snakes). They breathe through lungs. they have eyes and ears
- Amphibians
They are poikilothermic organisms. They lay jelly covered eggs in water. They have eyes and ears and have four limbs. They go through external fertilisation and
- Birds
- Mammals
prepIGCSE 