IGCSE BIOLOGY SECTION 1 LESSON 1

Content Section 1 The nature and variety of living organisms a)Characteristics of living organisms b)Variety of living organisms

Content Lesson 1 a) Character- istics of living organisms a)Characteristics of living organisms 1.1 Understand that living organisms share the following characteristics: – they require nutrition – they respire – they excrete their waste – they respond to their surroundings – they move – they control their internal conditions – they reproduce – they grow and develop. BONUS: Classification of living organisms

How many species?

About 1.4 million species have been described.

It has been estimated that there may be as many as 8.7 million species!

The vast majority have therefore not been identified.

Group Estimated total number of species Percentage of total already described Animals7.7 million12% Fungi0.61 million7% Plants0.30 million70% Protozoa0.04 million22% Chromists (plant-like) 0.03 million50%

Suppose you landed on another planet in our galaxy.

What signs of life would you look for?

What are the characteristics of living organisms?

MRS GREN

Movement Respiration Sensitivity Growth Reproduction Excretion Nutrition

Movement Most single-celled creatures, and larger animals, move about as a whole. Fungi and plants make movements with parts of their bodies. Movement does not necessarily involve locomotion (movement of an organism from place to place)

Respiration All living organisms break down food to obtain energy. Most organisms need oxygen for this (aerobic respiration) whereas others are able to respire without oxygen (anaerobic respiration). Taking in oxygen and removing carbon dioxide is the process of breathing. Glucose + oxygen  Carbon dioxide + water C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O

Sensitivity All living organisms respond to their environment. Sensitivity is the ability of living organisms to respond to stimuli. A stimulus is a change in the external or internal environment of an organism. Plants, for example, respond to gravity. This is known as geotropism.

Sensitivity Living organisms are also aware of their internal environment and are able to respond to changes and restore the body to its normal state. This regulation of the internal environment is known as homeostasis.

Growth Bacteria and single-celled creatures increase in size. Many-celled organisms increase the number of cells in their bodies, become more complicated and change their shape as well as increasing in size.

Reproduction Off spring are produced by the process of reproduction. Single- celled organisms and bacteria may simply keep dividing into two (eg. binary fission). Many- celled plants and animals may reproduce sexually or asexually.

Excretion Excretion involves the removal of waste products from the body, such as carbon dioxide ( a product of respiration). Living organisms expel these substances from their bodies in various ways.

Nutrition Nutrition is the process of obtaining food. There are two main methods of obtaining food – aututrophic nutrition (green plants) and heterotrophic nutrition (organisms use ready- made organic compounds as their food source).

MRS GREN

Movement Respiration Sensitivity Growth Reproduction Excretion Nutrition

CLASSIFICATION – a method of scientific taxonomy used to group and categorize organisms into groups such as a genus or species.

These groups are known as taxa.

The modern system of putting different organisms into certain groups was developed by the Swedish botanist and zoologist Carl Linnaeus in the eighteenth century. He gave each species a Latin name, consisting of the genus and the species. This is known as binomial nomenclature.

For example, the scientific name for the rabbit is Oryctolagus cuniculus. It is known by this name all over the world by the scientific community. Similarly, the binomial name for human beings is Homo sapiens. Homo is the genus, and sapiens is the species.

Classification Kingdom The largest group of organisms recognised by biologists. But how many?

Classification Kingdom The largest group of organisms recognised by biologists. But how many? For many years most biologists favoured the use of two kingdoms, Plants and Animals.

Classification Kingdom The largest group of organisms recognised by biologists. But how many? For many years most biologists favoured the use of two kingdoms, Plants and Animals. Modern classification tends to favour the adoption of 5 kingdoms – Prokaryotes (Monera), Protoctista, Fungi, Plants and Animals

Classification Kingdom Monera (Prokaryotes) Bacteria and Blue-green algae ProtoctistaAmoeba, Paramecium FungiMoulds, Mushrooms, Yeast Plants Algae, ferns and mosses, conifers and flowering plants Animals Jellyfish, worms, arthropods, molluscs, echinoderms, fish, amphibia, reptiles, birds and mammals.

Classification Kingdom Viruses are not considered to be living, so are not included in this classification scheme.

Classification Eg. Lion

Classification KingdomAnimalia

Classification KingdomAnimalia PhylumVertebrates

Classification KingdomAnimalia PhylumVertebrates ClassMammals

Classification KingdomAnimalia PhylumVertebrates ClassMammals OrderCarnivores

Classification KingdomAnimalia PhylumVertebrates ClassMammals OrderCarnivores FamilyFelidae (cats)

Classification KingdomAnimalia PhylumVertebrates ClassMammals OrderCarnivores FamilyFelidae (cats) GenusPanthera

Classification KingdomAnimalia PhylumVertebrates ClassMammals OrderCarnivores FamilyFelidae (cats) GenusPanthera Speciesleo

Classification Panthera leo

End of Section 1 Lesson 1 In this lesson we have covered: Species diversity Characteristics of living organisms Classification