Chapter 2: Characteristics of Life Leaving Certificate Biology Higher Level

Chapter Definitions Diversity of living organisms: refers to the large variety of organisms on Earth Life: describes an organic-based object that possesses the characteristics of metabolism and continuity of life Metabolism: the sum of all the chemical reactions in a living organism Continuity of life: describes how living organisms arise from living organisms of the same type

Characteristics of Life The characteristics of life: defined as the common characteristic ways of fulfilling the organism’s functional need for metabolism and continuity: 1.Organisation 2.Nutrition 3.Homeostasis/Excretion 4.Response 5.Reproduction

Characteristics of Life 1.Organisation: refers to the different levels of complexity in living organisms: cell → tissue → organ → organ system → organism → population The cell is the building block of life Molecules (proteins, fats, carbohydrates) organised into organelles, organised into cells, organised into tissues, organised into organs, organised into systems, organised into an organism Disruption of organisation leads to malfunction of metabolism and/or continuity of life

Characteristics of Life 2.Nutrition: the way in which living organisms obtain and use food All our energy ultimately comes from the Sun Plants create glucose from carbon dioxide and water using the energy in sunlight - photosynthesis Herbivores eat the plants and the flow of energy begins – the food chain Carnivores eat the herbivores The chemical energy in the bonds of glucose is converted by a cell’s machinery to other forms of energy so the organism can do work

Characteristics of Life 3.Excretion: the getting rid of waste products of metabolism from the body An organism’s body has ways to maintain its internal environment (homeostasis) Excretion is one way in which an organism maintains its internal environment Excretion in animals occurs via lungs, kidneys and skin Excretion in plants occurs via stomata (leaves) and lenticels (stem) Excretion in single-celled organisms (e.g. bacteria) occurs via diffusion

Characteristics of Life 4.Response: is the way in which living organisms react to their environment A living organism responds to environmental changes thereby maintaining a favourable metabolic environment In animals the stimulus is detected by sense organs that respond to light, sound, temperature, chemical equilibrium, touch, movement and direct mainly muscles to produce movement In plants responses are usually very slow – they respond to light and water by altering the direction of growth – tropisms (e.g. phototropism and geotropism)

Characteristics of Life 5.Reproduction: the way in which an organism or organisms interact to create a new individual Every living organism has the inherent ability and need to reproduce – 2 methods: 1.Asexual reproduction: formation of offspring by one individual organism (all offspring are genetically identical to the parent) 2.Sexual reproduction: formation of offspring from two parents (male and female)