Chapter 2: Characteristics of Life

Chapter 2: Characteristics of Life
• 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
The five characteristics of life:
1. Organisation
2. Nutrition
3. Homeostasis/Excretion
4. Response
5. Reproduction
Organisation: 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

Nutrition: 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

Excretion: 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

Response: 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)

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, and occurs by usually by one of two 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)