Definitions:
Life: describes an object made of organic chemicals that demonstrates metabolism and continuity of life
Continuity of life: how living organisms arise from living organisms of the same type
Diversity of living organisms: the large variety of organisms on Earth
The five characteristics of life:
1. Biological Organisation
2. Nutrition
3. Excretion
4. Response
5. Reproduction
Organisation:
Organisation refers to all the 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:
Nutrition is 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
Excretion:
Excretion refers to 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
Response:
Response refers to 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)
Reproduction:
Reproduction refers to 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:
- Asexual reproduction: formation of offspring by one individual organism (all offspring are genetically identical to the parent)
- Sexual reproduction: formation of offspring from two parents (male and female)
