What Is Life? Characteristics of Living Things

Characteristics of living things:
1. Responds to stimuli
2. Requires nutrition*

*Nutrition: 4 stages:
Feeding (putting food in mouth)
Digestion - Physical (chewing/mastication), Chemical (enzymes)
                 - Purpose: To break food into simple, diffusible forms
Absorption (absorbing these simple, diffusible forms)
Assimilation (making use of these simple, diffusible forms)
--> There are 3 forms of carbohydrates:
Monosaccharides (e.g. glucose, basic forms which our bodies can absorb)
Disaccharides
Polysaccharides (e.g.cellulose, glycogen (a storage form of carbohydrates), starch (storage in plants only)

3. Requires oxygen - so that they can respire**
(exception: anaerobic life forms!)

**Respiration: 2 types:
Aerobic
- Process: glucose + oxygen --> respiration--> energy + water + carbon dioxide
Anaerobic (in the absence)
- Process: glucose --> respiration --> energy + alcohol + carbon dioxide
(the above process is alcoholic fermentation in plants - replace glucose with grapes for wine and wheat for beer)
- Creatures that use this form of respiration: yeast, microscopic lifeforms in deep sea vents, volcanos
- We use anaerobic respiration with aerobic respiration when running
(the process for this is the same except alcohol is replaced with lactic acid. This is stored in our muscles and causes muscle cramps when its maximum level is reached. It makes you gasp for oxygen to break down the lactic acid)

4. Requires water
5. Grows
6. Dies eventually - life cycle
7. Produces waste