Overview
This lecture covers the basic functional characteristics of life, using the MR H GREN mnemonic, and illustrates these concepts with examples of unicellular organisms.
Cell Theory & Life Characteristics
- All living things are made of one or more cells.
- The functional characteristics of life can be remembered as MR H GREN: Metabolism, Response, Homeostasis, Growth, Reproduction, Excretion, Nutrition.
Metabolism
- Metabolism refers to all chemical reactions within cells and organisms.
- Catabolic reactions break down compounds (e.g., glucose breakdown in cellular respiration).
- Anabolic reactions build up compounds (e.g., protein and lipid synthesis).
- Viruses lack metabolism and are not considered living.
Response (Sensitivity)
- All living things respond to internal and external stimuli (e.g., light, chemical, pressure, temperature).
- Responses include movement or growth towards or away from stimuli.
Homeostasis
- Homeostasis is the regulation of the internal environment (e.g., water, pH, temperature) within a certain range.
Growth & Development
- Growth means increasing in size.
- Development means transformation over time so young become like adults.
Reproduction
- All living things reproduce, either asexually (one parent; identical offspring) or sexually (two parents; genetically unique offspring).
Excretion
- Organisms remove waste products; methods vary by organism type (e.g., cell membrane, leaves, roots).
Nutrition
- Organisms require energy, obtained from organic molecules or by synthesizing food (photosynthesis).
Unicellular Organisms Examples
Paramecium (Heterotroph)
- Engulfs food via oral groove; digests using enzymes.
- Excretes solids via anal pore, liquids via contractile vacuoles.
- Moves with cilia in response to stimuli.
- Maintains homeostasis via cell membrane/vacuoles.
- Reproduces asexually by division or sexually by fusion.
Chlamydomonas (Autotroph)
- Contains chloroplasts for photosynthesis to make food.
- Excretes waste such as oxygen by diffusion.
- Eye spot detects light; flagella enable movement towards light.
- Contractile vacuoles for water regulation.
- Absorbs minerals and grows until division.
- Reproduces both asexually and sexually.
Key Terms & Definitions
- Metabolism — all chemical reactions occurring in cells/organisms.
- Homeostasis — maintaining a stable internal environment.
- Asexual Reproduction — reproduction without fusion of gametes, producing genetically identical offspring.
- Sexual Reproduction — reproduction involving fusion of sex cells from two parents, producing genetically unique offspring.
- Excretion — removal of waste products from the organism.
- Autotroph — organism that produces its own food.
- Heterotroph — organism that obtains food by consuming other organisms.
Action Items / Next Steps
- Memorize the MR H GREN characteristics of life.
- Review examples of how Paramecium and Chlamydomonas fulfill life functions.