Unicellular Organisms
3 Key points
- Made up of only one cell.
- Usually live in water
- Carries out all the functions to sustain life within itself
Examples of Unicellular organisms
4 categories
- All Bacteria
- All Protists
- Some Algae
- Unicellular Fungus
Bacteria
3 examples
- E.coli
- Streptococcus
- Halobacteria
Protists
3 Examples
- Amoeba
- Euglena
- Paramecium
Algae
2 examples
- Chlorella
- Chlamydomonos
Fungus
1 Example
Saccharomyces (yeast)
Multicellular Organisms
They are all eukaryote cells - with the following features:
- The cells must have the same DNA (except for reproductive cells).
- The cells must be connected and must communicate and cooperate to function as a single organism.
- Have different cells that are specialized and respon
Unicellular vs Multicellular
Comparison of Size
- *Unicellular**: Microscopic size – surface area to volume ratio limits size
- *Multicellular**: Macroscopic size – increasing number of cells allows increased body size
Unicellular vs Multicellular
Comparison of Lifespan
- *Unicellular**: Short lifespan due to energetically expensive workload
- *Multicellular**: Long lifespan as work is efficiently divided between specialized cells
Unicellular vs Multicellular
Comparison of Reproduction
- *Unicellular:**
- Mostly asexual, clonal reproduction
- Whole organism is involved in reproduction
- *Multicellular:**
- Mostly sexual reproduction
- Only cells specialized for reproduction will reproduce (gametes)
Definition
Cell differentiation
When unspecialized cells (stem cells) become specialized to perform a specific function.
Definition
Stem Cells
Cells that have the capacity to self-renew by cell division and to differentiate into different types of cells along different pathways. They are unspecialized cells.
Characteristics
Stem Cells
3 Points
Stem Cells
- Differentiate along a pathway
- Expression of genes are regulated by switching on or off genes
- Example: A pancreatic cell that specializes in producing digestive enzymes will have these genes switched on but a cardiac muscle
Definition
Meristems
- In plants, cell differentiation derives from the meristem tissue.
- Meristems are unspecialized cells located at the tips of shoots and roots.
- Organs such as flowers and leaves develop from the shoot apical meristems
- Root growth from the root apical meristems
Advantages of Multicellularity
7 Points
- It is more energy efficient as they are not wasting energy carrying out all the functions necessary for life.
- Longer lifespans as they are energy efficient.
- Sexual reproduction and genetic recombination leads to increasing
Disadvantages to multicellularity
- Unicellular organisms are made up of only one cell.
- These organisms &usually live in water.
- In one-celled organisms, the cell carries out all the < functions to sustain life within itself.
Exam
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