Multicellularity, Development, and Reproduction Flashcards
3 Inter-related Phenomena
- Constraints on cell size
- Multicellularity: development + specialization
- Reproduction in Eukaryotes
Cell Size
- SMALL SIZE IS NECESSARY; cells rely on diffusion to bring nutrients in and eliminate waste. The larger the cell, the more challenging it is for them to exchange with their environment
- this struggle occurs both at the cell surface and within the cell
Surface-to-Area Ratio
- as the radius of the cell increases, the SA and volume increase
- the cell’s volume increases more rapidly than its SA as it grows larger
- as a cell increases in size, its SA:V ration DECREASES
Why does SA:V matter for cell size
- Plasma membrane surface area
- Internal transport
Plasma Membrane SA
- the PM is the cell’s only interface with the environment
- if the cell needs to take up nutrients/ eliminate waste, it must go across the membrane
- each patch of the membrane can only exchange so much as a given period of time because of its limited channels
- if a cell grows too large, its membrane will not have enough exchange capacity (surface area) to support the rate of exchange for its increased metabolic activity (volume)
Internal Support
as cells get larger, it takes longer to transport materials inside them, since there is more distance for the material to cover before it reaches its destination
Eukaryote Cell Size
there is a general upper limit on cell size, where eukaryotic cells can grow bigger than prokaryotes due to their structure + metabolic features. Some adaptations are:
1. Cell Geometry
2. Reproduction
3. Internal Complexity
4. Multicellularity
Eukaryote Cell Size: Cell Geometry
some cells are long + thin or have many protrusions from their surface, increasing SA relative to volume
Eukaryote Cell Size: Reproduction
a cell can divide into 2 cells when it becomes too large to survive as one
Eukaryote Cell Size: Internal Complexity
Internal organelles are present that compartmentalize + perform specific tasks
- internal “tracks” called cytoskeletons can be used to transport materials at a faster rate than diffusion
Eukaryote Cell Size: Multicellularity
an organism is made up of multiple, specialized cells
Multicellularity + Cell Specilization
Multicellularity typically also requires cell specialization, where different cells carry out different functions from one another + have different morphologies optimized for those functions
- EX: circulatory system VS respiratory system
- Other organ systems have developed further specialization of cells + tissues and efficiently control body functions
- SA:V applies to other areas of animal development
- this evolution resulted in the requirement for DEVELOPMENT
Development
changes in an organism’s size, shape, and function during specific life stages; regulated by 5 essential processes whose timing is highly regulated and result in development of SPECIFIED TISSUE TYPES and MORPHOGENESIS:
1. Cell Proliferation
2. Programmed Cell Death
3. Cell Movement/Differential Expression
4. Induction
5. Cell Differentiation
Development: Cell Proliferation
reproduction of new cells via mitosis; this process is critical for adding new cells (and thus mass) to the body, making it larger
Development: Programmed Cell Death
death of specific cells; certain cells must due at certain stages for normal development
Development: Cell Movement/Differential Expression
movement to new locations in the body (ANIMALS) or differential expansion of cells in a specific direction (PLANTS)
- Plant cells cannot move due to their cell wall, and instead expand this way to cause the plant to bend
Development: Induction
cell-to-cell communication / signaling; critical for cells recognizing where they are in the body during development and what cell they should become
- can occur directly between immediately adjacent cells or over long distances in concentration gradients
Morphogen
signaling molecule that helps specify cell fate that is present in a concentration gradient; the amount of this a cell detects determines the fate
- INDUCTIONNNNN
Development: Cell Differentiation
the process of becoming a specific cell type; often the final result of all the other processes, where a cell goes from unspecified (embryonic) to a final, specialized type
Morphogenesis
development of an organism’s overall shape
Eukaryotic Reproduction
development occurs FOLLOWING reproduction in multicellular eukaryotes:
- Sexual
- Asexual
Eukaryotic Reproduction: Asexual
the offspring is an exact genetic copy of the parent; has advantages over sexual reproduction including relative speed + low energy cost compared to finding + courting a mate
- Mitosis
- Multiple Fission
- Budding
- Fragmentation
- Spores
- Parthenogenesis
- Polyembryony
- Vegetative Growth
Mitosis
splitting into 2 halves; all eukaryotes use mitosis either to produce a new organism or produce new cells within a multicellular organism
Multiple Fission
splitting into more than 2 cells; some fungi and microbial eukaryotes reproduce this way
