BIOL #15: Animal Structure & Function Flashcards
Anatomy & Physiology
Anatomy is the study of an organism’s physical structure.
Physiology is the study of how the physical structures in an organism function.
Adaptations
Biologists who study animal anatomy and physiology are studying adaptations
- Adaptations are heritable traits that allow individuals to survive and reproduce in a certain environment better than individuals that lack those traits.
Adaptation results from evolution by natural selection.
- Natural selection favors those variations in a population that increase relative fitness (fitness = the production of offspring)
Biologists who study anatomy and physiology study compromise and constraint as well as adaptation.
Limitations on Adaptations
Genetics
- Natural Selection can only act on pre-existing variation within a population.
- New mutations must arise and be expressed in the phenotype in order for traits to be exposed to selection.
Existing Morphology
- Current morphology may limit the directions of future evolutionary change (i.e. historical contingency).
Physical Laws
- Laws of physics (e.g. drag or locomotion) make some adaptive solutions more likely than others, many times leading to convergent evolution (similar adaptations in distantly related organisms).
Trade-offs
- Inescapable compromises between traits (e.g. trade-off between quality and quantity of offspring).
- Trade-offs may be the most important constraint on adaptations because trade-offs are pervasive (common) in nature.
Adaptation vs Acclimatization
Adaptation is a genetic change that occurs over generations within a population in response to natural selection.
Acclimatization, or acclimation
- is a phenotypic change that occurs within an individual in response to a short-term change in environmental conditions.
The immediate process of an animal acclimating is not adaptation BUT the ability to acclimate is itself an adaptation.
Form, Function, and Adaptation
If a structure found in an animal is adaptive—meaning that it helps the individual survive and produce offspring—it is common to observe that the structure’s size, shape, or composition correlates closely with its function.
The mechanism responsible for correlations between structure and function can be straightforward:
- If a mutant allele alters a structure such that it functions more efficiently, individuals with that allele will have greater fitness (i.e. more offspring), resulting in an increased frequency of the allele in the population over time.
Form, Function, and Adaptation: Galapagos Finches
Changes in the alleles of genes that affect beak development have resulted in speciation and specialization on different food sources.
- Some alleles produce high beak growth, others produce little beak growth
Form, Function, and Adaptation: Stickleback Fish
Heavily armored marine stickleback have repeatedly invaded freshwater habitats with and without piscivorous predators.
- Those population inhabiting lakes without piscivorous predators typically lose much of their antipredator morphology (spines, body armor) over time because it is otherwise costly to maintain.
- Alleles of certain genes are responsible for production of body armor and spines and the frequency of these alleles in the high predation/low predation populations differ.
Structure-Function Correlation In Molecules and Cells
Correlations between form and function start at the molecular level
- For example, protein shape correlates with their role as enzymes, structural components of the cell, or transporters.
Similar correlations between structure and function occur at the level of the cell.
- For example, cells that secrete digestive enzymes contain a lot of rough ER and Golgi apparati (these cells must synthesize many enzymes and secrete them)
Likewise, cell shape and function correlate.
- For example, absorptive cells have a large surface area (e.g. microvilli are cytoplasmic protrusions)
Body Plans: Simple vs Complex
The rate at which gases, nutrients, and waste products diffuse across membranes depends in part on the amount of surface area available for diffusion.
The rate at which nutrients are used and waste products are produced depends on the volume of the cell.
As a cell gets larger, its volume increases much faster than its surface area does.
The opportunity for exchange with the environment depends on the number of cells in an organism’s body that have contact with the environment.
Single-celled organisms (e.g. amoeba) have a sufficient membrane surface area in contact with its environment to carry out all necessary exchange.
For multi-cellular organisms, many animals with a simple internal organization have body plans that enable direct exchange between almost all their cells and the external environment.
A hydra has a sac-like body plan with body walls that are only two cell layers thick. Because it’s gastrovascular cavity is open to the external environment, both cell layers are in contact with the external aquatic environment
Animals with complex internal organization typically have more cells, and thus, lower overall SA:V ratios (not all cells can be in contact with the external environment) than organisms with simple body plans.
All cells in animals must be bathed in fluid and have access to oxygen, nutrients, and other resources.
Animals with complex internal organization have evolutionary adaptations that enable sufficient nutrient and gas exchange with the fluid environment:
- Cells may have modifications to increase surface area
+ Flattening, folding, and branching are effective ways for structures to have a high surface area/volume ratio.
Interstitial Fluid
Animals with complex internal organization have evolutionary adaptations that enable sufficient exchange with the fluid environment:
- Internal body fluids link exchange between body cells
+ The space between many cells is filled with fluid called interstitial fluid
+ Circulatory fluid, such as blood, increase efficiency of cellular exchanges
Complex Benefits
Animals with complex internal organization have evolutionary adaptations that enable sufficient exchange with the fluid environment
Animals with complex internal organization have some distinct benefits over simple body plans despite the greater challenges of gas and nutrient exchange with the environment:
- Sensory organs and skeletal systems can provide protection and allow for controlled movement
- Internal digestive organs can break down food gradually, controlling the release of stored energy
- Specialized filtration systems can allows for animals to maintain relatively stable internal environments even when exposed to changing external environments (especially advantageous for animals living on land).
Tissues, Organs, Organ Systems
Animals are multicellular—their bodies contain distinct types of cells that are specialized for different functions.
A tissue is a group of similar cells that function as a unit.
Different types of tissues are further organized into specialized structures called organs
A gland can be a specialized group of similar cells (tissue) or organ that secretes specific molecules or solutions (e.g. hormones or enzymes).
Organs and Organ Systems
Organs are part of larger units called organ systems
- Organ systems consist of groups of tissues and organs that work together to perform one or more functions.
- Some organs are part of multiple organ systems
Tissues Types
The specialized and complex organ systems of animals are built from a limited set of cell and tissue types
- e.g. lungs and blood vessels have distinct functions but are lined with tissues that are the same basic type and share many of the same properties
Embryonic tissue (undifferentiated) gives rise to four adult tissue types (differentiated), all of which have a structure highly correlated with its function:
1) Epithelial
2) Connective
3) Muscle
4) Nervous
Epithelial Tissues
The epithelial tissues (epithelia) are sheets of cells that cover the outside of the body, line the surfaces of organs, and form glands.
Epithelia
- provide protection (via tight junctions)
- regulate the transfer of heat between the interior and exterior of structures
- regulate the transfer of water, nutrients, and other substances.
Epithelial cells typically form layers of closely packed cells.
