Standards - Question 2 (1996)
2. Structure and function are related in the various organ systems of animals.
Select two of the following four organ systems in vertebrates:
respiratory
digestive
excretory
nervous
For each of the two systems you choose, discuss the structure and function of
two adaptations that aid in the transport or exchange of molecules (or ions).
Be sure to relate structure to function in each example.
Overall Commentary for Question 2
The intent of Question 2 was to test the students' understanding of the relationship
between structural and functional adaptations related to the transport of molecules and ions in
representative vertebrate systems. Students were to choose to discuss two adaptations in each
of two organ systems.
Standards were established to ensure that students were graded on the first two systems
that they mentioned. Within each system, the first two adaptations that were specifically identified
by the student were scored; otherwise, the first two adaptations that were identified by the Reader
were scored.
Students could earn a maximum of three points for a correctly explained adaptation and
functional relationship. They would have to name (or describe) a structural adaptation and its
functional significance and explain how that structural adaptation aids in the transport/exchange of
molecules or ions. This would earn a student two (2) points. The third point was for elaboration.
This point was awarded only if there was a substantive addition when describing a structural or
functional adaptation already introduced, or an extension into further detail supporting the
relationship. Some structural or functional adaptations did not have an elaboration point.
Identifying specific molecules or ions that are transported was often awarded an elaboration point.
Students who successfully earned three points on each of two adaptations and
relationships could earn a maximum of six (6) points for one system. This set of standards did not
allow any student to earn a score of one (1) point and no student could earn 10 points unless two
structural or functional adaptations were presented and discussed for each of two systems.
The following lists are not meant to be exhaustive. These standards allow for Reader
discretion on additional structural and functional adaptations. The standards also allow for
Reader discretion in awarding elaboration points.
RESPIRATORY SYSTEM
Structural adaptation Functional significance (HOW it aids
transport)
Alveolus Provides increased surface area
Moist, related to how it aids
exchange/transport One cell-thick membrane
(basement membrane)
Site of oxygen/carbon dioxide exchange
(elaboration)
Close proximity of capillary bed to
surface promotes absorption
Lung Same as for alveolus - well described
Gill Same as for alveolus
Muscles (diaphragm or intercostal muscles) Muscular contraction promotes bulk flow
of air
Cilia Moves mucus/dirt removed from tract
Counter-current exchange Increases gas transport through gill
filaments
1996 - Question 2 -
Standards p. 2
Jaw, throat pouch, nostril valves (amphibians) Provides positive pressure gradient into
lungs
Cartilage rings in trachea and bronchi Keeps airways open
Respiratory pigments (etc.) Establishes concentration gradients
Moist skin Facilitates transport of gases
(Amphibians)
Moist pleural membrane Allows lungs to expand upon contraction of diaphragm and intercostal muscles
Maintains lung inflation
Bone structure in birds Allows continuous air flow
DIGESTIVE SYSTEM
Structural adaptation Functional significance (HOW it aids
transport)
Villi, Microvilli, folds Increases surface area for absorption
Small Intestine Increases surface area for absorption
Close proximity of capillary bed to surface Promotes absorption
Rugae (in stomach) Same as for Villi, microvilli, folds
Membrane characteristics Associated with various membrane
transport mechanisms
(i. e. carrier proteins, etc.)
Folds and diameter of large intestine Facilitates absorption of water
Symbiotic bacteria (look for absorption link) Associated with vitamin K synthesis for
transport
(caecum) Digests cellulose and fatty acids for
better absorption
Smooth muscles Promotes bulk flow (muscle
contraction/peristalsis)
Enzymes/Acids/Bile Breaks down food (linked to
absorption/to enable absorption/for increase
in surface area)
Sphincter muscles Regulates flow
Relative lengths of digestive systems Provides more surface area for
absorption
Teeth/Saliva Breaks food into smaller pieces for
eventual absorption/ease of
swallowing/bulk transport
EXCRETORY SYSTEM
Structural adaptation Functional significance (HOW it aids
transport)
Loop of Henle Provides increased length/surface area
Establishes concentration gradient
Allows for selective absorption
Allows for counter-current exchange
Glomerulus/Bowman's Capsule Site of filtration (includes selective
nature)
Collecting Duct Allows for differential permeability for
water
Site of reabsorption (aided by ADH)
Distal Convoluted Tubule Site of secretion
1996 - Question 2 -
Standards p. 3
Nephron Increases surface area with huge # of
nephrons
Site of filtration, secretion, reabsorption
Filters, secretes, reabsorbs
Proximal Convoluted Tubule Increases surface area with microvilli
Organs, systems associated with (Lungs release Carbon dioxide, sweat
glands release water
excretion which are not part of and salts, liver releases bile, etc.)
the Urinary system.
NERVOUS SYSTEM
Structural adaptation Functional significance (HOW it aids
transport)
Na+/K+ Pump Establishes resting potential/gradients
Gated/ Open Channels Causes depolarization of membrane,
initiates action potential
Synapse Regulates transmission of impulse from
neuron to neuron
Pre-Synaptic Knobs Releases neurotransmitters and/or
neuromodulators
Releases Ca++ and/or exocytosis from
synaptic vesicles
Receptors on Post-Synaptic Recognize neurotransmitters (results in
depolarization)
Neuron Relates to ion transport
Releases neurotransmitters and
neuromodulators
Myelin sheath Promotes impulse transmission at nodes
Insulates to promote transmission at nodes