Untitled Flashcards Set

Transport in Plants
• Movement of Xylem Sap:
o Xylem sap can move at speeds of up to 15 meters per hour in vessels, and this
movement can even occur against gravity in tall trees.
o Some examples of impressive heights for water transport in trees include redwood
trees (110 meters), Douglas fir (100 meters), and Sitka spruce (90 meters).
o The primary forces behind xylem sap movement are root pressure and
transpiration pull.
o Root pressure contributes to the "push" force, creating pressure in the roots and
pushing water up.
o The "pull" force is primarily driven by transpiration, which is the loss of water
from leaves.
• Transpiration Pull:
o Leaves play a significant role in water loss through transpiration.
o Mature maple trees, for instance, can lose up to 200 liters of water per hour on a
sunny day.
o The cohesion and adhesion properties of water are essential in this process.
Cohesion refers to water molecules sticking together due to hydrogen bonding.
o Xylem cells, including tracheids and vessel elements, are hollow and joined end
to end to facilitate water movement.
o The cell walls of these xylem cells are composed of lignin, which is hydrophobic.
o The Transpiration-Cohesion-Tension Theory explains the process by which water
is pulled up the plant through xylem due to transpiration in the leaves.
• Movement of Phloem Sap:

2
o Phloem sap moves from sources (where it's made or stored, like leaves) to sinks
(where it's used or stored, like roots, terminal buds, flowers, fruits, or seeds).
o Some organs can act as both sources and sinks depending on the plant's needs.
• Phloem Loading:
o Phloem sap is propelled by hydrostatic pressure, which is created by the high
sucrose concentration in the phloem.
o This high solute concentration lowers water potential (y).
o Water, obtained from the xylem, is drawn into the phloem at the site of phloem
loading, creating pressure that pushes the sap away from the source.
• Regulation of Stomata Opening and Closing:
o Stomata are regulated by specialized epidermal cells called "guard cells" that
flank the stomatal pore.
o Guard cells have unique features, such as chloroplast development and
reinforcement of their cell walls.
o They can take up or release water to open or close the stomatal pore, which
controls gas exchange.
• Uptake of Water by Guard Cells:
o Decreasing water potential (y) by taking up water from the surrounding tissue
allows guard cells to become turgid and open the stomata.
o This process is achieved by increasing the concentration of potassium ions (K+)
in guard cells.
o ATP-driven proton pumps move H+ ions out of the guard cells, favoring the
uptake of K+ and Cl- ions.
• Regulation of Stomata Opening:
o Light, specifically blue light, can activate the proton pump in guard cells.
o The pump is a receptor in the plasma membrane of guard cells.
o Light fuels photosynthesis, causing the accumulation of sugar in guard cells and a
decrease in water potential (ys).
o Decreased intercellular CO2 concentration also stimulates guard cell swelling.
• Regulation of Stomata Closing:
o In darkness, the proton pump is turned off, leading to the loss of K+ and Cl- ions
from guard cells.
o Water follows ions, leading to guard cell flaccidity and stomatal closure.
o Water stress or the hormone abscisic acid (ABA) can also trigger stomatal closure
by inhibiting the proton pump.
Study Questions:
What provides the “push” and what provides the “pull” for the movement of sap against gravity?
What happens to Ψp in relation to sucrose concentration?

3
Why does a maple leaf drying provide negative pressure to move water?
How do solutes move in the apoplast in phloem loading? Where is pressure the highest?
How is active transport involved in phloem loading?

4
Plant Nutrition
• Autotrophs:
o Plants are autotrophs, meaning they are capable of producing their own food.
o They are nourished by simple molecules drawn from their environment.
o Key processes for plant nutrition include photosynthesis and respiration.
o Photosynthesis is the process by which plants form carbohydrates from carbon
dioxide (CO2) and water (H2O) using energy from the sun.
o Respiration involves breaking down carbohydrates to release energy for various
cellular processes.
o Plants also use carbohydrates to produce cellulose, a component of cell walls.
• Carbon, Hydrogen, and Oxygen:
o Plants obtain carbon (C), hydrogen (H), and oxygen (O) directly from the
environment.
o Carbon dioxide (CO2) is taken from the atmosphere.
o Hydrogen and oxygen are sourced from soil water and transpired from leaves.
• Mineral Elements:
o Besides carbon, hydrogen, and oxygen, plants require various mineral elements
for normal growth and development.
o These mineral elements are often referred to as "mineral nutrients."
o Elemental analysis reveals that herbaceous plants contain approximately 80-85%
water (fresh weight) and 95% carbohydrates (dry weight).
• Cell Wall:
o The plant cell wall is primarily composed of carbohydrates and provides
structural support to the plant.
• Mineral Deficiency Symptoms:
o Inadequate availability of a particular mineral element can lead to characteristic
symptoms in plants.
o For example, magnesium (Mg) deficiency can cause yellowing of the leaf tissue
between veins.
o Understanding these symptoms is valuable for guiding soil amendments and
correcting deficiencies.
• Parasitism:
o Some plants, known as parasitic plants, establish a parasitic relationship with
other plants.
o The roots of parasitic plants grow into host plants and extract nutrients.
o Parasitic plants may or may not be photosynthetic.
o They extract sugars and mineral elements from the host plant, affecting its health.

5
• Nitrogen:
o Nitrogen (N) is often the most limiting mineral element for plant growth.
o Although atmospheric nitrogen (N2) is abundant (comprising 78% of the
atmosphere), plants cannot directly utilize it due to the N2 bond.
o Nitrate ions (NO3-) in the soil are a usable source of nitrogen for plants, provided
by nitrogen-fixing bacteria.
• Nitrogen Cycle:
o The nitrogen cycle involves the conversion of atmospheric N2 to forms that can
be used by plants.
o Nitrogen-fixing bacteria, such as Rhizobium, play a crucial role in this process.
o They convert N2 into ammonium (NH4+), which is accessible to plants.
o In return, plants provide carbohydrates to the nitrogen-fixing bacteria.
• Adaptations to Ensure Sufficient Nitrogen:
o Some plant adaptations help ensure sufficient nitrogen:
o In bogs, plants adapt to low nitrogen availability in acid soil.
o Some carnivorous plants, such as the Venus flytrap and sundew, obtain nitrogen
from capturing and digesting insects.
o Certain angiosperms, such as legumes (peas, beans, alfalfa, clover), form
symbiotic relationships with nitrogen-fixing bacteria (Rhizobium) to obtain
nitrogen.
o These adaptations allow plants to thrive in nitrogen-deficient environments.

6
Plant Development and Hormones
• Special Feature of Plants: Dynamic Architecture
o Unlike animals, plants exhibit indeterminate growth and continuously develop
throughout their lives.
o They respond to internal and external cues to adapt their growth and form.
• Germination
o The process by which a seed develops into a seedling.
o Triggered by external cues such as water, light, fire, mechanical breakdown of the
seed coat, or chilling (stratification).
o Germination involves the activation of the dormant embryo within the seed.
• Seed Structure
o Seeds contain an embryo, which includes the root and shoot apical meristems.
o They can have one or two cotyledons (seed leaves).
o Stored food reserves are found in cotyledons or endosperm.
o The embryo is in a dormant state until germination.
• Germination Process
o The first trigger for germination is often water imbibition.
o Water activates the embryo.
o The embryo produces gibberellin (GA), a hormone.
o GA stimulates aleurone cells to produce a-amylase, an enzyme that digests starch
into sugars.
o Sugars support the growth of the seedling.
• How Gibberellin Works
o GA enters aleurone cells, where it activates the transcription of the a-amylase
gene.
o This transcriptional activation is achieved through signal transduction, including
the removal of a repressor.
• Plant Hormones
o Small molecules that regulate growth, coordinate physiological processes, and
mediate responses to the environment.
o Effective at very low concentrations and can work in various tissues and organs.
o Examples include gibberellin (GA), auxin, cytokinin, abscisic acid (ABA), and
ethylene.
• Auxin
o The first plant hormone discovered.
o Involved in phototropism and apical dominance.
o Auxin is responsible for stem elongation and root formation.
o It plays a role in suppressing axillary bud growth close to the terminal bud.
o It moves through polar transport within the plant.

7
• Cytokinin
o Promotes branching and lateral shoot formation.
o Counteracts the inhibitory effects of auxin on axillary buds.
• Abscisic Acid (ABA)
o A plant hormone that plays a crucial role in water stress responses.
o It induces stomatal closure and leads to dormancy in seeds and winter buds.
• Ethylene
o A gaseous plant hormone involved in fruit ripening, leaf senescence, and leaf
abscission.
• External Cues: Light
o Light energy is essential for photosynthesis and serves as an external cue for plant
responses.
o Light can trigger flowering and is required for seed germination in many plant
species.
▪ Short-day and long-day plants
▪ Critical daylength threshold must be crossed to switch on the flowering
growth. The kind of plant influences response (days must be
shorter/longer than critical daylength for which kind of plant?)
o Light is absorbed by pigments, such as chlorophyll and phytochrome.
▪ Phytochrome has two states, Pf and Pfr, named for what INACTIVATES
them. Pr is inactivated by red light, turning it to the Pfr state, the active
state (causes growth).
▪ Pfr is inactivated by far red light, which is what occurs as the days begin
to shorten.
▪ Phototropin absorbs blue light, telling the plant it needs to undergo an
auxin-induced change to “find” the nearest light source.
• Polar transport and IAA involved.

7
• Cytokinin
o Promotes branching and lateral shoot formation.
o Counteracts the inhibitory effects of auxin on axillary buds.
• Abscisic Acid (ABA)
o A plant hormone that plays a crucial role in water stress responses.
o It induces stomatal closure and leads to dormancy in seeds and winter buds.
• Ethylene
o A gaseous plant hormone involved in fruit ripening, leaf senescence, and leaf
abscission.
• External Cues: Light
o Light energy is essential for photosynthesis and serves as an external cue for plant
responses.
o Light can trigger flowering and is required for seed germination in many plant
species.
▪ Short-day and long-day plants
▪ Critical daylength threshold must be crossed to switch on the flowering
growth. The kind of plant influences response (days must be
shorter/longer than critical daylength for which kind of plant?)
o Light is absorbed by pigments, such as chlorophyll and phytochrome.
▪ Phytochrome has two states, Pf and Pfr, named for what INACTIVATES
them. Pr is inactivated by red light, turning it to the Pfr state, the active
state (causes growth).
▪ Pfr is inactivated by far red light, which is what occurs as the days begin
to shorten.
▪ Phototropin absorbs blue light, telling the plant it needs to undergo an
auxin-induced change to “find” the nearest light source.
• Polar transport and IAA involved.

8
Flowers and Control of Flowering:
• Floral Components
o Sepals
▪ Most leaflike. Poinsettias’ big red petals are actually these, not petals!
▪ Protect flower bud
o Petals
▪ Attract pollinators
o Stamen
▪ Produces pollen from the Anther
o Pistil
▪ Bears ovules in single structures called carpels
▪ Ovules produce embryo sac
o Carpal
▪ A singular reproductive organ structure
▪ Stigma: landing for pollen
▪ Style: tube for pollen tubes to traverse down
▪ Contains the ovary and ovule
o Floral organs arranged in whorls
• Pollination
o Pollen recognition at stigma
▪ If not compatible, pollen does nothing
▪ If compatible, pollen germinates
▪ Forms pollen tube, which grows through style
▪ Reaches the ovary and the ovules
▪ Releases sperm into embryo sac
• Endosperm
o 3N triploid: 1N from sperm + 2 x 1N from polar nuclei
o Forms nutritious tissue for the single cell embryo’s development.
o As embryo becomes mature, loses water, causing dormancy
o Embryo produces gibberellin (a hormone, GA) when it contacts water
▪ GA diffuses throughout seed, eventually targeting aleurone
▪ Aleurone cells then produce alpha-amylase
▪ Alpha-amylase (some of this is in your mouth right now) digests sugars,
which allows the embryo to begin to digest the nutritious endosperm
“sink.”

9
Homeostasis
• Textbook Def: Homeostasis is the stability of the internal environment of an individual,
such as a constant body temp and the physiological or behavioral feedback responses that
maintain that stability.
• Organisms need to maintain a stabler internal environment.
• Enzymes are greatly influenced by temperature.
• Some extreme environments also affect how animals achieve
thermoregulation (arctic, desert, salt water, rain forests)
• Requires energy!
• Homeostasis Parameters
• Temp (thermoregulation)
• pH, more specifically blood pH.
• Blood glucose
• BP
• Heart and Respers
• Behavioral feedback responses
• [O2]
• [CO2]
• [Na+]
• [Ca2+]
• Thermoregulation
• Daily and seasonal temp variations can be very dramatic, especially in some
ecosystems
• Temp affects enzyme reactions (catalyzed and uncatalyzed)
• Effects on these reactions are variable, coordinating metabolism can be hard
• Examples of Temp. Regulation
• These are examples of feedback loops
• Blood vessels
▪ Heat conserved when the body is cold, surface veins are constricted
(vasoconstriction).
▪ Heat leaves the body when the surface veins are dilated, vasodilation.
• Q10 Temperature Coefficient
• Sensitivity of some physiological processes within a 10 degree (Celsius) range
of temperature. Essentially, how much do they change.
• Q10 = (RT)/(RT-10)
• Q10 = 3 means the rate triples at a 10 degree C rise.
• Q10 = 2 means it doubles with each 10 degree rise in temp.
• Q10 = 1 means it is not temperature sensitive.
• Homeotherms vs Poikilotherms

10
• Homeotherms: same temperature. Animals the keep a steady internal body
temperature.
• Mammals: Brown vs white adipose tissue.
• White stores triglycerides in most forms of body fat. Glucose can be
converted to triglycerides.
• Brown adipose tissue: often in the upper back and shoulder regions. ONLY
for heat production. Non-shivering thermogenesis. Human adults often don't
have brown fat.
• Insects: only some species; usually only at certain times, such as a bee flying.
Muscles generate heat when it's flying.
• Increases metabolic rate as the temperature deviates from the thermo-neutral
zone (TNZ) where external temp does not affect metabolic rate.
• REGULATORS
• Poikilotherms: variable temperature. Animals that vary their body temperature
along with the environment.
• Most other animals, frogs, lizards, fish
• CONFORMERS
• For both: metabolic rate increases as external temperature rises.
• Extreme examples:
▪ Antarctic fish: possess antifreeze proteins to regulate the extreme temps
around Antarctica
▪ Wood frogs: essentially freeze, but remain alive. Metabolism rate ~ 0.
▪ Tardigrades: cockroaches of the microbe world. They just live.
• Endotherm: an animal that gets heat from its own internal sources
• Ectotherm: obtains heat from external environment, has to move to regulate its heat and
warmth.
• Ex: a lizard makes an underground burrow. The temperature of the lizard
fluctuates around a set point, as it will lay in the sun on a basking rock until
it's too hot, then it will come back into the burrow to cool.
• Small- vs Large-bodied Options
• Behavioral: Small animals have more options to regulate thermal activity.
• Includes locating and moving to microenvironments and microclimates.
• Clothing is a behavioral response to temperature.
• A mouse hiding in a wall is a response to cold temperatures.
• Structural and Physiological: Larger animals rely more on these
• Fat, developing structures like dens
• Adaptions like hair, countercurrent mechanisms
• Sweating and panting

10
• Homeotherms: same temperature. Animals the keep a steady internal body
temperature.
• Mammals: Brown vs white adipose tissue.
• White stores triglycerides in most forms of body fat. Glucose can be
converted to triglycerides.
• Brown adipose tissue: often in the upper back and shoulder regions. ONLY
for heat production. Non-shivering thermogenesis. Human adults often don't
have brown fat.
• Insects: only some species; usually only at certain times, such as a bee flying.
Muscles generate heat when it's flying.
• Increases metabolic rate as the temperature deviates from the thermo-neutral
zone (TNZ) where external temp does not affect metabolic rate.
• REGULATORS
• Poikilotherms: variable temperature. Animals that vary their body temperature
along with the environment.
• Most other animals, frogs, lizards, fish
• CONFORMERS
• For both: metabolic rate increases as external temperature rises.
• Extreme examples:
▪ Antarctic fish: possess antifreeze proteins to regulate the extreme temps
around Antarctica
▪ Wood frogs: essentially freeze, but remain alive. Metabolism rate ~ 0.
▪ Tardigrades: cockroaches of the microbe world. They just live.
• Endotherm: an animal that gets heat from its own internal sources
• Ectotherm: obtains heat from external environment, has to move to regulate its heat and
warmth.
• Ex: a lizard makes an underground burrow. The temperature of the lizard
fluctuates around a set point, as it will lay in the sun on a basking rock until
it's too hot, then it will come back into the burrow to cool.
• Small- vs Large-bodied Options
• Behavioral: Small animals have more options to regulate thermal activity.
• Includes locating and moving to microenvironments and microclimates.
• Clothing is a behavioral response to temperature.
• A mouse hiding in a wall is a response to cold temperatures.
• Structural and Physiological: Larger animals rely more on these
• Fat, developing structures like dens
• Adaptions like hair, countercurrent mechanisms
• Sweating and panting

11
• Microenvironments
• Environments within a larger habitat that contains different conditions can
have different microclimates.
• Ex: snow, shade, sun rocks, root systems like mangroves, thermoclines like
with depth changes in the ocean.
• Countercurrent Heat Exchange Mechanism (CHEM)
• Two currents flowing in opposite directions.
• Not concurrent. Concurrent means the same direction.
• Literally a liquid cooling system.
▪ Ex: two veins in a bird's leg pass along warmth as the arteries pump away
from the warmer core of the bird, and the vein receives warmer blood.
This way, the body cavity does not have to adjust the heat.
▪ Ex2: In Grant's gazelle, the veins provide countercurrent exchange of heat
to keep the brain cool.
• Other Adaptations
• Surface area: fennec fox ears help dissipate the heat to keep itself cool.
• Hibernation: State with low body temp, almost conforming to outside
temperature. Many small animals hibernate in protective environments during
resource-scarce periods of time.
• Heterotherms: Homeotherms that hibernate in winter.
• Bears go into a state of torpor, not hibernation. You can wake them up easily.
• Heterotrophic Metabolism
• Cell Metabolism in Heterotrophs
• Cells need to break down to rebuild 2-3% of its protein molecules every day.
Each cell uses 10^14 ATP molecules every day.
• Know mechanisms that allow for acquiring food for energy production.
• Ex: Food Web of Energy from Yellowstone
• Feedback Regulation
• Negative: Stressor causes deviation from a set point or range. Our physiology
will send us back to that state. Stabilizes system.
• Positive: Reinforces the feedback. Speeds up or amplifies process/change that
is occurring. Not typically involved in homeostasis. Some event may cause
feedback to stop.
▪ Ex: Mammal birth.

12
• Feedforward Regulation: Stimulus is not a downstream product of
process/pathway.
▪ Ex: lactose effect on lac operon. Without lactose, transcription and
translation do not occur. With lactose or allolactose, receptor is freed.
Polymerase can now transcribe those genes. Now, lactose can be broken
down.
▪ Lactose and Allolactose are allosteric inhibitors. Removes the repressor
from a gene by repressing the repressors.

13
Muscles
• Definition: Muscles are contractile tissues found only in animals, responsible for
generating force and movement. They convert chemical energy (ATP) into mechanical
energy.
• Significance: Muscles play crucial roles in various physiological functions such as
locomotion, maintaining posture, supporting organs, and regulating bodily processes like
digestion and blood circulation.
Terms Associated with Muscles:
• Endoskeleton: An internal skeleton composed of bone or cartilage found in vertebrates. It
provides structural support and serves as attachment points for muscles.
• Exoskeleton: A rigid external skeleton found in arthropods and some other invertebrates.
It protects the body and provides attachment sites for muscles.
• Bone: A hard, mineralized connective tissue primarily composed of collagen and calcium
phosphate. Bones provide support, protection, and serve as anchoring points for muscles.
• Cartilage: A flexible connective tissue with a firm consistency. It provides cushioning
between bones, flexibility, and support.
• Joints: Points of articulation between bones where movement occurs. Muscles attach to
bones across joints, allowing movement.
• Tendons: Tough, fibrous connective tissues that attach muscles to bones. Tendons
transmit the force generated by muscles to bones, facilitating movement.
Types of Muscles:
Skeletal Muscles:
• Attached to bones via tendons and are under voluntary control.
• Composed of long, multinucleated muscle fibers.
• Contractile units called sarcomeres contain actin and myosin filaments arranged in a
striated pattern.
• Skeletal muscles produce movement by pulling on bones when they contract.
Cardiac Muscle:
• Found exclusively in the heart and responsible for involuntary contractions that pump
blood throughout the body.
• Cardiac muscle cells are branched, interconnected, and contain intercalated discs.

14
• Contraction of cardiac muscle is rhythmic and coordinated to maintain blood circulation.
Smooth Muscle:
• Found in the walls of hollow organs, blood vessels, and other structures.
• Smooth muscle cells are spindle-shaped and lack striations.
• Contraction of smooth muscle is involuntary and is involved in processes like digestion,
blood vessel constriction, and peristalsis.
Skeletal Muscle Structure and Function:
• Muscle Fibers: Skeletal muscles are composed of bundles of muscle fibers, each
containing multiple myofibrils.
• Myofibrils: Long cylindrical structures within muscle fibers, consisting of repeating
sarcomeres.
• Sarcomere: The basic contractile unit of muscle, containing overlapping actin and myosin
filaments.
• Sliding Filament Theory: Describes how actin filaments slide past myosin filaments
during muscle contraction, shortening the sarcomere.
Initiation and Regulation of Muscle Contraction:
• Neuromuscular Junction: The site where motor neurons synapse with muscle fibers,
releasing neurotransmitters that trigger muscle contraction.
• Excitation-Contraction Coupling: The process by which electrical signals from motor
neurons initiate muscle contraction by triggering the release of calcium ions from the
sarcoplasmic reticulum.
Muscle Fiber Types and Metabolism:
• Fiber Types: Skeletal muscle fibers can be classified into slow-twitch (type I), fast-twitch
oxidative (type IIa), and fast-twitch glycolytic (type IIb) fibers based on their contraction
speed and metabolic characteristics.
• Metabolism: Skeletal muscles rely on ATP for energy, which is generated through three
main pathways: immediate (phosphagen) system, anaerobic glycolysis, and aerobic
metabolism (oxidative phosphorylation).
Sample Study Questions:

15
Define muscles and explain their importance in animal physiology, providing examples of their
diverse functions.
Compare and contrast endoskeletons and exoskeletons, discussing their structural differences and
roles in supporting muscles.
Describe the structure and function of skeletal muscles, including the organization of muscle
fibers and the role of sarcomeres in contraction.
Explain the sliding filament theory of muscle contraction, detailing the interactions between
actin and myosin filaments.
Discuss the neuromuscular junction and the sequence of events leading to muscle contraction,
from nerve impulse to calcium release.
Differentiate between slow-twitch, fast-twitch oxidative, and fast-twitch glycolytic muscle fibers,
including their metabolic properties and functional differences.
Analyze the metabolic pathways involved in ATP production for muscle contraction, and explain
how they vary depending on the intensity and duration of activity.
Outline the regulation of muscle contraction, including the role of calcium ions, troponin, and
tropomyosin in controlling actin-myosin interactions.
Describe the unique characteristics and functions of cardiac and smooth muscles, and explain
why they are considered involuntary.
Discuss the adaptations of muscle types found in invertebrates, such as catch muscles,
asynchronous flight muscles, and hydrostatic skeletons, and their significance in various
organisms' physiology.

16
Neurons
Sensory Input:
• Involves gathering information from sensory receptors located throughout the body, such
as touch, taste, smell, sight, and hearing.
Integration:
• Processing and interpretation of sensory input to produce appropriate responses. It
involves activities like thoughts, memories, decisions, and sensation.
Motor Output:
• Response to sensory input by activating effector organs (muscles or glands) to produce a
specific response.
Neuron Structures:
• Cell Body: Contains the nucleus and organelles responsible for maintaining the neuron's
metabolic functions.
• Dendrites: Branch-like extensions that receive signals from other neurons or sensory
receptors.
• Axon: A long, slender projection that conducts electrical impulses away from the cell
body.
• Axon Terminals: Structures at the end of the axon that release neurotransmitters to
communicate with other neurons or target cells.
Resting Membrane Potential:
• The electrical potential difference across the cell membrane of a neuron when it is at rest.
• Maintained by the unequal distribution of ions (such as Na+ and K+) across the
membrane.
• Negative inside the cell compared to the outside, typically around -70 millivolts (mV).
Membrane Channels:
• Gated Channels: Protein channels in the cell membrane that open or close in response to
specific signals.
• Ligand-Gated Channels: Open in response to the binding of a specific molecule (ligand).
• Voltage-Gated Channels: Open or close in response to changes in membrane potential.
Graded Potentials:

17
• Short-lived changes in membrane potential that vary in strength and decay over distance.
• Occur in response to the opening of ligand-gated ion channels.
• Can be excitatory (depolarizing) or inhibitory (hyperpolarizing).
• Initiate action potentials through summation.
Action Potentials:
• Brief, rapid changes in membrane potential that propagate along the axon.
• Consist of depolarization, repolarization, and hyperpolarization phases.
• All-or-none response that does not weaken with distance.
Saltatory Conduction:
• Rapid propagation of action potentials along myelinated axons.
• Action potentials "jump" from one node of Ranvier to the next, increasing conduction
velocity.
• Allows for efficient transmission of nerve impulses over long distances.
Sample Study Questions:
Define the basic functions of the nervous system and provide examples of each.
Describe the structures of a neuron, including the cell body, dendrites, axon, and axon terminals.
Explain the process of sensory input and how it is integrated within the nervous system.
Discuss the role of membrane channels in generating and propagating electrical signals in
neurons.
Compare and contrast graded potentials and action potentials, including their characteristics and
functions.
Outline the phases of an action potential and their significance in neuronal communication.

18
Explain how graded potentials can lead to the initiation of an action potential through
summation.
Define resting membrane potential and discuss the factors that contribute to its establishment.
Describe the phenomenon of saltatory conduction and its importance in speeding up nerve
impulse transmission.
Discuss the significance of neurotransmitters and synaptic transmission in neuronal
communication, including how action potentials trigger the release of neurotransmitters at

19
Sensory Systems
• Animals rely on sensory information to navigate their environment, locate resources,
detect danger, and communicate with others.
• Sensory systems have evolved to perceive various stimuli, both internal and external,
enabling animals to interact effectively with their surroundings.
Types of Sensory Modalities:
• Visual Sensation: Perception of light wavelengths, shapes, and patterns.
• Auditory Sensation: Detection and interpretation of sound waves and vibrations.
• Olfactory Sensation: Recognition of chemical substances through smell.
• Gustatory Sensation: Perception of different tastes, such as sweet, sour, salty, bitter, and
umami.
• Tactile Sensation: Sensory input related to touch, pressure, texture, and vibration.
• Temperature Sensation: Detection of temperature changes, including hot and cold stimuli.
Transduction Mechanisms in Receptor Cells:
• Transduction Process: Conversion of sensory stimuli into electrical signals that can be
processed by the nervous system.
• Receptor cells contain specialized proteins that initiate transduction by converting
specific stimuli into electrical signals.
• Graded potentials, proportional to the intensity of the stimulus, are generated in response
to sensory input.
Transmission and Interpretation of Sensory Signals:
• Action potentials are initiated in sensory neurons and transmitted to the central nervous
system (CNS) for integration and interpretation.
• Sensory information is relayed to appropriate processing regions in the brain, where it is
analyzed, interpreted, and translated into meaningful perceptions.
Types of Receptor Proteins:
• Ionotropic Receptors: Integral membrane proteins that function as ion channels, directly
allowing ions to flow across the cell membrane in response to specific stimuli.
• Metabotropic Receptors: Receptor proteins coupled to intracellular signaling pathways,
activating secondary messenger systems that modulate ion channels and cellular
responses.

20
Specific Sensory Systems:
• Stretch Receptors: Mechanoreceptors sensitive to changes in muscle length and tension,
contributing to proprioception and motor control.
• Olfactory System: Detection of odorants through chemoreceptor cells in the olfactory
epithelium, which contain specific odorant receptor proteins.
• Auditory System: Perception of sound waves through mechanoreceptor cells in the inner
ear, where vibrations are converted into electrical signals.
• Visual System: Reception of light stimuli by photoreceptor cells in the retina, containing
opsin proteins that respond to different wavelengths of light.
• Arthropod Vision: Compound eyes composed of ommatidia, each housing photoreceptor
cells and a lens, enabling rapid detection of motion and changes in the environment.
Sensory Systems Humans Cannot Use:
• Some animals possess sensory abilities beyond human perception, such as detecting
electromagnetic wavelengths beyond the visible spectrum or perceiving electric fields.
Sample Study Questions:
Explain the process of transduction in sensory receptor cells, including the role of graded
potentials.
Discuss the transmission pathway of sensory signals from receptor cells to the central nervous
system and their interpretation in the brain.
Compare and contrast ionotropic and metabotropic receptor proteins, providing examples of
each.
Describe the structure and function of stretch receptors and their significance in proprioception.
How does the olfactory system function in detecting and processing odorants, and what role do
chemoreceptor cells play?

21
Outline the auditory pathway in humans, including the structures involved in sound detection and
signal transduction.
Explain how photoreceptor cells in the retina contribute to vision, detailing the types of opsins
involved and their response to light stimuli.
Compare the visual systems of humans and arthropods, highlighting differences in eye structure
and function.
Provide examples of sensory systems that humans cannot use and discuss their significance in
animal behavior and ecology.
Discuss the evolutionary advantages of possessing diverse sensory modalities in animals,
considering their ecological roles and survival strategies

21
Outline the auditory pathway in humans, including the structures involved in sound detection and
signal transduction.
Explain how photoreceptor cells in the retina contribute to vision, detailing the types of opsins
involved and their response to light stimuli.
Compare the visual systems of humans and arthropods, highlighting differences in eye structure
and function.
Provide examples of sensory systems that humans cannot use and discuss their significance in
animal behavior and ecology.