Basic principles of animal form + function Lecture 13

Question 1

Distinguish between anatomy and physiology.

Answer 1

Anatomy: the study of an organism’s physical structure (form).

Physiology: the study of how the physical structures in an
organism function.

—> Biologists who study anatomy and physiology are essentially studying adaptations.

Question 2

Define adaptation and explain how adaptations occur via natural selection.

Answer 2

• Adaptation: a heritable trait that allows individuals to survive and reproduce in a certain environment better than individuals who lack the trait.
• Adaptations occur from evolution by natural selection.
• Natural selection occurs when individuals that carry certain alleles leave more offspring than individuals with different alleles of the same gene.
• Difference in reproductive success —> increase frequency of selected alleles from one generation to the next —-> evolution of a given trait.

Question 3

• Explain why no adaptation is perfect (hint: your answer must address historical and genetic constraints and trade-offs). *

Answer 3

1. Adaptations are limited by the nature of traits that already exist.
   • Evolution adds onto or modifies what already exists.
   • Example:
   • Human spine is a highly modified form of a vertebral column that evolved from an ancestor that walked on all fours.
   • Allows us to stand upright, but it is far from perfect for this purpose.
2. Adaptations are limited by the alleles that are present in a population.
   • Natural selection selects the best of the available variations in a population.
   If a particular variation (allele) is not available, natural selection cannot act on it.
   • In order for the human spine to become more optimal, alleles would have to exist that allow for this improvement.
3. All animals face trade-offs.
   • Inescapable compromises between traits.

• Trade-offs involve compromises.
• Desert animals that sweat to cool off face dehydration.
• Eagles beak good for tearing meat, but not so good for weaving nest materials.
• Key points:
• If a structure is adaptive, its likely that its size, shape, and
composition correlates with its function.
—> In studying anatomy (form) and physiology (function), biologists are therefore studying adaptations.
• No adaptation is perfect due to constraints (historical + genetic) and trade-offs…and the laws of physics!

Question 4

Explain how physical laws constrain body size and shape.

Answer 4

• The laws of physics that govern strength, diffusion,
movement, and heat exchange all limit the possible
range of animal forms.
• Impose constraints on the range of possible animal sizes and shapes

• As body dimensions increase:
• A thicker skeleton is required to maintain adequate
strength + support.
• Applies to both endoskeletons and exoskeletons
• Muscles required for locomotion must represent an
increasing fraction of the total body mass
• At a certain size, mobility becomes limited.
• A large animal has very different body proportions
than a smaller animals.
• A mouse scaled up to the size of an elephant with its body proportions would not be able to support its body weight!
• Posture also differs.
• Elephant’s legs are held in a more upright position.
• Erect posture supports more body weight than the crouched position of the mouse.
• However, the elephant is less agile than the mouse, which has a much more maneuverable body design

• Another example: 
• Laws of hydrodynamics constrain the 
shapes that are possible for aquatic 
organisms that swim fast. 
• Water is 1000X more dense than air. 
• Any bump on body surface impedes a 
swimmer more than a runner or flyer. 
---> Leads to fusiform shape that minimizes 
drag through water.

Question 5

Explain how the size and shape of an animal’s body affect its interactions with the environment (hint: think surface-area-to-volume ratio).

Answer 5

• Rate of exchange of material across a plasma membrane is proportional to the membrane’s surface area.
• However: The rate at which nutrients are used and waste products are produced depends on the volume of the cell.
• i.e. the amount of material that must be exchanged to sustain the life of the cell is proportional to volume.

As an organism grows larger, volume increases much faster than surface area

• Imposes an upper limit on cell size –> SA:V ratio is one of the physical constraints on the size of single celled organisms.
• Beyond this upper limit, there is not enough surface area to service the entire volume of the cytoplasm.

A multicellular animal is composed of many cells, each with its own plasma membrane across which exchange can occur.
• A multicellular organisation therefore only works if all cells have access to an aqueous environment, either inside, or outside of the animal’s body.
• Many animals have body plans that enable direct exchange between almost all cells in their bodies and the external environment. ex. tape worm, jellies

Question 6

Explain how complex organisms are able to carryout sufficient exchange to support their metabolism (i.e. what adaptations do they exhibit?). Provide specific examples to support your answer.

Answer 6

• Evolutionary adaptation: Extensively folded or branched internal surfaces.
• Typically lie within the body, where they are protected from abrasion and desiccation, but are connected to the external environment via openings on the body surface (e.g., mouth, spiracles).
• Internal body fluids + circulatory fluids link exchange surfaces to body’s cells.

Examples:

1) Highly branched structures- Capillaries
2) Flattened structures- Lamellea
3) Folding surfaces with projections- Lining of small intestine, showing villi

Question 7

Define metabolic rate and basal metabolic rate.

Answer 7

• Metabolic rate: amount of energy an animal uses per unit of time.
• Sum of all the energy-requiring biochemical reactions that occur during a given time interval.
• Energy is measured in joules, or in calories (cal) or kilocalories (kcal).
• Energy consumption in animals depends largely on aerobic respiration - metabolic rate often measured indirectly in terms of oxygen consumption (mL O2/hr)
• Basal metabolic rate: rate at which an animal consumes oxygen while at rest, on an empty stomach, under normal temperature and moisture conditions, and experiencing no stress.
• Measure of the minimal metabolic rates that power the basic functions that support life, such as cell maintenance, breathing, and heartbeat.

Question 8

Describe the relationship between body size and basal metabolic rate, and body size and mass-specific basal metabolic rate.

Answer 8

• Larger animals have more body mass and therefore require more chemical energy (i.e. an elephant consumes way more oxygen per hour than a mouse does).
• HOWEVER, on a gram per gram basis, small animals have much higher BMRs than large animals do.
• i.e. a gram of elephant tissue consumes much less energy than a gram of mouse tissue.

Question 9

Provide two hypotheses for the observed inverse relationship between mass-specific basal metabolic rate and body size

Answer 9

• Leading hypothesis:
• As the size of an organism increases, its mass-specific BMR must decrease or the SA available for exchange will fail to keep up with metabolic demands of the organism.
• Small animals can “live fast” (mature sooner, produce more offspring faster), but must eat more food per gram of tissue than a large animal.
• As body size increases, less energy cost per gram of tissue, but must “live slow”; also, larger fraction of body required for exchange.

2nd hypothesis
• Smaller animals require a higher metabolic rate to maintain a stable body temperature.
• The smaller the animal, the higher its surface-to-volume ratio —> greater heat loss.
• However, this hypothesis only applies to organisms that use their metabolism to maintain body temperature!
• Inverse relationship also observed in ectotherms.

Question 10

Define tissue.

Answer 10

groups of cells that function as a unit.

Question 11

Epithelial Tissue

Answer 11

1) Epithelial tissue
• Covers the outside of the body and lines the surfaces of organs within the body.
• Provides protection against mechanical injury and infection, and regulates the transfer of heat and substances between the interior and exterior of the body.
• Occurs as sheets of cells that are closely joined and often are riveted together by tight junctions.
• Some form glands – groups of cells that secrete chemical solutions.
• Has apical and basolateral surfaces that differ in
structure and function.

Question 12

Connective Tissue and differentiate between 6 types of connective tissue

Answer 12

• Consists of sparse population of cells scattered through an ECM that is secreted by the connective tissue cells
themselves.
• Matrix can be liquid, jellylike, or solid.
• Each type of connective tissue secretes a distinct type of ECM –>structure and function varies widely.
• In general, connective tissue functions to bind and support other tissues

1. Loose connective tissue binds epithelia to underlying tissues and functions as packing material, holding organs in place.
2. Adipose tissue is a specialized form of loose connective
   tissue that stores fat in adipose cells; functions in
   cushioning, insulation, and fuel storage.
3. Fibrous connective tissue has a large number of collagenous fibers organized into parallel bundles, maximizing nonelastic strength.
   • Tendons attach muscles to bones.
   • Ligaments join bones to bones at joints.
4. Cartilage has an abundance of collagenous fibers in a rubbery matrix, making it a strong yet flexible support material.
5. Bone is a mineralized connective tissue.

6.Blood has cells surrounded by a liquid ECM called plasma.
• Liquid matrix enables rapid transport of blood cells,
nutrients, and wastes.
• Erythrocytes (red blood cells) – oxygen transport.
• Leukocytes (white blood cells) – defense.
• Platelets (cell fragments) – clotting.

Question 13

Muscle Tissue and differentiate between the 3 different types of muscle tissues

Answer 13

• Long cells (muscle fibers) containing actin
and myosin; enable muscle cells to contract
when stimulated by nerve impulses.
1. Skeletal muscle
• Attached to bones by tendons.
• Striped (striated) appearance.
• Voluntary movements.
2. Cardiac muscle
• Contractile walls of the heart.
• Striated like skeletal muscle, but also branch and
interconnect via intercalated disks
• Unconscious contraction of the heart.
3. Smooth muscle
• Walls of the digestive tract, urinary bladder, arteries,
and other internal organs.
• Lacks striations, spindle-shaped.
• Involuntary body activities, including churning of the
stomach and constriction of arteries.

Question 14

Describe the functional unit of nervous tissue.

Answer 14

The functional unit= neuron
Consists of a cell body with two more processes, dendrites and axons
-dendrites transmit impulses from their tips towards the rest of the neuron
-axons transmit toward another neuron or an effector (muscle cells that carries out a body response)

Question 15

Nervous Tissue

Answer 15

Nervous tissue senses stimuli and transmits

signals from one part of the animal to another.

Question 16

Define organ.

Answer 16

structures that serve a specialized function and that consist of several types of tissues.

Question 17

Explain why any organism is more than “just a collection of individual cells, tissues, and organs” (or a “sac of cells”).

Answer 17

• System: consists of several organs and tissues that
work together to carry-out one or more specific functions.
• Each system accomplishes a specific task for survival and reproduction and each works in conjunction with other systems.
• Efforts of all systems must be coordinated for the animal to survive.

Question 18

Compare and contrast the nervous and endocrine systems.

Answer 18

Notes

Question 19

Define homeostasis.

Answer 19

• Homeostasis is the maintenance of relatively constant
chemical and physical conditions in animal’s cells,
tissues, and organs.
• No matter the size, shape, complexity or lifestyle of an animal, it must be able to control its internal environment.
• Internal conditions may vary as an animal’s environment changes; however, they are always kept within a tolerable range.

Question 20

Differentiate between conformational homeostasis and regulatory homeostasis. Explain how an animal may be both a regulator and a conformer.

Answer 20

1. Conformational homeostasis occurs in animals that conform to their surroundings, which themselves are fairly stable.
   • e.g., Antarctic cod body temperature matches that of surrounding water at -1.9C.
2. Regulatory homeostasis requires a mechanism that adjusts the internal state to keep it near a specific value.
   • These adjustments keep the internal state within certain limits no matter what the external conditions.

• An animal may maintain homeostasis by regulating some internal conditions and allowing others to conform to the environment.
• e.g., Most freshwater fishes regulate their internal solute concentration but allow their internal temperature to conform to external water temperature.

Question 21

Explain why homeostasis is important.

Answer 21

• Why is homeostasis so important?
• Maintains internal body conditions (i.e., temperature, pH, solute concentrations…etc.) at a level that allows the molecules, cells, tissues, and organs to function at an optimal level.
Examples from BIO111?
• e.g., Several factors, including temperature and pH, can influence the structure and function of enzymes; most enzymes function within a very narrow range of conditions.
• e.g., Temperature affects membrane permeability and thus the rate of diffusion. (as warm up membrane becomes more fluid and therefore more permeable)

Question 22

Explain how the regulatory systems of animals achieve homeostasis through negative feedback (hint: your answer should describe the 3 functional components of a homeostatic control system). Include a diagram.

Answer 22

• Homeostatic systems are largely based on negative
feedback.
• Negative feedback occurs when effectors reduce or oppose a change in internal conditions.
• Example: a rise in blood pH would trigger effectors that reduces the rise in pH.

• To achieve homeostasis, animals needs a system that:

1) Measures the level of a given variable.
2) Adjusts the level accordingly.

• Regulatory systems constantly monitor internal conditions.
• Each variable (e.g., pH, temperature…etc.) has a set point – a normal or target value or range.
• Fluctuations in the variable above or below the set point serve as the stimulus – detected by a sensor.
• An integrator evaluates the incoming sensory information.
• If necessary triggers a response in an effector, a structure that helps return the variable to the set point.

Question 23

Differentiate between negative feedback and positive feedback mechanisms.
Which type of mechanism contributes to homeostasis?

Answer 23

• Homeostatic systems are largely based on negative
feedback.
• Negative feedback occurs when effectors reduce or oppose a change in internal conditions.
• Example: a rise in blood pH would trigger effectors that reduces the rise in pH.

• Positive feedback involves a change in some variable that triggers mechanisms that amplify rather than reverse the change.
• Example: During childbirth, the pressure of the baby’s head against receptors near the opening of the mother’s uterus stimulates uterine contractions.
• These contractions cause greater pressure against the uterine opening, heightening the contractions, which cause still greater pressure.

Question 24

Define thermoregulation and explain why it is important.

Answer 24

• Thermoregulation: the process by which animals maintain their internal temperature within a tolerable range.
—> Why is thermoregulation critical to survival?
• Although different species of animals are adapted to different environmental temperatures, each species has an optimal internal
temperature range.
• Thermoregulation helps keep body temperature within this optimal range, enabling cells to function effectively as external temperature fluctuates.

Question 25

Describe the four physical processes by which animals exchange heat with their environment.

Answer 25

Conduction, convection, and radiation can all cause heat

gain or heat loss, but evaporation leads only to heat loss.

Question 26

Describe the two ways by which animals obtain heat, including the names given to animals that (mainly) use each method.

Answer 26

• Endothermic - mainly use metabolic heat to regulate their body temperature (e.g., birds + mammals).
• Ectothermic - mainly gain their heat from the external
environment (e.g., snakes + most fish).

Question 27

Explain why endothermy and ectothermy should be regarded as opposite extremes along a continuum rather than mutually exclusive strategies. Provide examples to
support your answer.

Answer 27

• A bird is an endotherm, but may warm itself in the sun on a cold morning, just as a lizard does.
• On a cold morning, a bumblebee will shiver by contracting its flight muscles to generate heat for
flight.

Question 28

Describe the advantages and disadvantages of endothermy and ectothermy.

Answer 28

What are the advantages + disadvantages of ectothermy?
• Advantages:
• Because their heat source is primarily the external environment rather than internal metabolism, ectotherms require much less food than endotherms of equivalent size.
• Can use greater proportion of energy for growth + reproduction.

• Disadvantages:
• Chemical reactions are temperature dependent – digestion and
muscle activity slow when body temperature decreases.
• Less successful in cold environments.

• What are the advantages + disadvantages of endothermy?
• Advantages:
• Can maintain stable internal body temperatures despite external
temperature fluctuations.
• In a cold environment, an endotherm can generate enough heat to keep its body substantially warmer than its surroundings.
• Many endotherms, but few ectotherms, are active at below-freezing temperatures.
• Being able to generate a large amount of metabolic heat enables endotherms to perform vigorous activity for much longer.
• Sustained intense exercise is usually only possible for endotherms.
• Disadvantages:
• Is expensive!!
• Energy used to produce heat unavailable for growth + reproduction.

Question 29

Describe, in brief, how the energy budgets of ectotherms and endotherms of similar size differ.

Answer 29

??

Question 30

Differentiate between heterothermy and homeothermy.

Answer 30

• Heterotherm: an animal with a body temperature that varies with its environment.
• Homeotherm: an animal that maintains a relatively stable internal temperature.

Question 31

Define torpor.

Answer 31

Sometimes enter an inactive state with lowered temperature

Question 32

Discuss the role of hair, feathers, and adipose tissue in insulation (or conserving heat).

Answer 32

• Land mammals and birds react to cold by raising their fur or feathers to trap a thicker layer of air.
• Animals also secrete oily substances to repel water.

Question 33

Explain the role of vasoconstriction and vasodilation in modifying the transfer of body heat with the environment

Answer 33

• Vasodilation: increases blood flow and heat transfer by increasing the diameter of superficial blood vessels near the body surface.
• Vasoconstriction: reduces blood flow and heat transfer by decreasing the diameter of superficial vessels.

Question 34

List several animal adaptations to augment evaporative cooling

Answer 34

Panting, sweating (mammals only), gaping, and bathing are all adaptations to augment evaporative cooling.