Category Archives: IBHL-2 Biology

E.6c Food, Sleep, Sex

7. Outline two examples illustrating the adaptive value of rhythmical behavior patterns.

Example: moonrats, Echinosorex gymnura

  • nocturnal
    • foraging at night in lowland forests, by smell
    • for invertebrates, which are also active at night
    • when predators are less active
    • rest in holes during the day, where they are difficult to locate

Example: red deer, Cervus elaphus

  • reproduce in the autumn, following an annual cycle
    • both males and females are only sexually active in autumn months
    • males fight to establish dominance hierarchies
    • females form herds associating with a single dominant male, with whom they mate
    • gestation occurs over winter, offspring born in spring
    • system maximizes fitness for:
      • young: maximizing feeding time before 1st winter
      • females: mate only with highest quality male
      • males: large genetic payoff for dominant male, at cost of no genetic payoff for excluded males

E.6b Reciprocal Altruism

reciprocal altruism = benefitting nonrelatives at cost to self, possibly self-sacrifice

  • origins: kin selection due to inclusive fitness produces familial altruism
  • genetic basis for behaviors which allow for self-sacrifice
  • extended to nonrelatives only under conditions which resist exploitation
  • repeated encounters + recognition of individuality
  • respond in kind (tit-for-tat; do unto others as they do to you)
  • recognition and punishment of cheaters
  • example: vampire bats

E.6a Kin Selection

Describe the social organization of honey bees and one other non-human example.

honey bees

  • 30,000 workers which are sterile and one fertile queen
  • queen lays fertilized eggs in wax chambers built by workers
  • eggs fed (up to 1300 times/day) by nurse workers (for 6 days)
  • cells sealed, pupate (for 12 days), emerge as sterile worker (rest for 1-2 days)
  • queen produces pheromones which keep workers sterile
  • remain in hive as nurse for about a week
  • spend additional time as housekeeper, wax producer
  • become guard, making brief trips outside hive
  • become forager, collecting nectar and pollen
  • workers thus build, maintain and protect hive
  • over winter, workers huddle around queen to keep warm
  • in spring, queen lays unfertilized eggs, which develop into haploid male drones
  • drones mate with queen from other hive during her nuptial flight
  • queen stores sperm for lifetime (5-7 years)
  • workers evict drones when they are not needed
  • when pollen nectar peaks (spring), diet affects developing eggs
  • richer diet: some eggs develop as queen candidates, workers enlarge cells
  • old queen departs with about half of workers
  • swarming behavior as workers + queen find and create new hive location
  • in old hive, 1st new queen emerges; others queen candidates killed by workers

E.3b Learned Behavior

4. Discus how the process of learning can improve the chance of survival.

Moths learn by classical conditioning

  • moths vary in their ability to learn by classical conditioning (variation)
  • moths that are better at learning by classical conditioning will better associate black and orange caterpillars with noxious taste, and avoid getting sick, increasing survival chances (natural selection)
  • alleles allowing classical conditioning are passed on to offspring at a higher rate than alleles without classical conditioning ability (heritability)
  • thus, classical conditioning alleles accumulate (evolution)
  • and the trait becomes common in the population (adaptation)

Bears learn by trial and error/operant conditioning

  • bears vary in their ability to learn by operant conditioning (variation)
  • bears that experiment with various methods to catch salmon obtain more resources than those that don’t, increasing their survival chances (natural selection)
  • alleles that lead them to attempt operant conditioning are passed on to their offspring at a higher rate than alleles without operant conitioning ability (heritability)
  • thus, operant conditioning alleles accumulate (evolution)
  • and the trait becomes common in the population (adaptation)

Goslings imprint on their mothers

  • goslings vary in their ability to imprint (variation)
  • goslings that are able to imprint on their mother, will avoid predators by remaining close to her, increasing their chances of survival (natural selection)
  • alleles allowing imprinting are passed on to their offspring at a higher rate than alleles without imprinting ability (heritability)
  • thus, imprinting alleles accumulate (evolution)
  • and the trait becomes common in the population (adaptation)

E.3a Innate Behavior

taxis:

  • locomotion of an organism
  • in a particular direction
  • in response to an external stimulus
  • examples:
    • Planaria moves towards food = positive chemotaxis
    • Euglena moves towards light = positive phototaxis

kinesis:

  • the movement (as opposed to growth) of an organism or a cell
  • in response to a stimulus
  • such that rate depends on intensity, but not direction, of the stimulus
  • example:
    • woodlice move about less in optimum, humid, conditions, and more in unfavorable, dry conditions

E.4c Drugs

6. Discuss the causes of addiction, including genetic predisposition, social factors and dopamine secretion.

genetic predisposition:

  • the tendency toward addiction is variable, with studies indicating that genetic factors have some influence
  • alcoholism, especially, tends to run in families

social factors:

  • a variety of social factors correlate positively with addiction:
    • cultural traditions
    • peer pressure
    • poverty
    • social deprivation
    • traumatic life experiences
    • mental health problems

dopamine secretion

  • many addictive drugs are excitatory at dopaminergic synapses, also known as the reward pathway
  • addiction is a result of dopaminergic synapses responding to regular use
    • reduction in the number of dopamine receptors in post-synaptic neurons
    • reduction in the release of dopamine from pre-synaptic neurons
  • tolerance to a drug
    • a result of decreased number of receptors
    • leading to increased dosage to produce the desired effect
  • withdrawl
    • with reduction of receptors
    • normal level of dopamine fails to produce pleasure

E.4b Neurotransmitters

depression

  • caused by deficiency of norepinephrine (NE) and/or serotonin (ST)
  • psychoactive drugs can increase the levels of NE/ST at synapses
  • increase in secretion of NE/ST from pre-synaptic neurons
  • suppression of NE/ST deactivating enzymes at post-synaptic neurons
  • inhibition of NE/ST uptake by pre-synaptic neurons
  • elevate mood in normal people
  • alleviate depression in the chronically depressed

E.4a Synapses

EPSPs: excitatory post-synaptic potentials

  • post-synaptic neurons have receptor proteins specific to excitatory neurotransmitters
  • binding neurotransmitter makes post-synaptic membrane permeable to Na+, which moves across post-synaptic membrane
  • causing depolarization of the post-synaptic membrane
  • enzymes catabolize neurotransmitters
    • monoamine oxidase catabolizes norepinephrine
    • acetylcholine esterase catabolizes acetylcholine
    • examples of excitatory neurotransmitters
      • epinephrine
      • dopamine
      • serotonin

E.5b Brain Function

Explain sympathetic and parasympathetic control of the heart, movements of the iris, and flow of blood to the gut.

autonomic nervous system:

  • sympathetic:
    • fight-flight-excercise
  • parasympathetic:
    • restorative, resting, digesting

heart

  • sympathetic:
    • heart rate accelerates, pumping more blood to muscles
  • parasympathetic:
    • heart rate slows, body relaxes, less blood needed to muscles

E.5a Brain Structure

pupil reflex: when a bright light shines into one eye, the pupils of both eyes normally constrict

  • retina detects light intensity
  • impulses to brain in optic nerve
  • brain stem/medulla controls the reflex
  • sympathetic system causes dilation
  • parasympathetic system causes constriction
  • sympathetic neurons are in spinal nerve T1
  • parasympathetic neurons are in cranial nerve III
  • pre- and postganglionic fibers of symp/parasymp
  • neurotransmitters of symp/parasymp
  • polysynaptic reflex