Biological%20Timing%20Responses%20in%20Animals

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Biological Timing Responses in Animals
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Biological Clocks

• These are internal timing system which continue
  without external time cues.
• They control the timing activities of plants and
  animals.

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Uses of Biological Clocks

• Control of daily body rhythms such as sleep,
  blood pressure, temperature, blood cell count,
  alertness, urine composition, metabolic rate and
  sex drive.
• Reproductive timing i.e. animals in heat,
  courtship rituals, simultaneous release of sperm
  and eggs into water.

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Uses of Biological Clocks

• Preparation for migration by eating a lot.
• Preparation for winter by storing food,
  increasing coat thickness or colour and
  hibernating.
• Solar (sun) or Stellar (stars) navigation

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Endogenous Rhythms

• Controlled by an internal Biological clock.
• Circadian daily activity period (24hrs)
• Circatidal Tidal period (12.4hrs)
• Circasemilunar spring/neap tide (14.7 days)
• Circalunar monthly activity (29 days)
• Circannual yearly activity (365 days)

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Exogenous Rhythms

• This is a rhythm that is controlled by the
  external environmental stimuli detected by the
  organisms.

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Circadian Rhythms

• Animals are active at different times of day
• Diurnal
• Active during the day, inactive at night.
• Nocturnal
• Active at night, inactive during the day.
• Crepuscular
• Active at dawn and dusk e.g. fruit flies

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Circadian Rhythms

• Arrhythmic
• No regular pattern
• These organisms are usually found in areas where
  changes in the microclimate are negligible. E.g.
  in caves, deep under the ocean or soil.

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Circadian Rhythms in Humans

• Sleep Awake rhythms
• Vary from person to person
• Children sleep about 12 hrs per night
• Teenagers sleep about 9 hrs per night
• Adults on average sleep about 7-8 hrs
• Elderly people make do with 6hrs (and nap during
  the day.)

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Circadian Rhythms in Humans

• Temperature
• This rises during the day and drops at night, the
  lowest point being at 3 am.
• Heart Rate
• This keeps in step with temperature.

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Circadian Rhythms in Humans

• Pain
• This varies during the day. We are more sensitive
  to the pain of a needle at noon, but are more
  sensitive to the pain of cold at night.

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Circadian Rhythms in Humans

• Alcohol Metabolism
• We break down alcohol most efficiently between
  4pm and 11pm.

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Circadian Rhythms in Humans

• Efficiency of Learning
• This follows the temperature curve except it
  takes an unexplained dip at lunch time which is
  not related to eating lunch.

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Circadian Rhythms in Humans

• Renal Excretions
• The kidneys are the blood filters, they control
  the amount of ions in the blood by excreting any
  excess and holding back ions if their blood level
  is low.
• These follow a rhythm of excretion of chemicals
  such as calcium and potassium and of volume.

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Circadian Rhythms in Humans

• Birth and Death
• You are most likely to be born or to die in the
  early morning

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Circadian Rhythms in Humans

• Hormone Secretion
• Varies but most are secreted at night.

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Disturbing Sleep Rhythm

• Jet Lag
• These days when travelling great distances is
  possible in a very short time, we can cause a
  complete reversal of our day and night.
• Our biological clock has a phase shift of 12 hrs.

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Things to Note.

• It takes about 3 days to sleep at the new time.
• All our other rhythms take longer to adjust, so
  they get out of phase with the sleep/awake cycles
  and with each other.
• It can take about 10 days to synchronise.
• Until then, we do not feel so good and do not
  perform as well as usual.

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Things to Note

• All these symptoms together are what we call Jet
  Lag.

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Think About This.

• After the holidays, when you dont use your alarm
  clock, you are tired when you come back to
  school.
• It is because you were free running during the
  holidays.
• Most students shift their clock by at least 2
  hours, many by up to 4 hours.
• You are suffering from Jet Lag

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Shift Work

• Sleepiness can cause mistakes, a common sign is
  using the wrong words in conversations or
  forgetting the end to a sentence.
• Shift work causes more distress than jet lag, as
  the days off-duty return the person to normal
  time.
• Shifts of 10 days on and 4 days off with
  different starting times are the worst

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Shift Work

• Remember the hormone and other rhythms take about
  10 days to synchronise.
• A person working these times can have 4 shifts
  in 10 days
• They become moody and depressed.
• They become extremely irritable.
• They cant sleep.
• They are more susceptible to infections.
• They have more accidents on the job
• They are not as efficient as day workers

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Circamonthly (Lunar) Cycles

• Some animals synchronise their behaviour with the
  phases of the moon.
• The positions of the sun and moon generate our
  tidal patterns, so the response to these tidal
  changes during a 24hr period is considered to be
  a lunar cycle.

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Circamonthly (Lunar) Cycles

• The ovulatory cycles of primate females is about
  4 weeks long but there is no firm evidence that
  these are synchronised with the lunar month.

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Circamonthly (Lunar) Cycles

• The spawning behaviour of certain marine worms is
  synchronised by the moon, which ensures that eggs
  and sperms will be released at the same time.
• The spawning of the palolo worm is governed by a
  combination of tidal, lunar and annual rhythms.

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Circatidal (tidal) Rhythms

• The Grunion is a fish that spawns on land.
• From April to June, on the 3 or 4 nights that the
  spring tide occurs at precisely high tide, the
  fish squirm onto the beach.
• The female buries her tail in the sand.
• The male wraps around her to release sperm.
• Then they catch the outgoing tide.

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Circatidal (tidal) Rhythms

• By the time the tide next reaches that part of
  the beach, 15 days later, the young grunions have
  hatched and catch a ride out to sea.

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Circannual (Yearly) Cycles

• These result from the rotation of the earth
  around the sun over a period of 365.25 days.
• On top of this is the earths rotation on its own
  axis, set at an angle of 23.45º to the sun.
• This results in the seasonal changes which
  dictate many responses seen in organisms.

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Circannual (Yearly) Cycles

• E.g. animals may migrate to and from breeding
  grounds twice a year, and have many annual cycles
  of reproduction and hibernation.

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Hibernation

• This is the way that animals survive over winter,
  usually by slowing down their metabolism.
• Small animals are particularly susceptible to the
  cold as they have a large surface area to their
  volume and can lose heat rapidly.

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Hibernation

• Most animals that hibernate lay down a vast
  quantity of fat before the onset of winter, then
  find a warm burrow and go into a form of
  suspended animation.
• Insects also suspend development in addition to
  the drop in metabolic rate this is called
  diapause.
• Often triggered by a decrease in day length.

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Aestivation

• This is a form of summer hibernation.
• When the soil gets too dry, earthworms will dig
  down deep and curl into a ball, secrete mucus and
  will aestivate until the soil becomes moist again.

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Migration

• This is the annual movement of animals from their
  breeding area to another area where they do not
  breed, and then the return journey back again.
• It is usually triggered by the shortening day
  length or a drop in temperature.

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Reproduction

• Animals need to produce their offspring when the
  conditions are most favourable.
• For most animals this is in the spring.
• Animals come into breeding condition in response
  to increased day length, temperature, rainfall,
  increasing food, etc.
• Animals detect environmental clues through the
  skin, and detect light through the eyes or the
  pineal gland.

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Reproduction

• This causes secretion of various hormones which
  ready the sex organs and produce sex hormones.
• It also starts the appropriate behaviour for
  courtship and reproduction.

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