BIS2C 2018 WINTER Pre LAB-8 Comparative Metazoan Biology
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Module
BIS2C 2C BIS2C
Institution
University Of California, Davis
Pre-lab: Introduction to Lab 8
In this, the *nal lab of the quarter, you will be asked to solve a series of small puzzles in
metazoan evolution. In BIS 2A you learned about mechanisms of genetic change, and in BIS
2B you learned how natural selection operates on individuals to produce genetic ch...
you will be asked to solve a series of small puzzles in metazoan evolution in bis 2a you learned about mechanisms of genetic chang
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University Of California, Davis
BIS2C 2C BIS2C
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Section: *
C08
Pre-lab: Introduction to Lab 8
In this, the *nal lab of the quarter, you will be asked to solve a series of small puzzles in
metazoan evolution. In BIS 2A you learned about mechanisms of genetic change, and in BIS
2B you learned how natural selection operates on individuals to produce genetic change in
populations. You realize now that agents of natural selection can be biotic factors, such as
interactions with predators and prey, as well as abiotic factors, such as temperature or
moisture levels. You should recall mechanisms of speciation and the relationship between
speciation and phylogeny. In this lab, you will synthesize the material from the entire series
and use your skills in reading trees and inferring patterns of change to explain what has
happened in particular lineages. You will research particular issues using textbooks,
published papers, and the web. Prepare your talk and give it as a mini-lecture, without notes
if you can.
Some of the problems you will solve involve transitions from water to land or from land to
water, within a lineage. Problems associated with water-to-land transitions involve
desiccation (drying), respiration, reproduction, and support of the body. A short refresher on
each of these problems is given below.
Desiccation
Animals that live on land lose water to the environment through permeable skin and
permeable membranes. Thus, land animals add various substances (e.g., waxes, oils,
hardened coatings such as scales) to the skin to reduce water loss. Protecting the
permeable membranes used in respiration is more diIcult because these membranes
cannot be coated and still function.
This study source was downloaded by 100000850872992 from CourseHero.com on 03-05-2023 21:25:27 GMT -06:00
Cellular respiration takes place in mitochondria. Mitochondria are intracellular, so every cell
in a multicellular body needs to have a supply of oxygen. Oxygen diffuses only over very
short distances—from the cell membrane to the mitochondrion in the cytoplasm. Oxygen
diffuses into cells across a wet cell membrane. In sum, every cell needs an oxygen source
just outside the cell membrane and the membrane must be kept moist. These two stringent
requirements constrain terrestrial animal body plans.
The simplest multicellular animals are aquatic. Water contains dissolved oxygen, although
the concentration of oxygen is far less in water than in air (recall lab 2 in 2B). If the animal is
only two cell layers thick and is surrounded by water, it can meet the requirements above
without any special respiratory or circulatory systems because every cell is in contact with
the water.
Multilayered metazoans cannot rely on diffusion. They have to solve the twin problems of
oxygen pick-up and oxygen distribution to all cells. A respiratory structure such as a lung or
a gill is a means of oxygen pick-up. A circulatory system (blood in tubes with a pump) is a
means of oxygen distribution.
Gills are thin membranous sacs, or Saps, that pick up oxygen from water. Lungs are cavities
lined with thin membranes that pick up oxygen from air.
1. Why are gills typically external and lungs typically internal? (
You may enter up to 150 characters. )
The oxygen diffusion cells need to be wet. Fish has gills which are usually
surrounded by water, so it is external. Land is dryer than water. So land animals'
lungs need to be internal to keep the cell wet.
2. How is surface area expanded in a lung? ( You may enter up
to 150 characters. )
There are over 700 million air sacs in the lungs called alveoli. This signi*cantly
increase the surface area.
This study source was downloaded by 100000850872992 from CourseHero.com on 03-05-2023 21:25:27 GMT -06:00
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