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Chapter 40 overview, Chapter 42 overview and 42.1
Chpt 40:
Q: How is size of an organism constrained/determined by physical laws and
environment.
Shape, features of an organism called the “body plan” and is determined by
evolution and genome.
Limited by physical laws. Mainly efficient exchange of materials with
external environment for survival.
Fig. 40.2 Physical Laws. Aquatic environment controls the shape of fast
aquatic swimmers ( 80km/h).
Water is 1000x denser thn air therefore greater drag ( friction) cf. air.
Ex. swimmers cf runners. ( shave, caps etc).
Fig. 40.3. Exchange with external environment. Surface area to vol ratio.
a) single cell has the entire surface area in contact with environment.
b) Multicellular only works if ALL cells in an aquatic environment. Hydra
has a gastrovascular cavity so both cell layers in contact with external
environment. Or flat shapes like tapeworm.
Fig. 40.4. Complex animals – each cell is bathed in fluid and have folds on
internal surfaces.
Benefits of complex body form:
a) Protective outer covering.
b) Muscles for rapid movement ( peristalsis, limbs).
c) Internal digestive organs – controlled release of stored energy in food
and can maintain a stable internal environment cf changing external
one.
d) Suitable for life on land.
Fig. 40.4
Respiratory system – brings in O2 and takes out CO2 and H2O.
Circulatory system – transports nutrients and O2 to cells and takes away
waste and CO2 from cells.
Kind of system depends on the selective pressures of the environment
organism is living in.
Invertebrates:
- Simple body plan.
- No circulatory system needed Ex. Hydra.
- Gastrovascular cavity and body wall ( 2-cell thick).
- Fluid in body continuous with outside so both layers bathed in fluid.
Fig. 42.3:
- In multicellular organisms diffusion distance too big for efficient
exchange of nutrients and waste therefore develop a circulatory
system. Have fluid ( blood), tubes ( blood vessels) and pump ( heart).
a) Open:
-Insects, mollusks.
- Body fluid = hemolymph, pumped by 1 or more hearts into sinuses where
chemical exchange occurs.
- Ostia valves closed when heart contracts and hemolymph returns
through these.
- Low BP therefore less energy.
- Also acts as a hydroskeleton in mollusks.
b) Closed:
- Earthworms, squid, octopuses and all vertebrates.
- Have high BP therefore high energy.
- More efficient transport systems for higher metabolic rate.
Both systems are widespread and both have pros and cons.
Fig. 42.4 – comparisons.
a) Fish:
- 2 chambers (1 ventricle, 1 atrium).
- 2 capillary beds so lose pressure and this restricts the aerobic
metabolic rate.
b) Amphibians:
- 3 chambers (1 ventricle, 2 atria).
- Some mixing in single ventricle.
- Heart has both oxygenated and deoxygenated blood.
- Blood pumped 2nd time ( pulmonary and systemic) = double circulation.
c) Reptiles ( EXCEPT birds):
- 3 chambered heart (1 ventricle and 2 atria).
- Septum partially divides single ventricle therefore less mixing.
- In crocodiles complete septum divides ventricle into left and right.
- 2 arteries from heart for systemic circulation.
- Arterial valves allow blood to be diverted from pulmonary circulation
to systemic circulation.
d)
-
Mammals and Birds:
4 chambered heart ( 2 ventricles and 2 atria).
Complete septum.
Left side has O2 rich blood.
Right side has deoxygenated blood.
NO MIXING.
Double circulation so pressure restored to systemic circuit after
lungs.
Essential for the endothermic way of life!
10x more energy cf. equal size ectotherm so 10x more O2 and fuel for
cellular respiration!!!
Different reptilian ancestors for mammals and birds so 4-chambered
heart evolved INDEPENDENTLY in each line = convergent evolution.
Heart:
- ATP to increase hydrostatic pressure of blood so blood moves DOWN
a pressure gradient (high to low), and back to heart = blood pressure.
Open system::
- Fluid ( hemolymph) bathes tissues and organs directly.
- No separation between circulatory and interstitial fluid.
Closed system:
- Blood confined to vessels and kept separate from interstitial fluid.
- Cardiovascular system – heart, arteries, veins, capillaries –
characteristic of vertebrates.
Sinus:
- Any space surrounding organs of animals with open circulatory system.