Tuesday, January 18, 2011

Adaptation Group 4

1. How do mangrove plants such as Avicennia obtain oxygen when their roots are buried in the mud?
Simple physical diffusion through the lenticels and along the aerenchyma is probably the main mode of gas movement in mangrove roots. There is also a more convincing interpretation of the observed pressure changes which provide a mechanism for the mass flow of air into a root to supplement diffusion: Lenticels are hydrophobic, so that while a root is covered by water they are in effect closed: neither air nor water can enter. Respiration removes oxygen from the air spaces and produces carbon dioxide. Because it is highly soluble in water, the carbon dioxide does not replace the volume of oxygen removed, and gas pressure within the root is therefore reduced. After a root is covered by the tide, oxygen within it falls, carbon dioxide levels do not increase to compensate, and pressure falls. When the tide recedes and the lenticels are again open, air is sucked in.

Reference: Hogarth, P. J. The biology of mangroves. Oxford University Press. 228 p.

2. How are xerophytes adapted to survive prolonged drought?
Structural Adaptations:
Succulent stems or leaves
Leaves adapted into spines and have a thick waxy cuticle to reduce water loss
Number of exposed stomata is reduced to reduce water loss
Deep and large number of roots below the surface

Physiological Adaptations:
The fold their leaves in the day to reduce number of stomata that is exposed
during the dry season,they shed their leaves to reduce water loss
Some stomata open at night instead of in the day


3. How do polar bears survive in regions where temperatures are constantly freezing?
The polar bear's fur is oily and water repellent, therefore the hairs don't mat when wet, allowing the polar bears to easily shake free of water and any ice that may form after swimming, therefore they can survive in freezing water.
Their thick fur keeps them warm in frigid air and water, skin is black to absorb heat from the sun's rays to help keep them warm, their pads provide traction on ice, have short ears and tails to minimize heat loss, their fat layers keep them warm, and their nostrils close underwater.

Source: http://www.kidzone.ws/sg/polarbear/polar_bear.htm

4. How do deep-sea anglerfish locate its prey in darkness?
Anglerfish have a piece of dorsal spine that protrudes above their mouths like a fishing pole—hence their name. Tipped with a lure of luminous flesh this built-in rod baits prey close enough to be snatched.


5. Why can't a saltwater fish survive in freshwater aquarium? What are the differences in pH between seawater and freshwater ponds?
The pH level of seawater is about 8. Osmosis causes the cells in saltwater fish to constantly lose water, which the fish has to replace by drinking salt water, desalinating it with special organs and replenishing the water in its cells.

Done by: Chin Fan, Zheng En, Jun Jie and Wen Yue

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