Quiz

1. The four animals show changes in limb shape and size over time, indicating that the Basilosaurus evolved from a Mesonychid.
2. Australia
3.Dragonflies, birds, bats are examples of convergent evolution. The three animals all have wings, but the underlying structure of those wings are completely different. The feature just evolved out of necessity for all animals.
4. DNA sequences reveal the amount of genetic coding different animals have in common with each other. Primates and humans only differ in genetic makeup by a 0.5 -1.0% difference.
5. Homology refers to similarities between animals. For example, horses and donkeys have genetic coding for cytochrome C so similar that they are homologous for all but 1 amino acid in the selection we examined in class. Whales and other mammals have homologous limb structures, just that taaktalik the fish with feet had homologous structures with humans and other wrist-ed creatures.

Common Descent

We are descendants of fish.

Many other animals are also descended from fish.
Which is to say, we have a common ancestor with many animals.

The process of determining common descent consists of examining differences in amino acid sequences . For example, we examined a section of Cytochrome C protein's amino acid code. We compared the sequences of different animals, and counted the number of differences. If there are many discrepancies, then the two animals are less related. Horses and donkeys only have 1 difference, whereas horses and yeast have 44 differences. Horses and yeast have 44 differences as well, but yeast and wheat have 47 differences.
Based on our data, we can construct a cladogram.
The closer a branch is to the original animal on the cladogram, the more closely the two are related.

Osmosis Lab

For the past two days we've been learning about diffusion and osmosis.
Osmosis is a particular type of diffusion that involves water.
Diffusion is essentially the dispersion of a substance from a place with high concentration of itself to a place with low concentration. In the case of osmosis water is moving from a place of high concentration  of water (pure H20 or low molarity of solute) to a place with low concentration of water (high molarity of solute) through a semi permeable membrane.

A solution on one side of the membrane is hypertonic if has more solute particles than the other solution. The other solution would be hypotonic because it has less solute particles. To reach equilibrium/ homeostasis/ be isotonic, the hypotonic solution would send water to the hypertonic solution so that their solute concentrations average out. Water continues to move from side to side, but at the same rate so that the isotonic/ equal solute concentrations remain constant. 

Water potential describes the likelihood that water will enter a solution. the lower/ more negative it is, the higher the chance that it will be flooded. Water potential is equal to the pressure potential of the cell (so for plants it would be the cell wall pressure) plus the solute potential, which is 0 for pure water and goes increasingly negative as solute is added. Water potential is measured in bars, which are the same value as atms.

Our bodies contain water, so osmosis plays many integral roles in our organs. Our blood cells, for example, will burst if our blood contains too much water- the interiors of the blood cells become hypertonic to the blood and plasma, and because animal cells don't have cell walls to exert back pressure, the water will continue to enter the blood cell until the cell membrane rips open. The shards of burst cell could travel and lodge in bad places, or the cells could all pile up somewhere and cause an aneurysm. The opposite will happen if you are de-hydrated. Instead of bursting, your cells will shrivel up as all the water leaves the cell for the bloodstream. And the cells wouldn't be able to cary oxygen around as successfully.

We did a series of experiments on osmosis: pictures in next post

Cabbage Juice Indicator

Cabbage juice contains anthocyanidin, which is a sugar molecule attached to a cyanin molecule.
Cyanidin acts as a pH indicator because it changes color when it gains or loses H+ ions.

Color change is based on the wavelength of light that a molecule will absorb.
When the electrons of a compound are confined to one position, the wavelengths of light needed to jump energy levels are high energy. When there are many resonance structures that give the elrctrons options, then the wavelengths don’t need to be so high energy. Blue light absorption is associated with confined electrons and red light absorption with free movement.

If the cyanidin is in acidic solution and takes up the H+ ions, the wavelength absorbed by the compound will be blue, and as a result the color refracted, which we observe, will be red. If the cyanidin is in basic solution, and the H+ ions are taken from the cyanidin compound, the color we observe will be blue.

If there were to be acid rain on a red cabbage patch, the cabbage would become more red. 

WATER!

Dihydrogen Monoxide is responsible for many facts of life that we take for granted.

The beach is typically cooler than the inland regions.

The ocean is cold even when the temperature on the beach is hot.

Small bugs can walk on water.

You can slightly overfill a glass with water, and it won’t overflow.

Dry porous materials draw up water.

Ice floats.

We sweat to cool down.

It feels hotter on a hot, humid day than on a hot, dry day.

The explanations for all these things comes down to the unique molecule that is water. Water is made of two hydrogen atoms and one oxygen atom. When they bond, the oxygen atom is more electronegative (ie electron hungry) than the hydrogen atoms, so the electrons of both Hydrogens tend to spend their time around the Oxygen atom. This results in a slight positive charge on each of the hydrogens that isn’t quite a proper charge, but a positive dipole. The oxygen likewise has two negative dipoles.

So on each water molecule there are four dipoles- and because the elements in question are hydrogen and oxygen, the intermolecular bonds that are formed between the positive dipole of Hydrogen and the negative dipole of Oxygen are H-bonds.

Because of the ease with which water can break and form weak intermolecular bonds, it has a heat capacity of 4.184 joules/ gram Celsius. This means that to heat one gram of water up one degree Celsius, it takes 4.184 joules.

So:

The beach is typically cooler than the inland regions because the ocean and the water vapor from the ocean take won’t heat up as easily.

The ocean is cold even when the temperature on the beach is hot because the sand has a lower heat capacity than water does.

Small bugs walk on water because h-bonds allow for cohesion of water molecules and thus a surface tension that, when treaded upon with the fuzzy feet of small bugs, can hold the bug’s weight.

You can slightly overfill a glass with water, and it won’t overflow because water has such strong cohesive properties that it can sit on top of itself when there is no surface to adhere to. The same property can be observed on a wet penny.

You can also place a toothpick on an overfilled penny and observe the strength of water’s surface tension, which makes it easier to visualize how water bugs walk on water.

Dry porous materials draw up water because some water is attracted to the stronger bonds of the material (adhesion), and the rest of the water tags along because the water molecules are cohesive due to their h-bonds.

Ice floats because water freezes in a hexagonal lattice shape that is less dense than the h-bonded liquid structure.

We sweat to cool down because the heat that allows sweat to evaporate comes from our body.

It feels hotter on a hot, humid day than on a hot, dry day because if there is water vapor pressure in the air, it is harder for your sweat to evaporate (think boiling water in high atmospheric pressures), no matter how much body heat you have. You literally can’t cool down as efficiently. On a hot humid day, drinking water can sub in for the cooling effects of sweating.

-D