2.A.3

1. Why is matter necessary for biological systems?

Matter is what everything is made up, including biological systems. Matter can neither be created nor destroyed, only transformed. Yet biological systems need matter in order to grow and reproduce. Trees, for example, aid in the transformation of matter as they take in carbon dioxide and produce oxygen. This oxygen is then used by humans and animals during cellular respiration to grow.

Explain the uses of carbon, hydrogen, oxygen, nitrogen, phosphorous and sulfur in biological systems.

These four elements alone make up 96% of all living things. Nitrogen and hydrogen are found in the air necessary for living organisms, including animals and humans. Air is actually composed of 78% nitrogen and 22% oxygen. Phosphorous and sulfur are found in electrolytes, which are necessary for homeostasis, digestion, neurological function, and several other functions of the body.

Oxygen, which composes roughly 20% of the air we breath is important to humans in order to be able to perform cellular respiration, during which carbs are broken down into ATP by our body.  Cellular respiration also creates water, carbon dioxide, and heat.

Carbon is important as it is used to build carbohydrates, lipids, proteins, and nucleic acids. What allows carbon to be the building block is its characteristic of having four valence electrons. This allows it to form a total of four other bonds, something that is important to the construction of the carbs, lipids, proteins, and nucleic acids.   

Diagram the exchange of matter between organisms and the environment.

Source: www.bigelow.org

What function does nitrogen serve in proteins?  In nucleic acids?

Nitrogen is found in amino groups necessary for the formation of peptide bonds, which will then form polypeptide bonds. Nitrogen then aids in the formation of hydrogen bonds in the secondary and tertiary structures of proteins, where polypeptide bonds are found.

With nucleic acids, nitrogen is what makes up the nitrogenous bases that are part of nucleotides, which then make up polymers that then make up nucleic acids.These nitrogenous bases are paired up Adenine to Thymine and Guanine to Cytosine to create DNA. The two long chains of  the DNA helix are paired together by the nitrogenous bases via hydrogen bonds.


What function does phosphorus serve in nucleic acids?  In phospholipids?

Phosphorus is what makes up the phosphate group found in nucleic acids. This phosphate group is important as it connects nucleotides, thus creating a sugar backbone. Phosphate in phospholipids make up the heads. These heads are hydrophilic and mix with water to make up the outside layer the plasma membrane and keep the structure of the cell.

Why do biological systems need water?

Water is necessary in hydration synthesis and hydrolysis in order to create and break down polymers for the body's use and the formation of proteins. Water also helps with the regulation of body temperature. Humans sweat to keep cool since water's high specific heat allows it to absorb more heat before changing temperature. Then, when sweat evaporates, it takes this heat with it. Water is also important due to it being the universal solvent. Within humans, it aids to dissolve urea and uric acids. Water also serves are transport within the body, moving hormones and cells.


How does the structure of a water molecule relate to its function(s)?

Water’s hydrogen bonds are what give water the ability to perform the majority of its functions since unique properties of water like adhesion and cohesion are due to these hydrogen bonds. Water contains one oxygen molecule and two hydrogen molecules, These molecules have unequal electronegativities, resulting in a partially negative charged oxygen molecule and a partial positive charge of the hydrogen molecules. Hydrogen bonds are formed when the negative oxygen molecule in one water molecule is attracted to the positive charged hydrogen atom in a different water molecule.



How does the polarity of water lead to the emergence of unique properties in liquid water?

Due to the unequal electronegativty between hydrogen and oxygen molecules, water is charged and said to be polar. This polarity then results in the formation of hydrogen bonds, whose strength comes in number. This polarity is what allows, for example, ice to float on water. Hydrogen bonds spread out when they freeze and make water less dense in the frozen states than in the liquid state. Polarity also gives water its adhesion and cohesion. Adhesion is what allows water to stick to the sides of trees and such to move up the trunk to the leaves. Cohesion is what allows water to stick to itself. For this reason, insects that are light enough are able to walk on water.



Explain why surface area-to-volume ratios are important in affecting a biological system’s ability to obtain necessary resources or eliminate waste products.

The surface area-to-volume decreases as a cell gets bigger. If a cell were to lose surface area, its need for nutrients would actually increase. This increase in nutrient demand would then lead to a demand for more cell surface area in order for an increased amount of nutrients exchanged to occur. This is what maintains the surface area-to-volume ratios.The cell membrane must be large enough to allow the necessary resources to pass through the membrane and wastes to exit. But also, the cell cannot be small enough that it does not allow for space of the necessary organelles for cellular functions.

Identify several (more than 4) chemical elements and molecules that function as key building blocks (e.g., C, N, H2O, sugars, lipids, proteins) or are eliminated as wastes.

1. Hydrogen
2. Oxygen
3. Hydroxyl
4. Glucose and Fructose
5. Nitrogen

Explain the physical considerations that determine the upper and lower limits to cell size.

Cells cannot expand to much because then they will be unable to sustain their large size. Diffusion of oxygen will be inefficient and the cell will need too many nutrients. It will no longer be able to feed itself. However, if a cell is too small, then there will not be enough space for the organelles necessary for cells to carry out their functions.

Explain why smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.

Smaller cells have the more favorable ratio because they have the greater amount of volume for the least amount of surface area. Their smaller size allows cells to be more efficient in diffusion, since oxygen and carbon dioxide do not have to diffuse so much. We can also gets nutrients in more easily and waste products out.


Using any model, calculate simple surface area-to-volume ratios for cubic and round cells and explaining how this impacts procurement of nutrients and elimination of wastes.


Calculations being at minute 4:40 and end at minute 8:45. In order to calculate the cell value for round cells, follow the same procedure, except use formulas for the volume and surface area of a sphere instead. 

Explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination. [SP 6.2]

A perfectly, small round sphere is a shape that will be able to obtain the most volume for the least amount of surface area. The fact that cells are both very small and round aids the rates of nutrient intake and waste elimination. These processes are actually speed up. The more surface area, the more nutrients the cell can take in. Molecules will move into and out of the cell at a faster pace as well since they have less distance to cover if the surface area is high and the volumn is small. This increases the rate of diffusion and nutrients like oxygen can enter the cell more quickly and waste like carbon dioxide can leave quicker.



Represent graphically or model quantitatively the exchange of molecules between an organism and its environment, and the subsequent use of these molecules to build new molecules that facilitate dynamic homeostasis, growth and reproduction. [SP 1.1, 1.4]

Source: hyperphysics.phy-astr.gsu.edu

The molecules exchanged here are CO2 and oxygen. These are exchanged by trees into the environment. Animals then use these molecules in the production of ATP, their source of energy.