3.1 Chemistry of Life

09/10/2012 § 1 Comment

Here we are, starting the third unit of the year, and it’s only the middle of October! (Not even, we’re still in the first half of October, I’ll say.) Classmates that are reading this (and why you’re actually reading this, I’ll never know), please note that this is only the third unit out of the eleven we’ll be doing this year. You know. Just a heads up.

(Also, formatting of this blog will be a little different and more sectioned because this unit involves chemistry, which was never one of my best subjects.)

Chemical Elements and Their Roles

Alright, so elements! Elements are pure substances made up of just one kind of atom, each with its own unique properties, both physical and chemical. The four most common elements we can find in our daily lives are carbon, hydrogen, oxygen, and nitrogen.

The roles of chemical elements in eukaryotes and prokaryotes vary but some of the important functions include the following:

  • sulfur (S) is needed to make two of the twenty amino acids in proteins
  • calcium (Ca) acts as a messenger a binds to proteins to regulates processes within the cell, including transcription
  • phosphorus (P ) is a vital component of ATP and other DNA molecules
  • iron (Fe) is needed to make cytochromes, a protein used in electron transport during aerobic cell respiration
  • sodium (Na) is pumped into the cytoplasm of a cell to initiate osmosis by altering the concentrations inside the cell

Atoms can combine to form a molecule by making a covalent bond. If the atom (or molecule) has an electric charge, we refer to it as an ion. Therefore, it is important to remember that all ions are charged.

Organic and Inorganic Compounds

Both organic and inorganic compounds can be found in all living organisms. Organic compounds are compounds that contain carbon. Three kinds of organic compounds found living organisms include those we’ve already discussed: lipids, proteins, and carbohydrates. Inorganic compounds are then the opposite of that but there does exist a few carbon compounds that are still inorganic – these are simple carbon compounds that include carbon dioxide, carbonates, and hydrogen carbonates. All compounds that don’t contain carbon are inorganic. Organic compounds are large and are called macromolecules because they are made up of small and simple subunits.


Water (H2O) is molecule made up of one oxygen atom and two hydrogen atoms, held together by covalent bonds. This bond creates an unequal sharing of electrons, giving the water molecule an unequal charge distribution. The unequal charge distribution (somewhat negative and somewhat positive at the same time) is what allows water molecules to stick together through hydrogen bonds. A hydrogen bond is an intermolecular force that forms when a hydrogen molecule in a polar covalent molecule (like water) is attracted to a negative atom of another polar covalent molecule.

Except, hydrogen bonds aren’t exactly bonds. Unlike covalent bonds, a hydrogen bond is more of an interaction between two molecules. It doesn’t institute a change in chemical properties between the particles like a covalent bond would and is not as strong as a covalent bond or ionic bond – which explains why water is so flexible and can take many forms in its liquid or gas forms.

The Properties of Water

  • Cohesion – water can be used as a transport medium, for example in plants (water can be sent to the tops of the tallest trees without breaking), because they can stick together thanks to the hydrogen bonds between them.
  • Solvent properties – because of its polarity, many different substances dissolve in water (including inorganic particles, organic substances, ions, and enzymes) and therefore plays a part as a medium for metabolic reactions. It is also a transport medium again here because of its ability to carry different substances to living organisms.
  • Thermal properties: heat capacity – acting again as a transport medium for heat, water can carry heat easily, for example via the blood in a human’s body. They can do this because of their large heat capacity – only large amounts of energy (heat) can break the hydrogen bonds.
  • Thermal properties: boiling point – water has a high boiling point (100°C) in order for it to change from its liquid state to its gas form; hence, in its liquid form, because the majority of the water on Earth is below boiling point, it can act as a medium for metabolic reactions.
  • Thermal properties: the cooling effect of evaporation – below water’s boiling point (100°C), it can evaporate by taking heat energy from the liquid water (because heat energy is necessary to break the hydrogen bonds), thus cooling the water. This evaporation leaves a trail of sweat (human skin) or transpiration (plant leaves) that can cool. Water is then a great coolant.


Essay Questions

  1. Outline the thermal, cohesive, and solvent properties of water. (5 marks)
  2. Describe the significance of water to living organisms. (6 marks)
  3. Describe the use of carbohydrates and lipids for energy storage in animals. (5 marks)
  4. List three functions of lipids. (3 marks)
  5. Describe the significance of polar and non-polar amino acids. (5 marks)
  6. Outline the role of condensation and hydrolysis in the relationship between amino acids and dipeptides. (4 marks)
  7. Describe the structure of proteins. (9 marks)
  8. List four functions of proteins, giving an example of each. (4 marks)
  9. Distinguish between fibrous and globular proteins with reference to one example of each protein type. (6 marks)
  10. option i – Lactase is widely used in food processing. Explain three reasons for converting lactose to glucose and galactose during food processing (3 marks)
    option ii – Simple laboratory experiments show that when the enzyme lactase is mixed with lactose, the initial rate of reaction is highest at 48°C. In food processing, lactase is used at a much lower temperature, often at 5°C. Suggest reasons for using lactase at relatively low temperatures. (2 marks)
  11. Outline how enzymes catalyze reactions. (7 marks)
  12. Explain the effect of pH on enzyme activity. (3 marks)
  13. Compare the induced fit model of enzyme activity with the lock and key model. (4 marks)
  14. Draw graphs to show the effect of enzymes on the activation energy of chemical reactions. (5 marks)
  15. Explain, using one named example, the effect of a competitive inhibitor on enzyme activity. (6 marks)

Okay, so obviously there are a lot of essay questions for this unit, but it is a long unit, so it’s understandable. Plus, most of the essay questions only add up to 2 to 4 marks. The italicized questions are the ones that this chapter has either answered or touched upon. We will be returning to these essay questions for each blog to see which ones have been answered and which ones are awaiting explanation. C’mon, guys, it’s going to be okay.



Page 44 elemental composition of living organisms

1. State the three most frequently occurring elements in living organisms, which are omitted from the bar charts.

carbon, hydrogen, and oxygen

2. State which are the fourth and fifth most frequently occurring elements are in:

a) Canis —> nitrogen (N) and calcium (Ca)

b) Chara —> potassium (K) and calcium (Ca)


a) Calculate the difference in nitrogen content between Canis and Chara.

82% (Canis) – 21% (Chara) = 61%

b) Suggest a reason for the difference in nitrogen content.

Canis (a dog, basically) is a larger organism than Chara (a simple pondweed) and will therefore require more nitrogen, which is one of the four most common elements found in all living things. The bigger size of the Canis entails a larger necessity for nitrogen. Chara itself is just smaller than Canis and doesn’t require as much nitrogen.

4. Using the detain the bar chart, compare the elemental composition of Canis and Chara.

While the top fourth to eleventh elements of Canis includes chlorine (Cl), the top fourth to eleventh elements of Chara includes manganese (Mn). Canis has an equal number of a non-metallic elemental composition (4/4) while Chara has an unbalanced elemental composition of its non-metallic-metallic elements (¾).  Canis also has a far greater composition of nitrogen (around 82%) as opposed to Charis’s composition of only 21% nitrogen. Similarly, Canis holds a composition of about 37% phosphorus while Chara only holds a grand total of about 3-4% phosphorus. On the other hand, while Canis has only about 7% potassium (K), Chara has a composition of about 35% potassium. Both Canis and Chara have about the same composition of sulfur (about 1-2%).

§ One Response to 3.1 Chemistry of Life

  • Dave Ferguson says:

    Grade 5 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them in a variety of situations.

    1. Nitrogen, Calcium and potassium
    2. a) Nitrogen, Calcium     b) Potassium, Calcium
    3. a) Chara 22 mg g-1. and Canis 82 mg g-1; [(82 – 22)/22] x 100% = 272% higher nitrogen content in Canis  b) Canis is an animal and contains more protein than Chara, which is plant; Nitrogen helps build protein thus there is more Nitrogen for Canis.
    4. Canis has higher nitrogen, phosphorus and calcium; On the other hand, Chara has higher Magnesium and Potassium; The total mass of elements per g dry matter is higher in Canis;. Sodium and Sulphur’s level are the same in both graphs; Canis has an insignificant amount of Mn/Chara has an insignificant amount of Cl

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