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IB Biology Objectives
Topic 2: The Chemistry of Life


Topic 1: Cells
Topic 2: The Chemistry of Life
Topic 3: Genetics
Topic 4: Ecology and Evolution
Topic 5: Human Health and Physiology
Topic 7: Cell Respiration and Photosynthesis
Topic 8: Genetics
Topic 9: Human Reproduction
Topic 10: Defense Against Infectious Disease
Topic 11: Nerves, Muscles, and Movement
Topic 12: Excretion
Topic 13: Plant Science
Option E: Neurobiology and Behaviour
Option H: Further Human Physiology

2.1 - Chemical Elements and Water

2.1.1 State that the most frequently occurring chemical elements in living things are carbon, hydrogen and oxygen.

  • The most frequently occurring chemical elements in living things are carbon, hydrogen and oxygen.

2.1.2 State that a variety of other elements are needed by living organisms including nitrogen, calcium, phosphorus, iron and sodium.

  • A variety of other elements are needed by living organisms including nitrogen, calcium, phosphorus, iron and sodium.

2.1.3 State one role for each of the elements mentioned in 2.1.2.

  • Nitrogen is a major element of proteins and nucleic acid (for DNA and RNA). Calcium is neccesary for bone and tooth formation, blood clotting, and nerve impulse transmission. Phosphorus is also used for bone and tooth formation, and to balance acid and base concetrations in the body. Iron is a part of hemoglobin, a molecule needed to carry oxygen in the blood. Sodium balances both water in the body and acid/base concentration. It also functions in nerve function.

2.1.4 Outline the difference between an atom and an ion.

  • An atom has the same amount of protons as electrons, so it is neutral in charge. An ion has either a positive or negative charge because there are unequal numbers of electrons and protons. A positive ion is called a cation, while a negative ion is called an anion.

2.1.5 Outline the properties of water that are significant to living organisms including transparency, cohesion, solvent properties and thermal properties. Refer to the polarity of water molecules and hydrogen bonding where relevant.

  • Water is transparent which allows light to filter into the oceans. This allows for aquatic plants to absorb light and perform photosynthesis. Since the ancestor of all plants originated in the ocean, the transparency of water has had a immeasurable influence on life as we know it.
  • Water is also cohesive, that is it binds to itself, due to the polarity of the water molecule. The positive, hydrogen side of the molecule binds to the negative, oxygen side of another water molecule. This bond is called a hydrogen bond Thus, a glass of water could be considered one giant molecule, because all of the water molecules inside of it are bonded to one another. This property allows for transport of water against gravity in plants.
  • Water is the universal solvent because it is capable of dissolving many organic and inorganic particles. All the reactions in cells must take place in aqueous solution.
  • Water's polarity also inhibits movement of its molecules. Since all the molecules are connected, they cannot freely move about as other, nonpolar molecules do. Heat, the kinetic energy of molecules, is thus restricted and so water has a high specific heat (it must absorb large amounts of energy in order to change states). This means that water can serve as a temperature insulator, and does so in organisms of all kinds.

2.1.6 Explain the significance to organisms of water as a coolant, transport medium and habitat, in terms of its properties.

  • Water's high specific heat allows it to absorb large amounts of energy and act as an insulator for all living things. For example, our bodies use water in the for of sweat to lower body temperature. The sweat absorbs a large amount of heat, and then evaporates carryiing that heat away from the body.


2.2 Carbohydrates, Proteins, and Lipids


2.2.1 Define Organic


            Organic: Compounds containing carbon that are found in living organisms,                      except hydrogen carbonates, carbonates and oxides.



2.2.2 Draw the basic structure of a generalized amino acid




2.2.3 Draw the ring structure of glucose and ribose










2.2.4 Draw the structure of glycerol and a generalized fatty acid.




2.2.5 Outline the role of condensation and hydrolysis in the relationship between monosaccharide, disaccharides and polysaccharides; fatty acids, glycerol and glycerides; amino acids, dipeptides and polypeptides.

            For monosaccharide, fatty acids, and amino acids to become disaccharides, glycerol, and dipeptides, a condensation reaction needs      to         occur. When these monomers covalently bond, a water molecule is      released; this             is a condensation reaction. When many monomers join together through           condensation reactions, polymers result.  In a hydrolysis reaction, the addition of       a water molecule breaks down the covalent bonds and polymers break down   into monomers.

                        Hydrolysis                                         Condensation

Action             water used in bonding                      water released in bonding

Sugars            disaccharide ==> monosaccharide          monosaccharide ==> disaccharide

Fats                fat ==> fatty acid + glycerol  fatty acid + glycerol ==> fat

Glycerides      triglyceride ==> glycerol                   glycerol ==> triglyceride

Peptides        polypeptide ==> dipeptide               dipeptide ==> polypeptide

                        dipeptide ==> amino acid                amino acid ==> dipeptide




2.2.6       Draw the structure of a generalized dipeptide, showing the peptide       linkage.




2.2.7       List two examples for each of monosaccharides, disaccharides and polysaccharides.

            Examples of monosaccharides are glucose, fructose, and galactose.              Examples of disaccharides are sucrose, maltose, and lactose.  Examples    of         polysaccharides are starch, glycogen, cellulose, and chitin.

2.2.8       State one function of a monosaccharide and one function of a    polysaccharide.

            The monosaccharide glucose is used to produce ATP.  The      polysaccharide          glycogen is used to store glucose until needed for ATP formation.

2.2.9       State three functions of lipids.

            Lipids are used as storage depots for energy (fats), as a structural       component     of the cell membrane (phospholipids), provide support (cholesterol), and create hormones (testosterone, estrogen, progesterone).

2.2.10  Discuss the use of carbohydrates and lipids in energy storage.

            The use of carbohydrates in energy storage is through its sugar polymers,      glycogen in animals and starch in plants. These sugars are released when            the demand for sugar increases. Animals use lipids, mainly fats, for long-term      energy storage.

Topic 2.3 - Enzymes
2.3.1 Define enzyme and active site.
An enzyme is a globular protein functioning as a biological catalyst. An active site is the site on the surface of an enzyme to which substrate or substrates bind.
2.3.2 Explain enzyme-substrate specificity.
An enzyme has an active site that fits with one specific substrate, like a lock and key.
2.3.3 Explain the effects of temperature, pH and substrate concentration on enzyme activity.
For all enzymes, there is an optimum temperature at which the maximum amount of collisions occur in the active sites. As the temperature decreases, there is less movement and fewer collisions, so enzyme activity decreases. There is a limit to which the enzyme activity can increase because at a certain temperature the enzymes denature. This means that the enzyme changes shape and no longer fits with its substrate. Also, as the substrate concentration increases, so does the enzyme activity, but there is also a limit to the increase in enzyme activity because there is a limit to how quickly the enzymes can catalyze each reaction. There is a specific pH at which the enzyme will denature, and so pH also plays a part in enzymatic activity.
2.3.4 Define denaturation.
Denaturation is a structural change in a protein that results in a loss of its biological properties.
2.3.5 Explain the use of pectinase in fruit juice production, and one other commercial application of enzymes in biotechnology.
Pectinase is used in fruit juice production to break down the acidity of the juices. Also, during oil spills, oil-digesting bacteria are used to clean up the spills since these bacteria have enzymes that can break down oil.

2.4 DNA Structure

2.4.1   Outline DNA Nucleotide structure in terms of sugar (deoxyribose), base          and phosphate.

            DNA is composed of phosphate group, deoxyribose, and nitrogenous base   (adenine, guanine, cytosine, thymine).  The phosphate group is attached to one      side of the sugar, and the nitrogenous base is attached on the other side of the     sugar. 

2.4.2       State the names of the four bases in DNA.

            Adenine, Guanine, Thymine, Cytosine

2.4.3       Outline how the DNA nucleotides are linked together by covalent bonds into a single strand.

o       phosphate and sugar share an electron (covalent bonding)

o       nucleotides join to form polymer (DNA strand)

o       backbone = phosphate-sugar-phosphate-sugar

o       bases project to one side of polymer


2.4.4       Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds.

            Each sugar of the backbone (sides of the "ladder") is covalently bonded to a nitrogenous base. Each of these bases forms hydrogen bonds with its      complimentary nitrogenous base, forming the '"rungs" of the "ladder". The sides   of the ladder are composed of alternating sugar and phosphate groups. The rungs are each composed of two nucleotides which are attached to the sugars of           opposite sides of the DNA ladder and are attached to   each other by hydrogen        bonds.



2.4.5   Draw a simple diagram of the molecular structure of DNA.


Topic 2.6 - Transcription and Translation

2.6.1. Compare the structure of RNA and DNA.

RNA has the ribose sugar while the DNA has the deoxyribose sugar in its structure. RNA is only one single strand while DNA has a double helix with two strands. Also, the thymine nucleotide of DNA is replaced by uracil in RNA (uracil, like thymine, attaches to adenine by hydrogen bonds).
2.6.2. Outline the DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase.
The synthesis of RNA uses DNA as a template. First, the two strands of DNA are separated in a specific place. Then, with the help of RNA polymerase, RNA nucleotides attach to their complimentary bases on one side of the exposed DNA strand. This creates a single strand of complimentary nucleotide bases. After this is done, the RNA molecule separates from the DNA.
2.6.3. Describe the genetic code in terms of codons composed of triplets of bases.
The genetic code for an amino acid is contained in DNA as a series of three nitrogenous bases. Each of these triplets (codons) code for a particular amino acid.
2.6.4. Explain the process of translation, leading to peptide linkage formation.
After transcriptions, the mRNA moves out of the nucleus into the cytoplasm where the mRNA attaches ro a ribosome. In the cytoplasm there are transfer RNA (tRNA) molecules. These molecules are composed of a short RNA molecule folded into a specific shape. Each tRNA molecule is shaped so that it bonds to a certain amino acid. Each tRNA molecule also has an anticodon which compliments a certain mRNA codon. Once the mRNA attaches to a ribosome, it acts as a sort of conveyor belt. The tRNA molecules attach to the mRNA according to the complimentary nature of their bases. For example, a tRNA molecule with the anitcodon ACC will carry the amino acid tryptophan. This tRNA molecule will attach to the codon UGG on the mRNA because UGG complements ACC. After two tRNA molecules are attached to the mRNA, they bond and the first tRNA molecule is released. Then another tRNA molecule connects to the mRNA etc, and the polypeptide is created.
2.6.5. Define the terms degenerate and universal as they relate to the genetic code.
Degenerate means that multiple triplets code for the same amino acid. For example, UUU and UUC both code for phenylalanine. Universal refers to the fact that this genetic code occurs in all living organisms.
2.6.6. Explain the relationship between one gene and one polypeptide.
One gene corresponds to one polypeptide. It does not, however, always code for a protein, because many proteins consists of more than one polypeptide.

Topic 2.7 - Cell Respiration
2.7.1. Define cell respiration.
Cell respiration is the controlled release of energy in the form of ATP from organic compounds in cells.
2.7.2. State that in cell respiration, glucose in the cytoplasm is broken down into pyruvate with a small yield of ATP.
In cell respiration, glucose in the cytoplasm is broken down into pyruvate with a small yield of ATP.
2.7.3. Explain that in anaerobic cell respiration, pyruvate is converted into lactate or ethanol and carbon dioxide in the cytoplasm, with no further yield of ATP.
In anaerobic cell respiration, pyruvate is converted into either lactate by lactic acid fermentation or ethanol and carbon dioxide during alcohol fermentation. This produces no further yield of ATP. The ethanol and carbon dioxide are produced in yeast whereas lactate is produced in humans.
2.7.4. Explain that in aerobic cell respiration, pyruvate is broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.
In aerobic respiration, each pyruvate enters the Krebs cycle, a series of chemical reactions within the mitochondria. Just before this cycle, the pyruvate is decarboxylated, which produces the carbon dioxide, and the remaining two-carbon molecule reacts with a reduced Coenzyme A, and at the same time one NADH+H+ is formed. The pyruvate then enters the cycle, with the end result being the production of 3 NADH, 3 H+, 3 carbon dioxide molecules, and one ATP. The NADH and H+ molecules will be used in the electron transport chain (ETC), where the H+ will react with oxygen to produce water. The result of the ETC is a large yield of ATP.

 Topic 2.8 - Photosynthesis

2.8.1. State that photosynthesis involves the conversion of light energy into chemical energy.

  • Photosynthesis involves the conversion of light energy into chemical energy.

2.8.2. State that white light from the sun is composed of a range of wavelengths (colors).

  • White light from the sun is composed of a range of yi on its structure, absorbs different wavelengths that correspond to different shades of color. The remaining wavelengths or colors are reflected and give rise to the percieved color of the plant.

2.8.3.  State that chlorophyll is the main photosynthetic pigment.

            State that chlorophyll is the main photosynthetic pigment.

2.8.4   Outline the differences in absorption of red, blue and green light by chlorophyll.

            Chlorophyll absorbs red and blue light from the sunlight that falls on      leaves. Therefore, the light reflected by the leaves is diminished in red and   blue and appears green.


2.8.5. State that light energy is used to split water molecules to give oxygen and hydrogen, and to produce ATP.

  • Light energy is used to split water molecules to yield oxygen and hydrogen, and to produce ATP.

2.8.6. State that ATP and hydrogen are used to fix carbon dioxide to make organic compounds.

  • ATP and hydrogen are used to fix carbon dioxide to make organic compounds.

2.8.7. Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by the increase in biomass.

  • The rate of photosynthesis can be measured directly by the production of oxygen because oxygen is produced as water is split in photosynthesis. The more oxygen, the greater the rate at which photosynthesis is occurring. Carbon dioxide is needed for the Calvin cycle which eventually produces the carbohydrates of photosynthesis. Therefore, the more carbon dioxide, the greater the rate of photosynthesis. An increase in biomass means that more photosynthesis is occurring since the latter produces sugars which increase the biomass of the plant.

2.8.8. Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis.


            An increase in temperature causes an increase in photosynthesis.       However, in    very high temperatures, the rate of photosynthesis dramatically drops after a      period of time, due to the denaturing of key enzymes and proteins. The more         light you have, the more photosynthesis occurs, as there is now more energy to          drive the reaction. However, light intensity can lead to overly high temperatures          and their previously noted damaging effects. Also, the more carbon dioxide you    have, the greater the rate of photosynthesis. Carbon dioxide is used as the base       molecule that will eventually be converted into a sugar. The greater abundance        of it, the more will enter the plant, and the greater the rate at which             photosynthesis can proceed.