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What is DNA?
Deoxyribonucleic acid, abbreviated DNA, is a macro molecule containing genetic information which characterizes each organism this information is used in the development and maintenance of the organism. Smaller segments of DNA are known as Genes. DNA is wrapped around proteins forming longer structures known as chromosome having an ‘X-like’ figure. DNA consists of two strands that are in opposite directions often called DNA double helix. In biological terms DNA contains what is known as a backbone made of phosphate groups and sugar groups. Attached to each phosphate-sugar complex (specifically the sugar) is a base/nucleobase forming what is known as a nucleotide. These bases are what are responsible for genetic coding.

DNA
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Shortly before cell division DNA needs to be duplicated so that the resulting daughter cells, after the cell has divided, contain equal amounts of DNA. The process whereby the DNA duplicates to produce new ones is known as DNA Replication.

Here are the major steps involved in DNA replication:

Step 1
The protein Helicase splits the double stranded DNA molecule forming two single stranded templates. (These templates are what will be the guide for the formation of the new strands; that is each strand will be copied to produce new ones. In the end there will be two DNA double helix, each made from one of the old strand and a new strand.)

Helicase unwinds DNA Double Helix





Step 2
After the DNA double strand has been split special binding proteins known as Single-Stranded DNA Binding proteins (SSB) then come along and attach to the recently separated DNA strands preventing the strands from reannealing. Without these proteins the strands could easily reform the double helix.

SSB prevents DNA Reannealing





Step 3
DNA polymerase comes along and attaches itself to one strand, as it moves along this strand it joins incoming nucleotides together continuously in the 5' to 3' direction forming a new strand. Because the newly formed strand is continuous, it is called the leading strand. However the second strand allows for nucleotides to be synthesized in a discontinuous pattern, the newly formed strand is impeded and is therefore called the lagging strand. In order for replication to begin on the second strand RNA primase comes along and synthesizes RNA primers. A different DNA polymerase then comes along and joins the incoming nucleotides also in the 5' to 3' direction (but is moving in a different direction from the continuous strand; please refer to diagram below). This DNA polymerase however synthesizes shorter discontinuous strands and stops where it meets another RNA primer; the polymerase will then go back up to another newly formed RNA primer and again start to synthesize more nucleotides.

Action of DNA Polymerase





Step 4
The enzyme RNAse H then comes and removes the recently synthesized RNA primers on the lagging strand. This leaves small gaps in what should be the newly synthesized strand. Because this isn’t a continuous strand but more like fragments we would call them Okazaki fragments. (Note: The leading strand also had to have RNA primers to begin replicating, however this didn’t pose any problems because the type of DNA polymerase used caused the strand to be continuous.)

Okazaki Fragments





Step 5
DNA Ligase then comes and fills the short gaps between the Okazaki fragments to form the new COMPLETED strand (lagging strand). The replication process is now complete and we have two new double stranded DNA.

Two newly formed DNA


References:

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What is Cellular Respiration?
Cellular respiration is a metabolic process involving many different reactions taking place; organic compounds are oxidized in these reactions and energy is produced. These organic compounds are known as respiratory substrates. Respiratory substrates include:

     o Carbohydrates
     o Lipids
     o Proteins

When these substrates are oxidized cells can use the energy produced to carry out their normal processes. The main aim of cell respiration is to produce energy; this energy is in the form of ATP.

The many reactions which take place during cellular respiration can be divided into three stages:
  1. Glycolysis: This stage involves the oxidation of glucose forming pyruvate and takes place in the cytoplasm of the cell (2ATP’s produced)
  2. Krebs cycle: Breaks down pyruvate from glycolysis forming carbon dioxide and hydrogen (in the presence of oxygen) or forms ethanol/lactate (in the absence of oxygen). This stage takes place in the matrix of the mitochondria. (2ATP’s produced)
  3. Electron Transfer System: In this stage the hydrogen is oxidized by oxygen forming water and takes place in the inner membrane of the mitochondria. (34ATP’s produced)
Cellular Respiration Image
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Somewhere along these stages numerous amounts of ATP are produced which can then be utilized by the cell itself.
The availability of oxygen is what determines the fate of pyruvate, therefore different products can be obtained from these stages depending on whether oxygen is made available or not. There are two types of respiration, these are:
  1. Aerobic Respiration
  2. Anaerobic Respiration


Aerobic Respiration

When glucose is broken down in the cytoplasm the product formed is known as pyruvate. From this point the pyruvate can take one of two routes depending on whether oxygen is available or not. In aerobic respiration oxygen is made available. The purpose of this oxygen is to oxidize the pyruvate from glycolysis to ultimately form carbon dioxide and water (ATP’s are also produced along the way). The first stage involves the Krebs cycle where the pyruvate was broken to form carbon dioxide and hydrogen. This hydrogen then moves along to hydrogen carriers in the second stage (electron transfer chain) where it goes through a number of carriers and finally gets oxidized by oxygen forming water. Combining the equations from glycolysis, Krebs cycle and the electron transfer chain we get:

     C6H12O6+ 6O2  => 6CO2 +6H2O + 38ATP (Energy)

Note that 38 ATP’s are produced in aerobic respiration, compare this with the amount of ATP’s produced during anaerobic respiration and you should see why aerobic respiration is more efficient than anaerobic respiration.

Anaerobic Respiration (Fermentation)

In this type of respiration oxygen is absent which therefore means different products will be formed from the point where pyruvate left glycolysis. It might seem odd but there are organisms that can actually survive with and without oxygen, such organisms are termed facultative anaerobes. There are even organisms that can’t survive in the presence of oxygen; these organisms are called obligate anaerobes.
Remember from aerobic respiration that the purpose of the oxygen was to combine with hydrogen in the final stage to ultimately form water. However since oxygen is not present there is no acceptor at the end of the final stage (electron transfer chain) to combine with hydrogen. Since there is no final acceptor the hydrogen goes back and combines with the pyruvate preventing the release of any energy.
Anaerobic Respiration has two Pathways which depend on the type of organism:

   1. Anaerobic Respiration in Fungi

In fungi such as yeast Pyruvate is ultimately converted into ethanol and carbon dioxide (Alcoholic Fermentation) with an overall production of 2 ATP’s, allot of energy however still remains locked within ethanol.


     C6H12O6  => 2Ethanol + 2CO2+ 2ATP (Energy)


Despite being an inefficient source of energy production this process still has some uses. Uses of fermentation by Yeast include:

  • The production of alcoholic drinks such as wine and beer.
  • The Carbon dioxide produced is used in the manufacture of bread, because it allows for the dough to rise.
  • Though the energy still remains trapped in ethanol in countries such as Brazil it is used to make gasohol which can then be used to fuel cars.


  2. Anaerobic Respiration in Animals


In certain tissues such as muscle tissues in animals the pyruvate formed from glycolysis is ultimately converted to lactate with the formation of 2ATP’s, no carbon dioxide is produced in this type of anaerobic respiration. In animals buildup of lactate can result in a sensation of fatigue and cramps.


     C6H12O6   => 2Lactate + 2ATP (Energy)


As is the case with ethanol in fermentation much of the energy remains locked within the lactate which therefore means this path is also inefficient. The energy can however be released from the lactate if oxygen is later made available.

Image Showing Aerobic and Anaerobic Respiration
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Mesothelioma is a fatal disease that should be treated immediately to prevent further complications. Individuals who have been exposed to asbestos should get tested to determine if they have developed mesothelioma cancer or any asbestos related disease. Researchers and scientists are striving to find effective treatment options for providing the best possible treatment for mesothelioma patients. Since mesothelioma diagnosis is very poor because symptoms closely associated with other lung illnesses and take decades to manifest. Therefore, oncologists are trying to discover diagnostics methods that make mesothelioma prognosis process easy.

Electronic Nose - An Effective and Non Invasive Way to diagnose Mesothelioma
A team of researchers from Italy and the Netherlands have tested an electronic nose for mesothelioma diagnosis by testing a patient's breath. It is effective in diagnosing malignant pleural mesothelioma in which cancer cells aggressively spread. Because some other effective diagnostic methods for mesothelioma carry a high risk of complications, especially in elderly, as they get the disease because of its long latency.

Breath Test Shows Accuracy in Mesothelioma Diagnosis
In this study, the researchers conducted an experiment on three different groups of people: people with mesothelioma, people with a long-term professional exposure to asbestos but no mesothelioma symptoms, and healthy individuals. The results were encouraging looking for easier, non invasive and more accurate diagnostic method for mesothelioma. The electronic device showed 92.3% sensitivity and 85.7% specificity in distinguishing between mesothelioma patients from those who had been exposed to asbestos. The device also showed 85% accuracy in distinguishing mesothelioma patients from the healthy controls. The researchers repeated the measurements many times and yielded the same results.
Researchers of the Department of Respiratory Diseases at the University of Bari in Italy, and the Department of Respiratory Medicine in the Academic Medical Centre of the University of Amsterdam in the Netherlands, expect that electronic device that is referred as Cyranose 320 has diagnostic potential for malignant pleural mesothelioma. Researchers found that the device was approximately 80 percent accurate in determining whether a patient had mesothelioma. However, researchers continue to perform test to make sure that the results are consistent.
Prior diagnosing mesothelioma with this electronic device, the most common method for diagnosing mesothelioma is a test called a thorascopic biopsy. In this procedure a thin tube is inserted through an insertion to remove a piece of tissue. This procedure is somewhat risky because as it can cause lung collapsing, blood loss, embolism, hemorrhaging, subcutaneous emphysema and hemoptysis and other complications, especially in elderly patients.

Since, mesothelioma is caused by asbestos exposure can take decades to manifest, so by the time patient is diagnosed, the chances of recovery are reduced greatly. However, if the disease can be diagnosed earlier and more accurately, the patient can get the immediate mesothelioma treatment. According to researchers, electronic nose has diagnostic potential for mesothelioma and it is a non-invasive, safe and accurate tool for diagnosing mesothelioma, thus reducing the risks of complications in mesothelioma patients.

About The Author
Rachel Smith is a web enthusiast and professional webmaster of mesotheliomaresourceonline. She loves to write about mesothelioma research findings that help people and their loved ones suffering from mesothelioma.

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Glycolysis is one of three processes which occur in cellular respiration. It involves a glucose molecule going through a number of stages to produce 2 molecules of pyruvate in the end. This pyruvate is then passed on to another process of cellular respiration known as the Krebs cycle where another set of stages take place. The three most common stages of glycolysis are:

  1. Phosphorylation: Where a phosphate is removed from ATP and added to glucose.
  2. Lysis: Involving the splitting of fructose bisphosphate.
  3. Dehydrogenation: Involving the removal of hydrogen from triose phosphate.

However the above mentioned processes are just a summary of the major stages taking place. Now we’ll look at the 7 stages of glycolysis:

Stage 1
ATP donates a phosphate group to the glucose molecule containing 6 carbons. This is done to make the glucose molecule more reactive to continue through stages to come.

Stage 2
After the phosphate has been added the entire glucose phosphate molecule gets reorganized to form a fructose phosphate molecule.

Stage 3
A second ATP then comes along and further donates another phosphate group to the fructose phosphate again making it more active. Now fructose bisphosphate is formed.

Stage 4
After the addition of yet another phosphate to fructose phosphate forming fructose bisphosphate, the molecule then splits into two triose phosphate molecules each containing 3 carbons. The original molecule of fructose bisphosphate contained 6 carbons therefore when it splits each molecule would therefore have 3 carbons attached.

Stage 5
In this stage two things happen:

  1. Hydrogen atoms are lost from both triose phosphate molecules and gained by NAD. There is no net change in the concentrations of NAD and reduced NAD, because two oxidized NAD(one for each molecule of triose)are reduced when hydrogen is added forming 2 reduced NAD(again one for each molecule).
  2. Inorganic phosphate is again added to each triose phosphate molecule therefore making it more reactive.

Stage 6
Just after adding a phosphate group another is removed from each triose bisphosphate molecule. 2 ADP molecule gains these phosphate and forms 2 ATP (remember 1 from each molecule).

Stage 7
Two things happen in this stage:

  1. Another phosphate group is removed from each triose phosphate molecule 2 ADP molecules gains this phosphate to form 2 ATP molecules. The net synthesis of ATP in glycolysis is 2 because 2 ATP’s are lost in the first stages but in the end 4 ATP’s are produced.
  2. A water molecule is removed from each triose phosphate molecule. 2 pyruvate molecules are formed in the end.

The diagram below shows a representation of the stages above. Read through the stages and try to identify them in the diagram below.
Tip: Click on image to see larger view

Stages of Glycolysis

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What is the Mitochondria
The mitochondria also known as “the power house of the cell” plays a major role in cellular respiration. They can be found in eukaryotic cells where they perform aerobic respiration involving a number of reactions. Another important feature one should note about the mitochondria is that it uses ATP for energy supply, ATP means Adenosine Triphosphate. They can be found in large quantities in cells that require large amounts of energy for example liver cells which have approximately 1000 mitochondria and muscle cells.

Mitochondria
Via appliedsciencehelp.co.uk


What is Cellular respiration?
Respiration is a process involving the release of energy through oxidation which can later be used by cells; this energy is in the form of ATP. The biochemical process that occurs in cells is known as cell respiration and when the process takes place in the presence of oxygen it is termed aerobic respiration if oxygen is absent then we can say that anaerobic respiration is taking place.
Many cellular processes take place in the mitochondria such as the Krebs cycle and the electron transport system. Numerous amounts of ATP are produced along the way during these processes. The structure of the mitochondria also contributes greatly to cellular respiration:

  • The inner membrane of a mitochondria is highly folded so that a larger surface area is formed on which respiratory processes can take place.
  • There are numerous amounts of protons present in the mitochondria mainly in the inner membrane space. There is a higher concentration of protons in the inner membrane than in the matrix of the mitochondria, therefore using our knowledge of osmosis and diffusion right away we should probably realize that some form of transfer must happen involving the flow of protons from the area of high concentration to the area of lower concentration. This is where the stalked particles of the mitochondria come in. The role of the stalked particles is to allow the flow of protons back to the matrix of the mitochondria where there are fewer concentrations of protons present.
  • All we've been discussing so far is the transfer of protons, but what about the electrons. By now we should all know that an atom is not only made up of protons but also electrons in this case the atom is hydrogen. What happens is that once the protons have entered the matrix they will then recombine with the electrons to form the hydrogen atom. The hydrogen atom will then combine with oxygen to form water.
  • The membrane of the mitochondria is ion impermeable meaning it doesn't allow ions to pass through therefore active transport is needed for ions to cross.
  • Above we mentioned ATP as a source of energy but how does ATP really come about?... ...Well ATP (Adenosine Triphosphate) is made from a combination of ADP (Adenosine Diphosphate) and inorganic phosphate. It is the driving force of the protons as mentioned above that causes ADP to combine with inorganic phosphate.
  • The stalked particles contain the enzyme that catalyzes the reaction. The enzyme is known as Adenosine Triphosphatase.
  • The Phospholipid bi-layer is composed of two layers the first layer comprises hydrophobic tails that are structured inwardly. The other layer comprises hydrophilic heads that are turned outwardly. The head attracts water but rejects any protons present.
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You can now download the cape biology syllabus here for free. The CAPE BIOLOGY SYLLABUS which is similar to the A-Level syllabus provides students and teachers with an outline of the topics that should be covered within the school year. The syllabus is divided into two units:

  1. Unit 1 which should be covered within as students first year of sixth form
  2. Unit 2 which should be covered during the second year of sixth form.

Many persons have often times complained that the cape biology syllabus is too extensive which makes it difficult for teachers to complete in such a short period of time. Therefore it is up to the students to work on some topics on their own so it is essential that every student gets a copy of the syllabus whether hard copy or soft. I recommend you time your studying wisely using the syllabus and not always depend on the teacher. Remember that the exam is written based entirely on the syllabus so there’s not a question that will be given in the exam that isn’t covered in this syllabus.

Download Cape Biology Syllabus

You can also download the 2006 schools report here. This report identifies areas in past paper cape exams where students made mistakes and gives the correct answer.
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What are Inhibitors?
Some molecules are capable of lowering the activity of enzymes by binding with them; such molecules are known as Enzyme Inhibitors. Inhibitors can be used as poisons as well as medicines. Two major types of inhibitors are Competitive and Non-Competitive.

Competitive Inhibition
In competitive inhibition the inhibitor and the substrate compete for placement in the active site of the enzyme. These inhibitors are said to have the same shape to that of the substrate and prevents the enzyme/substrate complex from forming. This is done when the inhibitor enters the active site thus preventing the substrate from entering. Therefore the rate of reaction is decreased due to less substrate molecules binding to the active site. This type of inhibition can be overcome by increasing the substrate concentration.

Competitive Inhibition

Non-Competitive Inhibition
In this form of inhibition the inhibitor does not compete with substrate for a place in the active site but however does reduces enzyme activity by binding to another site on the enzyme known as the Allosteric site. Unlike the competitive inhibition, non-competitive inhibition prevents the formation of products from substrates (enzyme/product complex). Another thing to note about these inhibitors is that they are unaffected by substrate concentration thus most of them are permanent.

Non-competitive Inhibition

Examples of inhibition:
The inhibitor poison malonate can prevent respiration by binding to the enzyme Succinate Dehydrogenase thus preventing succinate from entering the active site by competing with it.
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What are Enzymes?


Enzymes are molecules which catalyze chemical reactions. Enzyme molecules are large and globular and possess catalytic properties. Before modern discoveries all enzymes where thought to be proteins, but that belief was dismissed when some where proved to be made of RNA, however most enzymes are proteins. The configuration of an enzyme molecule is as a result of bonding such as hydrogen bonding, ionic bonding, disulphide bridges and hydrophobic interactions.

A Catalyst can alter the rate of a reaction without having itself undergo any permanent change. This therefore means that they can be used more than once.

Enzyme Function


In previous lessons we learned that the activation energy is the minimum energy required for a reaction to take place. Therefore reactions need to exceed their activation energy in order for them to take place. Enzymes reduce this need for activation energy thus allowing reactions to take place more readily.

It also reduces the temperature at which reactions take place thus allowing them to take place at temperatures lower than normal.

The lock and key mechanism refers to the way the substrate molds itself to fit into the active site of the enzyme in the same way a key fits a lock.

Terms you should know: 

Active site: - This is the part on the molecule of an enzyme into which the substrate fits.
Activation energy: - Minimum energy required for a reaction to take place.
Substrate: - The molecule at the beginning of a reaction that is later converted into products.
Specificity: - Enzymes are specific to reactions they catalyze and the substrates involved.
Enzyme Catalyzed Reaction
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Metabolism


Chemical reactions are constantly taking place within living organisms this is known as metabolism.
Metabolism can be divided into two groups these are:

  1. Anabolism
  2. Catabolism

Anabolism Vs Catabolism


Anabolism is simply a phase of metabolism which results in the buildup of simple chemicals into more complex ones while Catabolism is the reverse; it involves the breakdown of complex chemicals into simpler ones.

In spontaneous chemical reactions the products will have a higher entropy that the reactants meaning they will have less free energy. However for chemical reactions to take place an initial input of energy is needed, this initial input of energy is known as the activation energy.

All chemical reactions are said to be reversible; simply put their direction is determined by their conditions. An example of this would be pH, high and low pH can cause reactions to proceed in opposite directions respectively.

Reactions are capable of releasing energy, in biology these are known as exergonic while some can absorb free energy these are known as endergonic.
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Osmosis is a kind of diffusion in which water molecules move through a partially permeable membrane from a more dilute solution to a more concentrated solution.

Isotonic Solutions
Isotonic means the concentration of the solute is the same as that of the cell. In these solutions no change occurs to the cell. The diagram below shows the effect of isotonic solutions on cells.




Hypotonic/Weak Solutions
A Hypotonic solution is one in which the concentration of the solute in the solution is less than that of the cell. Examples of these include dilute sugar solutions or water. In these solutions the plant cell will absorb water by osmosis to become turgid (stiff), the cytoplasm and vacuole will also increase in volume and the cell wall will stretch. The diagram below shows a plant cell in a hypotonic solution.





Hypertonic/Strong Solutions
A Hypertonic solution is one in which the concentration of the solute in solution is greater than the concentration in the cell. Here the cells have a higher water potential than the solute. The plant cell loses water by osmosis to become flaccid, its vacuole decreases in volume and the plasma membrane shrinks from the cell wall. The diagram below shows this effect:




Other Resources:

To perform a lab/experiment involving plant cells immersed in different solutions click here
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Substances can enter or leave the plant cell through two known processes these are active and passive transport. Active processes involve the use of energy while passive processes do not involve the use of energy but depends mainly on the permeability of the membrane. Active processes deal with the transfer of molecules and particles whereas passive processes involve diffusion, facilitated diffusion and osmosis.

What is Diffusion?
Diffusion can be defined as the movement of particles from an area where they are at a high concentration to areas where they are at a lower concentration. This will continue until the particles' concentration is uniformed throughout.

What is facilitated Diffusion?
This involves the movement of specific molecules down a concentration gradient (difference in concentration). This is done using a carrier protein, which binds to the molecule allowing it to pass through the membrane. Examples of these include amino acids and glucose.

What is Osmosis?
This is the movement of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential. Having a partially permeable membrane means it only allows for some molecules to pass through but not all usually it does not allow for larger solute molecules to pass through.

Active Transport
This is the movement of molecules against a concentration gradient (from lower to higher concentration) with the use of energy. The energy supplied comes from ATP of the mitochondria.

The table below shows examples where the processes mentioned above are operative:


Process
Cases where process is taking place
Diffusion
Gas exchanges in photosynthesis:
·         More carbon dioxide is outside the leaf than inside so carbon dioxide will diffuse into the leaf while the opposite happens for oxygen.
Facilitated Diffusion
Glucose is too large to pass through pores of the membrane therefore it has to bind to a specific carrier protein in order to pass through.
Osmosis
In the roots of plants water is absorbed from the soil.
Active Transport
Re-absorption of salts in the proximal convoluted tubule.


Other Resources:

   Click here to see a PDF containing a more detailed explanation.
   Read Exocytosis | Endocytosis
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These are cellular organelles found in animals they have many functions including breaking down waste materials as well as cellular debris using acid hydrolase enzymes. The digestive enzymes of a lysosome works around a pH of 4.5, it is the membrane surrounding this organelle that allows for these enzymes to work at this pH. Lysosomes contains a variety of enzymes namely, protease, amylase, phosphoric acid and lipase.

Below are some common functions of lysosomes:

  • Lysosomes as stated above, contains numerous amounts of enzymes, some of these enzymes are capable of digesting a wide variety of substances.
  • They are capable of digesting membranes and organelles, this function is of great importance because it allows cells to remodel or replace old organelles.
  • They are often called “suicide bags” because of their ability to rapidly digest an entire old cell.
  • Digesting foreign bacteria and other waste substances.
  • Digesting macromolecules.

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The Golgi apparatus is a composition of parallel membranes enclosing the cisternae, which is a flattened fluid-like space. The cisternae are slightly curved causing the entire structure to appear concave. Unlike others the Golgi is not a stationary cell organelle it disappears at the early stages of mitosis and re-appears during the late stages. The Golgi’s main function is to process proteins that are synthesized in the Endoplasmic Reticulum. It also has other functions these are listed below.


Functions of the Golgi apparatus:

  • Carries out its function of transporting and storing lipids.
  • Manufactures Glycoproteins, these are required in secretions.
  • The production of secretary enzymes.
  • Helps in the formation of Lysosomes.

Golgi Apparatus 
(image taken from here)
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Endoplasmic Reticulum
What is the Endoplasmic Reticulum?


In its simplest form these are membranes forming channels within the cytoplasm, they are continuous with the nuclear membrane and enclose the Cisternae (cellular spaces).


Types of Endoplasmic Reticulum(ER):
  • Rough Endoplasmic Reticulum(RER)
  • Smooth Endoplasmic Reticulum(SER)
Rough Endoplasmic Reticulum


RER is covered with ribosomes; these are tiny granules which help in the synthesis of proteins. It is because of these ribosomes why the RER has its name. Rough endoplasmic reticulum is found mainly in cells that are growing rapidly or that secrete proteins, some are also found in the pancreas which secretes insulin.

Smooth Endoplasmic Reticulum


SER has its name because it contains no ribosomes. Unlike RER it is mainly found in cells that secrete Steroids and lipid substances and serves its functions in many metabolic processes.

Functions of the Endoplasmic Reticulum:

  • It manufactures proteins and enzymes.
  • It manufactures Steroids as well as lipids.
  • It has a large surface area which allows for biological and chemical reactions to take place.
  • Collects and stores synthesized materials.
  • The cell carries out many processes including the transport and exchange of materials; therefore it is the ER which acts as a pathway for these transport and exchanges.
  • Maintenance of cellular shape by forming a structural skeleton.
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Water plays a vital role in the survival of different organisms. Water is said to occupy more than 70% of the earth’s surface and occupies approximately 60% of volume in plants and animals. Without water human and all life existence would be impossible. The diagram below shows the structure of a molecule of water, it is formed by the bonding of two hydrogen atoms to a central oxygen atom.


Looking at the diagram above one can see how the hydrogen atoms are bonded to the oxygen causing a polarity in the molecule; it is this polarity that causes more molecules to attract to each other through strong molecular bonds. When water changes phase the molecules are arranged differently this is further explained in the topic Different States of matter


Here are some physical properties of water and how they relate to their role and functions:
  1.  Water is a universal solvent: - This means it is capable of dissolving a wide variety of chemical substances, this feature allows water to carry solvent nutrients from infiltration, ground water flow, runoff and in different living organisms.
  2. Water is a Good Conductor of Heat: - It is said to conduct heat better than any other liquid except mercury. This feature is especially useful to lakes and other large water bodies; this allows them to maintain a uniform vertical temperature profile.
  3. Water has a High Surface Tension: - Meaning it has an elastic as well as adhesive structure. This allows it to aggregate in drops and not to spread over a surface as a thin film. It also sticks to the sides of vertical surfaces and not fall due to gravity. This feature is especially useful to plants, it enables them to move water from the roots to their leaves, and also the movement of blood in blood vessels in animals.
  4. Water has a high Specific heat: - The specific heat of a substance is the amount of heat required to change its temperature, therefore seeing that it has a high specific heat capacity it has to absorb allot of energy to get hot which takes quite some time and also releases energy slowly when in a cool setting. This helps to explain why sea breeze occurs at day but land breeze occurs at night, because it has a higher specific heat. This also helps in the moderation of the earth’s climate and also in the regulation of body temperature.
  5. Water has a neutral pH in the pure state: - This feature enables it to be neither acidic nor basic but changes pH when added to another substance
  6. Water is able to remain liquid over a wide range of temperatures 0-100 degrees Celsius: - This feature is of great importance because it is able to remain in the liquid form in most places on earth.
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 The late scientists Schwann and Schleiden devised a theory known as the Cell Theory which posed that a cell is the basic unit of structure and function in living organisms. A cell is surrounded by a membrane known as the Cell Surface Membrane which is a thin membrane acting as a barrier for the cell contents, its function is to control what molecules enter and leave the cell. All cells contain a structure known as the nucleus which comprises the chromatin, which is a coiled form of a chromosome, and the nucleolus. Next is the cytoplasm which contains the organelles, and is a jelly-like structure found between the cell surface membrane and the nucleus. Despite these common structures present in both animal and plant cells, they also have distinguishing features.

The table below analyzes the common differences between plant and animal cells.
    Plant Cell                                    Animal Cell                            
      Has a rigid cell wall
 Has no cell wall
          Has Chloroplasts
Has no chloroplast
       Has a Large Central vacuole   
       May have small vacuoles      


The image below shows more differences and similarities as well as the structures of  the plant and animal cell.

Image taken from evolution.berkeley.edu
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Genes are the fundamental units of inheritance which have the function of transmitting information from generation to generation. They are found on the portion of DNA that codes for polypeptide. Similar to genes are alleles which are the alternative form of a gene. However an allele can exist in more than two pairs.

Dominant Gene:- Is one that shows its effect in the phenotype in both homozygous and heterozygous conditions.
Recessive Gene:- A  gene that only expresses itself when in homozygous conditions.

Homozygous Vs Heterozygous

Homozygous refers to two identical alleles found on the same chromosome  while heterozygous refers to alleles that are unidentical.

Mono-hybrid Inheritance:

This is inheritance involving only one pair of contrasting characteristics.

Types of mono-hybrid inheritance:

Complete Dominance
  1. Complete Dominance:- This is where the dominant gene shows its effect more in the phenotype (75% in offsprings to be exact).

Characteristics of Complete Dominance:

  • Phenotypic ratio->> 3:1
  • Genotypic ratio->> 1:2:1
  • Both parents possess the same genotype and are heterozygous.

Incomplete Dominance/Codominance

In incomplete dominance each allele has the ability of expressing itself to some extent when in the heterozygous condition.  This is because of intermediate alleles, which are alleles which lask dominant and recessive relationship.


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When a mRNA( messenger RNA) leaves the nucleus it enters the cytoplasm. A group of ribosomes attract the mRNA, an attachment can then be formed. This attachment is known as a polysome.
tRNA( transfer RNA) on the other hand binds with its respective amino acid. This is determined by the anti-codon on the CCA end of the tRNA. A tRNA-amino acid complex is then formed.
The tRNA-amino acid complex is attracted to the codon of the mRNA by its anti-codon using complementary base pairing.

In its simplest form when the mRNA attaches itself to the ribosome, the first tRNA-amino acid complex  will then be attracted to the first codon on the mRNA. Similarly a second tRNA-amino acid complex will arrive and will be attracted to the second codon on the mRNA. The ribosome will then hold the mRNA and tRNA complex together until the amino acids are joined by a peptide bond. The ribosome will continue along the codons of the mRNA for each respective amino acid that arrives. A peptide chain would be formed by these amino acids. However the chain need to stop at some point. At this point a termination code or nonsense code will be used. When the ribosome reaches this code the chain will be cut off. The polypeptide chain will then form its relevant protein structure
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Vessels are very long, tubular looking structures and are the characteristic conducting units of angiosperm xylem. There are several cells that make up this structure and they are all connected end to end in a row. The vessel element represent each of the cells of a xylem vessel which is equivalent to a tracheid. How are vessels formed? well vessels are formed when vessel elements that are close bond as a result of the disintegration of their walls
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A protein molecule can lose its specific three dimensional shape either temporarily or permanently this is referred to as Denaturation. This change in shape prevents the molecule from carrying out its normal function. These however can be caused by different agents namely:
  1. Heat/Radiation
  2. Heavy metals.
  3. Detergents/organic solvents
  4. Strong Acids.
  5. Alkalis.
Although proteins denature some will again refold to their original structure, this is known as renaturation .
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