B.O.D.In respond to Question 31 Paper 1 SPM 2009

From a study on river X, this finding is obtained: Biochemical oxygen demand (B.O.D) value is high: Which statement is correct about the river: 

1. The river is POLLUTED. 2.The content of dissolved OXYGEN is LOW 3.The river contains LESS/NO living aquatic organisms. 4.The DECOMPOSITION activity by microorganisms is HIGH. 

Many students get confused over the B.O.D stuff which is related with the BOD experiment to test the pollution in different water samples.. 

Biochemical oxygen demand or BOD is a chemical procedure for determining the uptake rate of dissolved oxygen by the biological organisms in a body of water.

It is not a precise quantitative test, although it is widely used as an indication of the quality of water.

Moderately polluted rivers may have a BOD value in the range of 2 to 8 mg/L.

Municipal sewage that is efficiently treated by a three-stage process would have a value of about 20 mg/L or less. Untreated sewage varies, but averages around 600 mg/L in Europe.

The following notes will help you to understand more abot BOD:

Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, manure, sewage, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need to live.

Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose this waste. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline.

Nitrates and phosphates in a body of water can contribute to high BOD levels. Nitrates and phosphates are plant nutrients (maybe from organic fertilisers) and can cause plant life and algae to grow quickly. When plants grow quickly, they also die quickly. This contributes to the organic waste in the water, which is then decomposed by bacteria. This results in a high BOD level.

The temperature of the water can also contribute to high BOD levels. For example, warmer water usually will have a higher BOD level than colder water. As water temperature increases, the rate of photosynthesis by algae and other plant life in the water also increases. When this happens, plants grow faster and also die faster. When the plants die, they fall to the bottom where they are decomposed by bacteria. The bacteria require oxygen for this process so the BOD is high at this location. Therefore, increased water temperatures will speed up bacterial decomposition and result in higher BOD levels. 

When BOD levels are high, dissolved oxygen (DO) levels decrease because the oxygen that is available in the water is being consumed by the bacteria. Since less dissolved oxygen is available in the water, fish and other aquatic organisms may not survive. 

Test Procedure: 

The BOD test takes 5 days to complete and is performed using a dissolved oxygen test kit. 

The BOD level is determined by comparing the DO level of a water sample taken immediately with the DO level of a water sample that has been incubated in a dark location for 5 days. 

The difference between the two DO levels represents the amount of oxygen required for the decomposition of any organic material in the sample and is a good approximation of the BOD level. 1.Take 2 samples of water 2.Record the DO level (ppm) of one immediately using the method described in the dissolved oxygen test. 3.Place the second water sample in an incubator in complete darkness at 20 °C for 5 days. If you don't have an incubator, wrap the water sample bottle in aluminum foil or black electrical tape and store in a dark place at room temperature (20 °C or 68 °F). 4. After 5 days, take another dissolved oxygen reading (ppm) using the dissolved oxygen test kit. 5. Subtract the Day 5 reading from the Day 1 reading to determine the BOD level.

6.Record your final BOD result in ppm. 

RESULT: 

BOD Level(in ppm) Water Quality 1 - 2 Very Good:There will not be much organic waste present in the water supply. 3 - 5 Fair: Moderately Clean 6 - 9 Poor: Somewhat PollutedUsually indicates organic matter is present and bacteria are decomposing this waste. 100 or greater Very Poor: Very PollutedContains organic waste. 

NOTE: Generally, when BOD levels are high, there is a decline in DO levels. This is because the demand for oxygen by the bacteria is high and they are taking that oxygen from the oxygen dissolved in the water. If there is no organic waste present in the water, there won't be as many bacteria present to decompose it and thus the BOD will tend to be lower and the DO level will tend to be higher.

..As for our experiment in our Bio Lab (Malaysian version), we are using methylene blue solution (which is blue in colour ) and will DECOLORIZE faster if there is less dissolved oxygen in the water sample…Vice versa… 

…The more polluted the water sample is, the faster the methylene blue solution to decolorise .. 

Isotonic, hypotonic and hypertonic

Red blood Cells/ erythrocytes

Plant cells

Explain what hypotonic, hypertonic and isotonic solutions are

1. Hypotonic solution refers to a solution that contains less solute compared to the cytoplasm of the cell.2. If the solution surrounding the cell is hypotonic, osmosis causes water to have a net flow into the cell,3. Hypertonic solution refers to a solution, has a higher concentration of solutesthan another solution, so that water is drawn out of the cells and into the solutionby osmosis.4. A hypertonic solution is the opposite of a hypotonic solution.5. isotonic solution - is a solution where the solute concentration of the solution that the cell is in is the same as the solute concentration of the cell's cytoplasm.

Explain the effect of hypotonic, hypertonic and isotonic solutions on plant cell and animal cell.

Animal and plant cells in an isotonic solution

When a cell is placed in a solution where the solute concentration is the same on both sides of the cell membrane, they neither gain nor lose water by osmosis.

Such a solution is said to be isotonic.

Cell in an isotonic environment is in a state of equilibrium with its surroundings.

When the amount of impermeable solute is the same on the inside and outside of the cell, osmotic pressure becomes equal; the force of water trying to exit and enter the cell balances out.When red blood cells are placed in a 0.9% salt solution, the cell will neither shrink nor swell. So 0.9% sodium chloride (salt) solution is isotonic to blood cells.

When onion cell is placed in an isotonic solution such as 5% sucrose solution, there is no change in its shape because there is no net movement of water by osmosis.

Plant cells in an isotonic environment are flaccid, and they will wither.

The equilibrium of water movement is unable to provide plant cells with internal pressure for structural support, and therefore plants prefer to live in a hypotonic environment.

In this situation, the concentration of solutes inside plant cells is higher than outside, and the plants use active transport to transport solutes in. This also ensures the concentration of water will be higher outside plant cells than inside.

Explain plasmolysis, deplasmolysis, heamolysis and crenation.

Animal and plant cells in a hypotonic solution

1. When an animal cell is set to a hypotonic environment the cell will eventuallylyse (rupture) due to the osmotic pressure.2. A red blood cell placed in a hypotonic solution (e.g., pure water/distilled water) water will enter by osmosis. The red blood cell would take in a lot of water and might lyse ("hemolysis")due to pressure inside. This is a possible because animal cells have no tolerance under hypotonic situations.3. In a plant, the cell will not lyse but become turgid because of its strong cell wallthat prevents it from bursting. These allow the buildup of turgor within the cell. When the turgor pressure equals the osmotic pressure, osmosis ceases.In fact, it is the osmotic pressure (or turgor pressure) that helps keep the plant from wiltingand losing its shape.4. Turgidity is important in young plants where its help in support.

Animal and plant cells in a hypertonic solution

1. In animal cells, being in a hypertonic environment results in crenation, where the shape of the cell becomes distorted and wrinkled as water leaves the cell by osmosis.2. Examples of hypertonic solution is sea water, 5% sodium chloride solution, 30% sucrose solution3. In plant cells, the cell membrane pulls away from the cell wall, but the cell remains joined to the adjacent cells at points called plasmodesmata. This condition is known as plasmolysis.

4. Plasmolysis is the seperation of plant cell cytoplasm from the cell wall as a result of water loss. The plant cell becomes flaccid (soft and weak)5. If the plasmolysed cell is placed in a hypotonic solution, it will absorb water causing the cytoplasm to expand and comes into contact with the cell wall again. This is called deplasmolysis.

The effects and applications of osmosis in everyday life

1. Osmosis has a number of life-preserving functions: it assists plants in receiving water, it helps in the preservation of fruit and meat, and is even used in kidney dialysis.2. In addition, osmosis can be reversed to remove salt and other impurities from water.3. The excessive use of chemical fertilizers will cause the plant cells to lose water. Plant cells plasmolysed and later on the whole plant wilt.4. Dissolved ions from chemical fertilisers such as phosphates, nitrates, calcium, and magnesium, in the soil around the roots and root hairs, will cause the increase in solute concentration, but decrease in water molecules concentration, hence, water diffuse from the cell sap into soil water by osmosis.5. When water is drawn out of the plant cell, the cytoplasm shrink away from the cellulose cell wall and cause plasmolysis.6.Plasmolyzed cells lose turgidity and support, causing the whole plant to wilt.7. Osmosis helps us in preserving food. So that it last longer. By using a concentrated salt or sugar solution, all the water molecules within the food cells are drawn out by osmosis.8. The food without water will hinder the bacteria and fungus from growing.9. Animals living in an aquatic environment which are not isotonic to their body tissue may face problem due to the process of osmosis.10. For example, unicellular organism such Paramecium sp. Living in fresh water, Paramecium has a higher concentration of materials inside the cell than are present in the outside environment. Thus, water is constantly flowing into the cell through the process of osmosis. Paramecium has two contractile vacuoles that eliminate water entering the cell by through osmosis and help maintain osmotic equilibrium.11. Paramecium must constantly be expelling water to prevent the cell from becoming bloated with water and potentially bursting.12.The plasma membrane, being semi permeable to certain substances will act as a gate keeper, regulating what goes in and out of the cell.13. If there is any defect in the plasma membrane, many essential processes in the cells cannot be carried out. Thus the proper functioning of the plasma membrane is important to our health.14. In order to maintain the proper function of the plasma membrane and the cell as a whole, it is important for us to take care of our food and water intake.

Questions for you to try out:

1. Cucumber slices are immersed in 0.1% sucrose solution. After 3 hours, the slices are found to be turgid and hard.Which of the following statements explains this phenomenon?A The cucumber cell wall prevents it from shrinkingB The cell sap is hypotonic towards the sucrose solutionC The high concentration of the cell sap in the vacuole causes water to diffuse inD The cucumber cell wall allows the sucrose molecules to diffuse into the cell

2. A plant cell immersed in distilled water. Which of the following is true about the movement of water molecules in the early stage?A The rate of water molecules exiting the cell is higher than entering the cellB The rate of water molecules entering the cell is higher than exiting the cellC No water molecules are entering or exiting the cellD The rate of water molecules entering and exiting the cell is the same

3. Siti is going to prepare some mango pickle. First, she cuts and washed the mangoes. Then she adds vinegar and sugar to the mangoes. After one month, the mango pickle remains in good edible condition becauseI The pH of the solution is lowII The bacteria that cause food spoilage loses water to the surroundingsIII The dehydrated condition of the fruit inhibits the grouth of bacteriaIV The high concentration of vinegar in the pickles is not conducive to the growth of bacteriaA I, II and III onlyB I, III and IV onlyC II, III and IV onlyD I, II, III and IV

4. A plasmolysed cell can revert to its normal condition by beingA Immersed in pure waterB Immersed in a concentrated salt solutionC Immersed in 10% sugar solutionD Taken out quickly from the solution

5. Which of the following processes is affected by the presence of a metabolic poison?A Absorption of water by root hairsB Uptake of iodine by algae living in the seaC Absorption of digested food in the small intestineD The movement of amino acids across the plasma membrane

6. Preservation of the food by eliminating water from the food involvesA osmosisB simple diffusionC active transportD facilitated diffusion

ESSAY QUESTION:1(a) A student made the following observation.

The effects of distilled water on red blood cells differ from those on onion cells whenboth are placed in equal volumes of distilled water.

Explain the student’s observation. [5 marks]

(b) Some housewives believe soaking vegetables in salt solutionbefore cooking can help eliminate the harmful effects ofinsecticides that are sprayed on the vegetables.(i) Explain why vegetables become soft if they are soaked too long

in salt solution.(ii) Suggest how the housewives can restore the vegetables whichHave become floppy to their normal condition. [5 marks]

Suggested Answer:1(a)- Distilled water is hypotonic to the cytoplasm of red blood cells and the cell sap of the onion cells.(1m)- Osmosis occurs, resulting in a net flow of water from the surrounding into thecell.(1m) - The red blood cells will swell and eventually burst (1m)- The vacuoles in the onion cells expand, and the plant cells become turgid (1m)- However, the cell wall prevents the onion cells from bursting because it is toughand rigid (1m)

(b)(i) -Vegetables which are soaked too long in a salt solution will become soft becausethe salt solution is more hypertonic than the cytoplasm of the vegetable cells (1m)-Water flow out of the cells, causing the cytoplasm and the vacuoles to shrink (1m).-The plasma membranes pull away from the cell walls (1m)-In this condition, the cells are said to be plasmolysed (1m)(ii) To make the vegetables crisp again, housewives can soak the vegetables in water (1m)

Plasma membrane- Sample QS

The figure shows a fluid mosaic model of the plasma membrane

(a) Explain the functions of the structures X, Y and Z in the movement of substances across the plasma membrane[4 marks]

(b) All movements of substances have to pass through a plasma membrane. Explain why the plasma membrane is known as a semi permeable membrane(6 marks)

Suggested Answer:

(a)· Structure X allows hydrophobic molecules which can dissolve in lipids such as fatty acids, glycerol, steroid hormones, vitamins A, D, E and K to move in and out of the cell.

· Structure Y allows bigger molecules which do not dissolve in lipids like glucose and amino acids to move in and out of the cell.

· Structure Z allows small charged molecules to move in and out of the cell.

(b)

· The plasma membrane is known as a semi permeable membrane because it only allows the passage of certain molecules and limits the passage of other molecules.· It consists of two layers of phospholipids with protein molecules scattered in them· Molecules that can pass through the plasma membrane easily are those that can dissolve in lipid and small uncharged molecules.· Molecules which cannot move through the plasma membrane but require proteins include large molecules that do not dissolve in lipid and small charged molecules.· Channel protein does not require the binding of a molecule and conformational change to open.· Channel protein allows molecules to steadily diffuse across the membrane through diffusion.· However a carrier protein allows specific molecules to cross the cell membrane by undergoing a conformational change upon the binding of the molecule.· The conformational change opens a hole through which the molecule can enter or leave a cell.

Pore protein Versus Carrier protein

The protein molecule that forms a channel or a pore is known as channel or pore protein, while the protein that acts as a carrier is known as carrier protein.

Both are transport proteins which regulate the movement of water-soluble molecules and ions through the plasma membrane.

Carrier protein· a protein which transports specific molecules or ions pass through the plasma membrane in which it is embedded and into the cell.

What is the difference between the behavior of Channel Protein and Pore protein?

Answer:

Channel proteins do not require the binding of a molecule and conformational change to open.

Channel proteins allow molecules to diffuse across the membrane through diffusion .

whereas

Carrier protein allow specific molecules to cross the cell membrane by undergoing a conformational change upon the binding of the molecule.

The conformational change opens a hole through which the molecule can enter or exit a cell.

***Carrier protein is used in BOTH facilitated diffusion (which is a passive transport) and Active traansport!!