Trial SPM Bio Sabah 2009

Let's try the Trial Questions from `The land below the Wind'....
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Trial Bio Johor 2009

Here are the Johor Trial questions for P1, P2 and P3.
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Nitrogen Cycle

• All life requires nitrogen-compounds, e.g., proteins and nucleic acids.
• Air, which is 78% nitrogen gas (N2), is the major reservoir of nitrogen.
• But most organisms cannot use nitrogen in this form.

• Plants must secure their nitrogen in "fixed" form, i.e., incorporated in compounds such as:

• nitrate ions (NO3−)
• ammonia (NH3)
• Animals secure their nitrogen (and all other) compounds from plants (or animals that have fed on plants).

Four processes participate in the cycling of nitrogen through the biosphere:

• nitrogen fixation
• decay
• nitrification
• denitrification

Microorganisms play major roles in all four of these.

Nitrogen Fixation
The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy.

Three processes are responsible for most of the nitrogen fixation in the biosphere:

• atmospheric fixation by lightning
• biological fixation by certain microbes — alone or in a symbiotic relationship with some plants and animals
• industrial fixation

Atmospheric Fixation
The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates that are carried to the earth. Atmospheric nitrogen fixation probably contributes some 5– 8% of the total nitrogen fixed.

Industrial Fixation
Under great pressure, at a temperature of 600°C, and with the use of a catalyst, atmospheric nitrogen and hydrogen (usually derived from natural gas or petroleum) can be combined to form ammonia (NH3). Ammonia can be used directly as fertiliser, but most of it is further processed to urea and ammonium nitrate (NH4NO3).

Biological Fixation
The ability to fix nitrogen is found only in certain bacteria and archaea.

• Some live in a symbiotic relationship with plants of the legume family (e.g., soybeans, alfalfa).
• Some establish symbiotic relationships with plants other than legumes (e.g., alders).
• Some establish symbiotic relationships with animals, e.g., termites and "shipworms" (wood-eating bivalves).
• Some nitrogen-fixing bacteria live free in the soil.
• Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of semi-aquatic environments like rice paddies.

Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP.

Although the first stable product of the process is ammonia, this is quickly incorporated into protein and other organic nitrogen compounds.

Decay
The proteins made by plants enter and pass through food webs just as carbohydrates do. At each trophic level, their metabolism produces organic nitrogen compounds that return to the environment, chiefly in excretions. The final beneficiaries of these materials are microorganisms of decay. They break down the molecules in excretions and dead organisms into ammonia.

Nitrification
Ammonia can be taken up directly by plants — usually through their roots. However, most of the ammonia produced by decay is converted into nitrates. This is accomplished in two steps:

• Bacteria of the genus Nitrosomonas oxidise NH3 to nitrites (NO2−).
• Bacteria of the genus Nitrobacter oxidise the nitrites to nitrates (NO3−).

These two groups of autotrophic bacteria are called nitrifying bacteria. Through their activities (which supply them with all their energy needs), nitrogen is made available to the roots of plants.

Both soil and the ocean contain archaeal microbes, assigned to the Crenarchaeota, that convert ammonia to nitrites. They are more abundant than the nitrifying bacteria and may turn out to play an important role in the nitrogen cycle.

Many legumes, in addition to fixing atmospheric nitrogen, also perform nitrification — converting some of their organic nitrogen to nitrites and nitrates. These reach the soil when they shed their leaves.

Denitrification
The three processes above remove nitrogen from the atmosphere and pass it through ecosystems.
Denitrification reduces nitrates to nitrogen gas, thus replenishing the atmosphere.
Once again, bacteria are the agents. They live deep in soil and in aquatic sediments where conditions are anaerobic. They use nitrates as an alternative to oxygen for the final electron acceptor in their respiration.

Thus they close the nitrogen cycle.

Are the denitrifiers keeping up?
Agriculture may now be responsible for one-half of the nitrogen fixation on earth through

• the use of fertilisers produced by industrial fixation
• the growing of legumes like soybeans and alfalfa.

This is a remarkable influence on a natural cycle.

Are the denitrifiers keeping up the nitrogen cycle in balance? Probably not. Certainly, there are examples of nitrogen enrichment in ecosystems. One troubling example: the "blooms" of algae in lakes and rivers as nitrogen fertilisers leach from the soil of adjacent farms (and lawns). The accumulation of dissolved nutrients in a body of water is called eutrophication.

Mutation

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Eutrophication

Eutrophication, strictly speaking, means an increase in chemical nutrients -- typically compounds containing nitrates or phosphates -- in an ecosystem. It may occur on land or in water. The term is however often used to mean the resultant increase in the ecosystem's primary productivity -- in other words excessive plant growth and decay -- and even further impacts, including lack of oxygen and severe reductions in water quality and in fish and other animal populations.

Eutrophication is frequently a result of nutrient pollution such as the release of sewage effluent and run-off from lawn fertilisers into natural waters (rivers or coasts) although it may also occur naturally in situations where nutrients accumulate (e.g. depositional environments) or where they flow into systems. Eutrophication generally promotes excessive plant growth and decay, favours certain weedy species over others, and is likely to cause severe reductions in water quality . In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen in the water, needed for fish and shellfish to survive. The water then becomes cloudy, coloured a shade of green, yellow, brown or red. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation, fishing, hunting, and aesthetic enjoyment are hindered. Health-related problems can occur where eutrophic conditions interfere with drinking water treatment.

Revision F4

Here are some notes on photosynthesis, digestion in ruminant and rodent
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Flour Beetles

Tribolium confusum and Tribolium castaneum

Red and confused flour beetles attack stored grain products such as flour, cereals, meal, crackers, beans, spices, pasta, cake mix, dried pet food, dried flowers, chocolate, nuts, seeds, and even dried museum specimens. These beetles have chewing mouthparts, but do not bite or sting. The red flour beetle may elicit an allergic response, but is not known to spread disease and does not feed on or damage the structure of a home or furniture. These beetles are two of the most important pests of stored products in the home and grocery stores. The confused flour beetle apparently received this name due to confusion over about its identity as it is so similar to the red flour beetle at first glance.

The red flour beetle is of Indo-Australian origin and is found in temperate areas, but will survive the winter in protected places, especially where there is central heat. In the United States, it is found primarily in the southern states. The confused flour beetle, originally of African origin, has a different distribution in that it occurs worldwide in cooler climates. In the United States it is more abundant in the northern states.

Although small beetles, about 1/4 of an inch long, the adults are long-lived and may live for more than three years.

The red flour beetle is reddish-brown in colour and its antennae end in a three-segmented club. Whereas the confused flour beetle is the same colour but its antennae end is gradually club-like, the "club" consisting of four segments.

The red and confused flour beetles live in the same environment and compete for resources. The red flour beetle may fly, especially before a storm, but the confused flour beetle does not fly. Eggs, larvae, and pupae from both species are very similar and are found in similar environments. The eggs are white, microscopic and often have bits of flour stuck to their surface. The slender larvae are creamy yellow to light brown in colour. They have two dark pointed projections on the last body segment.

These beetles can breed throughout the year in warm areas. The life cycle takes from 40 to 90 days, and the adult can live for three years. All forms of the life cycle may be found in infested grain products at the same time

The red and confused flour beetles may be present in large numbers in infested grain, but are unable to attack sound or undamaged grain. The adults are attracted to light, but will go towards cover when disturbed. Typically, these beetles can be found not only inside infested grain products, but in cracks and crevices where grain may have spilled. They are attracted to grain with high moisture content and can cause a grey tint to the grain they are infesting. The beetles give off a displeasing odour, and their presence encourages mould growth in grain.

Keep in mind that these beetles may infest areas other than the pantry. Be sure to inspect spices, pet food, and flower arrangements. Also keep in mind that some stuffing in furniture or stuffed animals may have natural products that these beetles could feed on. Also be aware of areas in which any of these products may have spilled, like under the refrigerator or stove. These beetles are able to locate very small bits of food. Once all of the infested material has been removed, be sure to vacuum and clean up the area around the infestation. If you have shelf paper, it would be wise to remove it, thoroughly clean under it with soap and hot water, and replace it with new paper. Be sure to pay close attention to the cracks and crevices of any cabinets. To prevent re-infestation, all grain products should be stored in containers with tight fitting lids, or stored in the freezer. Also consider where the infestation came from. It is likely that you could have a re-infestation by purchasing infested grain products from the same business. When shopping, look for those "leaky packages". If you suspect a beetle infestation, don't buy the product.