Summer 2014 selection

Explanation/disclaimer: click to expand/contract

Comment on a diagram comparing human populations in 1700 and 2010:

1700 has more mean children per woman

Role of microorganisms in producing nitrates:

Ammonium compounds are converted into nitrogen compounds

Explain why coastal waters are productive fishing areas

In coastal waters there are high levels of energy in the fish

The nutrients from their decay reach higher depths

More nutrients mean more food sauces for fish

High levels of nutrients e.g. nitrates are used by fish to make protein

Explanation of increase in diversity of birds as farmland was left to develop into woodland::

The trees support more species as food sources are higher

As birds changed the farmland into woodland ...

Birds may have adapted themselves

Comments on plant productivity of sun and shade plant:

CO2 taken in by plants is converted into carbon and passed on through each trophic level

The plant gets nutrients from soil for better growth, despite low light intensity

The sun plant will overshadow the shade plant so that the shade plant can receive a favoured low light intensity for ps

It respires less. This allows it more time to photosynthesise

The graph is less steep than the sun plant, indicating it relies less on light intensity for photosynthesis

Shade plant has a higher rate of photosynthesis in the dark

The shady plant has a higher rate of ps at low light intensities

It releases less CO2 at low light intensies to allow more for photosynthesis

Photosynthesis is more efficient at uptaking energy as it can do so at lower light intensities

Explanation of high frequency of HbC allele in areas where malaria occurs:

The HbC allele has developed a resistance to malaria

Selection pressure and adaptation introduced the HbC allele

As less people with HbC are killed by malaria there is less need for them to leave the area

Due to mutation HbA becomes HbC in order to survive

The HbC allele occurred to prevent malaria

People without the HbC allele are dead and cannot pass on the allele

The haemoglobin has changed via genetics from generation to generation

This is due to the malaria virus being non-resistant

Those with the HbC allele have a higher risk of survival

People reproduce in these small areas

This allele survived due to better adaptation

Why does respiration produce more ATP in the presence of oxygen rather than in its absence?

Oxygen is the final exceptor ... final terminator

With aerobic respiration you get to go further with one molecule of oxygen

Aerobic respiration is more efficient as less energy is lost as heat

Glycolysis can only occur without oxygen

Less ATP is used in aerobic respiration than in anaerobic, so more is left over after

Without oxygen, less electrons are converted into water

Ethanol is a store of ATP

Anaerobically water (H2O) is used which has half the oxygen content than an O2 molecule, which halves the rate of ATP production

Oxygen contains electrons which can release energy when moving through the electron transfer chain

If this did not happen then the electron would go back up the chain

It can use oxygen as the last receiver of the glucose molecule

Intraspecific competition by an introduced plant species:

It requires less oxygen to photosynthesise

Its a large plant and can eat other species

Economic consequence:

Destruction of tourist sights

Explanations why drying to constant mass provides a reliable estimate of biomass:

There would be no water or other elements that would add to the biomass

Samples were heated until the biomass was constant

Water levels vary within each plant

Regular weight checks show more accurate weights as short time gaps are used.

Reheating makes sure that temperature remained constant, so results were not due to temperature change.

Reheating and reweighing removes anomalous data

Heating burns all the fresh mass in the plant

This technique shows the true value of the plant

This means that anything that is not biomass has been released

It removes any molecules that may not be appropriate for the test

Reheating reduced the aquatic mass

This took into account the mass of the species rather than just the number as water contains no energy

Comment on best concentration of biocide:

This concentration was best at not accumulating in the food chain

Advantages of fungus as biological control agent:

The fungus will recognise the Hydrilla

The fungus has not seen the other native species before so is less likely to attack them

In the Light Independent Reaction:

These TP molecules then break down into RuBP

A carbon molecule will be removed, producing 2 TP molecules

The LIR takes place in the dark as it does not require light to photosynthesise

As carbon from carbon dioxide binds with RuBP, oxygen is released

In this process, carbon is turned into glucose

Every six cycles this cycle produces something useful to plants

... using NHdp and ATP ...

This process is repeated 6 times for efficiency - on the 6th time TP is turned into glucose and RuBP

Human activities and global warming:

Burning fossil fuels release CO2 into the atmosphere which is a greenhouse gas

Burning fossil fuels release CO2 which was locked up in the fossils

CO2 is a greenhouse gas which increases the thickness of the ozone layer

The industrial revolution caused a sharp increase in the number of cars

Global warming is due to the increase of fossil fuels in the atmosphere

Humans have contributed to global warming by reproducing

So more CO2 is in the atmosphere where it prevents UV light from leaving the earth and warming it up

All of this increases the thickness of the atmosphere meaning light relecting off the surface of the earth can no longer escape

There are more people being born every year which increases CO2

Method of estimating number of bluebells in a small woodland:

The land used would be put on a grid

You must ensure samples are collected randomly

A computer could be used at random

You must find co-ordinates through random means

Use the mark-release-capture method

This way you can work out the estimated bluebells

This process should be repeated enough times to produce a running mean

Using the axis, visit all the co-ordinates

Count the number of daisies in the quadrat

Multiply your mean number of bluebells by the difference between your quadrat size and your woodland size

Divide all the amounts to get a mean total of the population

Now you can stop and use the data to run a statistical test to estimate the number of bluebells.



Why is the genetic code described as universal?

It's coded with one singular language by all species of animals and living organisms

Everyone uses the same four bases which form nucleotides

Each amino acid is the same in all organisms

The codes within amino acids apply to all living organisms

There are few exceptions. It is the same for all organisms

Because nearly everyone uses it in different countries

The whole world uses the same four bases to form triplets that code for amino acids

Consequences of base deletion

This would result in a completely different protein structure as it is made of one less and one different amino acid

When a base is deleted it causes genetic shift

Amino acids are coded for by multiple triplets

Due to the degenerative nature of the genetic code it may not be affected

An intron does not code for DNA

Turning of worms

A taxis is a movement towards a directional stimulus

Worms cultured at 17 °C would be better respiring at 17 °:C

Things you didn't know about nerve impulses


In a non-myelinated axon:
... the speed of the action potential is equal to the wavelength generated
... sodium ions must diffuse the entire length of the axon
... the impulses are allowed to jump
... there is more diffusion, which takes time
... energy escapes as it travels along
... the impulse is subjected to electrical resistance
... has one large node of ranvier
... impulse takes longer to travel past all the sodium/potassium pumps and gates
... impulse has to be passed through every cell

Myelinated axons:
... allow neurotransmitters to pass the synaptic gap faster
... have a greater O2 concentration
... have an electrical conductor made of Schwann cells surrounding their membrane
... sodium ions jump from node to node
... have a layer of fat which keep them warmer
... the impulses are more confined so less energy is lost
... as it is insulated the impulse cannot leave the axon
... reduces friction
... allows a myelin head to bind to it which moves the axon along
... the nerve impulse can jump between the non-myelinated parts of the myelinated axon
... has an insulating layer that prevents conduction of a nerve impulse
... schwann cells are insulators and electrical charge jumps through the sheath
... this allows action potentials to jump from one node of ranvier to others
... the electrical impulse travels directly down the axon and does not change course onto another neurone - faster if it does not detour
... help reduce the loss of ions across the axon
... acts as insulator, reducing loss of charge
... impulse is more direct and so travels in a straighter line
... impulse only has to jump between axons, resucing the disruption of the impulse
... the mylon shief conducts energy so causes the pulse to jump from one unmylonated shief part to another
... myelin sheath presents a synapse in certain places. The action is greater than wave action.
... This is quicker than sending signals from one side of the axon to the other
... The schwann cells are raped around the axon
... allow statutory conduction
... The fatty coating attracts the impulse


Results may be different if the dementia did not involve loss of mental ability

The standard error bars do not overlap so the differences are statistically different

This will increase the number of eggs available to develop into follicles

The corpus lupus will not form

Phosphocreatine allows the actin sheet around the muscle to unwind, allowing the myelin head to cause a contraction

If a dog gets too warm its nose will start running

Carrier proteins on the cell surface will allow certain substance to travel in and out, due to their big size

... myocardial infraction ...

Enzymes become less efficient as people get older

Older people have thicker muscle fibres

Less anaerobic enzymes are available in the upper arm

Why are 2 carrier proteins needed in transporting a protein into the mitochondrial matrix?

Molecule is too large so must be grabbed at both ends

Comments on DNA probe technique with different genotypes

The alleles have different sequences of amino acids

The DNA base sequence (for the homozygote) was AA

Less DNA will attach to the probe so there will be less green lights

As DNA is double stranded, only one strand can have the allele A

Measurements to calculate rate of carbon dioxide production

Use a potometer to measure CO2 concentration

Measure the length of the part of the ecosystem

Before the experiment the plants should not have done any respiration - only photosynthesis

Why is there a delay between rise in photosynthesis rate and rise in respiration rate?

Photosynthesis has to drop past a certain point for respiration to occur

The tree must convert all of the light into ATP first

Takes time for oxygen to drop from the leaves

Photosynthesis and respiration cannot occur at the same time

Takes time for the gaseous to be exchanged

Delay is due to time

Continuous prose

Photosynthesis starts when light excites a chlorophyll molecule so much that its electrons leave the molecule all together

To regenerate RuBP the cycle must spin 6 times

Fish with a low affinity for oxygen require a high supply of oxygen in the water

All energy is recycled into the ground where it is used by organisms

In animals the nervous systen transmits the sun's energy to chemical energy

The (light dependent) process will hydrolyse H2O

Water diffuses by osmosis out of the stomata and is evaporated by the sun's heat

Ectotherms move to the sun when they are cold

In organisms that are too hot, such as humans, the hair follicles relax

Plants open and close their stomata, insects open and close their spiracles, fish open and close their gills.

There is a loss of energy from sunlight to producers as not all waves of light can be absorbed

There is very little energy left by the time it reaches the tertiary level. For this reason tertiary consumers need to eat a lot of food.

The sun provides solar waves

Humans are not eaten by anything alive

To create heat from contraction of muscles shiving occurs

Producers make the light into glucose via photosynthesis, which can be used by other organisms

When light hits chlorophyll, electrons are omitted

.. The venal end of the capillary

Energy such as CO2 is released by saprobionts

Glucose is used to produce energy at the rate of 1:38

On the underside of a plant are stomata

Food is passed down from the mouth to the stomach where all food substances are broken down

Energy can be added to an ecosystem via fertiliser

In cold conditions vasoconstriction occurs so less blood is lost by evaporation

A food chain cannot support more than 2 consumers

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