AQA Biology A2 Unit 4 Revision Thread Watch

Artymess
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(Original post by gcseangel)
I thought the climax community would have only the dominant species existing in the ecosystem. Therefore the biodiversity would be low.
So when exactly is the biodiversity the highest in succession?

This question and answer firing is really helpful.
theres always one who breaks the chain :P the climax community does consist of only the dominant species, but theres a dominant species for every niche, and since conditions are more favourable and theres more variety when it comes to plants able to grow there are plenty of niches to be occupied by different dominant species. Biodiversity is highest between the pioneer species colonising and the climax community becoming established as there is a larger number of different species present all competing interspecifically to be the dominant species of a particular niche

photphosphorylation is where ATP is made in the light dependant stage, a high energy electron from either photosystem II or photosystem I (cyclic photophosphorylation) provides the energy for ADP + Pi -> ATP

Oxidative phosphorylation is where ATP is synthesized using the energy from electrons that have entered the electron transport chain in the mitochondria

Substrate level is where ATP is synthesized using energy provided by the reactions of a respiratory substrate (occurs in glycolysis and krebs cycle)

explain how an influx of nitrates into a water supply results in Eutrophication
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raceforthefishman
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(Original post by Artymess)
theres always one who breaks the chain :P the climax community does consist of only the dominant species, but theres a dominant species for every niche, and since conditions are more favourable and theres more variety when it comes to plants able to grow there are plenty of niches to be occupied by different dominant species. Biodiversity is highest between the pioneer species colonising and the climax community becoming established as there is a larger number of different species present all competing interspecifically to be the dominant species of a particular niche

photphosphorylation is where ATP is made in the light dependant stage, a high energy electron from either photosystem II or photosystem I (cyclic photophosphorylation) provides the energy for ADP + Pi -> ATP

Oxidative phosphorylation is where ATP is synthesized using the energy from electrons that have entered the electron transport chain in the mitochondria

Substrate level is where ATP is synthesized using energy provided by the reactions of a respiratory substrate (occurs in glycolysis and krebs cycle)

explain how an influx of nitrates into a water supply results in Eutrophication
Nitrates might leach into the water...such as a river.
The nitrate level in the water is no longer a limiting factor to certain organisms, and so their growth can bloom (such as algae)
They slowly reduce the level of oxygen in the water so an oxygen gradient is set up.
There is no longer enough oxygen dissolved in the water to support life such as fish and plants lower down in the water.
They die and sink to the bottom.The dead material is then broken down by decomposers -- who normally have toxic/harmful products at the end of their respiration. These waste products begin to fill the water making it putrid and only suitable for anaerobically respiring organisms.

The water has been Eutroph-ed :yy:

What things need to be considered when taking samples in field work to give reliable results
(not very good question sorry)
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jimmy303
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An increase in the amount of resources means that algae can form chemical compounds such as amino acids (that form proteins), nucleic acids and ATP which all contain nitrogen, meaning that a greater amount of growth occurs.

A layer of algae/algal bloom or mat forms on the surface of the water, blocking the sunlight. This reduces the amount of photosynthesis of submerged plants and algae at lower levels, eventually resulting in their death.

Saprophytes (decomposers) then feed on the dead material (detritus), increasing in numbers as more cell division is possible with the available resources. More respiration occurs because of the greater number of decomposers, increasing the Biological oxygen Demand, and removing a high amount of the oxygen from the water.

This means that fish and other animals die as a result of a lack of oxygen, and anaerobic organisms become more common than aerobic organisms.

Hope that's what you wanted!

Edit: Got beaten to it, but wanted to put my answer anyway. I'll answer the second question:

What things need to be considered when taking samples in field work to give reliable results

Umm something like to make sure that the samples are random? If they're bias the results may reflect what the bias person expects the results to be. Oh and also that a large number of samples are taken.

Explain the difference between Gross Primary Productivity and Net Primary Productivity.
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boggybop
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The total quantity of energy that the plants in a community convert into organic compounds such as carbohydrates is referred to as the gross productivity. However, much of this is used during respiration, so whatever remains is referred to as the net productivity.

Net productivity = gross productivity – respiratory losses

Describe and explain the differences between the population pyramids of Stage 1 and Stage 4 countries
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Vim216
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(Original post by boggybop)
The total quantity of energy that the plants in a community convert into organic compounds such as carbohydrates is referred to as the gross productivity. However, much of this is used during respiration, so whatever remains is referred to as the net productivity.

Net productivity = gross productivity – respiratory losses

Describe and explain the differences between the population pyramids of Stage 1 and Stage 4 countries
Stage 1 has high birth and death rates, low life expectancy. A regular pyramid shape, wide at the bottom and getting narrower as you go up on both sides. This is because the high birth rate causes a large number of individuals in the lower age groups, whereas the high death rate and low life expectancy causes this to peter out as we go up the pyramid.
Stage 4 has low birth and death rates, high life expectancy. We'd see a shape that is relatively wide in the middle, narrower at the bottom and narrower still at the top. Compared to a stage 1 country, the bottom would be much narrower, and the top much wider. This is because a country in stage 4 has a lower birth rate, so there are less individuals in the youngest age groups. It also has a lower death and higher life expectancy, which explains why there are higher numbers in the older age groups.



What are the advantages and disadvantages of biological control and chemical control?
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boggybop
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(Original post by VimalanK)
Stage 1 has high birth and death rates, low life expectancy. A regular pyramid shape, wide at the bottom and getting narrower as you go up on both sides. This is because the high birth rate causes a large number of individuals in the lower age groups, whereas the high death rate and low life expectancy causes this to peter out as we go up the pyramid.
Stage 4 has low birth and death rates, high life expectancy. We'd see a shape that is relatively wide in the middle, narrower at the bottom and narrower still at the top. Compared to a stage 1 country, the bottom would be much narrower, and the top much wider. This is because a country in stage 4 has a lower birth rate, so there are less individuals in the youngest age groups. It also has a lower death and higher life expectancy, which explains why there are higher numbers in the older age groups.



What are the advantages and disadvantages of biological control and chemical control?
Chemical controls have the advantage of being very fast acting, and only need to be applied in small amounts due to the high concentrations of the pesticides. However, the chemical controls are not always specific to the pest, not always biodegradable (which could lead to bioaccumulation), and could lead to widespread resistance to the pesticide.

Biological controls will not allow resistance to develop, however they are much slower to act, and the natural predator or parasite could become a pest itself in not correctly managed.

Explain geographical isolation.
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Orihime
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(Original post by boggybop)
Chemical controls have the advantage of being very fast acting, and only need to be applied in small amounts due to the high concentrations of the pesticides. However, the chemical controls are not always specific to the pest, not always biodegradable (which could lead to bioaccumulation), and could lead to widespread resistance to the pesticide.

Biological controls will not allow resistance to develop, however they are much slower to act, and the natural predator or parasite could become a pest itself in not correctly managed.

Explain geographical isolation.

Populations become separated , geographically, no interbreeding so no gene flow between the populations. Each population is exposed to different enviromental conditions so natural selection acts on each population differently depending on the abiotic environment, some individuals are more likely to survive, reproduce and pass on their alleles in each population so the allele frequecy and type within the gene pool change as some individuals are more reproductively successful. Mutations also play a part and they cause further varition between the gene pools... Some generations later; the two populations have accumulated large differences in their gene pools so now they're essentially different species. If they try to breed with each other, they won't produce fertile offspring - this demonstrates that they're different species.

Describe the importance of anaerobic respiration
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Artymess
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It allows reduced NAD to get rid of its hydrogen and continue glycolysis, providing the cell with ATP to prevent cell death

Where abouts in the chloroplast do the light dependant and light independant reaction occur?
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boggybop
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(Original post by Artymess)
It allows reduced NAD to get rid of its hydrogen and continue glycolysis, providing the cell with ATP to prevent cell death

Where abouts in the chloroplast do the light dependant and light independant reaction occur?
The light dependent reaction takes place in the thylakoids of the chloroplast, and the light-independent reaction takes place in the stroma of the chloroplast (which contains the necessary enzymes required to carry out the light-independent reactions).

Describe a predator/prey relationship, and the outline the types of competition involved.
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xxxpenguinnnxxx
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I got 16% in my mock last week...

Gosh my teacher actually hates me
Not exactly looking forward to parents' evening on Tuesday...
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TwilightKnight
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I litterally can't make myself sit down and learn this ********. It's the most tedious **** ever. The Textbook is a pile of arse too, much prefer the OCR Heinmann ones.

Maths revision? Fun.
Chemistry revision? Interesting.
Biology revision? Having to be able to parrot fashion 80 odd pages for a test, not fun.

Sigh.
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Vim216
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(Original post by boggybop)
The light dependent reaction takes place in the thylakoids of the chloroplast, and the light-independent reaction takes place in the stroma of the chloroplast (which contains the necessary enzymes required to carry out the light-independent reactions).

Describe a predator/prey relationship, and the outline the types of competition involved.

Predator numbers fluctuate with prey numbers. When predator numbers are high, prey numbers fall since predators are killing them. However, intraspecific competition between predators when prey numbers are low leads to predator numbers falling. Prey numbers then rise since there are fewer predators. (not sure where interspecific competition could be involved in this?)

(Original post by xxxpenguinnnxxx)
I got 16% in my mock last week...

Gosh my teacher actually hates me
Not exactly looking forward to parents' evening on Tuesday...
Just push through it! I know it's hard, but there are a lotta people in the same boat. Focus on the stuff your weakest on and drill through it till you feel more confident about it. Make sure to do questions and look at mark schemes!




Distinguish between the terms gene and allele
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HighSkies
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(Original post by VimalanK)
Distinguish between the terms gene and allele
A gene is a section of DNA which codes for a sequence nucleotide bases that usually determines a single characteristic of an organism. It does this by coding for particular polypeptides.

An allele is a different form of a gene.

Describe how adding inorganic fertiliser to fields can lead to the death of fish in a nearby stream.
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klgyal
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(Original post by HighSkies)
A gene is a section of DNA which codes for a sequence nucleotide bases that usually determines a single characteristic of an organism. It does this by coding for particular polypeptides.

An allele is a different form of a gene.

Describe how adding inorganic fertiliser to fields can lead to the death of fish in a nearby stream.
Adding inorganic fertiliser to fields can cause it to leach into the nearby stream. This will increase the growth of algae( called the algal bloom). The algae growing at the surface of the water will prevent light from reaching algae beneath the surface. These algae will photosynthesis less and eventually die. Saprobiotically microogransims will break down the dead remains of the plant to release nutrients and their numbers will multiply. The saprobiotic microorganims use up oxygen for aerobic respiration and this will decrease the oxygen concentration in the water. Fish living in the water that require oygen for aerobic respiration will die due to the lack of oxygen available in the water that will prevent them from respiring.

What is meant by the term ecological niche?
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XCLNC
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(Original post by klgyal)
Adding inorganic fertiliser to fields can cause it to leach into the nearby stream. This will increase the growth of algae( called the algal bloom). The algae growing at the surface of the water will prevent light from reaching algae beneath the surface. These algae will photosynthesis less and eventually die. Saprobiotically microogransims will break down the dead remains of the plant to release nutrients and their numbers will multiply. The saprobiotic microorganims use up oxygen for aerobic respiration and this will decrease the oxygen concentration in the water. Fish living in the water that require oygen for aerobic respiration will die due to the lack of oxygen available in the water that will prevent them from respiring.

What is meant by the term ecological niche?
Ecological Niche includes all the biotic and abiotic conditions required for an organism to survive, reproduce and maintain a viable population.

What are the advantages of ATP as an energy storage molecule?
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klgyal
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(Original post by XCLNC)
Ecological Niche includes all the biotic and abiotic conditions required for an organism to survive, reproduce and maintain a viable population.

What are the advantages of ATP as an energy storage molecule?
energy is released in a single step reaction, energy is released in small managable quantities

explain what is meant by monoculture?
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jimmy303
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explain what is meant by monoculture?
The growth of a single type of crop over a wide area.

Explain the advantages of a monoculture.
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klgyal
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(Original post by jimmy303)
The growth of a single type of crop over a wide area.

Explain the advantages of a monoculture.
is there any advantages??? i know some disadvantages
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juuu :)
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I'm guessing the advantages of a monoculture would be that no nutrients in the soil get wasted on weeds and plants you don't want present?

and maybe that there's maximum productivity if there is no competition for any resources?

not sure if i'm right :hmmmm:

um does anyone know how to define an ecosystem? my textbook says something about interacting abiotic and biotic factors? but my teacher said it was " a community of organisms together with its associated physical environment"....

thank you guys
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raceforthefishman
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Surely, yield is an advantage of a monoculture (if we're talking about farming)
For instance, all the energy put into that particular ecosystem is focused entirely on that one species and therefore giving the highest yield. If you were growing a crop perhaps...(as there is no comptetition etc.)

When would it be appropriate to use a transect in a study?
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