16/06/10 Edexcel Bio 4(6BI04)

my_anon

Hi guys,
Ive just found this thread that would be useful for all of us.
http://www.thestudentroom.co.uk/showthread.php?t=1286287
Join it & let the revision begin!

No.

Anyway, I will continue studying this Unit 4. I've finished photosynthesis, ecology and evolution. I only really understand photosynthesis though. :mad:

Global warming is next! Topic 6 (infection and immunity shouldn't be too hard for me).

Reply 23

Oops i didnt see this thread :p:

! Thanks for pointing it out Doughboy. Let me post the things on my other thread to this thread!

Reply 24

Doughboy

No.

Anyway, I will continue studying this Unit 4. I've finished photosynthesis, ecology and evolution. I only really understand photosynthesis though. :mad:

Global warming is next! Topic 6 (infection and immunity shouldn't be too hard for me).

I've gone through topic 5 as well! I understand everything except for the following markscheme points:

Discuss how understanding the carbon cycle can lead to methods to reduce atmospheric levels of carbon dioxide (including the use of biofuels and reforestation).

Describe the role of the scientific community in validating new evidence (including molecular biology, eg DNA, proteomics) supporting the accepted scientific theory of evolution (scientific journals, the peer review process, scientific conferences).

Explain how reproductive isolation can lead to speciation.

What things dont you understand other than the points above? Maybe we can help eachother out :smile:

.

Reply 25

my_anon

Hi guys,
Ive just found this thread that would be useful for all of us.
http://www.thestudentroom.co.uk/showthread.php?t=1286287
Join it & let the revision begin!

You should have just told me that there was already a thread for this Unit! I would have posted my stuff to this thread.

Reply 26

dime_piece

I've gone through topic 5 as well! I understand everything except for the following markscheme points:

Discuss how understanding the carbon cycle can lead to methods to reduce atmospheric levels of carbon dioxide (including the use of biofuels and reforestation).

Well, this is simple. Just look at the parts of the cycle that reduce or could reduce carbon dioxide from the atmosphere. Photosynthesis uses up CO2 in the cycle, so by planting more trees (reforestation) we can increase the effect of photosynthesis. In the cycle, we see that burning fossil fuels increases the CO2 levels. Sp, if we find a way to replace fossil fuels we are decreasing the levels of CO2 being added to the atmosphere. Biofuels are carbon neutral (they make no net addition of carbon dioxide) to the atmosphere. If this because biofuels are made from plants/crops. As we grow plants/crops they build biomass by taking in CO2. When we make and then burn biofuels from these plants the amount of CO2 emitted from burning will be roughly equal of the amount of CO2 taken in by these plants while they were growing.

Describe the role of the scientific community in validating new evidence (including molecular biology, eg DNA, proteomics) supporting the accepted scientific theory of evolution (scientific journals, the peer review process, scientific conferences).

I'll get back to you on this one. But there isn't a hard and fast answer to this.

Explain how reproductive isolation can lead to speciation.

By reproductively isolating species, we ensure that these is no influx of alleles from other populations. Allele flow only occurs within each isolated population. This means that natural selection will separately act on each isolated population and the increase allele frequency of alleles in a given population will not be the same for another population because there are different selective pressures in each area of isolation. Natural selection isn't the only thing that leads to evolution. Natural selection changes a species, but natural selection and reproductive isolation lead to the formation of new species. I don't really understand this topic, so hopefully someone can comment on what I just said...

What things dont you understand other than the points above? Maybe we can help eachother out :smile:

.

Reply 27

Doughboy

Thanks!

Reply 28

shuvo_roy

I find global warming really really boring.......what type of questions might Edexcel ask from this chapter? Hope all they ask is to interpret data from graphs!

Reply 29

poojatanwani7

shuvo_roy

I find global warming really really boring.......what type of questions might Edexcel ask from this chapter? Hope all they ask is to interpret data from graphs!

snappp. It asked a question on dendrochronology in the sample paper but yeah I hope it's just graph interpretation because it is really annoying.

Reply 30

Hey can someone explain the following point to me:

Explain how the concept of niche accounts for distribution and abundance of organisms in a habitat.

Thanks in advance!

Reply 31

Niche is the organisms role in its habitat (and how it interacts with biotic and abiotic factors). Large trees need a high metabolism to keep them alive (this is part of their niche). As a result, you're not going to find large trees in colder regions. Instead, these large trees are distributed in regions closer to the equator.

If two species occupy the same niche, this means that they're competing for the same resources in the same habitat. For example, the red and grey squirrels both compete for the tree dwelling habitat niche and for acorn-eating niche. Because of this competition, the resources (space and food) available to each species is less than if only one species was present. So since each species obtains less resources than if one species was present, the population size/abundance of each species would be less when both species are present. There would be a higher abundance of either species if the other was present.

The niche concept and abundance can also be explained in another way. Let's take into account that red and grey squirrels. They are both occupying the same/similar niche. If one species is better adapted in obtaining a given resource or is better adapted in surviving then that better adapted species will eventually out-compete the other species. I think one of the squirrel species I mentioned above was bigger than the other and so in the winter, this bigger species survived and so in the absence of food and warmth, the bigger species survived better in the winter and eventually out-competed the other.

I am unable to explain how niche affects distribution/abundance without using examples, sorry!

Does this make sense?

EDIT:

The niche concept is summarised in the competitive exclusion principle: Two species cannot coexist in the
same habitat if they have the same niche. They will compete, and one species will win the competition. This
principle also works in reverse: if two species are observed to compete then they must have the same
niche. The competitive exclusion principle may apply whenever a new species is introduced to an
ecosystem. For example American grey squirrels are out-competing and excluding the native red squirrels
in England, and the Australian barnacle is out-competing and excluding the native English species on rocky
shores. These native species are declining and may eventually become extinct.

Reply 32

obviouslystudying

1

Doughboy

Does this make sense?

sort of, but is all of that required?

btw, if anyones got the Jan unit 4 (Bio, Chem, Phy) papers, MS please contact, have searched for them but currently doing 4 AS and A2 subjects this june and really pressed for time so probably missed them if its around here.

Reply 33

Doughboy

Niche is the organisms role in its habitat (and how it interacts with biotic and abiotic factors).
Does this make sense?

Yes it does! I think my main problems was that i didnt understand that a niche meant (how it interacts with biotic and abiotic factors), i learnt it as the effects of abiotic & biotic factors on population size & distribution.
Oh and i love your use of examples! :p:

Thats how i learnt it too, with the same examples.

Reply 34

Models of Global Warming
• In order to investigate the relationship between CO2 and Earth’s temperature, scientists have created models of global warming.
• These huge computer models are used for predicting the future.
• When making these models, certain factors are to be considered:
o Rates of photosynthesis across the world
o Rates of CO2 production by natural causes
o The exchange of CO2 between the atmosphere and oceans
o The effect of changing temperatures on all of these factors
• Higher and lower estimates are made in models:
o higher estimate assumes no change in production of gases
o lower estimate takes into account reduction in carbon emissions
• We can extrapolate available data on which to base our estimates in the models and make predictions about what will happen to temperature in the future
• There are many limitations in creating these models and extrapolating the data:
o It is impossible to predict exact the impact of CO2 on global warming
o It is impossible to predict the impact of global warming on particular aspects of the world climate
o We do not know how current trends in the use of resources and technologies may change

Effects
• FLOODING – ice broke away from the Antarctic Peninsula and eventually melted into the sea. Many scientists believe that the thinning of the ice is a clear indication of global warming. As ice melts, the volume of water in the seas and oceans will increase, causing sea levels to rise. As the water gets warmer, its volume increases, resulting in an even bigger impact on sea levels. Many humans and animals live less than 1 metre above current sea levels!
• CLIMATE CHANGE – rising temperatures affect weather and rainfall patterns. Low rainfall/drought = shortage of water for crops and nutrition. High rainfall = erosion of topsoil.
• EFFECT ON ORGANISMS – temperature has an effect of enzyme activity which in turn affects the whole organism (think rate of metabolism here!). A 10 degree increase in temperatures will double the rate of an enzyme-controlled reaction. However, there is an optimum temperature for many enzyme-controlled reactions and if the temperature increases beyond that point the enzyme starts to denature and the reaction rate falls. As a result increasing temperature could have different effects on processes, including RATE OF GROWTH and REPRODUCTION. If plants grow faster they will take up more carbon dioxide and may therefore reduce atmospheric carbon dioxide levels. In other places, temperatures may exceed the optimum for some enzymes and organisms there will die.
• SEASONAL CYCLES – season cycles affect life cycles. Global warming seems to be affecting both life cycles and the distribution of species. Warmer temps. = plants grow and flower earlier. Insects become active earlier in the warmth and the plant food they need is available. Insects are emerging earlier than bird chicks so the birds are missing the peak insect population and raising fewer chicks. For some animals, breeding earlier in the year may mean they can fit more than one breeding cycle in, so those populations will increase. The embryos of some reptiles are sensitive to temperature as they develop  temperature determines whether the baby reptiles are male or female.
• CHANGES IN SPECIES DISTRIBUTION – Plants emerging in colder regions are getting rarer. A change in climate could affect the range of many different organisms. If organisms involved in the spread of disease are affected, partners of world health could chance as well. Global warning could be responsible for a major increase in insect-borne diseases in Britain and Europe.

All of these factors will determine the extent survival of organisms. If some organisms are forced to migrate, they might not be able to compete with the other native species or they may even out-compete native species. Some species may become extinct and therefore biodiversity is reduced.

==
Just a summary from that silly Edexcel book.

Reply 35