Edexcel GCE Biology Unit 4 6BI04 June 2013

It is the gradual change in structure and species composition in a community.
There are two types:
- Primary
- Secondary

Primary succession:
- starts with bare rock
- pioneer species like lichen/moss appear
- they grow, with time filling up small cracks/holes in the rock
- the rocks start breaking down ( sometimes with the help of erosion as well) - organic matter starts to collect
- eventually forming humus (organic matter that cannot be broken down further)
- humus soon becomes soil
- this allows for more species, like grass to grow and develop roots
- as more water and nutrients collect in the soil, bigger plants can grow, like trees etc.
- finally a climax community is formed.

Features of a climax community:
- made up of species of animals and plants
- maximum biodiversity is reached
- biodiversity remains constants until an interruption (e.g natural disaster, human activity)

Secondary succession:
- similar to primary succession
- but starts off with soil, instead of rock
- occurs after major damage to the habitat (fire, natural disaster etc)

Note:
*a climax community formed due human intervention is known as a plagioclimax

DNA and protein synthesis

1. Explain the nature of the genetic code (triplet code, non-overlapping and degenerate).
2. Explain the process of protein synthesis (transcription, translation messenger RNA, transfer RNA, ribosomes and the role of start and stop codons) and explain the roles of the template (antisense) DNA strand in transcription, codons on messenger RNA, anticodons on transfer RNA.
3. Explain how one gene can give rise to more than one protein through post-transcriptional changes to messenger RNA.

Could someone please briefly explain these spec points?

I cant access it.
Do you think you could link it?

heyyy broooo! ready for bio???

Do you have any good bio unit 4 notes?? i cant seem to find any :/

no i couldnt find any :/ just use the revision guide and our notes. don't know if thats enough though :/

Can u please answer this ? whats the use of antisense strand in DNA? its in the specification

Can someone please tell me the difference between Reverse transcriptase, DNA and RNA polymerase????

what your definition of gene flow would be? what context / example please?

what your definition of gene flow would be? what context / example please?

The main difference is in their function:
- DNA polymerase: assembles complementary DNA nucleotides along a single DNA strand, resulting in the formation of a double-stranded DNA molecule. This enzyme is involved in DNA replication.
- RNA polymerase: assembles complementary RNA nucleotides along a single DNA strand, resulting in a molecule of mRNA. This enzyme is involved in transcription
- Reverse transcriptase: as the name suggests, it does the opposite of transcription. It assembles complementary DNA nucleotides along a molecule of RNA (viral RNA) resulting in a single strand of complementary DNA (cDNA). This enzyme is involved in viral replication in host cells.

what your definition of gene flow would be? what context / example please?

This might be helpful
http://evolution.berkeley.edu/evosite/evo101/IIIC4Geneflow.shtml

ummm? can u be more specific ?

gene : sequence of amino acids that codes for a particular protein or function.

flow: u know the meaning

basically it means the transfer of genes form one organisms to another through sexual reproduction.

for example, if a geographical barrier arises between a population of a species, means they cannot interbreed therefor no gene flow between them.

okay I know this sounds so dumb, but seriously can someone please explain me what one earth HSW is? where can I find relavanet infos about HSW which is related to our specification?