Summary Edexcel iGCSE Biology Revision Notes on Section 7 of the CGP
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Course
Biology
Institution
GCSE
I used this document in my GCSE revision and it helped me to achieve a Grade 8 in my final biology GCSE exam (edexcel igcse board). These notes are made based on the CGP GCSE guide.
EVOLUTION
Theory of evolution
life began as simple
:
organisms from which more complex organisms evolved
>
↳
takes place over billions of years
Natural Evolution : Darwin concluded (based on
&
Iorganisms in a species
. show variation in their characteristics these things) that organisms
With the most suitable
. necessary resources for organisms
2 are limited
characteristics for the
↳ individuals compete for these resources to survive environment would be the
most successful competitors,
their chance of
. the successful
3 Of /increasing
organisms increase their "survival
" survival
Chance of breeding & passing on genes the cittest
C greater portion of the next generation has the better allele & strong characteristic
. that
helps survival
5 over generations , the characteristic is more common in the population increasing their
chance of survival
↳ 'best features' are naturally selected and the species is more adapted to its
environment
*
variations caused by environment are part of the natural selection process , only
not
genetic variations are passed on , influencing the evolution of a species
MUTATIONS & ANTIBIOTIC RESISTANCE
Mutations : rare
,
random changes in an Organisms DNA that can be inmerited
↳ changes the sequence of the DNA bases in a gene
↳ DNA ↳ produces a genetic variant
bases code for the amino acids that makes up a protein
↳ mutations can change the protein being coded for
↳ a mutation in a
gene that codes for an amino acid could change the Shape of
the enzyme's active site-altering its function
Mutations can stop the product of an enzyme entirely
↳ Mutations increase variation (due to the change in the phenotype
Affect level of mutations :
1) most mutations
,
↳ no effect on the phenotype e g:
.
↳ if the mutation occurs in an unimportant region of DNA
↳ is the mutated codon codes for the same amino acid as the original
if it occurs in
↳ a recessive allele
2) some mutations ,
↳ small effect on the phenotype e g
: .
↳ if the mutation has a slight effect on the proteins structure
↳ slightly actening the characteristic
3) very rarely
,
↳ significant effect on the phenotype e g: .
↳ if it results in a very different protein
↳ this protein can no longer
carry out its function
↳ these mutations can be harmful (e g cancer) . .
↳ these mutations can be advantageous (e g
. .
giving a survival advantage
Or mutations are
Risk increased by :
↳iomising radiation (X-rays gamma , ,
ultraviolet etc)
↳ mutagens (chemicals e g . chemicals .
in Tobacco
Bacterial Antibiotic Resistance
, I bacteria also
. develop random mutations in their DNA
↳ sometimes results in bacterium beingless accected by a particular antibiotic
↳ this is an advantage for bacteria since it survives better in its host and
reproduces more
↳ the allele for resistance is passed onto ospring , becoming more common in a
population of bacteria
↳ makes it get mid of an infection since some antibiotics are
difficult to
ineffective on the mutated bacteria
*
many 'Superbugs' are resistant to most known antibiotics (MRSA) are becoming
*
more common
ASEXUAL REPRODUCTION & MITOSIS
Mitosis reproduces itself by splitting to form two cels with identical sets
: When a cell
of chromosomes
Asexual reproduction : involves only one parent . The
offspring have genes that are
identical to the Ino variation between parent & spring
parent
Mic
a
Diploid cen : a cel fun set of chromosomes
with the
↳ to chromosomes , 23 pairs in humans
When the ceugets a signal to divide ,
it needs to duplicate
its DNA (So there's cel)
⑭
a copy for each new
↳ the DNA Cowms X-shaped chromosomes other
↳ each arm of the chromosome is an exact duplicate of the ↓
The chromosomes line up at the centre of the cel and cell fibres
⑮ Pull them apart
-
↳ the two arms of each chromosome go to opposite ends
D
Membranes form around each of the sets of chromosomes
↳ these become the nuclei of the two new cells
↓
them the cytoplasm divides
⑧ Now you have two new , genetically identical ceus
Mitosis is now all plants and animous a cloning
grow and repair damaged tissue
involves mitosis
SEXUAL REPRODUCTION & MEIOSIS
Meiosis : produces a haploid cells whose chromosomes are not identical
Sexual reproduction : the cusion of more and female gametes
. The offspring contains a
mixture of both parents' genes
↳ the mother and father produce gametes legg and sperm ceus)
gametes naploid :
Ceus contains half the number of chromosomes in a normal cell
↳ 23 chromosomes im humans
Stages of Sexual reproduction :
↳ fertilisation
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