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Biology Unit 2
Revision 2013…read more

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Chapter 7 ­ variation
Chapter 8 ­ DNA and meiosis
Chapter 9 ­ genetic diversity
Chapter 10 ­ the variety of life
Chapter 11 ­ the cell cycle
Chapter 12 ­ cellular organisation
Chapter 13 ­ exchange and transport
Chapter 14 ­ classification
Chapter 15 ­ relationships between organisms
Chapter 16 ­ adaption and selection
Chapter 17 - biodiversity…read more

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Chapter 7 - variation
Variation = the differences in characteristics between organisms
Variation is caused by genetic (genotype) and/or environmental
(phenotype) factors
Interspecific variation = between different species
Intraspecific variation = within the same species
Continuous = the variations have no limit, eg. Height, weight (they
can take any possible value)
Discontinuous = the variations have a limit eg. Eye colour (there is
a limited number of possible outcomes ­ only so many colours)
Genetic differences can be caused by:
Mutations ­ might or might not be passed onto next generation
Meiosis ­ mix up of genetic material
Fusion of gametes ­ mother and fathers gene come together and so
the offspring will be different…read more

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Chapter 7 (part 2)…read more

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Chapter 8 ­ DNA structure
DNA contains the genetic information for organisms. It is a polymer
and is made up from many nucleotides
A nucleotide is made from a deoxyribose sugar, a phosphate group
and a base (adenine, guanine, cytosine or thymine)
The nucleotides are joined together by phosphodiester bonds formed
in condensation reaction ­ form polynucleotide chains (nucleic acids)
Two polynucleotide chains line up ­ the sugar and the phosphate
group form the sugar-phosphate backbone and the bases point in
and towards each other ­ forming hydrogen bonds which keeps the
chains together
Adenine only bonds with thymine, and guanine only bonds with
cytosine = complementary base pairing
Thymine and cytosine are pyrimidines and adenine and guanine are
Only a purine and a pyrimidine can join together…read more

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Chapter 8 ­ genes and polypeptides
A gene is a sequence of bases which codes for a polypeptide
Every three bases (triplet code) codes for an amino acid and a sequence of these
amino acids make the polypeptide = determines development
The gene for a particular characteristic is on a specific place on the chromosome
= gene locus
Different versions of the same gene = alleles
Polypeptide uses RNA not DNA: RNA has a ribose sugar instead of a deoxyribose
sugar and uses uracil instead of thymine ­ it is just one strand
In polypeptide synthesis:
Transcription ­ the DNA partly unravels and enzymes make a strand of
messenger RNA (mRNA) which is complementary to the original DNA and the
mRNA leaves through the nuclear pores
Translation ­ the mRNA attaches to a ribosome and the transfer RNA (tRNA)
moves the amino acids to specific positions according to their triplet codes ­
enzymes link the amino acids and a polypeptide is formed
Genes include sequences of bases for coding polypeptides and sequences which
don't code for anything = introns = removed from mRNA during transcription
If a single gene is changed the proteins / enzymes will be non functional…read more

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Caitlin x



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