Section 4

Question 1

Describe the structure of DNA in eukaroyotic cells

Answer 1

Linear, long DNA which exists as chromosomes found in the nucleus
Wound around proteins called histones
The mitochondria and chloroplasts have their own DNA which is similar to prokaryotic cells becuase it is circular and shorter

Question 2

Describe the structure of DNA in prokaryotic cells

Answer 2

DNA in chromosomes but is shorter and circular
No histones

Question 3

What is a gene?

Answer 3

DNA contains genes
It is a sequence of DNAbases that codes for a polypeptide or functional RNA

Question 4

What is a genome and a proteome?

Answer 4

Genome - complete set of genes in a cell
Proteome - the full range of proteins that the cell is able to produce

Question 5

What are introns and exons?

Answer 5

Introns - sections of DNA which don’t code for amino acids
Exons - genes that do code for DNA

Question 6

What is an allele?

Answer 6

Different forms of the same gene

Question 7

What are homologous chromosomes?

Answer 7

Pairs of matching chromosomes with the same size and genes but with different alleles

Question 8

What is a locus?

Answer 8

Fixed position of an allele on the chromosome
Alleles coding for the same characteristic will be found in the same place

Question 9

Describe mRNA

Answer 9

Made during transcription
Carries the genetic code from the DNA to the ribosomes where it is used to make a protein during translation
A single polynucleotide strand
Has codons/ triplets - three bases which code for an amino acid

Question 10

Describe tRNA

Answer 10

Carries amino acids to the ribosomes
Single polynucleotide strand folded into a clover shape
H bonds between specific base pairs hold the shape
Has an anti codon - a specific sequence of three bases
Amino acid binding site at the other end

Question 11

Describe transcription

Answer 11

RNA polymerase attaches to DNA and breaks H bonds between the two strands
One of the strands is used as a template
RNA polymerase lines up free RNA nucleotides to complimentary base pairs with uracil instead of thymine
RNA polymerase joins the nucleotides making an mRNA strand
When RNA reaches a stop signal it detaches from the DNA
mRNA moves out of the nucleus and attaches to a ribosome

Question 12

What is splicing?

Answer 12

When introns are removed from pre - mRNA
Takes place in the nucleus
Doesn’t happen in prokaryotic cells as there are no introns

Question 13

Describe translation

Answer 13

mRNA attaches itself to a ribosome and the tRNA molecules carry amino acids to it
ATP provides energy needed for the bond between the amino acid and the tRNA molecule to form
A tRNA molecule with an anti codon that is complimentary to the codon on the mRNA attaches by complimentary base pairing
A second tRNA molecule attaches in the same way
These two amino acids are joined by a peptide bond
The first tRNA molecule moves away leaving the amino acid behind
A third tRNA molecule binds and the second tRNA molecule moves away until there is a stop codon

Question 14

What is the genetic code?

Answer 14

Sequence of codons in mRNA

Question 15

What does non- overlapping mean?

Answer 15

Each codon is read in sequence
Bases don’t share their bases

Question 16

What does degenerate mean?

Answer 16

there are more possible combinations of codons than there are amino acids
Some amino acids are coded for by more than one codon

Question 17

What does universal mean?

Answer 17

codons are all the same for all living things

Question 18

What does diploid mean?

Answer 18

Normal body cells have the diploid number of chromosomes meaning each cell contains two of each chromosome - one from mum and one from dad (46 chromosomes)

Question 19

Describe the process of meiosis

Answer 19

1) DNA unravels and replicates so there are two copies of each chromosome called chromatids
2) The DNA condenses to from double armed chromosomes each made from two sister chromatides joined by a centromere
3) Meiosis 1 - the chromosomes arrange themselves into homologous pairs
4) These are seperated
5) Meiosis 2 - the pairs of sister chromatides that make up each chromosome are seperated
6) Four haploid cells that are genetically different are produced

Question 20

What causes genetic variation in gametes?

Answer 20

Crossing over of chromatids
Independaent segregation of chromosomes
Random fertilisation

Question 21

Describe crossing over of chromatids

Answer 21

In meiosis 1 homologous chromosomes come together to pair up
The chromatids twist around each other and bits of chromatids swap over
The chromatids contain the same genes but a different combination of alleles

Question 22

Describe independant ssegregation of chromosomes

Answer 22

Each homologous pair of chromosomes is made up from one chromosome from mum and one from dad
When the homologous pairs are seperated in meiosis 1 it is random to which chromosome from each pair ends up in which cell
Resulsting in different combinations of mum and dad chromosomes

Question 23

What is a mutagenic agent and an example?

Answer 23

Things that increase the rate of mutations
Radiation, chemicals, viruses

Question 24

What is genetic diversity?

Answer 24

the number of different alleles of genes in a species or population

Question 25

How is genetic diversity increased?

Answer 25

Mutations in the DNA forming new alleles Different alleles being introduced into a population (gene flow)

Question 26

Describe the process of natrual selection

Answer 26

1) A mutation occurs leading to a new allele which can be advantageous 2) Individuals with this allele are more likely to survive and reproduce and pass the allele on than those without it 3) Allele frequency increases leading to evolution

Question 27

What is evolution?

Answer 27

The gradual change in a species over time

Question 28

What is an adaptation and what are the three types?

Answer 28

Features that help organisms to survive in their enviroment Behavioural Physiological Anatmoical

Question 29

What are behavioural adaptations?

Answer 29

The way an organism acts that increases its chance of survival e.g playing dead

Question 30

What are physiological adaptations?

Answer 30

Processes inside an organisms body that increase its chance of survival e.g when bears hibernate their metabolic rate slows down to conserve energy

Question 31

What are anatomical adaptations?

Answer 31

Structrual features of an organisms body that increase its chance of survival e.g Whales having blubber

Question 32

What is directional selection?

Answer 32

Individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce Could be in response to an enviromental change

Question 33

What is stabilising selection?

Answer 33

Individuals with alleles for average characteristics (middle range) are more likely to survive and reproduce When the enviroment isn't changing

Question 34

What is the taxonomy group names?

Answer 34

Kingdom Phylum Class Order Family Genus Species

Question 35

What three ways can we classify using DNA or proteins?

Answer 35

Genome sequencing Comparing amino acid sequences Immunological comparisons

Question 36

What is genome sequencing?

Answer 36

Comparing the DNA base sequence between different organisms to see how closely related they are

Question 37

What is interspecific/ intraspecific variation?

Answer 37

Inter - variation between different species Intra - variation within the same species

Question 38

What is standard deviation?

Answer 38

A mesure of the spread of values around the mean

Question 39

What is biodiversity?

Answer 39

the variety of living organisms in an area

Question 40

What is a habitat?

Answer 40

Where an organism lives

Question 41

What is a community?

Answer 41

All the populations of different species in a habitat

Question 42

What is species richness?

Answer 42

A measure of the number of different species in a community

Question 43

What is a species?

Answer 43

A group of similar organisms which can breed to produce live fertile offspring

Question 44

What is the equation for index of diversity?

Answer 44

d = N(N-1) -------------- ∑ n(n-1) N = total number of organisms of all species n = total number of organisms of one species ∑ = sum of