By: Arnav & the one and only amazing Kiara
Date of Exam: 20 December/2022 (Tuesday)
Biology Exam
Evolution
Definitions
Evolution: Process of development of life over a long period of time through natural
selection to best adapt to its environment
Species: Group of organisms with similar features that can reproduce fertile offspring
with each other
Genotype: The information in the DNA containing its characteristics
Phenotype: The outward appearance determined by the genotype and environment
caused by genetic variation within the species
Homologous: Same structure, Function different à common Ancestors
Analogous: Different structure, Function same à Different Ancestor (caused by
similar selection pressure)
Spontaneous Generation: Theory in which there is creation of living beings from non-
living materials
Key Stimulus: A stimulus which plays a decisive role in causing a certain behaviour (A
Red Traffic Light is the key stimulus for slowing down a car)
Speciation: When a species evolves into two or more species
Theories of Evolution
I. Lamarck’s Theory
Body parts that are most often used, forced by the environment will develop
strongly as opposed to not or little used body parts and then passed on to the next
generation.
II. Haeckel’s Theory
The early stages of development in an embryo shows the evolution history of the
species and its ancestors. Its is the process of evolution depicted in a much faster
process in the development of the embryo.
III. Darwin’s Theory
Species can evolve and change into different species over long periods of time given
the state of the environment they live in. The changes in development are extremely
small. He came up with that it also must be through natural selection.
Requirements for Evolution
I. Variation within the Species
Caused by differences in sexual reproduction and mutations
Needed to enhance the survival chance of a population
II. Sexual Reproduction
A lot of offspring produced so at least some survive
III. Mutations
A change in the alleles caused by a change in the DNA
Changes the genotype
IV. Selection Pressure
An environmental change that puts pressure of survival on the population
By: Arnav & the one and only amazing Kiara
Date of Exam: 20 December/2022 (Tuesday)
V. Reproductive Isolation
Different environments may require different characteristics/development
VI. Natural Selection (Survival of the Fittest)
Selection of organism that is best adapted to its environment and will survive
to produce offspring
Proof of Evolution
I. Fossil Record
Fossils are formed when dead organisms are covered with land and put in extreme pressure.
That means the structure of it is preserved. They can also be footprints.
You can tell how old a species
Geographically close fossils can show changes in the species
II. Homologous and Analogous Organs
Homologous
Similar Origin
Divergent Evolution (One species becomes more)
Different Function
divergent
Analogous
Different Origin
Convergent Evolution (Two species become closer to one)
Similar Functions
Convergent
III. Vestigial (Useless) Organs
No Function of the Organ
Remnant Parts of Ancestor
IV. DNA Comparison
Uses Phylogenetic Trees
Phylogenetic Trees
By: Arnav & the one and only amazing Kiara
Date of Exam: 20 December/2022 (Tuesday)
Genetics
Prokaryotic: Eukaryotic cells:
- No membrane bound cell - Membrane bound organelles
organelles - Membrane bound nucleus DNA
- NO nucleus-loop of DNA chromatin
- Bacteria and archaea - All multi-cellular organisms and
some uni-cellular
Life of cells
Cells have a life cycle
Called the cell cycle
A cell goes through a phase in which it increases in size then divides into two
There is a growth phase, The Interphase, and a phase of Cell division
DNA
The entire genetic material of an organisms is known as its genome
DNA = Deoxyribonucleic acid
DNA – the molecule that contain the instructions for growth and development of all
organisms
Consists of two strands of DNA wound around each other in what is called a Double
Helix structure
All nucleotides contain the same phosphate and deoxyribose sugar, but differs
when it comes to the base attached
Four bases are: Adenine, Cytosine, Thymine, Guanine
Complementary base pairs are: A and T, C and G
Base
Phosphate Hydrogen
bonds
DeoxyriboseDe
oxyribose
nucleotide
Gene
The DNA code for all inherited characteristics lies in the specific combination of the
bases
To express these characteristics, bases must be translated into proteins. Proteins
exist out of the building blocks call amino acids
By: Arnav & the one and only amazing Kiara
Date of Exam: 20 December/2022 (Tuesday)
Each DNA is made up of many genes coding for the formation of different proteins
which give us our characteristics
- A gene is a short length of DNA found on a chromosome that codes for one
specific protein
- Each gene codes for a specific protein by specifying the order in which amino
acids must be joined together
- Genes are responsible for an organism’s features. E.g., we all have a gene for eye
colour, e gene for skin colour, and genes for height
Chromosomes
In the nucleus of a cell, the DNA double helix structure supercoils to form structures
called chromosomes
They are only visible in cell division
Normal human cells contain 23 pairs of chromosomes
This is a diploid number
One chromosome from a pair is inherited from each parent
A pair is called homologous pair
- The 23rd pair of chromosomes are the sex
chromosomes
- In females the sex chromosomes are the same
(XX)
- In males they are different (XY)
- Homologous chromosomes are the same length
and have specific nucleotide segments called
genes in the same location or locus
- Gametes or sex cells contain just 23 individual
chromosomes
- This is half the full number if a body cell and us
called the haploid number or simply n
The nucleosome is the fundamental subunit of
chromatin
Each nucleosome is composed of DNA wrapped around a set of proteins called
histones
A histone is a protein that provide structural support to a chromosome
Genes are found in specific location on the chromosomes
By: Arnav & the one and only amazing Kiara
Date of Exam: 20 December/2022 (Tuesday)
Protein Synthesis
RNA
Like DNA, the nucleic RNA (Ribonucleic acid) is a polynucleotide – it is made of many
nucleotides linked together in a long chain
Unlike DNA, RNA nucleotides contain the nitrogenous bases A and U, G and C
Unlike DNA, RNA contains the base uracil
Unlike DNA, RNA molecules are only made up of one polynucleotide strand
An example of an RNA molecule is a messenger molecule (mRNA), which is the
transcript copy of a gene that encodes a specific polypeptide. Two other examples
are transfer RNA (tRNA) and ribosomal RNA (rRNA)
Transcript and translation
A gene is a sequence of nucleotide bases in a DNA molecule that codes for the
specific production of amino acids, that in turn makeup a specific polypeptide
(protein)
This process of protein synthesis occurs in two stages:
Transcription:
o DNA is transcribing and an mRNA (messenger) molecule produced
o Occurs in the nucleus
o Part of the DNA unwinds
o This exposes the gene to be transcribed
o A complimentary copy of the code from the gene us made up of single
stranded nucleic acid molecules known as mRNA
Translation:
o mRNA is translated and an amino acid sequence is produced
o occurs in the cytoplasm of the cell
o after leaving the nucleus, the mRNA molecule attaches to a ribosome
o in the cytoplasm, there are free molecules of tRNA with on one side a
specific amino acid attached
o two tRNA molecules fit onto the ribosome at any time, bringing the amino
acid they are each carrying side by side
o a bond is then formed between the two amino acids
o This process will go on and on until a stop codon is reached
o The amino acid chain then forms the final protein
Mutations
Mutations are rare random changes that occur in the sequence of DNA bases in a
gene or a chromosome
Can occur continuously
Mutations in a gene can sometimes lead to a change in the protein that the gene
codes for
I. The effects of Mutations
Most mutation do not alter the protein or only slightly so that no appearance or
function is changed
By: Arnav & the one and only amazing Kiara
Date of Exam: 20 December/2022 (Tuesday)
A small number of mutations code for a significantly altered protein with a different
shape
This may affect the ability of the protein to perform its functions for example of the
shape of the active site on an enzyme change, the substrate may no longer be able
to bind to the active site
II. The causes of Mutations
They can happen simultaneously and continuously, but their frequency can be
increases by exposure to Gamma rays, x-rays, ultraviolet rays, and certain types of
chemicals
Increase rates of mutations can cause cells to become cancerous
III. Semi conservative DNA Replication
DNA replication occurs in prep for cell division
This is when a parent cell divides to produce two genetically identical daughter cells
The hydrogen bonds between the base pars on the tow antiparallel polynucleotide
strands are broken
This unzips or unwinds the DNA double helix structure to form two single
polynucleotide DNA strands
Each of these new single strand’s act as a template for the formation of a new strand
This method of replicating DNA is known as semi-conservative replication because
half of the original DNA molecule is kept in each of the new DNA molecules
