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Biology ASTopic 3
Definition questions
Polygenic inheritance – When there is more than one gene for a single characteristic at different loci
and this arises continuous variation
Stem cell – An undifferentiated cell that can give rise to specialised cells and can divide to produce
more stem cells
Pluripotent cell – Unspecialised cells that can differentiate to give rise to almost any type of cell in
the body excluding totipotent cells
Molecular Phylogeny - molecular differences /similarities in DNA in proteins and the evolutionary
relationship between organisms
Heterozygosity Index – is a measure of genetic diversity within a population
Theory questions
3.1-5 Cells and organelles
Explain the route taken by a protein from the RER to outside the cell
Amino acids incorporated into proteins in ribosomes attached on RER
Proteins transported within RER
Proteins folded within lumen of RER
Proteins transferred from RER to Golgi apparatus in transport vesicles produced by RER
Vesicle fuses with membrane of Golgi apparatus
Proteins are modified inside the Golgi apparatus
Example glycoproteins - carbohydrate added
Then they are packages into secretory vesicles/lysosomes by Golgi apparatus
And leave the cell by exocytosis
Describe three structural differences between prokaryotic and eukaryotic cells
Prokaryotes have smaller ribosomes
Eukaryotes has a nucleus but prokaryotes don’t
Prokaryotes have the presence of plasmids/slime capsule
Cell walls in prokaryotic cells contain peptidoglycan but Eukaryotic they contain
chitin/cellulose
What happens when a substance inhibits mRNA synthesis?
No transcription
No translation
No proteins formed for a specific function
Describe how you could recognise the Golgi apparatus using a electron microscope
Smooth membrane no ribosomes
Cisternae in stacks
Membrane bound sac/cisternae
, Cisternae flatted/curved
Different sizes of cisternae
Presence of vesicles
Draw a fully labelled diagram of a nucleus in a electron microscope
Nuclear envelope
Nucleolus
Nuclear pores
Nucleoplasm
Chromatin
Explain why most scientists do not think mesosomas exist in bacterial cells
To see interior structures of bacterial cells they have to be viewed under a electron
microscope
They have gone under extensive preparation using various chemicals and they are dead
Scientists agree that mesosomes are produced by this procedure
Regard them as artefacts
Describe two ways in which bacteria may benefit from having plasmids
Contains genes that aid bacteria’s survival
Antibiotic resistance or toxin producing genes
Describe how scientist could have determined whether a cell is eukaryotic or prokaryotic
Have membrane bound organelles
Named membrane bound organelles
Size of ribosomes larger in eukaryotes
Eukaryotes contain DNA that is associated with histone proteins
Eukaryotes do not contain plasmids
Describe how a polypeptide is then proceed to from a glycoprotein
Polypeptide chain moves thought the endoplasmic reticulum then the Golgi
In the rER the polypeptide is folded - secondary/tertiary structure
In the Golgi the carbohydrate is added
The protein is transports around the cell in a vesicle
Describe the role of the Golgi apparatus
Modifies protein
Details of modification – addition of carbohydrate chains
Golgi apparatus packages proteins in secretory vesicles
For export from cells by exocytosis
Lysosomes
3.6-7 Fertilisation
Compare and contrast the acrosome reaction and the cortical reaction
, Similarities: both release enzymes by exocytosis and both involve vesicles
Differences: acrosome reaction causes the digestion of the zona pellucida but cortical
reaction causes the thickening of the zona pellucida
Describe and explain how, in mammals events following the acrosome reaction prevent more than
one sperm fertilising and egg
Sperm and egg cell membrane fuse
Cortical granules fuse with the cell surface membrane of the egg
These cortical granules are release its content into the zona pellucida by exocytosis
This causes the thickening of the zona pellucida preventing an other sperms from entering
and reaching the cell surface membrane
The sperm and egg nuclei fuse
There is a change in charge across the membrane
Describe the function of mitochondria in the sperm cell
They carry out aerobic respiration
This provides ATP/ energy
To move the flagellum of the sperm towards the egg
Describe and explain the adaption of a human egg cell
Zona pellucida – prevent polyspermy
Lipid droplets – provide energy
Haploid nucleus – diploid number restored at fertilization
Large cell size – increase the chance of fertilisation
Release of chemical – attract sperm
Membrane with sperm receptors - allow sperm to bind
A lot of mRNA present – allowing early translation of transcription factors
Explain the limitations of using the line on the graph to predict the swimming speed of sperm cells
Variation around the line
Gradient of the line may not remain the same
Explain why it is advantageous for the eel to have a larger egg cell
A larger cell will contain more lipid droplets which will provide more energy for the
development of the embryo
The eel’s larger egg is a bigger target for the sperm to hit aiding fertilisation in the open
water
Explain the function of each of the following structure of a sperm cell
Flagellum – movement to reach the egg cells
Mitochondria – aerobic respiration and ATP for movement
Acrosome – contains enzymes and digests zona pellucida
Describe how the structure of a pollen grain differs from that of a sperm cells
Pollen grain does not posses flagellum
Pollen grain does not have a acrosomes
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