Summary all questions that are repeated from papers all the way from 2008

Biology AS

Topic 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