Question
The electron micrograph shows part of a cell including a mitochondrion.
a. Outline how the structures labelled X and Y are adapted to carry out the function of the mitochondrion.
X:
Y: [2]
b. Explain how ATP is generated in mitochondria by chemiosmosis. [4]
▶️Answer/Explanation
Markscheme
X: large/increased SA area for ATP production/electron transport/oxidative phosphorylation/proton pumping
OR
X: small/narrow intermembrane space for generating proton gradient (rapidly/steeply);
Y: contains enzymes for Krebs cycle/link reaction;
a. protons pumped across inner membrane of mitochondria/into intermembrane space;
b. using energy released by flow of electrons/by electron transport/by electron carriers;
c. proton gradient established/maintained / proton motive force generated;
d. protons pass/diffuse back through inner membrane/membrane of cristae/to matrix;
e. through ATP synthase;
f. ATP production coupled to flow of protons / ATP from ADP and Pi using energy from protons;
Question
a. Outline the functions of rough endoplasmic reticulum and Golgi apparatus. [3]
b. Outline the control of metabolism by end-product inhibition. [5]
c. Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane. [7]
▶️Answer/Explanation
Markscheme
a. ribosomes on RER synthesize/produce polypeptides/proteins ✔
b. proteins from RER for secretion/export/use outside cell/for lysosomes ✔
c. Golgi alters/modifies proteins/example of modification ✔
d. vesicles budded off Golgi transport proteins «to plasma membrane»
OR
exocytosis/secretion of proteins in vesicles from the Golgi ✔
Accept “for use inside and outside the cell” for mpb.
a. metabolism is chains/web of enzyme-catalyzed reactions
OR
metabolic pathway is a chain of enzyme-catalyzed reactions ✔
b. end product/inhibitor is final product of chain/pathway ✔
c. inhibits/binds to/blocks the first enzyme in chain/pathway ✔
d. non-competitive inhibition ✔
e. end-product/inhibitor binds to an allosteric site/site away from the active site ✔
f. changes the shape of the active site/affinity of the active site «for the substrate» ✔
g. prevents intermediates from building up
OR
prevents formation of excess «end» product/stops production when there is enough
OR
whole metabolic pathway can be switched off ✔
h. negative feedback ✔
i. binding of the end product/inhibitor is reversible
OR
pathway restarts if end product/inhibitor detaches/if end product concentration is low ✔
j. isoleucine inhibits/slows «activity of first enzyme in» threonine to isoleucine pathway ✔
Allow mark points shown in clearly annotated diagrams.
To gain mpd, mpe and mpf the answer must be in the context of end-product inhibition, not enzyme inhibition generally.
a. hydrophilic is attracted to/soluble in water and hydrophobic not attracted/insoluble ✔
b. hydrophilic phosphate/head and hydrophobic hydrocarbon/tail in phospholipids ✔
c. phospholipid bilayer in water/in membranes ✔
d. hydrophilic heads «of phospholipids» face outwards/are on surface ✔
e. hydrophobic tails «of phospholipids» face inwards/are inside/are in core ✔
f. cholesterol is «mainly» hydrophobic/amphipathic so is located among phospholipids/in hydrophobic region of membrane ✔
g. some amino acids are hydrophilic and some are hydrophobic ✔
h. hydrophobic «amino acids/regions of» proteins in phospholipid bilayer «core» ✔
i. hydrophilic «amino acids/regions of» proteins are on the membrane surface ✔
j. integral proteins are embedded in membranes due to hydrophobic properties/region
OR
transmembrane proteins have a hydrophobic middle region and hydrophilic ends ✔
k. peripheral proteins on are on the membrane surface/among phosphate heads due to being «entirely» hydrophilic
OR
«carbohydrate» part of glycoproteins is hydrophilic so is outside the membrane ✔
l. pore of channel proteins is hydrophilic ✔
Allow mark points shown in clearly annotated diagram.
In any part of the answer, accept polar instead of hydrophilic and non-polar or apolar instead of hydrophobic.
Question
Draw the ultrastructure of a prokaryotic cell based on electron micrographs. [3]
▶️Answer/Explanation
Ans
a.cell wall;
b.plasma membrane; Clearly shown as a separate line under the cell wall or theinner line
c.cytoplasm AND 70S ribosomes; Do not allow (small) circles
d.nucleoid/naked DNA;
e.plasmid
OR
pili
OR
flagella/flagellum;
