Question
The electron micrograph shows the surface membrane of an animal cell.
(a) State the technique used to obtain this electron micrograph.
(b) Using the scale, calculate the magnification of the image.
(c) Identify the type of molecule that can be seen at region X.
(d) Outline the reason that images such as this falsified the Davson-Danielli model.
(e) Explain the reason that animal cells and tissues under investigation must be maintained in solutions with the same osmolarity.
Answer/Explanation
Answer:
(a) freeze fracture/etching
OR
involves freezing and fracturing cells;
(b) 140000 to 150 000 (X);
(c) protein/named membrane protein;
(d) the phospholipid bilayer was not coated by/sandwiched between two protein layers
OR
(transmembrane/integral) proteins are found within the phospholipid bilayer;
(e)
a. to prevent osmosis;
b. cells placed in the in the incorrect osmolarity might swell/burst/shrink;
c. hypotonic solution would cause water to enter cells/tissues;
d. hypertonic solutions would cause water to leave cells/tissues;
e. water loss would hinder (metabolic) reactions in cell cytoplasm
OR
distort appearance of the cells (for the investigation);
Question
The image shows a phospholipid bilayer that is a component of the cell membrane.
(a) Annotate the diagram to illustrate the amphipathic nature of phospholipids. [2]
(b) Outline a function of cholesterol in cell membranes. [1]
(c) Describe two pieces of evidence that show that eukaryotic cells originated by endosymbiosis. [2]
▶️Answer/Explanation
Ans:
a
a. line to circle labelled phosphate (head) and (tail) labelled fatty acid/hydrocarbon/lipid (tail);
b. label hydrophilic/polar/attracted to water/ and hydrophobic/non polar/not attracted to water;
b reduces fluidity of membrane / reduces permeability of membrane (to some molecules);
c
a. mitochondria/chloroplasts have their own DNA;
b. mitochondria can self-replicate/undergo a process like binary fission;
c. mitochondria/chloroplasts have double membranes;
d. mitochondria/chloroplasts have(70s) ribosomes;
e. mitochondria/chloroplasts are sensitive to antibiotics;
f. similar in size to bacteria