Question
(a) Fig. 2.1 is a transmission electron micrograph of a transverse section through a blood capillary that is surrounded by actively respiring cells.
fluid R
cell Q
Fig. 2.1
(i) Identify cell Q shown in Fig. 2.1.
…… [1]
(ii) Fluid R is formed from blood in the blood capillary.
State and explain one difference between the composition of fluid R and the composition of the blood in the capillary.
difference ……
explanation ……
…… [3]
(b) (i) The cell surface membranes of the respiring cells have a role in regulating the exchange of substances between the cells of the body and the blood.
Draw a diagram in the space below to show the arrangement of phospholipid molecules in the cell surface membrane.
[2]
(ii) Cholesterol is a molecule found in the cell surface membrane.
Describe one role of cholesterol in the cell surface membrane.
…… [1]
(c) Nicotine is one of the components of tobacco smoke. Nicotine can cross cell surface membranes and enter the bloodstream.
(i) Describe the short-term effects of nicotine on the cardiovascular system.
…… [2]
(ii) Nicotine is absorbed from the blood plasma into the cells of the capillary wall. Scientists have suggested that nicotine is transported from the blood plasma into these cells using a type of co-transporter mechanism.
Fig. 2.2 shows how nicotine may be transported from the blood plasma into a cell.
H+ ions move down their concentration gradient blood plasma out of the cell
cell surface membrane
cytoplasm co-transport protein nicotine is transported of the cell against its concentration gradient into the cell
Fig. 2.2
The co-transporter mechanism shown in Fig. 2.2 is different from the co-transporter mechanism that moves sucrose into the cytoplasm of a companion cell in phloem tissue.
Outline the similarities and differences between the co-transport of nicotine and the co-transport of sucrose.
…… [3]
[Total: 12]
Question 3 starts on page 8.
Mark scheme
2(a)(i) red blood cell ; A erythrocyte / red blood corpuscle 1
2(a)(ii) any valid difference one mark 3
fluid R / tissue fluid, has,
one from
fewer (named) proteins / no large proteins / no plasma proteins ;
A no named plasma proteins (albumen / fibrinogen)
A fewer plasma proteins only if stated, they are small / leave the blood
fewer / no, white blood cells ; A more macrophages
no red blood cells ;
no platelets ;
explanation to match difference 2 marks
(red blood cells, platelets, proteins, white blood cells) too large ;
(fewer white blood cells) ref to some, white blood cells / phagocytes / macrophages monocytes, are able to move through ;
cannot be, filtered / fit, through gaps / AW, between endothelial cells / in endothelial wall / in capillary wall ;
idea that not filtered out under pressure from, plasma / blood ;
or
fluid R / tissue fluid, has
one from
higher partial pressure / AW, of, carbon dioxide ;
A higher concentration / more
explanation to match difference 2 marks
produced by / waste of, (surrounding respiring) cells ;
A (waste) product of respiration
diffuses / AW, from cells to, (fluid) R / tissue fluid (before entering blood) ;
idea that blood has come from lungs, where carbon dioxide has been excreted ;
AVP ; e.g. diffusion through cells in capillary wall
2(a)(ii) or
fluid R / tissue fluid, has
one from
lower partial pressure / AW, of, oxygen ; A lower concentration / less
explanation to match difference 2 marks
carried by the blood (from the lungs) ; A blood is more oxygenated
diffuses / AW, from, red blood cells / Q / blood ;
idea that filtered out under pressure from, plasma / blood ;
AVP ; e.g. diffusion through cells in capillary wall
or
fluid R / tissue fluid, has
higher concentration of, glucose / amino acids / fatty acids ; A more
explanation
carried by the blood to the respiring cells ;
small ;
can be, filtered / fit, through gaps / AW, between endothelial cells / in endothelial wall / in capillary wall ;
idea that filtered out under pressure from, plasma / blood ;
AVP ; e.g. diffusion through cells in capillary wall
2(b)(i) bilayer drawn with heads pointed outwards and tails pointed inwards ; 2
phospholipid drawn with one (phosphate) head and two fatty acid tails ;
2(b)(ii) any one from: 1
cholesterol, maintains / regulates, the fluidity of the membrane ;
A reduces fluidity at high temperature / increases the fluidity at low temperatures
maintains / regulates, (mechanical) stability of the membrane / AW;
prevents entry of hydrophilic substances / AW / ions ;
2(c)(i) any two from: 2
increases heart rate ;
increases blood pressure ;
makes platelets stick together / makes blood more likely to clot ;
damage to, endothelium / endothelial wall / capillary wall ;
reduces blood flow to extremities / ref. vasoconstriction ;
2(c)(ii) any three from: 3
similarities max 2
both have a (co-)transport protein ;
both involve H+ / hydrogen ions / protons ;
H+ move down the concentration gradient / by facilitated diffusion ;
(sucrose and nicotine both) move against the concentration gradient ;
differences max 2
in nicotine transport, H+ ions and nicotine, move in opposite directions ;
ora for sucrose transport
H+ ions move from, the apoplast / cell wall, in sucrose transport (from the cytoplasm in nicotine transport ) ;
AVP ; e.g. ref to ATP