14.11 End of Chapter Questions
Question 1 – 6
1. Which of the following is an incorrect statement about the homeostatic control of the concentration of glucose in the blood? [1]
A Negative feedback is involved in the control of blood glucose.
B The concentration of glucose in the blood fluctuates within narrow limits.
C The hypothalamus is the control centre for blood glucose.
D The liver is an eff ector organ in blood glucose homeostasis.
C;
2. Glucose is small enough to be filtered from the blood in glomeruli in the kidney, but is not normally found in the urine. This is because glucose is: [1]
A reabsorbed in distal convoluted tubules
B reabsorbed in proximal convoluted tubules
C reabsorbed along the whole length of the nephrons
D respired by cells in the kidney
B;
3. Which of the following occurs in the body in response to the secretion of glucagon? [1]
A conversion of glucose to glycogen in liver cells
B decrease in the blood glucose concentration
C increased uptake of glucose by muscle cells
D production of cyclic AMP in target cells
D;
4. In response to dehydration, ADH is secreted by the posterior pituitary gland. One of its eff ects is to stimulate:
A a reduction in the glomerular filtration rate
B an increase in the number of aquaporins in the cell membranes of collecting duct cells
C an increase in the uptake of water by cells in the proximal convoluted tubules of nephrons
D an increase in the volume of urine produced by the kidneys [1]
B;
5. Rearrange the following statements to make a flow diagram of the mechanism of opening a stoma. [4]
- volume of guard cell increases
- H+ transported out of guard cells
- water enters guard cells by osmosis
- K+ diffuses into guard cells
- guard cells curve to open stoma
- water potential of guard cells falls
- K+ channels open
2, 7, 4, 6, 3, 1, 5
All correct = 4, subtract marks for mistakes.
Question 6
a. Explain the meaning of the term excretion. [3]
a excretion:
removal from the body;
of waste products of metabolism;
carbon dioxide / nitrogenous waste / urea / uric acid / any other example;
substances in excess of requirements;
water / salts / sodium ions / potassium ions / any other example;
b. The figure is a photomicrograph of part of the kidney.
i Name A, B, C and D. [4]
A distal convoluted tubule;
B Bowman’s capsule;
C glomerulus / capillary;
D proximal convoluted tubule;
ii Identify the region of the kidney shown in the figure and give a reason for your identification. [2]
cortex;
glomeruli / convoluted tubules, are only found in the cortex;
iii Calculate the actual maximum width of the structure labelled A. Show your working. [2]
distance = 10 mm
= 10 000 µm
= 10 000/180
actual distance = 56 µm
Question 7
The control of the water content of the blood is an example of homeostasis.
a Name the part of the body that monitors the water potential of the blood. [1]
hypothalamus;
In an investigation of the factors that influence urine production, a person drank one litre of water. The person’s urine was collected at half-hourly intervals for four hours after drinking. The results are shown as line A on the figure. On the following day, the same person drank one litre of a dilute salt solution and the urine was collected in the same way (line B). Dilute salt solution has about the same water potential as blood plasma.
b Calculate how much urine was produced in the two hours after drinking the litre of water. [1]
1555 cm3 (or any answer within the range 1150 to 1160 cm3 or equivalent in dm3);
c Explain why the person produced so much urine aft er drinking the litre of water. [4]
any four from:
water was absorbed into the blood;
water increases the water potential of the plasma;
any effect of an increase in water potential of the plasma on, cells / tissues, e.g. water enters cells by osmosis / cells will swell /
decreases efficiency of reactions inside cells / cells may burst;
osmoreceptors detect increase in water potential;
do not, secrete / release, ADH;
collecting ducts remain impermeable to water;
excess water lost in urine;
until water potential returns to, normal / set point;
d Suggest why the results during the second day were so diff erent from those on the first day. [2]
(after absorption of dilute salt solution) no change in water potential of blood plasma;
water and salt are not lost in the urine, so must remain in the body;
giving an increase in volume, of blood or body fluids;
body tolerates changes in blood volume, but not its water potential;
e Explain why negative feedback, and not positive feedback, is involved in homeostatic mechanisms. [5]
homeostasis is the maintenance of, (near) constant internal conditions / internal conditions within narrow limits;
negative feedback:
a deviation from the set point;
is detected by a receptor;
a control centre instructs effector to carry out a corrective action;
to reverse the change / return factor to set point;
positive feedback:
any (small) deviation in a factor leads to an increase in the change (not a reversal);
Question 8
An investigation was carried out to determine the response of pancreatic cells to an increase in the glucose concentration of the blood. A person who had been told not to eat or drink anything other than water for 12 hours then took a drink of a glucose solution. Blood samples were taken from the person at one hour intervals for five hours, and the concentrations of glucose, insulin and glucagon in the blood were determined.
The results are shown in the graph below.
a. i Explain why the person was told not to eat or drink anything other than water for 12 hours before having the glucose drink. [3]
glucose concentration may already be high;
if person had eaten within 12 hours;
effect of sudden increase would not be seen / so there was a sudden increase;
may already be a high concentration of insulin;
ii Use the information in the figure to describe the response of the pancreatic cells to an increase in the glucose concentration. [4]
β cells secrete insulin;
concentration of insulin increases over first hour after taking the glucose solution;
insulin concentration increases from 60 to 300 pmol dm-3;
α cells do not secrete glucagon;
glucagon concentration, remains constant / decreases;
from 42 to 36 pmol dm-3;
iii Outline the role of insulin when the glucose concentration in the blood increases. [5]
insulin: stimulates, liver / muscle, cells;
increase in uptake of glucose from the blood;
more glucose transporter molecules (GLUT4) insert into the cell surface membrane of muscle cells (not liver cells);
stimulates enzymes;
to increase conversion of glucose to glycogen;
brings about a decrease in the blood glucose concentration;
b. i Suggest how the results will change if the investigation continued longer than five hours without the person taking any food. [4]
blood glucose concentration decreases (below 4 mmol dm–3);
insulin concentration, remains constant (at 60 pmol dm–3) / decreases (below 60 pmol dm–3);
glucagon concentration increases (above 60 pmol dm–3);
glucose concentration then increases;
ii Outline the sequence of events that follows the binding of glucagon to its membrane receptor on a liver cell. [6]
membrane receptor activates G protein;
G protein activates enzyme (in membrane) that catalyses conversion of ATP to cyclic AMP;
cyclic AMP binds to inactive kinase enzyme;
activates kinase enzyme;
this is the first enzyme in an enzyme cascade;
kinase enzyme activates phosphorylase kinase enzymes;
active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes;
glycogen phosphorylase catalyses the breakdown of glycogen to glucose;
glucose diffuses out of the (liver) cell into the blood;
Question 9
a Explain what is meant by a biosensor. [2]
biosensor:
a device that uses a biological material such as an enzyme;
to measure the concentration of a chemical compound;
b Copy and complete the following passage describing the action of a biosensor.
Many people with diabetes use a biosensor to measure the concentration of glucose in their blood.
The biosensor uses the enzyme …………., which is …………. on a pad. This enzyme converts glucose into gluconolactone and ………….. An electrode in the biosensor produces a tiny …………. current, the size of which is …………. to the concentration of glucose in the blood. The current is read by the meter, which produces a reading for blood glucose concentration. If the reading is too high, the person needs to take …………. to lower it. [6]
glucose oxidase;
immobilised;
hydrogen peroxide;
electric;
proportional;
insulin;
Question 10
Abscisic acid (ABA) is a weak acid. Its structure can be represented as ABA-H. It dissociates into positively charged H+ ions (protons) and negatively charged ABA– ions as shown:
The following observations have been made by scientists:
• light stimulates proton (H+ ion) uptake into the grana of chloroplasts
• ABA-H can diff use into and out of chloroplasts, but ABA– cannot.
This information is summarised in the diagram below.
a Using all the information provided, predict what happens to the pH of the stroma in the light. [1]
increases;
b. i When light shines on the chloroplast, dissociation of ABA-H is stimulated. Explain why this happens. [2]
concentration of protons in the stroma decreases (as enter grana);
shifts equilibrium to the right;
ii Explain the effect that this will have on diffusion of ABA-H into or out of the chloroplast. [2]
increases diffusion into the chloroplast;
as concentration of ABA–H decreases;
so maintaining a concentration gradient into the chloroplast;
When the mesophyll cells of leaves become dehydrated, some of the ABA stored in the chloroplasts is released into the transpiration stream in the apoplast.
c ABA travels in the apoplast pathway to the guard cells. Explain why this is an advantage when the leaf is dehydrated. [2]
ABA stimulates closure of stomata;
less water vapour is lost;
Question 11
a Describe the structure of a kidney, including its associated blood vessels. [6]
gross structure:
(outer) cortex, medulla and pelvis;
renal artery and renal vein;
nephron / (kidney) tubule;
position of parts of the nephron in the kidney:
glomerulus (and Bowman’s capsule), proximal convoluted tubule (PCT) and distal convoluted tubule (DCT), in cortex;
loop of Henle and collecting duct, in medulla;
details of nephron and its blood supply:
glomerulus consists of capillaries;
podocytes, form inner layer of Bowman’s capsule / surround glomerular capillaries;
afferent and efferent arterioles;
capillary network, surrounds PCT / loop / tubule / nephron;
b Describe the mechanisms involved in reabsorption in the proximal convoluted tubule and describe how the epithelial cells of the proximal convoluted tubule are adapted to carry out this process. [9]
mechanisms:
active transport of sodium ions, out of PCT cells and into, blood / capillaries;
there is a lower concentration of sodium ions inside the PCT cells than in the filtrate;
this can be explained in terms of a concentration gradient sodium ions diffuse from filtrate into PCT cell through, a protein carrier / AW;
facilitated diffusion;
carrier also transports, glucose / amino acids, from filtrate to PCT cell;
co-transport mechanism;
sodium ions lower the water potential inside PCT cells compared with the filtrate;
water diffuses down water potential gradient into PCT cells by osmosis;
adaptations of PCT cells:
microvilli / brush border, to give a large surface area for, carrier proteins / cotransporter proteins ;
many mitochondria, to provide ATP for sodium pump proteins;
tight junctions (between PCT cells), prevent movement of filtrate between cells / ensures all movement occurs through cells;
basal / lateral, membranes, folded to give large surface area for sodium pump proteins;
many aquaporins (on all membranes) for movement of water, into PCT cell from filtrate / out of PCT cell to capillary;