Exam Qs

Question 1

Pressure must be maintained as blood flows through organs and vessels of the circulatory system. Describe two features of the circulatory system that could affect blood pressure.

Answer 1

force of ventricular contractions;
strength of elastic recoil (of blood vessels);
resistance to blood flow / AW;

Question 2

How does the circulatory system of a fish compare to that of a mammal?

Answer 2

he fish has a single (circulation) and
the mammal has a double (circulation) ✔

Question 3

A student was investigating the effect of cell size on the rate of diffusion into model cells. They had two cubes of agar containing phenolphthalein indicator as shown in Fig. 21.2.
Fig. 21.2
The student placed the cubes in beakers of dilute hydrochloric acid, which caused the indicator to become colourless. They then measured how much of each cube became colourless over time.
(i) State two ways the student could have ensured they had confidence in their results.

Answer 3

repeat (readings) ✓
calculate mean ✓
identifying anomalies ✓
use statistical test to identify difference

Question 4

In humans, a circulatory system is needed to transport substances around the body by mass transport. Explain why humans need a mass transport system.

Answer 4

(humans are) large / multicellular, organisms;
(humans have) low SA:Vol;

Question 5

Explain why the surface area to volume ratio of an organism determines whether it needs a circulatory system.

Answer 5

large(r) organism has small(er) SA : Vol ratio ✓
(rate of) diffusion (too) slow /
diffusion distance
(too) long ✓
for (sufficient), delivery / uptake of, oxygen
/ nutrients
OR
for (sufficient) removal of (named) waste products ✓
for, (aerobic) respiration / metabolic demands ✓

Question 6

F;
A;
B or D; E;

Question 7

Suggest why the foramen ovale is open in the fetus before birth.

Answer 7

lungs not, functioning / filled with air;
blood / haemoglobin, is, not oxygenated in the lungs / oxygenated in placenta (therefore) pulmonary circuit / lungs, bypassed;

Question 8

Another change occurring after birth is that fetal haemoglobin is replaced with adult haemoglobin.
State one difference between fetal haemoglobin and adult haemoglobin and give one reason why this difference is essential to the fetus.

Answer 8

fetal haemooglobin has a higher affinity for oxygen
so it can bind with oxygen in the placenta

Question 9

Describe how the structure of llama hamoglobin is likely to be different from that of camel haemoglobin with . reference to the four levels of protein structure.

Answer 9

difference in primary structure different amino acid / polypeptide sequence
one amino acid changed.
amino acid change could cause change to secondary structure
initial coiling or folding of polypeptide chain
α-helix
β-pleated sheet hydrogen bonding.
amino acid change could cause change to tertiary structure
further coiling of secondary structure ionic bonding
disulphide bonds
hydrophilic / hydrophobic bonds 3D shape.
amino acid change has not changed quaternary structure
alpha and beta subunits still able to form haemoglobin in both camel and llama.

Question 10

Explain why it is important for the survival of the llama that the llama haemoglobin dissociation curve is to the left of the camel haemoglobin dissociation curve.

Answer 10

(llama) haemoglobin needs higher affinity for oxygen (1)
(so) can pick up oxygen at lower partial pressure (of oxygen) (1)

Question 11

Outline how the structure of haemoglobin enables it to transport oxygen.

Answer 11

has four polypeptide chains
AND
(4) haem / iron?containing (prosthetic) groups;
each haem group can carry, one oxygen molecule / O2
OR
each haemoglobin molecule can carry four oxygen molecules;
idea of reversible binding / AW OR
cooperative binding / AW

Question 12

Viruses do not use erythrocytes as host cells, whereas the malarial pathogen Plasmodium spends part of its life cycle inside erythrocytes.

Answer 12

virus is unable to / cannot, replicate / reproduce, on its own / outside a host cell or virus requires host cell, machinery / DNA / RER / ribosomes, for protein synthesis
or
virus does not contain, RER / ribosomes, for protein synthesis ✔
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___
Plasmodium
idea that Plasmodium is using the host cell to hide from the immune system
or
for Plasmodium to complete its life cycle or
for Plasmodium to use as a source of food (for, growth / reproduction) ✔

Question 13

Explain why erythrocytes do not make use of any of the oxygen that they are transporting.

Answer 13

oxygen is bound to haemoglobin (while being transported) ✔
2 lack mitochondria ✔
3 (therefore) no aerobic respiration ✔
4 (moved by mass flow so) doesn’t need,
energy / ATP, to move
or needs less, energy / ATP (for metabolic processes) ✔

Question 14

With reference to the structure of blood vessels, explain why oxygen is not released until the blood reaches the capillaries.

Answer 14

arteries / arterioles, have thick wall
or
capillary wall is, thin / one cell thick / only endothelium ✔
2 no diffusion (through artery wall)
or
diffusion distance (too) large for artery or
diffusion occurs (through capillary wall) or
short diffusion distance for capillary

Question 15

Erythrocytes contain haemoglobin, which is a globular protein.
Blood vessel walls contain collagen, which is a fibrous protein.
Describe the differences between globular and fibrous proteins using haemoglobin and collagen as examples.
In your answer you should refer to collagen and haemoglobin.

Answer 15

Globular
G1 ball (shaped) / spherical / AW;
G2 hydrophilic / (R-)groups / regions, on outside (of 3-D structure) / hydrophobic (R-)groups on inside;
G3 form H-bonds with water;
G4 soluble;
G5 example of globular protein (other than haemoglobin);
H1 haemoglobin, carries / transports, / oxygen / carbon dioxide;
H2 haemoglobin contains, prosthetic group / haem / Fe2+ / iron ion (to allow oxygen to be carried);
H3 (polypeptide chains within) haemoglobin have tertiary structure (in a ball shape);
F1 Fibrous linear / long (chain);
F2 (chains can) form (H) bonds with
adjacent, chains (within a molecule); F3 insoluble / few hydrophilic groups;
F4 strong / provide strength; F5 have structural role;
C1 collagen has high proportion of glycine, so chains can lie close together / AW;
© OCR 2020. You may photocopy this page. 43 of 53 Created in ExamBuilder
7 max
G1 IGNORE round / globular
G5 ACCEPT (named) enzyme / hormone / antibody / channel / carrier
G5 IGNORE metabolic / transport
H1 ACCEPT references to buffering
H2 IGNORE Fe3+
H3 ACCEPT haemoglobin has tertiary structure
F1 ACCEPT straight / rope-like F1 IGNORE strand
F2 IGNORE fibre / fibril
F2 ACCEPT ‘strand’ as AW for ‘chain’ for F2 only
F2 ACCEPT crosslink as AW for bond for F2 only
F2 DO NOT CREDIT molecule as ‘AW’ for ‘chain’
F2 IGNORE attractions / (named) covalent bonds
F4 IGNORE flexible / inelastic / withstands pressure

C2 collagen forms, crosslinks / covalent bonds, between molecules;
C3 crosslinks / ends of molecules, are staggered to avoid, weak points / AW;
C4 collagen forms part of, tendon / cartilage / ligament / bone / connective tissue / bronchi / bronchioles / trachea / skin;

Question 16

Suggest why a single HbA1C test cannot indicate accurately the mean blood glucose concentration for a period longer than twelve weeks.

Answer 16

HbA1C / glycosylated Hb, contained within, red blood cell(s) / erythrocyte(s);
red blood cells / erythrocyte(s), have limited life span / live for 8 to 12 weeks
or
red blood cells / erythrocyte(s), break down after, 12 weeks / 3 months;
3 HbA1C / glycosylated Hb, broken down, in liver / by hepatocytes / by Kupffer cells;

Question 17

Describe how the hydrogencarbonate ions are produced in the erythrocytes.

Answer 17

1 carbon dioxide, enters / diffuses into, erythrocytes ;
2 (carbon dioxide) combines / reacts, with water ;
3 correct ref to carbonic anhydrase;
4 forms carbonic acid ;
5 (carbonic acid) dissociates to form hydrogencarbonate ions and, hydrogen ions / protons ;

Question 18

High concentrations of carbon dioxide in the blood reduce the amount of oxygen transported by haemoglobin.

Answer 18

Bohr (effect / shift) ;
Explanation (any 2 of the following marks)
2 reduces affinity (of Hb) for oxygen ;
3 formation of haemoglobinic acid / hydrogen ions interact with haemoglobin ;
4 prevents, fall in pH / build-up of H+, in cells
OR provides buffering effect ;
5 alter, structure / shape, of haemoglobin ;
6 more oxygen released where, needed / more respiration / carbon dioxide concentration high ;
7 CO2 binds to haemoglobin forming carbaminohaemoglobin ;

Question 19

Explain why the blood off-loads more oxygen to actively respiring tissues than to resting tissues.
[1]

Answer 19

in actively respiring tissues
1 more / high levels of, carbon dioxide (produced)
or
high pCO2 ✔
2 lowered affinity of haemoglobin for oxygen✔
3 (CO2 results in) dissociation of carbonic acid / increase of H+, leading to the release of oxygen ✔
4 more oxygen released at same pO2 / suitable data quote from graph ✔

Question 20

Blood contains erythrocytes. Erythrocytes are full of haemoglobin. Describe the role of haemoglobin in transporting oxygen around the body.

Answer 20

1 (haemoglobin has) high affinity for oxygen ;
2 oxygen binds to haemoglobin in, lungs / alveoli / high pO2 ;
3 oxyhaemoglobin ;
4 oxygen released, in tissues / where needed / where pO2 is low / where respiration is occurring ;