Blood

Question 1

What is blood plasma?

Answer 1

Fluid portion of the blood containing mostly water, proteins,waste products, nutrients

Question 2

What is serum?

Answer 2

The liquid that separates from blood when a clot is formed

Question 3

How do red blood cells work? (2)

Answer 3

1) Oxygen binds to the iron in haemoglobin to be transported around the body.
2) It contains large quantities of carbonic anhydrase (enzyme) to catalyse the reaction the reaction of CO2 to HCO3- (for the transport of CO2 in the blood)

Question 4

What are antigens?

Answer 4

Proteins on the surface of red blood cells
Type A: A antigen; Type B: B Antigen; Type AB: both A and B antigens, Type O: no antigens

Question 5

What are antibodies?

Answer 5

They are produced by plasma cells as part of the immune response, and will bind to objects in the blood that they recognise as alien. The blood serum contains antibodies to the surface antigens, hence:
Type A: anti-B; Type B: anti-A, Type AB: none; Type O: anti A and B

Question 6

What are Rhesus antigens?

Answer 6

Refers to D antigen. Positive means D antigen exists and vice versa

Question 7

How do we make blood typing more specific than ABO?

Answer 7

Identify more antigens to reduce the probability of people in a population having the same blood type

Question 8

Name 4 types of blood tests.

Answer 8

1) Benzidine Colour Test (toxic; not used anymore)
2) Kastle-Meyer Colour Test
3) Luminol Test
4) Precipitin Test

Question 9

How does the Kastle-Meyer Colour Test work? (4)

Answer 9

1) Swab the sample
2) Zinc reduces pink phenolphthalein to colourless form (acidic: colourless; alkali: pink)
3) Add reduced Phenolphthalein to swab
4) Blood will catalyse the reduced form to the pink alkali form

Question 10

What is the downside of the Kastle-Meyer colour test?

Answer 10

Blood is not the only catalyst. False positives will occur since any catalyst of the oxidation will give a position. Hence, it is only a presumptive test for blood.

Question 11

How does the Luminol Test work? (2)

Answer 11

Blood catalyses the following reaction:
1) When luminol is treated with hydrogen peroxide in the presence of alkali and a catalyst, it gives 3-aminophthalate in an excited state
2) After dropping back down to ground state, due to the energy difference, it gives off blue light (electromagnetic radiation).

Question 12

What are the advantages of the Luminol Test?

Answer 12

1) Highly sensitive: can detect blood at 30PPM
2) Blood will still be in suitable condition for DNA analysis, hence is used at crime scene

Question 13

What is the function of precipitin test?

Answer 13

It can determine what species a blood sample came from.

Question 14

How does the precipitin test work? (4)

Answer 14

1) Inject human blood into a rabbit. Rabbit produces antibodies against human blood
2) Serum from the rabbit, that is sensitised to human blood, is removed from the rabbit
3) Take a human blood sample and treat it with rabbit serum. Using an electric field, antibodies and antigen will move towards each other
4) Antibodies will bind to components of the human blood, and will give a precipitin band if there is an interaction

Question 15

What are 2 factors that will affect blood patterns?

Answer 15

1) velocity of blood
2) angle of blood fall

Question 16

What are the 3 kinds of velocities of blood, and how do they affect blood patterns?

Answer 16

1) Low velocity spatter (1.5m/s), free fall and cast off
2) Medium velocity spatter (up to 30m/s), cast off
3) High velocity spatter (e.g. Gun shot) much smaller droplets

Question 17

How does the angle of blood fall affect blood patterns?

Answer 17

1) If falling at 90 degrees: blood drop is spherical and will give a circular mark on the floor
2) If falling at an angle: width and length of the mark will be different. Angle can be calculated by comparing width & length. Smaller angle = less spherical, more elongated

Question 18

How do we find the source of blood with the angle of fall?

Answer 18

We can find the convergence point, where the lines of blood fall all cross.