Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

A haemocytometer is a special microscope slide which can be used to count the numbers of blood cells in a sample of blood. • The surface of the slide has many small, equal-sized squares marked on it. • The depth of the liquid under each square is 0.1 mm • When counting, cells that touch top or left lines are counted but cells that touch right or bottom lines are not counted.

A doctor used a haemocytometer to determine the number of red blood cells per mm3 in a blood sample. He diluted the original blood sample by a factor of 200 times before putting some on a haemocytometer.

Figure 4 shows the distribution of cells in a typical small square.

In ten small squares of his haemocytometer, the doctor counted a total of 400 red blood cells.

Calculate the total number of red blood cells per mm3 of the original blood sample.

Show your working.

Answer ______________ per mm3

In an alpha (α) thalassaemia, a form of anaemia, red blood cells are less able to transport oxygen to respiring tissues.

Use your knowledge of haemoglobin to suggest why.

In a beta (β) thalassaemia, another form of anaemia, a person produces abnormal haemoglobin molecules with abnormal beta chains. This means red blood cells are destroyed more quickly.

A student used a chi-squared (χ2) test to determine whether the inheritance of β thalassaemia was due to a sex-linked or an autosomal gene. He obtained a χ2 value of 15.89

What can the student conclude?

Give a reason for your answer.

Explain how the stain allowed the doctor to count the white blood cells amongst all the red blood cells.