Describe the structure of glycogen.

During early pregnancy, the glycogen in the cells lining the uterus is an important energy source for the embryo.

Suggest how glycogen acts as a source of energy.

Do not include transport across membranes in your answer.

Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients.

1

2

In humans, after the gametes join at fertilisation, every cell of the developing embryo undergoes mitotic divisions before the embryo attaches to the uterus lining.

• The first cell division takes 24 hours. • The subsequent divisions each take 8 hours.

After 3 days, the embryo has a total volume of 4.2 × 10–3 mm3.

What is the mean volume of each cell after 3 days? Express your answer in standard form.

Show your working.

Answer = ______________ mm3