Which structure found in eukaryotes has a single membrane?

A. Nucleus

B. Lysosome

C. Chloroplast

D. Mitochondrion

The diagram shows a pedigree chart.

What does it reveal about the inheritance of the blood disorder beta-thalassaemia?

A. The allele is autosomal recessive.
B. The allele is autosomal dominant.
C. The allele is sex-linked.
D. The allele is co-dominant.