Biodiversity, Conservation and Environmental Issues — BIOLOGY STD 12 Science — Question

In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?

Blastula and Gastrula OR Give two differences between blastula and gastrula.

1. Draw a labelled diagram of L.S. of an embryo of grass (any six labels).
2. Give reason for each of the following:

1. Anthers of angiosperm flowers are described as dithecous.
2. Hybrid seeds have to be produced year after year.

Explain with an example, where a gene, which carries a major disadvantage in homozygous state, confers an advantage in heterozygous condition.

Haldane described ‘Hot dilute soup’ in his theory. Describe how this soup led to formation of some important molecules.

Draw a labelled schematic structure of a transcription unit. Explain the function of each component in the unit in the process of transcription.

If the duration of the atrial ‘systole is 0.1 second and that of complete diastole is 0.4 second, then how does one cardiac cycle complete in 0.8 second?

Describe the structure of HIV with a suitable diagram.

1. List the three different allelic forms of gene ‘I’ in humans. Explain the different phenotypic expressions, controlled by these three forms.
2. A woman with blood group'A'marries a man with blood group 'O'. Discuss the possibilities of the inheritance of the blood groups in the following, starting with 'yes' or 'no' for each:

1. They produce children with blood group ‘A’ only.
2. They produce children, some with 'O' blood group and some with 'A' blood group.

Resting potential of a nerve fibre.