Organisms and Populations — BIOLOGY STD 12 Science — Question

What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum? Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance?

Read the following and answer any four questions from (i) to (v) given below:

Stem cells hold the potential for manifold applications in biotechnology based next generation therapeutics. Scientists are trying to formulate better and more personalised treatment modalities against some seemingly irremediable diseases, by harnessing body's own stem cells and stem cell niche. Stem cells of different origin and level of potency are being investigated for tissue regeneration, treatment of bone defect, drug testing, gene therapy and cell based therapy for muscle damage, spinal cord injury, cancer therapy, etc. 'Tile properties of embryonic and adult stem cells to either self-renew or differentiate into multiple cell lineages make them an attractive source for cell therapies, tissue engineering and as model system for drug screening.

1. Stem cells are widely used in medical research. Which property of stem cells makes them particularly useful in this research?

1. They can be fused together to form a zygote.
2. They can divide and eventually give rise to a whole organism.
3. They can divide and be made to differentiate into various types of cell.
4. They will continue to divide indefinitely.

2. Stem cells can be divided into four main types. Which of the four types of stem cell can differentiate into a limited range of tissues?

1. Adult stem cells.
2. Embryonic stem cells.
3. Fetal stem cells.
4. Zygotic stem cells.

3. Which feature of stem cells obtained from blood in the umbilical cord enables their use in the treatment of a variety of blood cancers?

1. They can differentiate into bone marrow cells.
2. They can differentiate into any cellular component of blood.
3. They can replace blood stem cells affected by cancer.
4. They are totipotent.

4. The search for pluripotent stem cells is intense. The spennatogonium is the diploid precursor of haploid sperm in the development pathway of mouse gametes as shown below.

Scientists were interested to find out which stages of sperm development have stem cell capacity. Two experiments were carried out using sterile host males with testes that lacked germ cells. The results are shown in the table.

	Type of cells used	Result
Experiment 1	Secondary spermatocytes were injected	Fertility was not restored
Experiment 2	Spermatogonia were injected	Fertility was restored for the rest of the mouse's life

What property of a stem cell is missing in the secondary spermatocytes?

1. Specialisation.
2. Self-renewal.
3. Commitment.
4. A proper stem-cell niche.

5. Which feature of embryonic stem cells (ESCs) is illustrated below?

1. ESCs are capable of dividing.
2. ESCs are multipotent.
3. ESCs are pluripotent.
4. ES Cs show plasticity.

Describe the roles of pitutary and ovarian hormones during the menstrural cycle in human female.###Explain the various phases of menstrual cycle. Give a diagrammatic representation of various events during a menstrual cycle.

Observe the representation of genes involved in the lac operon given below.

1. Identify the region where the repressor protein will attach normally.
2. Under certain conditions repressor is unable to attach at this site. Explain.
3. If repressor fails to attach to the said site what products will be formed by z, y and a?
4. Analyse why this kind of regulation is called negative regulation.

Answer the following questions:
Explain the changes the primary oocyte undergoes while in different follicular stages before ovulation.

diagram.###What is transcription? Explain the transcription process in bacteria by making a labelled diagram.###Explain the transcription process in bacteria and make a diagram.

(a) Describe the observations made on collection of white winged moths and dark winged moths in England between the years 1850 and 1920. What did these observations lead to?
(b) How is the use of herbicides, pesticides and antibiotics by humans for various, comparable with the observations made on moths in the above question? What is this type of phenomenon called?

Draw a diagrammatic sketch of the sectional view of a typical anatropous ovule.

OR

Draw a labelled diagram of the sectional view of a typical anatropous ovule.

Mention the biological factors of ecology.

Answer the following questions:
Write the specific location and the functions of the following cells in human males:

1. Leydig cells.
2. Sertoli cells.
3. Primary spermatocyte.