Case study (4 Marks)

Question 14 Marks

Read the following text carefully and answer the questions that follow:
A pathogen is defined as an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes. The immune system of a person is suppressed. He was found positive for a pathogen in the diagnostic test ELISA.

i. Name the disease, the patient is suffering from. (1)
ii. Which pathogen is identified by ELISA test? (1)
iii. Which cells of the body are attacked by the pathogen? (2)
OR
Suggest preventive measures of the infection. (2)

Answer

i. The patient is suffering from AIDS (Acquired Immuno Deficiency Syndrome).
ii. HIV (Human Immunodeficiency Virus) identified by the ELISA.
iii. Helper T-cells, macrophages, B-lymphocytes are attacked by the pathogen.
OR
Preventive measures:
a. People should be educated about AIDS transmission.
b. Disposable needles and syringes should be used.
c. Sexual habits should be changed immediately.
d. High-risk groups should be discouraged from donating blood.
e. Routine screening may be done.

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Question 24 Marks

Read the following text carefully and answer the questions that follow:
Cleavage is the series of rapid mitotic divisions in zygote and forms blastula. The 2, 4, 8, 16 daughter cells are called blastomeres. Embryo with 64 blastomeres is known as blastocyst and has blastocoel cavity. Blastocyst gets implanted in uterine wall and leads to pregnancy.
i. Why the cells of the inner cell mass of blastocyst are called stem cells? (1)
ii. At which stage of embryonic development trophoectoderm develops? (1)
iii. What is the site of implantation? (2)
OR
What is the correct sequence of various structures formed during embryonic development? (2)

Answer

i. The embryo at 64 celled stage is known as blastocyst. It comprises of an inner cell mass which is attached to embryonic pole and an outer covering of cells which is known as trophoblast. The trophoblast later forms the chorion which is part of placenta. The inner cell mass has the property to undergo unlimited symmetrical divisions without getting differentiated.
ii. Embryo with 64 cells is called blastula (blastocyst) and has blastocyst cavity. Blastocyst is composed of an outer envelope of cells called trophoblast and inner cell mass.
iii. Implantation is the attachment of blastocyst to the uterine wall. The portion of blastocyst where the inner cell mass is located lies against the endometrium of uterus.
OR
Zygote → Morula → Blastula → Gastrula.

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BIOLOGY Case study (4 Marks)

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