biology : class12 Oocyst Formation : Causative Organism, Plasmodium, Life Cycle, Symptoms, Prevention : Malaria MCQ Questions and Answers
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Oocyst Formation
MCQ questions and answers.
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MCQ Questions
1. Which sequence most accurately describes the events leading to oocyst formation in Plasmodium inside the female Anopheles mosquito?
A.
Gametocytes fuse in the human liver, and the zygote forms an oocyst in hepatocytes
B.
Male and female gametes fuse in the mosquito midgut, the zygote elongates into an ookinete, and the ookinete penetrates the midgut wall
C.
Merozoites fuse in the mosquito salivary gland and migrate to the midgut wall
D.
Sporozoites fuse in the mosquito midgut and directly transform into oocysts
Correct Answer:
Male and female gametes fuse in the mosquito midgut, the zygote elongates into an ookinete, and the ookinete penetrates the midgut wall
Explanation:
After fertilization in the mosquito midgut, the zygote elongates into a motile ookinete. The ookinete penetrates the midgut epithelium and becomes attached to the outer surface, where it develops into an oocyst.
2. The immediate developmental transformation that enables the fertilized Plasmodium zygote to reach the mosquito midgut wall is its conversion into a:
A.
Merozoite
B.
Sporozoite
C.
Ookinete
D.
Schizont
Correct Answer:
Ookinete
Explanation:
The zygote becomes an elongated, motile ookinete. This form traverses the mosquito midgut epithelium and initiates oocyst formation on the outer midgut wall.
3. Where does the Plasmodium oocyst characteristically develop after the ookinete has crossed the mosquito midgut epithelium?
A.
Inside the mosquito salivary gland
B.
On the outer surface of the mosquito midgut wall
C.
Within the lumen of the mosquito stomach
D.
Inside the mosquito Malpighian tubules
Correct Answer:
On the outer surface of the mosquito midgut wall
Explanation:
The ookinete penetrates the midgut epithelium and settles beneath the basal lamina on the outer side of the midgut, where it rounds up and forms an oocyst.
4. Which feature most directly distinguishes the ookinete from the newly formed oocyst during Plasmodium development in the mosquito?
A.
The ookinete is motile and invasive, whereas the oocyst is a rounded developmental stage attached to the midgut wall
B.
The ookinete is produced in human red blood cells, whereas the oocyst is produced in human hepatocytes
C.
The ookinete contains sporozoites, whereas the oocyst contains only gametocytes
D.
The ookinete occurs in the salivary gland, whereas the oocyst occurs in the mosquito proboscis
Correct Answer:
The ookinete is motile and invasive, whereas the oocyst is a rounded developmental stage attached to the midgut wall
Explanation:
The ookinete is specialized for movement through and penetration of the midgut wall. After attachment outside the midgut, it rounds up and develops into the oocyst, which undergoes sporogony.
5. If Plasmodium zygotes form normally in a mosquito but cannot penetrate the midgut epithelium, which process would be most directly prevented?
A.
Formation of the oocyst on the external midgut surface
B.
Formation of gametocytes in human erythrocytes
C.
Release of merozoites from human liver cells
D.
Inoculation of sporozoites from the mosquito into a human
Correct Answer:
Formation of the oocyst on the external midgut surface
Explanation:
Midgut penetration by the ookinete is required for attachment to the outer midgut wall. Without this migration, the ookinete cannot establish the site at which the oocyst forms.
6. Which developmental event occurs within a Plasmodium oocyst and ultimately produces the forms that migrate toward the mosquito salivary glands?
A.
Gametogenesis producing male and female gametes
B.
Sporogony producing numerous sporozoites
C.
Schizogony producing merozoites for invasion of human erythrocytes
Explanation:
The oocyst undergoes sporogony, during which repeated nuclear divisions and cytoplasmic organization produce many sporozoites. These later migrate to the mosquito salivary glands.
7. A mosquito is experimentally prevented from ingesting Plasmodium gametocytes but is otherwise physiologically normal. Which outcome is most likely regarding oocyst formation?
A.
Oocysts form because merozoites independently develop in the mosquito midgut
B.
Oocysts form because sporozoites are already present in the mosquito salivary glands
C.
Oocysts do not form because fertilization and zygote formation cannot be initiated
D.
Oocysts form directly from the mosquito midgut epithelial cells
Correct Answer:
Oocysts do not form because fertilization and zygote formation cannot be initiated
Explanation:
Oocyst formation depends on the sexual stages ingested with infected blood. Without male and female gametocytes, gametes cannot form and fuse in the mosquito midgut to produce the zygote that becomes an ookinete.
8. Which statement best explains why oocyst formation is regarded as part of the sexual phase of the Plasmodium life cycle in the mosquito?
A.
The oocyst is produced after fusion of male and female gametes and develops from the resulting zygote
B.
The oocyst is produced by repeated asexual division of merozoites in human red blood cells
C.
The oocyst is formed by fusion of sporozoites in the mosquito salivary gland
D.
The oocyst develops from a human liver schizont without any gamete fusion
Correct Answer:
The oocyst is produced after fusion of male and female gametes and develops from the resulting zygote
Explanation:
Sexual reproduction begins in the mosquito when male and female gametes fuse. The resulting zygote becomes an ookinete, which penetrates the midgut wall and develops into an oocyst.
9. A microscopic examination of a mosquito midgut shows a rounded Plasmodium structure attached beneath the basal surface of the epithelium and containing developing sporoblasts. This structure is a:
A.
Gametocyte
B.
Ookinete
C.
Oocyst
D.
Merozoite cluster
Correct Answer:
Oocyst
Explanation:
A rounded structure attached to the outer midgut surface and undergoing development of sporoblasts is an oocyst. The ookinete is the motile precursor that penetrates the epithelium before rounding up.
10. Which intervention would most specifically interrupt Plasmodium oocyst formation without directly destroying parasites already present in human tissues?
A.
Blocking the transformation of the zygote into a motile ookinete or preventing ookinete penetration of the mosquito midgut
B.
Preventing merozoite invasion of human red blood cells
C.
Destroying schizonts in human hepatocytes
D.
Blocking sporozoite entry into human skin during a mosquito bite
Correct Answer:
Blocking the transformation of the zygote into a motile ookinete or preventing ookinete penetration of the mosquito midgut
Explanation:
Oocyst formation requires the zygote to become an ookinete and cross the mosquito midgut epithelium. Interrupting either step prevents the ookinete from reaching and establishing itself on the outer midgut wall.
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