Question
Give the term/ reason:
Why does zona pellucida layer block the entry of additional sperms?

Answer

To ensure the fusion of one sperm.

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Similar questions

A bright student of class XI, under peer pressure started taking drugs. He started neglecting studies, misbehaving with parents and friends in school. The principal of school counselled him, but it had no effect. His parents took him to a rehabilitation center. After a few months, he came back recovered.
  1. What is drug abuse?
  2. Name some commonly abused drugs and their source.
  3. What should be the attitude of his parents after his return?
  4. What values did the principal reflect through his initiative?
How can you, as an individual, prevent the loss of biodiversity?
Compare the life style of people living in the urban areas with those of rural areas and briefly describe how the life style affects their health.
Study the table given below and answer the questions that follow:
Species A
Species B
Name of interaction
(+)
(+)
(A)
(-)
(-)
(b)
(+)
(-)
(c)
(+)
(0)
(d)
+ = Beneficial interaction
- = Detrimental interaction
0 = Neutral interaction
Identify a, b, c and d in the given table and explain any three of them with the help of an example each.
  1. What is hydrarch succession?
  2. Compare the pioneer species and climax communities of hydrarch and xerarch succession respectively.
  3. List the factors upon which the type of invading pioneer species depend in secondary hydrarch succession. Why is the rate of this succession faster than that of primary succession?
Describe the mechanism of pattern of inheritance of ABO blood groups in humans.
The following table shows certain diseases, their causative organisms and symptoms. Fill the gaps.
  Name of the Disease Causative organism Symptoms
i. Ascariasis Ascaris ________
ii. ________ Trichophyton Appearance of dry, scaly lesions on various parts of the body.
iii. Typhoid ________ High fever, weakness, headache, stomach pain, constipation.
iv. Pneumonia Streptococcus pneumoniae ________
v. ________ Rhino viruses Nasal congestion and discharge, sorethroat, cough, headache.
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Define genetic engineering. Mention its main stages.
Ramesh visited a National Park on a school trip where he saw tiger eating a deer. He got disturbed and asked his teacher why is he doing so. His teacher replied that it is natural population controlling phenomenon.
  1. Which type of interspecific interaction is found between tiger and deer?
  2. State the role of predators.
  3. What other type of population interactions are seen in nature?
  4. State the values of Ramesh towards animals.
Describe the process of Oogenesis with suitable diagram.