Q23 of 43 Page 1

Draw a diagram of the sectional view of a human seminiferous tubule and label any six of its parts.


The various parts are:


1.Primary Spermatocytes: These are diploid in number (2n) which divide through meiosis.


2. Secondary spermatocytes: After primary spermatocytes divide meiotically ,secondary spermatocytes are formed.Which are haploid (n) in number.


3. Spermatozoa: It is the motile sperm.


4. Spermatids: These are motile haploid gametes formed from secondary spermatocytes.


5. Interstitial Cells:These cells are present in the male testes. These cells release male sex hormone called androgen.


6. Supporting cells of sertoli:These cells facilitates the movement of germ cell to spermatozoa.


More from this chapter

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21

Why DNA cannot pass through the cell membrane? How can the bacteria be made competent to take up a plasmid? Explain a method for introduction of alien DNA into a plant host cell. Name a pathogen that is used as a disarmed vector.

 22

Study the figure of vector pBR322 given below.


Identify A, B and C and explain their roles in cloning a vector.


OR


Many people are apprehensive of accepting GM crops. Give three reasons so as to convince them to use these crops.


 24

Which one of the two ‘‘in-situ’’ or ‘‘ex-situ’’ biodiversity conservation measures help the larger number of species to survive? Explain.

 25

(a) Draw the embryo sac of a flowering plant and label the following :

(i) Central cell


(ii) Chalazal end


(iii) Synergids


(b) Name the cell and explain the process it undergoes to develop into an embryo sac.


(c) Explain the development of endosperm in coconut.


OR


Write the duration and the events that occur in the ovary and the uterus during follicular and luteal phases of the menstrual cycle in humans. How do pituitary and ovarian hormones influence these two phases?