(i)A pair ovaries are present human female and an egg is released alternately from each ovary every month,i.e. an ovary release one egg after an interval of 56 days
(ii)Identical twins are monozygotic twins and are genetically limiar.A single egg after fertilization, undergoes cleavage, develops the two cells separate and develop into a new individual.Therefore the mother released only one egg.
(ii)Fraternal twins are dizygotic,i.e they are produced by the fertilisation of two different eggs by two separate sperms.There is a possibility that either an ovary has released two ova or the two ova come from each of the two ovaries.

Yes, if a pregnant woman has high blood pressure, the woman develops preeclampsia, which can threaten the lives of both the mother and the foetus.It can cause low birth weight and early delivery of  foetus,sometimes the child,born very early also may die.
High blood pressure can harm the mother's kidneys and other organs and also lower the number of platelets.

(i)The part labelled A is a vein and B is an artery, as media of artery is thicker than that of a vein and the elastic components of vein is small when compared to that of an attery
(ii)The umbilical artery contains higher amount of urea.The veins carry oxygenated, nutrient rich blood to foetus and arteries carry deoxygenated, nutrient depleted blood away from the foetus.

(i)The mitochondrion present in a cell are collectively referred to as chondriosome
(ii)Mitochondria are associated with cellular respiration (ie.oxidation of cellular nutrients) and energey generation of cell.Thus,it is also referred to as power house the cell.
(iii)Out of the total enzyme present in a cell,mitochondria alone contribute to 70%.The enzymes of Krebs, cycle are present in matrix of mitochondrial membrance) while that of Electron Transport System(ETS) and oxidative phosphorylation are situate in cristae

Difference between vasa efferentia and vasa deferentia are as follows

Spermatogenesis occurs at the age of puberty in testes.

(i) Fallopian tube
(ii) Ejaculatory duct
(iii) Acrosome
(iv) Gametogenesis
(v) Testis

(i) Gonada, reproductive ducts
(ii) Spermatozoa, androgens (testosterone)
(iii) Retia testes, caput epididymis
(iv) Cauda epididymis, ejaculatory ducts
(v) Urine, seminal fluid
(vi) Corpora cavernosa, corpus spongiosum
(vii) Spermatogenesis, spermiogenesis.

(i) (a) Sertoli cells
(b) Seminiferous tubule
(c) Spermatozoa
(d) Spermatogonia
(e) Interstitial cells.
(ii) Function of parts:
(a) Sertoli cells provide nutrition to developing spermatozoa.
(b) Spermatozoa are formed in the seminiferous tubules from spermatogonia that arise from germinal epithelial cells.
(c) These are male gametes which fertilize the ovum.
(d) The spermatogenic cells of germinal epithelium lining the seminiferous tubules by mitotic divisions produce spermatogonia. The latter undergo meiotic division to form spermatozoa.
(e) Interstitial cells secrete male sex hormones (Testosterone).

Meiotic division during oogenesis is different from that of spermatogenesis in the following ways

(i) Unequal cell division makes the ovum much larger than the other three polar bodies. As, ovum has more
cyloplasm and more organelles, it has a better chance of survival.
(ii) The male makes millions of tiny sperms, while the female makes only one egg per month that also arrested for second meiotic division, until just before fertilisation. This is a way of conserving energy.
(iüi) Sperm is smaller and motile as it has to move out of male system to female reproductive system. Larger egg has abundant reserve food, so thal embryo starts developing right after fertilisation.