Biology Past Paper PDF

# Start of OCR for page 1 ## Embryology - is the study of the early development of living organisms - All animals and Plants have the capacity to reproduce new individual to ensure the survival of their kind. ## Reproduction - single organism splits, buds, fragments to give rise to two or more...

# Start of OCR for page 1 ## Embryology - is the study of the early development of living organisms - All animals and Plants have the capacity to reproduce new individual to ensure the survival of their kind. ## Reproduction - single organism splits, buds, fragments to give rise to two or more individuals. - reproduction involves the fusion of two gametes, a male gamete "sperm" fuse with a female gamete "egg" to form the zygote or fertilized egg. ## Asexual - reproduction; It needs one Parent - Types: ### Splitting - the organism splits to two individuals - ex: Paramecium ### Budding - the organism produces a small bud which grows on the mothersbody. - Then breaks down to a new organism. - ex: Hydra ### Fragmentation - the organism fragments to more than two organisms forming a colony. - ex: Yeast ## Sexual - reproduction - it involves the fusion of two gametes, a male gamete sperm fuses with a female gamete "ovum" to form a zygote or fertilized egg. - in this case, the chromosomes (n) of sperm join with the chromosomes (n) of ovum forming the chromosomes (2n) of the zygote. - zygote undergoes embryonic developmental stages which involve the division of zygote cell to a large number of somatic cells containing diploid numbers of chromosomes (2n) that form the body of an embryo # Start of OCR for page 2 ## Gametogenesis - it is the production of gametes by parents which involves the reduction of the number of chromosomes to haploid sets of chromosomes in the resulting gametes. - The body of an organism contains many organs which are all formed of somatic cells (2n) even the gonads Test is in male and ovary in female, the cells lining these organs are diploid in chromosomes. - The origin of the haploid germ cells is those diploid cells lining the testis and ovary --the primordial germ cell-- which undergo a number of changes in two processes called 'spermatogenesis' (production of sperm) and 'oogenesis' (production of oum) through three phases in each process. ### Tis in the Testis of Rat - Testis are formed of a large number of seminiferous tubules in which countless numbers of sperms are formed. - Walls of seminiferous tubules are lined with the germinal epithelium 2n formed of cubical primordial germ cells from which sperms are produced. ### T's in Ovary of Cat: - The ovary of female is lined with the germinal epithelium consisting of primordial germ cells in which undergo oogenesis to produce mature ovum finally ### Spermatogenesis: - includes three phases: multiplication, growth and maturation phases. # Start of OCR for page 3 ## Multiplication Phase - the primordial germ cells undergo repeated mitotic divisions to produce a large number of spermatogonia, each containing diploid number of chromosomes. ## Growth Phase - spermatogonia grow in size to form larger cells known as primary spermatocytes, which contain diploid numbers of chromosomes. ## Maturation Phase - Each spermatocyte undergoes meiosis which consists of two successive nuclear divisions known as the first and second meiotic divisions. - The first division: results in the secondary spermatocytes; the nuclei contain the (n) chromosomes. - The second division: each secondary spermatocyte is divided into two spermatids, each having (n) chromosomes. - The four spermatids are produced from each primary spermatocyte. - The spermatids undergo certain changes known collectively as metamorphosis to form spermatozoa (sperms). # Start of OCR for page 4 ## Spermatozoon: ## Types of Sperms - Spherical Shape: Chordata : ex: fishes, amphioxucus. - Yod-Shape: Amphibia: ex: Toads, reptiles, aves, mammels. - Pear Shape: - Spirally Shape: - Spoon-shaped: