1. Write a note on sexuality in Organisms.
Ans. When male and female reproductive organs are present in the same plants, it is called monoecious. e.g. Maize, Castor, Coconut etc. But when male and female reproductive organs occur on different plants then they are called dioecious. e.g. Date Palm, Papaya etc.
When the both stamen and Pistil are present in the same flower, it is called bisexual flower but when either only stamen or Pistil is present, then it is called unisexual flower.
Unisexual and Bisexual species are also found in animals, e.g. Cockroach is unisexual while earthworm is an example of bisexual animal .
2. Describe embryogenesis in flowering plants.
Ans. In flowering plants, zygote formation takes place within ovary. After fertilization calyx and corolla of flower shed after fading up. However in some plants, e.g. physalis, calyx covers the fruit completely. Calyces also persist in tomato and brinjal. Ovary develops into fruit. Ovary further forms pericarp which gives protection to fruits and seeds. Ovule develops into seed. Embryo lies inside ovule. Seeds germinate under favourable condition after dispersal and it gives new plantlets after germination.
3. What is apomixis? Give suitable examples. Mention its significance in Horticulture and agriculture.
Ans. Apomixis is a form of asexual reproduction that mimics sexual reproduction, in which seeds are produced without fertilization. [1]
It is very common in grasses and species of Asteraceae family. It occurs by agamospermy, parthenogenesis and apogamy.
All new individuals/ embryos produced apomically are genetically similar to parents producing them and are clones of their parents.
Important Role of Apomixis in Horticulture/Agriculture- Apomixis plays several roles in horticulture and agriculture, particularly in hybrid seed industry. The hybrid varieties have more vigour but production of hybrid seeds is very costly and time-taken. Such seeds do not maintain hybrid vigour in progeny due to segregation of genes during meiosis. Its hybrids are made into apomicts, there will be no segregation of genes due to no meiosis, and the hybrid characters will pass on unchanged from one generation to the next. So, it will reduce the cost of Lubrid seeds by the farmers.
4. What is Parturition? Name the hormones which induce Parturition.
Ans. Parturition or child birth is the process of delivery of fully formed foetus or baby at the end of pregnancy through vigorous contractions of uterus. The average gestation period in Human beings is of 9 months at the end of which there is rapid uterine contractions leading to birth of child. This is called Parturition.
Hormones involved are Oxytocin & Relaxin. Oxytocin released ed from Neurohypophysis stimulates rapid uterine contraction, ] causing labor pain and delivery. After birth of child oxytocin contracts myoepithelial cells of mammary gland & further release of milk. Relaxin hormone secreted from placenta dilates cervix & pubic symphysis for each birth of child.
Parturition is a complex neuroendocrine mechanism which takes place at the end of pregnancy which results into parturition. = Signals for parturition starts from foetus as well as placenta which causes mild uterine contraction. This is called Foetal ejection reflex. It causes release of oxytocin from Maternal Pituitary to enhance uterine contraction. Then cervix opens with discharge of Mucus. Parturition completes in three stages-
5. Give an a/c of implantation. What is its significance?
Ans. Implantation is the attachment of embryo with uterus in blastocyst stage. After fertilization the mitotic division starts as zygote moves through the isthmus towards the uterus, forming 2,4,8, 16 daughter cells called blastomeres. This process is called cleavage.
The embryo with 8-16 blastomeres form Morula which later on transform into blastocyst. This process is called blastulation. Such dividing cells of blastocyst are called blastomeres. Such blastomeres are arranged into outer layer called Trophoblast and inner group of cells called Inner cell mass.
The blastocysts become embedded in endometrium of uterus. This is called implantation which leads to pregnancy.
Significance :
It leads to pregnancy.
After implantation, developing embryos are nourished by uterine wall with the formation of placenta.
6. What is Menstrual cycle? Mention various events with graphical representation.
Ans. Menstrual cycle is a cyclic event in Human female which starts from the age of 12-13 year at on set of Puberty and stops at the age of 45-50 years. The start of first menstrual cycle is called ‘Menarche’ while the stoppage of Final/Last menstrual cycle is called ‘Menopause’. The time taken to complete a menstrual cycle is 28-30 days which completes in three stages.
7. Give an a/c of effect of various factors on gene expression.
Ans. There is major effect of cellular environment on gene expression. Due to various chemicals, hormones, vitamins, pathogens the mechanism of protein-synthesis may be induced or inhibited. This is the characteristic feature of a living system to operate various metabolic processes. It also affects the functions of cells.
It has been observed in few cases that steroid hormones especially Estrogen and Progesterone control the mechanism of gene action. Sometimes gene activity stops due to methylation of nitrogenous bases and again it goes on by demethylation. It has been observed by experiments that due to re-arrangement of sequence of Nitrogenous bases, gene expressed is regulated.
There are some sensory receptor molecule present on the surface of cell which affect the gene expression.
8. Write a note on bacterial transformation.
Ans. The transfer of characters from one bacterial cell to another cell through DNA is called Transformation. Fredrick Griffith in 1928 has done his experiment on streptococcus pneumoniae bacteria which causes Pneumonia disease in
