Class 12th Biology 2016 Set3 Delhi Board Paper Solution
(a) Explain the post-pollination events leading to seed production in angiospersms.
(b) List the different types of pollination depending upon the source of pollen grain.
OR
(a) Briefly explain the events of fertilization and implantation in an adult human female.
(b) Comment on the role of placenta as an endocrine gland.
(a) As a result of pollen-pistil interaction, germination of pollen tube takes’ place carrying two male gametes. One male gamete fuses with the egg cell (syngamy), while the other fuses with two polar nuclei to form primary endosperm nucleus (PEN). The zygote develops into an embryo while the PEN develops to form endosperm. After double fertilisation, the ovule matures into a seed while the ovary matures into a fruit.
(b) Different types of pollination depending upon the source of pollen grain are :
Autogamy: Transfer of pollen grains from the anther to the stigma of the same flower. Geitonogamy : Transfer of pollen grain from the anther to the stigma of another flower of the same plant. Xenogamy : Only types of pollination which brings genetically different types of pollen grains to the stigma.
OR
(a) Fertilization : A sperm comes in contact with the zona pellucida layer ovum and induces changes to block entry of additional sperms. The entry of sperm induces completion of meiosis II leading to the formation of anootid and second polar body. The haploid nucleus of the sperm and that of the ovum fuse to form a dipolid zygote.
Implantation : The trophoblast layer of the blastocyst attaches to the endometrium of the uterus. The uterine
cells divide rapidly and cover the blastocyst which becomes embedded in the endometrium and implantation is completed.
(b) Placenta acts as an endocrine tissue and produces several hormones like :
human chorionic gonadotropin (hCG) human placental lactogen (hPL) Estrogens, progestogens, etc.
Popular Questions of Class 12th biology
- Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
- Q:- Why is reproduction essential for organisms? Answer
- Q:- Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals. - Q:- With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
- Q:- What is DNA fingerprinting? Mention its application.
- Q:- What is oogenesis? Give a brief account of oogenesis.
- Q:- Describe the structure of a seminiferous tubule.
- Q:- What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
- Q:- With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
- Q:- Explain the Law of Dominance using a monohybrid cross.
Recently Viewed Questions of Class 12th biology
- Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
- Q:- Draw a labeled diagram of a Graafian Follicle?
- Q:-
Explain the following terms with example
(a) Co-dominance
(b) Incomplete dominance - Q:- Briefly describe the following:
(a) Transcription
(b) Polymorphism
(c) Translation
(d) Bioinformatics - Q:- Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity - Q:- Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesised from it (DNA or RNA), list the types of nucleic acid polymerases.
- Q:- Define ecological pyramids and describe with examples, pyramids of number and biomass.
- Q:- Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
- Q:- If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
- Q:- Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.