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Class notes 12th grade NCERT Solutions - Biology for Class 12th
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Summary NCERT Solutions - Biology for Class 12th - Biology
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2
SECOND YEAR BOTANY – CHAPTER WEIGHTAGE
UNIT CHAPTER SCORE WEIGHT
VI 2 SEXUAL REPRODUCTION IN FLOWERING PLANTS 8
11 BIOTECHNOLOGY : PRINCIPLES AND PROCESSES 8
IX
12 BIOTECHNOLOGY AND ITS APPLICATIONS 8
13 ORGANISMS AND POPULATIONS 8
X
14 ECOSYSTEM 7
DR. SUNIL KUMAR. S, GFVHSS CHERUVATHUR BOTANY FOCUS AREA NOTE 2023
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3
Chapter – 1
SEXUAL REPRODUCTION IN FLOWERING PLANTS
Structure of microsporangium:
Each microsporangium surrounded by four wall layers
➢ Epidermis – Outermost layer provide protection.
➢ Endothecium:
contains radially elongated, compactly arranged hygroscopic cells which helps in the
protection and dehiscence of anther.
➢ Middle layer – multilayered and provide protection.
➢ Tapetum.
The innermost layer is tapetum which is multinucleated, with dense cytoplasm; it nourishes
the developing pollen grains.
The centers of each microsporangium contain homogenous cells called sporogenous tissues.
Pollen grain:
• Pollen grain represents the male gametophytes.
• It is spherical and measuring about 25-50 micrometer in
diameter.
• It is covered by two layers.
• The hard outer layer called the exine is made up of
sporopollenin, which is the most resistant organic material. It
can withstand high temperature and strong acids and alkali. No
enzyme can degrade sporopollenin.
• The exine has prominent apertures called germ pore where sporopollenin is absent.
• The inner wall of pollen grain is called intine. It is thin and continuous layer made up of cellulose
and pectin.
• On maturity, the pollen grain contains two cells, the vegetative cell and generative cell.
• The vegetative cell is bigger, has abundant food reserve and a large irregularly shaped nucleus.
• The generative cell is small and floats in the cytoplasm of vegetative cell.
• In 60% of angiosperms, pollen grains are shed at this 2-celled stage.
• In others the generative cell divides mitotically to form two male gametes and pollen grain are
usually shed 3-celled stage.
The Megasporangium (Ovule):
• Ovule is a small structure attached to the placenta of locule with a stalk called funicle.
• The body of the ovule fused with the funicle in the region called hilum.
• Hilum is the junction between the funicle and ovule.
• Each ovule has one or two protective envelops called integuments.
DR. SUNIL KUMAR. S, GFVHSS CHERUVATHUR BOTANY FOCUS AREA NOTE 2023
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