Class 12 Biology Chapter 2 Important Notes 2023

CHAPTER 2

SEXUAL REPRODUCTION IN FLOWERING PLANTS 
 
》All flowering plants show sexual reproduction.

2.1 FLOWER - A FASCINATING ORGAN OF ANGIOSPERM 

• Flowers are a morphological and embryological marvels and the sites of sexual reproduction. 


2.2 PRE - FERTILIZATION: STRUCTURES AND EVENTS 

• In the flower the male and female reproductive structures, the androcecium and the gynoecium differentiate and develop. You would recollect that the androecium consist of a whorl of stamens representing the male reproductive organ and the gynoocium represents the female reproductive ongan.

2.2.1 Stamen, Microsporangium and Pollen Grain 

• A shows the two parts of a typical stamen - the long and slender stalk called the filament, and the  terminal generally bilobed structure called the anther. The proximal end of filament is attached to the thalamus or the petal of the flower. The number and length of stamens are variable in flowers of different species.

• A typical angiosperm anther is bilobed with each lobe having two theca, i.e., they are dithecous.

• Often a longitudinal groove runs lengthwise separating the theca. 

• The bilobed nature of an anther is very distinct in the transverse section of anther. The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe.

• The Microsporangia develop further and become pollen sacs.  They extend longitudinally all  through the length of an anther and are packed with pollen grains.


Structure of microsporangium: In a transverse section, a typical microsporangium appears near circular in outline. It is generally surrounded by four wall layers the epidermis, endothecium, middle layers and the tapetum. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen. The innermost wall layer is the tapetum. It nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus. 

• When the anther is young, a group of compactly arranged homogenous cells called the sporogenous tissue occupies the centre of each microsporangium.

NEXT NOTES LINK HERE 👇

Comments

Popular posts from this blog

How To Ease Lower Abdominal Pain Naturally?

THE MALE REPRODUCTIVE SYSTEM CLASS 12

Basic Concepts Of Chemistry