Revision Notes for Class 12 Biology
Chapter 1 - Sexual Reproduction in Flowering Plants
Sexual Reproduction in Flowering Plants
• Sexual reproduction is the process by which new organisms are formed from the fusion of
male and female gametes from two parents.
• The flower is the primary reproductive structure. Within the flowers, the reproductive
organs, or sporophylls, are produced.
• Sporophylls are classified into two types: microsporophylls (stamen) and megasporophylls
(carpel).
• A carpel is an ovary that contains an ovule, a style, and a stigma.
• There are three types of stamen: filament, anther, and connective.
• Stamen is distinguished as filament, anther and connective.
• Sexual reproduction in flowering plants can be broken down into three steps:
i) Pre-fertilization
ii) Double fertilization
iii) Post-fertilization
Pre-Fertilization: Structure and Events
The following pre-fertilization events can be studied:
i) Pollen grain formation
ii) Embryo sac formation
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,iii) Pollination
iv) Pollen pistil interaction
Pollen Grain Formation
Male reproductive unit (Stamen)
• A stamen is an angiosperm's male reproductive unit. It is composed of an anther and a
filament. The anther is bilobed, with each lobe containing four pollen sacs or
microsporangia.
• A number of pollen grains are contained in each pollen sac. A dithecous anther's four
pollen sacs are located in the four corners.
• Dithecous anther: An anther with two lobes connected by a non-sporangious tissue called
the connective.
• The anther wall is composed of four layers of cells.
• To release pollen grains, anther dehiscence through slits.
Anther Development
• The development of an anther begins with a mass of homogeneous meristematic cells
surrounded by an epidermis.
• Four lobes are formed, as are four layers of archesporial cells.
• Archesporial cells: A primitive cell or group of primitive cells that divide to form two types
of cells: a primary parietal cell and a primary sporogenous cell.
• The parietal cell divides several times to form the anther wall, whereas the sporogenous
cell divides less frequently to form microspores or the pollen mother cells (PMC).
• The tapetum is the innermost layer of the cell wall that comes into contact with the PMCs.
In pollen formation, the tapetum plays a crucial role.
• Tapetum: This is a tissue found within the anther that feeds the growing spores.
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, • The endothecium is the layer beneath the epidermis.
Wall Layers of Anther
• The epidermis is a single layer of cells that serves as a protective layer.
• Endothecium is a single-layered second wall. Cells are thickened with cellulose and a trace
of pectin and lignin. It aids in the dehiscence of anthers.
• Middle layers – Ranges from 1-6. When the anther matures, the middle layer degenerates.
• Tapetum –
a) The anther wall's innermost layer surrounding the sporogenous tissue.
b) Tapetal cells contain nutrients.
c) They have multiple nuclei and are polyploid.
d) The ubisch bodies settle in the exine of the microspore wall.
e) There are two kinds of tapetum:
(i) Secretary / glandular – The tapetal cells remain in place throughout the development of
the microspore, eventually degenerating.
(ii) Amoeboid / periplasmodial – The tapetal cells rupture the radial wall, allowing the
protoplast to enter the pollen chamber. These protoplasts are now joining together to form
the periplasmodium.
Class XII Biology www.vedantu.com 3
Chapter 1 - Sexual Reproduction in Flowering Plants
Sexual Reproduction in Flowering Plants
• Sexual reproduction is the process by which new organisms are formed from the fusion of
male and female gametes from two parents.
• The flower is the primary reproductive structure. Within the flowers, the reproductive
organs, or sporophylls, are produced.
• Sporophylls are classified into two types: microsporophylls (stamen) and megasporophylls
(carpel).
• A carpel is an ovary that contains an ovule, a style, and a stigma.
• There are three types of stamen: filament, anther, and connective.
• Stamen is distinguished as filament, anther and connective.
• Sexual reproduction in flowering plants can be broken down into three steps:
i) Pre-fertilization
ii) Double fertilization
iii) Post-fertilization
Pre-Fertilization: Structure and Events
The following pre-fertilization events can be studied:
i) Pollen grain formation
ii) Embryo sac formation
Class XII Biology www.vedantu.com 1
,iii) Pollination
iv) Pollen pistil interaction
Pollen Grain Formation
Male reproductive unit (Stamen)
• A stamen is an angiosperm's male reproductive unit. It is composed of an anther and a
filament. The anther is bilobed, with each lobe containing four pollen sacs or
microsporangia.
• A number of pollen grains are contained in each pollen sac. A dithecous anther's four
pollen sacs are located in the four corners.
• Dithecous anther: An anther with two lobes connected by a non-sporangious tissue called
the connective.
• The anther wall is composed of four layers of cells.
• To release pollen grains, anther dehiscence through slits.
Anther Development
• The development of an anther begins with a mass of homogeneous meristematic cells
surrounded by an epidermis.
• Four lobes are formed, as are four layers of archesporial cells.
• Archesporial cells: A primitive cell or group of primitive cells that divide to form two types
of cells: a primary parietal cell and a primary sporogenous cell.
• The parietal cell divides several times to form the anther wall, whereas the sporogenous
cell divides less frequently to form microspores or the pollen mother cells (PMC).
• The tapetum is the innermost layer of the cell wall that comes into contact with the PMCs.
In pollen formation, the tapetum plays a crucial role.
• Tapetum: This is a tissue found within the anther that feeds the growing spores.
Class XII Biology www.vedantu.com 2
, • The endothecium is the layer beneath the epidermis.
Wall Layers of Anther
• The epidermis is a single layer of cells that serves as a protective layer.
• Endothecium is a single-layered second wall. Cells are thickened with cellulose and a trace
of pectin and lignin. It aids in the dehiscence of anthers.
• Middle layers – Ranges from 1-6. When the anther matures, the middle layer degenerates.
• Tapetum –
a) The anther wall's innermost layer surrounding the sporogenous tissue.
b) Tapetal cells contain nutrients.
c) They have multiple nuclei and are polyploid.
d) The ubisch bodies settle in the exine of the microspore wall.
e) There are two kinds of tapetum:
(i) Secretary / glandular – The tapetal cells remain in place throughout the development of
the microspore, eventually degenerating.
(ii) Amoeboid / periplasmodial – The tapetal cells rupture the radial wall, allowing the
protoplast to enter the pollen chamber. These protoplasts are now joining together to form
the periplasmodium.
Class XII Biology www.vedantu.com 3
