Exercises :
1. Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Ans : Parts where gametophytes develop :
- Male gametophyte develops in anther (microsporangium)
- Female gametophyte develops in ovule (inside ovary)
- Anther produces pollen grains
- Ovule contains embryo sac
- Both are reproductive parts of flower
2. Diffeentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
Ans : Microsporogenesis occurs in anther.
- Megasporogenesis occurs in ovule.
- Both involve meiotic division.
- Microsporogenesis forms microspores (pollen grains).
- Megasporogenesis forms megaspore.
3. Arrange the following terms in the correct developmental sequence :
Pollen grain,sporogenous tissue, microspore tetrad,pollen mother cell, male gametts.
Ans :
- Sporogenous tissue forms first
- Then pollen mother cells are formed
- Meiosis produces microspore tetrad
- Microspores separate into pollen grains
- Pollen grain forms male gametes
Ans. Parts of a typical angiosperm ovule :
- Funicle attaches ovule to ovary
- Hilum is point of attachment
- Integuments protect ovule
- Micropyle allows pollen tube entry
- Embryo sac contains female gametophyte
Ans . Monosporic development :
- Only one megaspore develops into embryo sac
- Other three megaspores degenerate
- Common in most angiosperms
- Functional megaspore undergoes mitosis
- Forms female gametophyte
Ans. 7-celled, 8-nucleate embryo sac :
- Egg apparatus has 1 egg + 2 synergids
- Three antipodal cells present
- One central cell with 2 polar nuclei
- Total 7 cells are formed
- Total 8 nuclei present
Ans. Chasmogamous flowers are flowers that open normally and expose their reproductive parts (stamens and pistil).
Key features:
- They have open petals, so pollinators like insects, wind, or water can reach them.
- They can undergo cross-pollination as well as self-pollination.
- They are usually showy and colorful to attract pollinators.
Ans. Strategies to prevent self-pollination :
- Dichogamy: different timing of maturity
- Herkogamy: different position of organs
- Self-incompatibility: genetic mechanism
- Dioecy: separate male and female plants
- These ensure cross-pollination
Ans. Self-incompatibility :
- It is a genetic mechanism
- Prevents fertilization by own pollen
- Pollen tube growth is inhibited
- No fusion of gametes occurs
- Hence no seed formation
Ans. Bagging technique :
- Flower is covered with bag
- Prevents unwanted pollen entry
- Used in plant breeding
- Helps in controlled pollination
- Ensures desired cross
Ans. Triple fusion is a process in flowering plants in which one male gamete fuses with two polar nuclei to form a triploid nucleus.
Where does it take place?
It occurs inside the embryo sac of the ovule, specifically in the central cell.
How does it take place?
After pollination, the pollen tube enters the embryo sac and releases two male gametes.
One male gamete fuses with the egg cell (this is fertilization).
The second male gamete fuses with the two polar nuclei present in the central cell.
This fusion of three nuclei is called triple fusion.
Nucleus involved:
The nuclei involved are:
One male gamete nucleus
Two polar nuclei (or a secondary nucleus formed by their fusion)
Ans. Dormancy of zygote :
- Zygote does not divide immediately
- Endosperm develops first
- Endosperm provides nutrition
- Supports embryo development
- Ensures proper growth
13. Differences between :
(a) Hypocotyl vs Epicotyl
- Hypocotyl below cotyledon
- Epicotyl above cotyledon
- Hypocotyl forms root part
- Epicotyl forms shoot part
- Both are parts of embryo
(b) Coleoptile vs Coleorhiza
- Coleoptile protects plumule
- Coleorhiza protects radicle
- Found in monocots
- Both are protective sheaths
- Help in seed germination
(c) Integument vs Testa
- Integument covers ovule
- Testa is seed coat
- Testa forms after fertilization
- Both provide protection
- Integument develops into testa
(d) Perisperm vs Pericarp
- Perisperm from nucellus
- Pericarp from ovary wall
- Perisperm in seed
- Pericarp in fruit
- Both have different origins
Ans. Apple as false fruit :
- Apple develops from thalamus
- Not only from ovary
- So it is called false fruit
- Ovary forms inner part
- Thalamus forms major edible part
Ans. Emasculation is the process of removing the anthers (male reproductive parts) from a bisexual flower before they release pollen.
When is it done?
It is done before anthesis (before the flower opens and anthers shed pollen).
Why is it done?
- To prevent self-pollination.
- To ensure that the flower receives only desired pollen from a selected plant.
- It helps in controlled cross-pollination during plant breeding.
Ans. Parthenocarpy is the development of fruits without fertilization, resulting in seedless fruits.
Fruits to select:
- I would select fruits like:
- Citrus fruits (orange, lemon)
- Grapes
- Watermelon
- Guava
Why these fruits?
- These fruits are commonly consumed fresh, and seeds can be inconvenient while eating.
- Seedless varieties have higher market value and consumer preference.
- In some cases, seeds are hard or numerous, reducing fruit quality.
Ans. Role of tapetum :
- Provides nutrition to developing pollen
- Helps in pollen wall formation
- Produces enzymes and materials
- Important for pollen viability
- Supports microspore development
Ans. Apomixis is a type of reproduction in plants in which seeds are formed without fertilization (no fusion of male and female gametes).
In simple words:
It is asexual seed formation, where the offspring are genetically identical to the parent plant.
Importance of apomixis:
- Maintains desirable traits: Since offspring are identical, useful characters (like high yield) are preserved.
- No need for pollination: Seed formation occurs even without pollinators.
- Fixation of hybrid vigor (heterosis): Once a good hybrid is produced, apomixis helps retain its superior qualities for many generations.
- Cost-effective for farmers: Farmers can reuse seeds without losing quality.
