Chapter 2, Sexual Reproduction in Flowering Plants
CBSE Board, Class XII Biology - NCERT Answers of Chapter Exercise Questions
To see answers of exercise question no 1 - 10 of Chapter 2, Sexual
Reproduction in Flowering Plants, click - Chapter 2, Sexual Reproduction in Flowering Plants - CBSE Class 12 Biology - NCERT Solutions
Question
11: What is triple fusion? Where and how does it take place? Name the nuclei
involved in triple fusion.
Answer: Triple
Fusion: It is the process of fusion of three nuclei, two polar
nuclei (fuse to form a diploid secondary nucleus) and a male gamete. It was
reported by Nawaschin in Lilium and Fritallaria.
Triple fusion occurs in
the embryo sac of the ovule of angiosperms. The nuclei involved are two polar
nuclei and a male gamete.
Question
12: Why do you think the zygote is dormant for sometime in a fertilised ovule?
Answer: Since, the zygote develops only
after a certain amount of endosperm is formed to assure nutrition to the
developing embryo, zygote is said to be dormant for this of period.
Question
13: Differentiate between:
(a)
hypocotyl and epicotyl;
(b)
coleoptile and coleorrhiza;
(c)
integument and testa;
(d) perisperm
and pericarp
Answer:
(a) Hypocotyl
1. The part of the embryonic axis
present below the cotyledon is called "hypocotyl".
2. Hypocotyl terminates with root cap
called radical.
3. It elongates faster during epigeal
germination.
Epicotyl
1. The part of the embryonic axis
present above the cotyledon is called "epicotyl".
2. Epicotyl terminates with stem tip
called plumule.
3. It elongates faster during hypogeal
germination.
(b) Coleoptile
1. Coleoptile is the foliaceous sheath
that covers the plumule in the embryo of cereals.
2. It belongs to the shoot system.
Coleorrhiza:
Fig: V. S. of Maize
Grain
1. Coleorrhiza is the protective
covering of the radical in the embryo of the cereals.
2. It belongs to the root system.
(c) Integument
1. It is the protective covering of
ovule.
2. It encircles the ovule completely
except at micropylar end. They are protective in nature.
3. It develops into the seed coat.
Testa
1. Testa is the outer covering of a
seed.
2. Testa is hard and provides
protection to the young embryo. Micropyle is also present here.
3. It develops from the outer
integument.
(d) Perisperm
1. Perisperm is the remnant of the
nucellus (of ovule) in the seed.
2. It is a single layer to store food.
3. It is a part of the seed.
Pericarp
1. Pericarp is the wall of fruit
formed by the ovary wall.
2. It may be divided into three layers
viz exocarp, mesocarp and endocarp.
3. It is a part of the fruit.
Question
14: Why is the apple called a false fruit ? Which parts of the flower forms the
fruit ?
Answer: A fruit is a matured ovary with or
without seeds. If any part of a flower other than the ovary becomes a part of
the fruit, the fruit is a false fruit.
In apple, the thalamus
grows over the true fruit and becomes fleshy and edible. The true fruit lies
within it. It has an inferior ovary, two or more seeded and fleshy syncarpous
fruit surrounded by thalamus. It is known as pome.
Question
15: What is meant by emasculation ? When and why does a plant breeder employ
this technique ?
Answer:
Emasculation
Removal of anther in bud
condition from a bisexual flower of female parent is called
"emasculation". Emasculation is not required in the female parent if
it produces unisexual flower. It is done manually by using forceps.
A plant breeder employs
this technique for the following reasons:
1. To produce
commercially superior varieties of plants.
2. When the flower to be
used as female parent is bisexual.
3. To prevent self-
pollination or contamination of the stigma with the self-pollen.
4. To produce desired
cross-pollination between different species.
5. To combine desirable
characters.
6. It is followed by
bagging.
Question
16: If one can induce parthenocarpy through the application of growth
substances, which fruits you would select to induce parthenocarpy and why ?
Answer: The term "parthenocarpy"
was coined by Knoll. The
development of fruits without fertilisation is called
"parthenocarpy". Parthenocarpic fruits are seedless, e.g., banana.
Parthenocarpy can be induced with the help of growth regulators like-
Gibberellins (GA3), Auxins (IBA). It can be natural or induced.
The fruits which I would
select to induce parthenocarpy are- grapes, oranges, lemons, etc because it is
easy for the preparation of juicy fruit and also they are very successful
commercially.
Question
17: Explain the role of tapetum in the formation of pollen-grain wall.
Answer: Tapetum
is the innermost wall layer of a microsporangium, where cells are large,
densely cytoplasmic and may be binucleate. The various roles played by tapetum
are as follows:
1. It acts as a
nutritive layer i.e., provides nourishment to pollen.
2. They store food
material.
3. Secretion of hormones
and various enzymes.
4. Transportation of
nutrients in anther locule during meiosis in spore mother cells.
5. Production of Ubisch
bodies coated with sporopollenin to cause exine thickening.
6. Secretion of
pollenkit (oily substance) outside mature pollen.
7. Secretion of proteins
for pollen to be compatible during recognisition.
Question
18: What is apomixes? What is its importance ?
Answer:
Apomixes
It is a special type of
asexual reproduction that mimics sexual reproduction. Development of embryo / seeds
without fertilisation is called "apomixes". The term
"apomixes" was coined by Wrinkler.
Importance of
Apomixes: Apomixes is
very important in agriculture as given hereunder -
1. Problems of Hybrid Seed Industry
(a) Hybrid seeds had to
be produced in every year. The progeny of hybrid seeds sdo not maintain hybrid
(desirable) characters. Hence, characters become unstable. It is due to seggregation
of characters.
(b) It occurs during
meiosis & sexual reproduction.
2. Production of Hybrid Seeds is costly
(a) Cost of hybrid seeds
become expensive to the farmers.
(b) The information is
genetically controlled from genetics of apomixes, which helps in transfer of
"apomictic gene" into crop plants and produce hybrid seeds with
desirable characters.
Click below to see answers of
exercise question no 1 - 10 of Chapter 2, Sexual Reproduction in Flowering
Plants
Chapter2, Sexual Reproduction in Flowering Plants - CBSE Class 12 Biology - NCERT Solutions
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