Core Ch 12 Reproduction in flowering plants
12.1 Asexual reproduction
Binary fission in bacteria:
Parent bacterial cell divides mitotically to form two daughter cells (e.g. Amoeba)
Vegetative propagation in flowering plants:
vegetative parts (leaves, stems or roots) of flowering plants develop into new plants
Process:
1. aerial part of the plant dies in winter; underground storage organ remains dormant
2. new aerial shoots develop from the buds when conditions are favourable; old
storage organ provides food for the growth of the shoots
3. adventitious roots are formedabsorb water & minerals from the soil; green leaves
start to develop
4. the shoots develop into new plants; old storage organ dries up as food is used up
5. green leaves fully developedcarry out photosynthesis to make food; some food is
transported to and stored in the new storage organ
Examples of storage organs:
Storage organ
Description
Example of plant
Stem tuber
Swollen end of
Potato
underground stem
Bulb
Short vertical underground
Onion, daffodil
stem with fleshy scale leaf
Corm
Short vertical underground
Gladiolus, water chestnut
stem surrounded by
protective scale leaf
Rhizome
Horizontal underground
Ginger, lotus
stem
Artificial vegetative propagation:
-cutting is one of the methods:
- cut a healthy leafplace it in waterplant it in soil after roots have developedthe
cutting grows & develops into a new plant
12.2 Sexual reproduction in flowering plants
12.2.1 Structure and functions of a flower
Floral part
Sepal (or calyx)
Petal (or corolla)
Function
Protects the flower bud
May be brightly coloured and scented to
attract insects
May have nectaries (glands) at the base to
produce nectar for insects to feed on
May have nectar guides to lead insects
towards the nectaries
Stamen (anther + filament)
Anther produces pollen grains which
carry male gametes
Carpel (stigma, style and ovary)
Stigma receives pollen grains
Style supports the stigma
Ovary produces ovule, which contains the
female gametes--ova
Bisexual flowers—flowers with both stamens and carpels (e.g. Cassia & Hibiscus)
Unisexual flowers—flowers with either stamens or carpels (e.g. squash plants & maize)
12.2.2 Pollination
Self-pollination: transfer of pollen grains to the stigma of the same flower or to the
stigma of another flower on the same plant
Cross-pollination: transfer of pollen grains to the stigma of a flower on a different plant
of the same species (greater genetic variations than self-pollination because it results in
fusion of gametes of two different parents)
Adaptive features of an insect-pollinated flower:
-anthers located inside the flower
-large, brightly coloured and scented petals; presence of nectar guidesattract insects
to land on
-broad and sticky stigma curls down to pick up pollen grains from insects
-pollen grains are rough, spiky and stickyhelp attach to insects
-nectaries secrete nectar to attract insects
Adaptive features of a wind-pollinated flower:
-feathery stigmas hang outside the flower to catch pollen grains in air
-anthers hang outside the flower to release pollen grains into the air
-thin and flexible filaments allow movement of the anthers in the wind to help the
release of pollen grains
-a large number of small, light, smooth and dry pollen grains are produced
12.2.3 Fertilization
1. Pollen grains land on the stigma of the same species
2. Sugary solution on the stigma stimulates the germination of pollen graindevelops
pollen tube
3. The pollen tube grows down the style and then into the ovary by secreting an enzyme
to digest the tissue of stylemale gamete is carried towards the ovule
4. The pollen tube grows through the micropyle; tip of the pollen tube bursts to release
the male gametes into the ovule
5. The male gamete fuses with the female gamete (ovum) to form a zygote
12.2.4 Floral parts after fertilization
Ovaryfruit
Ovary wallfruit wall
Ovuleseed
Ovumembryo
Integumentsseed wall
Sepals, petals, stamens, stigma, stylewither and fall off
12.2.5 Importance of seed & fruit dispersal
1. Reduce overcrowding & competition for resources (e.g. sunlight, water, nutrients,
space) among the daughter and parent plants
2. Allows the species to colonize new areas
3. Daughter plants can escape from pests and diseases associated with the parent plants
Mechanisms of seed dispersal:
-wind
-water currents
-animals (fleshy fruit wall is present)
12.3 Significance of asexual and sexual reproduction
Asexual reproduction by vegetative
Sexual reproduction by producing
propagation
flowers and seeds
Advantages:
Disadvantages:
-Desirable characteristics can be retained
-Desirable characteristics may not be
in the offspring
retained in the offspring
-No external agents are required
-External agents are required for
-Occurs at a relatively fast rate
pollination (wind/insect), seed and fruit
dispersal (wind/water/animals)
-Occurs at a relatively slow rate
Disadvantages:
Advantages:
-Offspring show no genetic
-Offspring show genetic
variationless adapted to environmental
variationsadapt to environmental
changes
changes
-Overcrowding & competition of
-Seeds can be dispersed over long
resources occur among offspring and
distances to reduce overcrowding &
parents
competition of resources among offspring
-Transmission of diseases from parents to
and parents
offspring is more likely (due to close
-Transmission of diseases from parents to
proximity)
offspring is less likely
Question bank 
1. Describe the sequence of events leading to fertilization after pollination is completed.
{CE 98 3b, CE 07 8a, DSE 17 3b}
-after landing on the stigma, pollen grains germinate to form pollen tubes (1)
-which carry the male gametes (1)
-pollen tube grows along the style towards the ovary to reach the ovule (1)
-the male gametes will be released to fuse with the female gametes in the ovule (1)
2. Give two reasons to explain why farmers prefer to grow the plant from its tubers
rather than employing sexual reproduction. {CE 98 3b}
-the desired quality of the plant can be maintained (1)
-because the daughter plants produced from the tubers are genetically identical to
the parent (1)
-the daughter plants can develop faster (1)
-as more food is available in the tuber for the development/the development is more
independent of environmental conditions (1)
3. Suggest one advantage and one disadvantage of self-pollination compared with
cross-pollination. {CE 00 2c}
-Advantage: the chance of pollination/fertilization is higher
less wastage of pollen grains
desirable characteristics of the parent are more likely to be transmitted
-Disadvantage: less genetic variationless adapted to environmental changes
4. In a genetic experiment, a scientist wanted to ensure that the stigma of a pea flower
only received the pollen grains of another pea flower. Suggest how the scientist could
achieve this by making use of a plastic bag and a brush. {CE 00 2c, CE 08 9a}
-Remove the anthers from the flower before they are mature (1)
-Use a brush to dust pollen grains of another pea flower onto the stigma of this
flower (1)
-Cover the flower with a plastic bag to prevent further pollination (1)
5. Give two advantages of vegetative propagation over the propagation using seeds. {CE
02 1a}
-this method is a faster way of producing daughter plant (1)
-the desirable characteristics of the parent can be retained in the daughter plant (1)
Reproduction (★★★★+)
{CE 98-3(b), CE 99-1(a), CE 99-3(c), CE 00-1(a), CE 01-4(c), CE 02-1(a), CE
04-2(a), CE 05-10(a), CE 09-8(b)}
1. The concept of cloning (both animals and plants)
2. Reproduction in flowering plants vs mammals {AL 06 PIIB-4(a)}
3. Comparison between egg and sperm (food reserve, size, mobility)
4. Clinical test for testing abnormality (amniocentesis, karyotyping, sex
determination)
5. Pregnancy
-function of amnion, amniotic fluid, uterus, umbilical cord and placenta{DSE
16 P1-2}
6. Reproduction in flowering plants
-Formation of pollen tube {DSE 17 P1-3(b)}
-The role and fate of different floral parts
-Features of wind-pollinated flowers vs insect-pollinated flowers
{DSE 14 P1-8, DSE PP P1-10(a)}
-Cross-pollination vs self-pollination {DSE 17 P1-3(a)(c)}
7. Seed dispersal {AL 00 PIIA-1(a)(b)}
8. Hormonal Control of menstrual cycle {AL 00 PIA-3(b)}
9. Treatment of infertility; biological principles of contraceptive pills
{AL 00 PIA-3(a), AL 06 PIIB-4(c), AL 11 PIA-2}