Chapter 12A Reproduction In Plants

Question 1

Define the term asexual reproduction [2] (2017/A5a)

Answer 1

Asexual reproduction is the process resulting in the production of genetically identical offspring from one parent,[1] without the fusion of nuclei of gametes.[1]
An example is grafting/ vegetative propagation OR asexual reproduction in amoeba

Question 2

Define the term sexual reproduction [3] (2015/A2)

Answer 2

Sexual reproduction involves the fusion of the haploid nuclei of a male and female gamete [1] to form a diploid zygote which is genetically dissimilar from its parents [1] through fertilisation. The male and female gametes are produced by meiosis in the gonads. [1]

Question 3

Describe and explain how the tip of part A (pollen tube) reaches the female nucleus inside the flower. [3] (2015/A2)

Answer 3

1. The growth of the pollen tube is controlled by the pollen tube nucleus. The pollen tube secretes enzymes to digest the surrounding tissue of the stigma and the style [1]
2. and penetrates through the style to the ovary. [1]
3. The pollen tube enters the ovule in the ovary through the micropyle [1]
4. The tip of the pollen tube absorbs sap and bursts to release the male gametes to reach the ovum which contains the female nucleus.

Question 4

Distinguish between sexual and asexual reproduction [4] (2013/10 E)

Answer 4

Sexual reproduction is the production of offspring from the fusion of haploid gametes (fertilization) and involves genetic recombination, which results in the offspring being genetically different from the parents. It involves 2 parents of the opposite gender. It is a slower method of reproduction.

Asexual reproduction is the production of offspring by mitosis only and does not involve fertilization and genetic recombination, hence the offspring produced are genetically identical to the parent. Involves only one parent. It is relatively quicker.

Question 5

Define the term pollination (2013/10 E)

Answer 5

Pollination is the transfer of pollen grains [1] from
the anther to the stigma of a flower. [1]

Some students referred to the
landing of pollen on the stigma,
rather than the transfer – this is
not desirable.
Description of pollen tube
growth and fertilisation are not
required.

Question 6

State two differences between wind-pollinated and insect-pollinated flowers. [4] (2013/10 E)

Answer 6

• Insect–pollinated flowers are usually large and conspicuous with brightly coloured petals. Petals are to attract insects. Wind-pollinated flowers are usually small, dull-coloured, and without petals. Flowers do not need to attract insects. [Diff-1; Reason-1]
• Insect-pollinated flowers have pollens which are fairly abundant. Pollens are larger with rough surfaces so they can cling to the body of insects. In wind-pollinated flowers and pollens are more abundant. Pollen grains have smooth surfaces and are tiny and light so that they are easily blown away by the wind. [Diff-1; Reason-1]
• Wind-pollinated flowers have a large feathery stigma to increase surface area to trap pollen grains in the air, while insect-pollinated flowers
  have a small enclosed stigma so that only pollen from visiting insects is transferred to it.
• Wind-pollinated flowers have an exposed, pendulous stamen so that pollen grains can be easily dislodged by wind, while insect-pollinated flowers have enclosed, upright stamen so that
  pollen grains can only be picked up by insects that visit the flower.

Question 7

The _____ is made of a modified leaf which encloses and protects the other parts of the flower in the bud stage.

Answer 7

Sepal

Question 8

The ______ Consists of the ______ and the ________. The ______ has 2 lobes, each containing 2 pollen sacs which produce pollen grains.
The pollen grain contains two male gametes. (self)

Answer 8

Stamen, anther, filament, anther

Question 9

The ______ (______) Consists of one or more _______ which capture pollen grains, a _____ through which the pollen tube grows, and an ovary which contains ovules.
The ovum is in the ovule. (self)

Answer 9

Carpel (pistil), stigmas, style

Question 10

Define cross-pollination (self)

Answer 10

The process of pollination whereby the pollen grains from the anther are transferred to the stigma of another flower on another plant of the same species.

Question 11

Define self-pollination (self)

Answer 11

The process of pollination whereby the pollen grains from the anther are transferred to the stigma of the same flower or a different flower in the same plant.

Question 12

Describe the process of fertilization (production of endosperm and details of development are not required) [3/4] (self)

Answer 12

The pollen tube enters the ovule through an opening called the micropyle.
1. Along the way, the generative nucleus divides to form two male gametes, and eventually, the pollen tube nucleus disintegrates
2. Within the ovule, the tip of the pollen tube absorbs sap and bursts to release the two male gametes
3. The haploid nucleus of one male gamete fuses with the haploid nucleus of the ovum to form the diploid zygote, while the nucleus of the other male gamete fuses with the definitive nucleus to form the endosperm nucleus. This results in double fertilisation.
4. The zygote then divides mitotically and develops into the embryo in the seed, while the endosperm nucleus divides to give rise to the food storage tissue called the endosperm.