10. Reproduction Flashcards
define asexual reproduction
Asexual reproduction is the process of producing a genetically
identical offspring from one parent without the fusion of gametes
define sexual reproduction
Sexual reproduction is the process involving the fusion of gametes, one from each
parents, to form a zygote during fertilisation. The outcome is genetically dissimilar
offspring.
function of sepals (2)
• Modified leaves which are found on the outermost ring of floral
leaves.
• They enclose and protect the flower when it is in bud stage
function of petals (3)
• Modified leaves which form the most conspicuous part of the flower.
- They are large and brightly coloured in insect-pollinated plants
- Form a platform for insects to land on
function of anthers (3)
• Male reproductive organs in plants
• The anther consists of two lobes and a vascular bundle
• Each lobe contains two pollen sacs, which contain pollen grains
(male gametes)
function of carpels (4)
• Female reproductive organ in plants.
• Stigma: Receptor of pollen grains. Secretes a sugary fluid that stimulates germination of pollen grains.
• Style: Holds the stigma in position to trap pollen grains.
• Ovary: Each ovary contains one or more ovules, which contains
female gametes
Outline the process of pollination
- pollination
- self pollination
- cross pollination
- favorability (2)
- Pollination is the transfer of pollen grains from the anther to the stigma, enabling
fertilisation. - Self pollination: transfer of pollen grains from the anther to the stigma of the same
flower or from the anther of a flower to the stigma of another flower on the same plant. - cross pollination: transfer of pollen grains from the anther of a flower to the stigma of a
flower of another plant belonging to the same species. - self pollination (- Bisexual flowers with anthers and stigma maturing at the same time
• Stigma being located directly below the anthers, allowing pollen grains to fall onto it) - cross pollination (• Plants bear only male or female flowers, thus self pollination is not possible
• In plants with bisexual flowers, the anthers and the stigmas mature at different times.
• The stigma and anthers are located very far away )
advantages (3) and disadvantages of self pollination
- Not dependent on external agents of
pollination such as insects or wind - Less wastage of pollen and energy.
During wind and insect pollination, a
great number of pollen grains are lost
as only a few pollen grains come into
contact with a stigma of a flower of
the same species - Only one parent plant is required
- There is less genetic variation, hence
the offspring is less adapted to
environmental changes.
(this is NOT the same as asexual
reproduction. There is fusion of gamete
thus offspring is NOT genetically similar
to parents)
advantages (2) and disadvantages (4) of cross pollination
- Greater genetic variation, hence the
offspring has a higher chance of
surviving environmental changes - Offspring may have inherited beneficial
qualities from both parents - Energy-consuming – lots of energy is
required to make large amounts of pollen
grains
4.A great number of pollen grains are
wasted due to the randomness of the
dispersal methods - External agents of pollination i.e. wind,
insects are required - Two parent plants are required
describe insect-pollination
Insect such as bees and butterfly enters the flower for the
nectar, pollen grains from the anthers stick onto the insect.
When they visit other flowers, the will be transferred to the
next flower sticky stigma.
describe wind pollination
Wind-pollinated flowers have their pollen carried away by the
wind when the exposed anthers shake in the wind. The
pollen grains may come into contact with large feathery
stigmas of another flower, they would be trapped
describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (8)
- function of fertilisation (1)
Fertilisation: The fusion of nuclei of the male gamete (pollen) and the female gamete (ovule)
1. After pollination, the pollen grains germinate in response to the sugary fluid secreted
by stigma.
2. A pollen tube grows out from each pollen grain. The cytoplasm and the two nuclei of
the pollen grain, namely generative nucleus and pollen tube nucleus, pass into the
pollen tube
3. Pollen tube secretes enzymes to digest the surrounding tissue of the stigma and style.
4. The generative nucleus divides to form two male gametes.
5. The pollen tube enters the ovule in the ovary through the micropyle.
6. Within the ovule, the tip of the pollen tubes absorbs sap and bursts, releasing the two
male gametes.
7. One male gamete fuses with the ovum to form the zygote, while the other male gamete
fuses with the definitive nucleus to form the endosperm nucleus
8. The ovule will develop into a seed and the ovary will develop into a fruit.
function of testes (2)
• Produces sperms (male gametes)
• Produce male sex hormones e.g. testosterone. Male sex hormones are
responsible for development and maintenance of secondary sexual
characteristics
function of scrotum (2)
• Testes are held in the scrotum, which are pouch-like sac outside the body
• This allows the scrotum to be at a lower temperature than body temperature,
which is essential for sperm production
function of sperm ducts
Transport sperm from the epididymis to the urethra
