Sexual vs. Asexual Reproduction

Sexual reproduction

• Two parents are needed for sexual reproduction.
  • Sexual reproduction happens with the fusion of a male gamete and female gamete. This process is called fertilization.
• Offspring produced from sexual reproduction are genetically different from the parents.
• Since there is variation among the population of a species, there is a higher chance that some of the organisms will survive in and adapt to new environments.
• However, time and energy is needed to find a mate for sexual reproduction.

• Only one parent is required for asexual reproduction.
• Offspring produced are genetically identical to the parent.
• In favorable conditions, a lot of offspring can be produced rapidly.
• However, adaptation to new environment may be difficult since there is no genetic variability.

Sexual Reproduction of Plants

Flowers are the reproductive part of plants. 

Structure of flower:

• Stamen is the male part of the flower and consists of an anther attached to a filament.
  • Male gametes (pollen grains) are produced at the anther.
• Carpel is the female part of the flower and consists of the stigma, style and ovary. 
  • Stigma is where pollen grain is collected.
  • Female gametes are produced and stored at ovules, which are located inside the ovary.

Reproduction in flowering plants begins with pollination, which is the transfer of pollen grains to the female part of a plant. Flowers can be pollinated either by insects or by wind, and these two types of flowers have undergone adaption to facilitate pollination.

👇 Frequently asked in IGCSE Biology : Comparing insect-pollinated flowers to wind-pollinated flower 👇

Insect-pollinated flower:

• To attract insects, insect-pollinated flowers have large and bright-coloured petals.
• Insect-pollinated flowers have a nectary that produces nectar that is attractive to insects.
• They produce sticky pollen grains that can stick on to insects easily.
• They produce a moderate number of pollen grains since insects can transfer pollen grains to stigma at a fairly high efficiency.
• The anther is encased inside the flower and stiff so that insects can brush past it.
• The stigma is encased inside the flower and sticky so that pollen grains can stick to the stigma when insects brush past it. 

• Since wind-pollinated flowers do not need to attract insects, they have small and dull-coloured petals.
• They do not need to attract insects, so wind-pollinated flowers do not have any scent or produce nectar.
• Pollen grains are smooth and light so that they can be carried away by wind easily.
• They produce a large number of pollen grains to increase the number of pollen grains being pollinated since only a small percentage of pollen grains actually reach other flowers.
• The anther is outside the flower and loose on long filaments so that pollen grains can be released easily.
• The stigma is outside the flower and feathery so that it can easily catch pollen grains being carried by wind.

What happens after pollination...

👇 Also important to understand for IGCSE Biology: The process of fertilisation 👇

Fertilisation

1. After pollen grains land on the stigma, a pollen tube is produced. 
2. The pollen tube grows down the style until it reaches the ovule in the ovary.
3. The nucleus of the male gamete travels down the pollen tube and fuses with the nucleus of the female gamete. This process is called fertilization.
4. After fertilization, the ovule becomes the seed, the ovule wall becomes the seed coat and the ovary becomes the fruit.

Germination

Germination is the process in which a seed develops into a young plant.

A seed consists of three different parts:

• Embryo: the part of a seed that later develops into a young plant
• Food store: storage of starch that can be used as food until the plant can produce its own nutrition through photosynthesis
• Seed coat: a hard protective layer

• Water: Water is needed to activate enzymes to digest the stored food
• Oxygen: Oxygen is needed for aerobic respiration, which can produce energy for germination.
• Warmth: A suitable range of temperature is needed for enzymes to work effectively. 

Asexual Reproduction of Plants

Plants can reproduce asexually, either naturally (e.g. runners) or artificially (e.g. cuttings).

Runners

Some plants, such as strawberries, have long stems that grow horizontally along the soil surface. These stems are called runners, and they have buds and roots that can grow into new plants.

Cuttings

A piece of the stem or root of a parent plant can produce a whole new plant, when placed in a suitable medium. Stem cutting will produce a new root, and root cutting will produce a new shoot.

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