Reproduction

• Plants cloned by taking cuttings can be produced cheaply and quickly.
• Sexual reproduction is the process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other.
• A gamete is a sex cell (in animals: sperm and ovum; in plants: pollen nucleus and ovum).
• Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells - we say they have a haploid nucleus.
• This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells.
• In human beings, a normal body cell contains 46 chromosomes, but each gamete contains 23 chromosomes.
• When the male and female gametes fuse, they become a zygote (fertilised egg cell) which contains the full 46 chromosomes, half of which came from the father and half from the mother - we say the zygote has a diploid nucleus.
• There are advantages and disadvantages of sexual reproduction, but also advantages and disadvantages of asexual reproduction.
• Asexual reproduction is the process resulting in genetically identical offspring being produced from one parent.
• Asexual reproduction does not involve gametes or fertilisation.
• Only one parent is required in asexual reproduction, so there is no fusion of gametes and no mixing of genetic information.
• In insect or wind-pollinated plants, pollination can either occur via cross-pollination or self-pollination.
• This means plants have to have mechanisms in place to transfer pollen from the anther (male part of the flower) to the stigma (female part of the flower).
• Flowers are the reproductive organs of plants and usually contain both male and female reproductive parts.
• Wind-pollinated flowers are usually structured to ensure that the pollen is shed into the open air and is then either blown by the wind or carried by air currents until it (by chance) lands on the stigma of a plant of the same species, resulting in pollination.
• The process of transferring pollen from the anther to the stigma is known as pollination and there are two main mechanisms by which it occurs: pollination where the pollen is transferred by insects (or sometimes other animals like birds or bats) and pollination where the pollen is transferred by the wind.
• Unlike the male gamete in humans (sperm), pollen is not capable of locomotion (moving from one place to another).
• Plants produce pollen, which contains a nucleus inside that is the male gamete.
• Insect-pollinated flowers are usually structured to attract insects and facilitate pollination by insects.
• Cross-pollination occurs when the pollen from one plant is transferred to the stigma of another plant of the same species.
• The structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function.
• As a result of asexual reproduction, the offspring are genetically identical to the parent and to each other, they are clones.
• Many plants reproduce via asexual reproduction.
• Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission.
• The method for taking cuttings involves gardeners taking cuttings from good parent plants, cutting a section of the parent plant with a new bud off, and either placing the cutting into water until new roots grow or sometimes placing it directly into soil.
• Germination is the start of growth in the seed, which contains the zygote, the fertilised egg cell, that divides into cells that then develop into the embryo plant.
• Some plants grow side branches, known as runners, that have small plantlets at their ends, which will grow roots and develop into separate plants when they touch the soil.
• Asexual reproduction in plants can occur naturally or humans can control asexual reproduction in plants artificially for their own uses.
• After taking in water, the seed coat splits, leading to the production of the plumule, the first emerging shoot, and radicle, the first emerging root.
• Sometimes, the stem of the cutting may first be dipped into 'rooting powder', which contains plant growth regulators (rooting hormones) that encourage new root growth.
• The cotyledons fulfil this role until the young plant grows its own leaves and becomes capable of making its own food via photosynthesis.
• A simple method to clone plants, mainly used by gardeners, is by taking cuttings, an artificial method of asexual reproduction.
• When the seed germinates, the embryo begins to grow into the young seedling, surrounded by structures known as cotyledons, which contain food reserves that supply the young seedling with food (and, therefore, energy for growth) when the seed starts to germinate.
• These cuttings are then planted and eventually grow into adult plants that are genetically identical to the original plant.
• Plants can reproduce asexually as well as sexually, with asexual reproduction only involving one parent and all offspring produced being exact genetic copies of each other and the parent plant, they are clones (genetically identical).
• There are advantages and disadvantages of asexual reproduction, but also advantages and disadvantages of sexual reproduction.
• The key differences between sexual and asexual reproduction include the number of parent organisms, how offspring are produced, the level of genetic similarity between offspring, the possible sources of genetic variation in offspring, the number of offspring produced, and the time taken to produce offspring.
• Fertilisation is defined as the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring.
• Each ovule contains an ovum, an egg cell that contains the female nucleus that a male pollen nucleus can fuse with.
• Unlike the male gametes in animals (sperm), the pollen grain has no ‘tail’ to swim to the ovary of the flower.