Sexual reproduction1 is a way of making a new individual by joining two special sex cells, called gametes2. In the sexual reproduction of animals and plants, the male and female gametes join to form a single fertilised cell3 called a zygote4, which develops into a new individual with a unique collection of genetic5 material. In a population6, this genetic variation7 is important because, if conditions8 become hard, there is a chance that some individuals will survive.
Many flowering plants are also able to reproduce asexually through various structures such as stolons9, rhizomes10 and tubers11. However, all individuals produced like this are clones of their parent, with no genetic variation12. This means that, if something happens that is fatal to one individual, such as a disease13 outbreak, it is likely to be fatal to all.
Pollination
Pollination14 is a very important part of the life cycle of a flowering plant15. It is part of the sexual reproduction process of flowering plants, which results in seeds that will grow into new plants. Flowers are the structures of flowering plants that contain all the specialised parts needed for sexual reproduction.
Plants have gametes, which contain half the normal number of chromosomes16 for that plant species17. Male gametes are found inside tiny pollen18 grains on the anthers19 of flowers. Female gametes are found in the ovules20 of a flower. Pollination is the process that brings these male and female gametes together.
Pollen can’t get from the anthers to the ovules on its own, so pollination relies on other things to move the pollen. The wind or animals, especially insects and birds, pick up pollen from the male anthers and carry it to the female stigma21. Flowers have different shapes, colours and smells, and often sugary nectar22 and nutritious23 pollen, to encourage animals to visit and pollinate them. Wind-pollinated flowers are shaped to make it easy for the wind to pick up or deposit pollen.
Many flowers can be pollinated by their own pollen – a process called self-pollination24. However, this does not always result in the genetic variation needed for species to survive. Many plants have ways to make sure they are only pollinated by pollen from a flower on a different plant, which is called cross-pollination25. Some have the male and female parts in separate flowers on the same plant, while others have male and female flowers on different plants. Many have the stigmas and anthers ripening at different times to prevent self-pollination.
Fertilisation
Only after pollination, when pollen has landed on the stigma of a suitable flower of the same species, can a chain of events happen that ends in the making of seeds. A pollen grain on the stigma grows a tiny tube, all the way down the style26 to the ovary27. This pollen tube carries a male gamete28 to meet a female gamete in an ovule29. In a process called fertilisation30, the two gametes join and their chromosomes combine, so that the fertilised cell contains a normal complement of chromosomes, with some from each parent flower.
The fertilised ovule goes on to form a seed31, which contains a food store and an embryo32 that will later grow into a new plant. The ovary develops into a fruit to protect the seed. Some flowers, such as avocados, only have one ovule in their ovary, so their fruit only has one seed. Many flowers, such as kiwifruit, have lots of ovules in their ovary, so their fruit contains many seeds.
Find out how the artificial control of pollination plays a part in the breeding of new fruit cultivars.
Activity ideas
Try one of these actvities with your students:
- Pollination pairs – students match native33 flowers with their pollinators, basing predictions on the main characteristics of flowers pollinated by wind, insects or birds.
- Pass the pollen – students take on the role of flower parts and act out the process of insect pollination.
- sexual reproduction: The formation of a new individual after the joining of male and female sex cells (gametes) from different parents. In some plants, sexual reproduction can involve gametes from the same parent.
- gamete: Male or female reproductive cells – a sperm or egg in animals, and pollen and ova in plants. Gametes contain only a single set of chromosomes.
- cell: 1. Building block of the body. A human is made of millions of cells, which are adapted for different functions and can reproduce themselves exactly. 2. A simple electrolytic device that enables chemical energy to be transformed into electrical energy.
- zygote: A fertilised egg (diploid cell) before cell division has begun.
- genetic: Of, relating to, or determined by genes.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- genetic variation: Slightly different sequences in the genetic code of different individuals from the same species. This is important for species adaptation to occur.
- condition: An existing state or situation; a mode or state of being.
- stolon: A special plant stem for asexual reproduction. It grows out sideways along the surface of the ground, and new plants grow up along it or just at the end.
- rhizome: Underground stem.
- tuber: A thickened underground stem, for example, a potato. A tuber stores food so the plant can lie dormant over winter and is a way of producing new plants asexually.
- genetic variation: Slightly different sequences in the genetic code of different individuals from the same species. This is important for species adaptation to occur.
- diseases: 1. An abnormal condition of an organism that impairs bodily functions. 2. In plants, an abnormal condition that interferes with vital physiological processes.
- pollination: The transfer of pollen grains from the anther to the part of the plant containing the ovules. This process is necessary for fertilisation and reproduction of the plant.
- flowering plant: A plant with a life cycle that includes the formation of seeds inside flowers. The scientific name for a flowering plant is angiosperm.
- chromosome: A structure within the cell nucleus made of a single coiled piece of DNA that contains the genetic blueprint of an organism.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- pollen: Dust-like grains that contain male sex cells (gametes) of flowering plants (angiosperms) and cone plants (gymnosperms). Pollen is made on the anthers of flowering plants.
- anther: Contains the pollen sacs of a plant and is the region where pollen is produced.
- ovule: 1. (Plants) In seed plants, contains female sex cells (gametes) inside an ovary. An ovule develops into a seed after fertilisation. 2. (Animals) A small egg (ovum).
- stigma: Part of the carpel – the female reproductive organ of a flower. During pollination, pollen from a male flower part (anther) is transferred to the sticky female stigma.
- nectar: A sugary liquid found in many flowers, made and stored in a nectary. Used to attract animals, which eat it and accidentally collect or deposit pollen at the same time.
- nutritious: Healthy for eating, containing lots of nutrients that are needed.
- self-pollination: The transfer of pollen from the male to the female part of the same flower or another flower on the same plant.
- cross-pollination: The transfer of pollen from one flower to another flower on a different plant. Genetic material becomes mixed, resulting in variation in the population and a better chance of survival.
- style: A stalk that connects the stigma to the ovary in the female reproductive part of a flower.
- ovary: 1. (Flowering plants) Contains the ovules in the female part of the flower. 2. (Animals) The female egg-producing organ involved in sexual reproduction.
- gamete: Male or female reproductive cells – a sperm or egg in animals, and pollen and ova in plants. Gametes contain only a single set of chromosomes.
- ovule: 1. (Plants) In seed plants, contains female sex cells (gametes) inside an ovary. An ovule develops into a seed after fertilisation. 2. (Animals) A small egg (ovum).
- fertilisation: (Reproduction) The joining of male and female sex cells (gametes), resulting in combining genetic material.
- seed: 1. Part of the sexual reproduction of angiosperms (flowering plants) and gymnosperms (cone plants). Contains an embryo and its food store, which creates a new plant when conditions are right. 2. Offspring or progeny.
- embryo: The product of a fertilised egg, from the zygote until the foetal stage. The undeveloped plant that forms when the ovule is fertilised.
- native: A species that lives naturally in a country, as opposed to species that have been introduced by the activity of humans.
