The previous posts have explained the processes involved in sexual reproduction in plants. But many species of plant can also reproduce asexually and this post is going to explain how and why this might occur… Now this is not a topic that is so exciting that it keeps many GCSE students awake at night but there is some good biology in here so pay attention!
Asexual reproduction is the term used for any reproductive strategy that produces genetically identical offspring. The term for a group of genetically identical organisms is a clone and so asexual reproduction is also called cloning. In animals and plants, asexual reproduction only involves one type of cell division, mitosis.
Sexual reproduction on the other hand always introduces genetic variation into the offspring. In the majority of cases, it involves the formation of two haploid gametes (produced in a specialised type of cell division called meiosis) which then fuse together in fertilisation to form a zygote.
This post is not the correct place to discuss the advantages and disadvantages of the two types of reproduction. But sexual reproduction comes at a cost for an organism: in plants this cost is the energy spent making attractive petals and scent to attract insect pollinators, the cost of wasting millions of pollen grains just to ensure some are transferred, the cost of making sweet tasty fruits for animals to eat. I am writing this the day after Valentine’s Day in the UK which illustrates the courtship costs for animals quite well…..
Asexual Reproduction in Plants:
Plants have evolved a variety of asexual strategies shown in the picture above. We only really need to consider one for your iGCSE exam and that is runners. Some plants, the classic example is the strawberry grow long horizontal stems outwards from the parent plant. When this “runner” touches the ground, root development is switched on and a new plant starts to grow upwards. When the runner dies back, you are left with two genetically identical plants, hence Asexual Reproduction.
(This diagram is a little misleading…. The runner is not the name of the offspring plant, it is the long horizontal structure growing outwards just above the soil from the parent plant)
If you are really interested in learning more about asexual strategies in plants, well you should probably get out more… But you could study how tubers (such as in potato) and bulbs (such as the onion) allow plants both to over-winter and also produce clones.
Artificial Methods of Asexual Reproduction in Plants
This is quite weird if you think about it….. A human can cause asexual reproduction in many species of plant by “taking a cutting“. As the name suggests this involves cutting off a small part of the plant (including a leaf and part of the stalk) and then sticking it into soil to grow a new plant. The only type of cell division in this process is mitosis and so the plant produced from the cutting will be a clone of its parent (genetically identical).
This is an example of artificial asexual reproduction in plants. It is a useful strategy for gardeners as it allows you to produce lots of new plants for your garden without shelling out hard-earned cash at the garden centre….
Cuttings work much better if in between taking the cutting and planting it in a small pot of compost, the cut end of the stalk is dipped in a mixture of chemicals calling a “rooting powder”
Rooting powder contains a mixture of plant growth substances (sometimes incorrectly called hormones) that can switch on the genetic programme of root production.
I hope you find this post useful. It probably holds the record for the dullest site anywhere on the World Wide Web…. Typing this has made me feel sleepy, so I am going to lie down…..
Please add comments/questions or tweet me if anything is unclear.