[BIO] Chapter 15 - Reproduction in Plants

© Hee Xin Wei (Copyrighted) Topic 1 5: Reproduction in Plants

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 0.5% in Paper 2 in the past 5 years •commonly tested in MCQ •straightforward chapter

flower structures pollination fertilisation Key Concept

reproduction •Reproduction is the biological process by which new organisms are produced to ensure the perpetuation of the species. •Two type of reproduction: 1.Asexual reproduction is the process of producing a genetically identical offspring from one parent without the fusion of gametes. asexual reproduction Advantages Disadvantages Asexual reproduction -Only one parent required as fusion of gametes is not required. -All beneficial qualities are passed onto the offspring. -Faster method of producing offspring as compared with sexual reproduction. -Since organisms are already in a suitable habitat, they can colonise the area rapidly. -No genetic variation in the offspring. Hence, species are may be wiped out if not well adapted to changes in the environment.

Reproduction sexual reproduction Advantages Disadvantages Sexual reproduction -Offspring may inherit beneficial qualities from both parents. -There is greater genetic variation in the offspring, thus species can be better adapted to changes in the environment. -Two parents are required (except in plants with bisexual flowers) as fusion of gametes is required -Slower method of producing offspring as compared to asexual reproduction 2.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.

structure of a flower plant Pedicle Carpels Sepal •Modified leaves which are found on the outermost ring of floral leaves. •They enclose and protect the flower when it is in bud stage. Petal •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. Anther •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) Filament Stalk that holds the anther in a suitable position to disperse pollen Carpels •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 structure of a typical insect-pollinated flower

Pollination self pollination Advantages Disadvantages Not dependent on external agents of pollination such as insects or wind 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) 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. 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. It is favoured when: •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

Pollination cross pollination Advantages Disadvantages Greater genetic variation, hence the offspring has a higher chance of surviving environmental changes. Energy-consuming – lots of energy is required to make large amounts of pollen grains. A great number of pollen grains are wasted due to the randomness of the dispersal methods. Offspring may have inherited beneficial qualities from both parents. External agents of pollination i.e. wind, insects are required. Two parent plants are required. 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. It is favoured when: •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.

mechanism of cross pollination 1.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. 2.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.

insect pollinated vs wind pollinated structure of a typical insect-pollinated flower Insect-pollinated Flowers Wind-pollinated Flowers Petals Large, brightly-coloured petals Small and dull petals, flower parts are protected by modified leaves called bracts Scent Flowers are fragrant or sweet smelling Flowers are scentless Nectar Present Absent Nectar guide (lines visible to insects, guiding them to nectar) Present Absent Stamen Not pendulous and do not protrude out of the flower long pendulous filaments and protruding anthers, so pollen grains are easily shaken off by the wind SGgma Small and compact, do not protrude out of the flower large, feathery and protrude out of the flower to provide a large surface area to trap pollen. Pollen grains Fairly abundant large and sGcky with rough surface so it can readily sGck to body insects Very abundant, small and light to be carried by the wind Bracts