Reproduction in Plants define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent. define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring. state the functions of the sepals, petals, anthers and carpels. outline the process of pollination. describe the growth of the pollen tube and its entry into the ovule followed by fertilisation.

Sexual VS Asexual Reproduction Sexual reproduction: process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring Asexual reproduction: process resulting in the production of genetically identical offspring from one parent Involves fusion of two gametes Does not involve fusion of gametes Requires two parents Require only 1 parent Variation in offspring Offspring are identical

Asexual reproduction Advantages: Offspring produced are identical to parents, hence higher chance of good characteristics of parents being passed to the offspring Only one parent is involved, hence do not depend on external agents, like wind or insect and able to reproduce rapidly Disadvantage: No genetic variations among offspring, hence less adapted to changes in the environment

Parts of a Flower stigma Petal style carpel ovary anther ovule stamen filament Sepal Receptacle Pedicel Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 22 April 2017 4

Parts of a flower Structure Function Sepals Protect the other parts of the flower in the bud stage Receptacle enlarged end of the flower stalk Pedicel Flower stalk Petals are brightly coloured to attract insects for pollination provide a platform for insects to land

Parts of a Stamen vascular bundle pollen sacs pollen tube nucleus pollen grains Stamen anther lobes generative nucleus Stamen with upper half of anther cut off Side view of a stamen Mature pollen grain Pollen grains Filament Anther Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 22 April 2017 6

Stamen Structure Function Stamen consists of an anther and a filament holds the anther in a suitable position to disperse the pollen Anthers produces pollen grains. When it matures, it splits open to release the pollen grains. Pollen grain contain the male gametes

Parts of a Carpel stigma Carpel The female part of a flower. All the carpels together make up the pistil. . A carpel consists of: - an ovary; a style above the ovary; and one or more stigmas. style ovary Side view of a carpel Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 22 April 2017 8

Carpel Structure Function Stigma It receives the pollen grains. The mature stigma secretes a sugary fluid that stimulates the pollen grains to germinate Style connects the stigma to the ovary Ovary contains one or more ovules

Pollination Pollination is the transfer of pollen grains from the anther to the stigma. Pollination is usually brought about by insects or wind. There are two types of pollination: a) Self-pollination b) Cross-pollination Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.

Self-Pollination Self-pollination: Pollen grains are transferred to the stigma of the same flower, or a different flower of the same plant. Features of plants that self-pollinate Bisexual flowers with anthers and stigma maturing at the same time. Stigma is found directly below the anthers. Plants with closed bisexual flowers transfer of pollen grains anther stigma Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.

Self-pollination Advantages Only one parent plant is required Beneficial qualities are passed down from parent plants to offspring because offspring inherit the parents’ genes Not dependent on external factors to pollinate Less pollen is wasted Disadvantages Less varieties of offspring produced since they are genetically similar to the parents. Hence, reduces the chance of the species surviving changes in the environment may lead to the offspring becoming weaker, smaller and less resistant to diseases.

Cross-Pollination Cross-pollination: Pollen grains are transferred to a flower in another plant of the same kind of species. Features of cross-pollinated plants: Have either male or female flowers. Anthers and stigmas of bisexual flowers mature at different times. Stigma of bisexual flowers may be located some distance away from the anthers . Plant A anther transfer of pollen grains stigma Plant B

Cross-pollination Advantages Offspring can inherit beneficial qualities from both parents. More varieties of offspring are produced. This increases the chances of the offspring surviving changes in the environment. More viable seeds that are capable of surviving longer before germination are produced. Disadvantages Require two parent plants Require external factors, like insects or wind More pollen is wasted

Insect pollinated plants Features Reasons Large petals To provide a landing platform for insects to rest Brightly-coloured; fragrant; presence of nectar To attract the insects Nectar guides To lead insects to the nectar Pollen grains with rough surface To cling on insects’ bodies Stigmas are sticky To be able to retain pollen grains settling on them from insects

Wind pollinated plants Features Reasons Protruding, large, feathery stigma To provide a large surface area to capture windborne pollen grains Long filament with protruding anthers To allow pollen grain to be carried away by wind Pollen grains are light and smooth To be carried away easily by the wind

Comparisons between insect-pollinated and wind-pollinated flowers Feature Insect-pollinated flowers Wind-pollinated flowers Petals large with brightly-coloured petals small and dull-coloured, without petals Nectar Present. Absent. Scent Fragrant and sweet-smelling Scent is absent. Stigmas small and compact and do not protrude out of flowers Protruding, large and feathery Stamens Not pendulous and do not protrude out of flower Long and pendulous filaments with protruding anthers Pollen Fairly abundant. Pollen grains are larger with rough surfaces. More abundant. Pollen grains are tiny with smooth surfaces. Nectar guides Absent Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.

Fertilisation One male gamete fuses with the ovum to form a zygote. The other male gamete fuses with the definitive nucleus to form an endosperm nucleus.

Fertilisation When a pollen grain germinates on the stigma, a pollen tube grows out of it. The pollen tube grows right through the style into the ovary. The pollen tube enters the ovule through an opening in the ovule wall called the micropyle. The tip of the pollen tube bursts, releasing the two male gametes into the ovule. One male gamete fuses with the ovum (female gamete) to form a diploid zygote. The other male gamete fuses with the definitive nucleus to form the endosperm nucleus. germinating pollen grain style stigma pollen tube ovary wall definitive nucleus male gametes ovule ovum (egg) micropyle funicle placenta

- Pollen grain settles on stigma and stigma secretes sugary fluid. - Pollen grains germinates. - Pollen grain produces a pollen tube. - Pollen tube grows through the style, into the ovary. - Pollen tube enters the ovule and releases two male gametes - One male gamete fuses with the ovum to form a zygote. - The other male gamete fuses with the definitive nucleus to form the endosperm nucleus

What happens after fertilisation? The ovule develops into the seed The ovary develops into the fruit The zygote develops into the embryo When the seed germinates, embryo develop in the new plant