SASS Bio Reproduction in Plants Notes

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT ST ANDREW’S SECONDARY SCHOOL Secondary 4 Biology (6093) Chapters 17: Reproduction in Plants Name: _______________________ ( ) Class: _________ Date: _____________ 12. REPRODUCTION IN PLANTS Content • Asexual Reproduction • Sexual Reproduction in Plants Learning Outcomes Candidates should be able to: (a) define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent (b) define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring (c) identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one, locally available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains using a microscope (d) state the functions of the sepals, petals, anthers and carpels (e) use a hand lens to identify and describe the stamens and stigmas of one, locally available, named, wind- pollinated flower, and examine the pollen grains using a microscope (f) outline the process of pollination and distinguish between self-pollination and cross-pollination (g) compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower (h) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (production of endosperm and details of development are not required) Use the knowledge gained in this section in new situations or to solve related problems. 1

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT 17.1 Reproduction Reproduction is the process of producing of new organisms. Asexual reproduction produces genetically identical offspring from one parent by mitosis. Sexual reproduction involves the fusion of gametes to form a zygote producing genetically dissimilar offspring (since gametes are obtained through the process of meiosis), typically involving two parents. Sexual Asexual No. of parents involved Typically involving 2 parent(s)* 1 parent involved Offspring genetics Offspring are genetically dissimilar from parents Offspring are genetically identical to parents No. of offspring produced Less offspring produced in a given time More offspring produced in a given time Adapting to environmental changes Species more likely to be able to adapt to changes in the environment Species less likely to be able to adapt to changes in the environment 17.2 Parts of a Flower Part of Description petal receptacle pedicel sepal ovule ovary filament style anther stigma 2

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT flower Sepal A modified leaf that enclose and protect the other parts of the flower in the bud stage. All the sepals together make up the calyx. Petal A modified leaf that forms the most obvious part of the flower. All the petals together make up the corolla. In insect-pollinated flowers, attract insects for pollination and provide platform for insects to land. Pedicel The flower stalk. Receptacle The enlarged end of the flower stalk. Stamen The male part of the flower. It consists of: a. Anther - produces pollen grain. b. Filament - holds anther in a suitable position to disperse pollen grains. Pollen grains can be found in pollen sacs contained in the anther. Pollen grains are haploid as they are produced by meiosis. The nucleus in the pollen grain is the male gamete. Carpel The female part of the flower. It consists of: a. Stigma that receives pollen grains and secrete a sugary fluid to stimulate germination of pollen grains b. Style that holds stigma at a suitable position to trap pollen grains. c. Ovary that will develop into a fruit after fertilisation. It produces and protects one or more ovules. The ovule develops into a seed after fertilization. It produces the haploid female gamete or ovum by meiosis. 17.3 Pollination 3

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT 1. Pollination is the transfer of pollen grains from the anther to the stigma. 2. Self-pollination involves the transfer of pollen grains from the anther to the stigma of the same flower or a different flower on the same plant. a. Advantages of self-pollination includes: i. Only one parent plant is required. ii. Beneficial qualities are passed down from parents to offspring. iii. Not dependent on external factors for pollination. iv. More likely to take place since stigma is closer to anther. v. Less pollen and energy is wasted. b. Disadvantages of self-pollination includes: i. Less varieties of offspring produced. ii. The probability of harmful recessive alleles being expressed in the offspring is higher as compared with cross-pollination. iii. Species may become weaker, smaller and less resistant to changes in the environment. c. Features favouring self-pollination i. Bisexual flowers with anthers and stigma maturing at the same time ii. Stigma situated directly below the anthers 3. Cross-pollination involves the transfer of pollen grains to the stigma of a flower from another plant of the same species. a. Advantages of cross-pollination includes: i. Offspring can inherit beneficial qualities from both parents. ii. Greater genetic variation in the offspring. iii. Produces seeds that are capable of surviving longer before germination takes place. b. Disadvantages of cross-pollination includes: i. Two different plants from the same species are needed. ii. Dependent on external factors for pollination. iii. Less likely to occur as compared to self-pollination. iv. More energy and pollen are wasted. c. Features favouring cross-pollination 4

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT i. Plants bear either male or female flowers, making self-fertilisation impossible. ii. Plants bear both male and female parts/flowers but anthers and stigma mature at different times and stigmas of plants are situated a distance away from the anthers. 4. Clitoria is an insect pollinated flower. a. The calyx is made up of five green sepals. b. The calyx is enclosed by the epicalyx made up of two leaves. c. The corolla is made up of five brightly coloured petals. d. The standard petal has nectar guide to help guide insects to where the nectar is located. e. The standard petal encloses two deep blue wing petals. f. The wing petals enclose the keel petals. g. Keel petals enclose and protect the reproductive organs of the flower. h. The androecium of the flower consists of ten stamens with long filaments. Nectars are collected at the bottom of the stamen trough. Only insects with proboscis (long tubular mouth) can reach the nectar. i. The pistil or carpel is made up of a stigma, a long style and an ovary containing a row of ovules. pedicel epicalyx calyx nectar guide standard petal keel petal wing petal corolla 5

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT 5. Events taking place in the pollination of Clitoria. State two visible features which indicate that the Clitoria is pollinated by insects. 1. Brightly coloured petals to attract insects. 2. Nectar guide is present to guide insects to collect nectar. Suggest a feature of the pollen produced by this flower. Pollen grains have rougher surfaces to latch on to hairy backs of insects. The insect lands on the standard petal. The insect follows the nectar guide into the flower. The insect forces its way between the two wing petals to collect nectar. The insect’s back forces the keel petals upwards to expose the anthers and stigmas. Pollen grains stick to the hairy back of the insect. At the same time, pollen grains from another flower, previously visited by the insect, is transferred from the insect’s back to the sticky stigma. 6

6093 Biology (2022) Chapter 17 Reproduction in Plants SASS_CT 6. Ischaemum muticum is a wind-pollinated flo