Transcript Slide 1
Sexual Reproduction in Flowering Plants c) Fruit Formation & Dispersal Learning objectives • Outline fruit formation. • Outline seedless fruit production • Outline fruit & seed dispersal and give with examples of wind/water/animal/self dispersal • Explain & emphasise the need for dispersal 2 Seed formation Endospermic & Non-Endospermic Monocots & Dicots Seed Formation • The zygote grows repeatedly by mitosis to form an embryo • An embryo consists of a plumule (future shoot), a radical (future root) and cotyledons (food stores needed for germination) 3n Endosperm nucleus 2n Zygote 4 Seed Formation • The endosperm nucleus (3N) divides repeatedly to form the endosperm in endospermic seeds. This endosperm acts as a food store for the developing seed 3n Endosperm nucleus 2n Zygote • e.g. maize 5 Seed Formation • In non-endospermic seeds the endosperm is used up in the early stages of seed development so the food is stored in the cotyledons • e.g. bean 3n Endosperm nucleus 2n Zygote 6 Seed Formation Endosperm Food store for developing embryo Embryo Plumule, radicle, cotyledons Integuments, becomes the seed coat 7 Seed Formation If all the endosperm is absorbed by the developing embryo the seed is a nonendospermic seed e.g. broad bean 8 Seed Formation If all the endosperm is not absorbed by the developing embryo the seed is an endospermic seed e.g. Maize 9 Seed types and structure Plumule (immature shoot) embryo All seeds Seed Radicle (immature root) Cotyledon (food supply or seed leaf) In some seeds endosperm Food store 10 Endospermic Seed e.g. Maize Endosperm Seed coat (testa) Cotyledon Plumule – will develop into a new shoot Radicle – will develop into a new root 11 Non-Endospermic seed e.g. Broad Bean Seed coat (testa) Cotyledon Plumule Radicle 12 Non–endospermic and Endospermic seed Endosperm Cotyledon Plumule Radicle e.g. Broad Bean e.g. Maize 13 Classification of seeds Classified according to two features: 1. Number of cotyledons (Seed leaves) Monocotyledon – one cotyledon • E.g. Maize Dicotyledon - Two cotyledons • E.g. Broad bean 2. Presence of endosperm Present – Endospermic e.g. maize Absent – Non-endospermic e.g. broad bean 14 Broad Bean – Non-Endospermic Dicot Testa 2 Cotyledons 15 Differences between monocots and dicots Feature Monocot Dicot Number of cotyledons 1 2 Venation Parallel Reticulate (Net) Vascular Bundle arrangement Scattered In a ring Usually in multiples of 3 Usually in multiples of 4 or 5 16 Number of petals 17 18 Fruit Fruit formation Seedless fruits Fruit and seed dispersal Fruit Formation • The ovule becomes the seed • The ovary becomes the fruit 20 Fruit Formation • A fruit is a mature ovary that may contain seeds • The process of fruit formation is stimulated by growth regulators produced by the seeds 21 Seedless Fruits Can be formed in two ways 1. Genetically • Either naturally or by special breeding programmes • e.g. seedless oranges 22 Seedless Fruits 2. Growth regulators e.g. auxins – If large amounts of growth regulators are sprayed on flowers fruits may form without fertilisation – e.g. seedless grapes 23 Fruit and seed dispersal • Need for dispersal – Minimises competition for light, water etc. – Avoids overcrowding – Colonises new areas – Increases chances of survival 24 Types of dispersal 1. 2. 3. 4. Wind Water Animal Self 25 Methods of dispersal 1. Wind Sycamore and ash produce fruit with wings Dandelions and thistles produce fruit with parachute devices Both help to disperse the seeds more widely using wind 26 Methods of dispersal 2. Water • Light, air filled fruits that float away on water • E.g. coconuts, water lilies 27 Methods of dispersal 3. Animal Edible fruit Animals attracted to bright colours, smells and food Seed passes through digestive system unharmed E.g. strawberries, blackberries, nuts 28 Methods of dispersal 3. Animal Sticky fruit Fruits with hooks that can cling to the hair of an animal and be carried away E.g. burdock, goose grass 29 Methods of dispersal 4. Self Some fruits explode open when they dry out and flick the seed away E.g. peas and beans 30 Go to the next stage in the life cycle Dormancy & Germination Thanks to PDST biology team 31