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World of Plants Sub topic (b) Growing plants Seed structure • Plants reproduce by making seeds. • Seeds contain an embryo and a food store. • Seeds are covered by a tough seed coat. Broad bean seed - opened up Food store Embryo plant Seed coat Parts of the seed • The embryo will grow into the new plant. • The food store provides energy for the growth of the new plant. • The seed coat protects the seed while it is in the soil. Seed coat Embryo plant Food store Dissected broad bean seed Germination • Germination is the growth of a seed. • During germination, a seed uses its food store for energy. • Plants can make their own food when they have grown their first leaves. Tomato seedlings, grown from seeds Investigation • When setting up an investigation we need to change something and this is called a ‘variable’ Seeds • We start by setting up the basic apparatus • In this case it will Cotton wool look like this: Boiling tube Investigation • • • • • • • • • • • Our variables will be: Water Light Heat Oxygen So we now want our investigation to be 5 boiling tubes 1. No light 2. No water 3. No heat 4. No oxygen 5. Has all four variables (acts as the control) Results • • • • • Tube 1 ( no light) - germinates Tube 2 (no water) - no germination Tube 3 ( no heat) – no germination Tube 4 ( no oxygen) – no germination Tube 5 (control) - germinates Conditions for germination • Seeds need warmth – a minimum temperature, oxygen and water if they are to germinate. (WOW) If any one of these factors is missing, the seeds will not germinate. • (Seeds don’t need light to germinate, but new seedlings need it after germination.) Germinating broad bean seed ( it doesn’t matter which way up the seed is put- the roots will grow down and the stem will grow up!) Effect of temperature (C) • Seeds don’t germinate in cold temperatures • % germination increases the temperature rises and most germination occurs at the optimum temperature • Above the optimum temperature % germination decreases because enzymes are being denatured Structure of a Flower • Sexual reproduction occurs in plants as well as animals. • The FLOWER contains the reproductive organs of a plant. • Flowers contain the male and female sex cells for reproduction. • Flowers of different plants may not be exactly alike, but they are built to the same basic plan. Different kinds of flowers Epiphyllum Maricopa A wild strawberry Flower Lily flower Stigma Anther Filament Bright petals Carpel - female part of flower 1 2 5 3 4 Stamens Anther • Stamens are the male parts of flowers - they consist of an anther and filament • The anther produces pollen grains which contain the male gamete • The filament supports the anther Filament Basic Structure of a flower 1 stigma 2 8 3 style 7 petals anther filament Ovary + ovule 6 4 5 sepals nectary Function of flower structures Structure Function Sepal 1 Protects the flower when it is in bud Petal Attracts insects to flowers by their bright colour 2or scent 3 Nectary Contains sugary liquid called nectar Stamen -Anther 4 Makes pollen grains, which contain the male sex cell -Filament Carpel -Stigma Supports the anther 6 -Ovary -Ovules Sticky to catch 5 the pollen grains Contains ovules Contain the7female sex cell Pollen • Pollen is made inside the anther • Pollen grains contain the male sex cell Unripe Anther Ripe anther splits open releasing pollen Pollen grains from different plants Ragweed Chamomile Willow tree • Pollen grains are like thumb prints – no two are the same! Pollination •Pollination is the transfer of pollen from anther to the stigma •There are two methods of pollination •Wind Pollination •Insect Pollination Insect pollinated flower • Insect pollinated flowers have • Brightly coloured and scented petals to attract insects • Insects feed on the sugary nectar How are these flowers different? Wind pollinated flower•Wind pollinated flowers have Feathery stigmas •Small dull flowers •Stigmas and stamens hang out Large stamens hang out Methods of Pollination Insect pollination Have a 1scent Wind pollination No scent Sticky, spiky pollen Large amounts of light 2 pollen Sticky stigma inside Feathery stigmas hang 3 flower outside the flower Stamens surrounded Large stamens hang 4 by petals outside flower 5 nectar Produce Don’t produce nectar Petals large & bright Petals small 6 & dull Insect Pollination Methods(C) Structure Explanation Brightly coloured petals 1 Scented petals Nectar 3 Spiky sticky pollen Sticky stigma inside 5 flowers Stamens surrounded by petals Attracts insects Attracts insects 2 Attracts insects sticks to4insects Insects leave pollen behind when they visit a flower Insects crawl into flower to 6 get nectar and pick up pollen Wind Pollination Methods (C) Structure Explanation Petals small and dull Don’t attract insects 1 Large amounts of light pollen Easily blown in wind 2 Feathery stigmas hang out3of flower Stigmas have a large surface area to catch pollen in wind Pollen blown away in 4 wind Large stamens hang out of flower Fertilisation (C) • Once the pollen has landed on the stigma the male sex cell inside has to get to the female sex cell inside an ovule. • To do this it grows a pollen tube down through the style • The pollen tube grows through the ovary wall and into an ovule. • The male gamete travels down the pollen tube and enters ovule • In the ovule the nucleus of the male gamete fuses with the female nucleus • Each fertilised ovule becomes a seed 1 2 3 4 Seed and fruit formation. • The flower is pollinated by an insect or wind, after this the pollen tube grows and fertilisation occurs. • After fertilisation the ovule becomes a seed. • After the seed has formed the ovary wall swells up and becomes a fruit (and the petals, sepal stigma and style all die). Seed dispersal (C) • Why do plants have to disperse (scatter) their seeds? • Stops new plant having to compete with the parent plant for : • Water / Nutrients / Root space • There are three methods of seed dispersal • Wind • Animal External • Animal Internal Wind dispersal (C) • These seeds have wings or parachutes so that they can be carried away by the wind e.g. dandelion and sycamore / ash dandelion ash sycamore Animal External (C) • These seeds have hooks which attach themselves to the fur of animals. • As the animals move about the seeds fall off. • e.g. cleavers (sticky willy) Wood avens Cleavers Animal internal (C) • These fruits are brightly coloured and juicy so that they attracts animals and make them want to eat them. • The seeds are undigested by the animals and are passed out in the animals faeces. • e.g. cherry or tomato Cherry seeds in faeces Cherry seeds Plant Propagation • Plants can be propagated naturally without using seeds and sexual reproduction. The plant will make copies of itself using asexual reproduction e.g. runners or tubers . • Or propagation might be artificial - gardeners can make new plants in a way that the plant is unable to do naturally - for example, cuttings and grafting. Tuber Cutting Asexual Reproduction • Asexual reproduction is the production of genetically identical offspring from a single parent • There are two methods of natural asexual reproduction used by plants 1. Runners – e.g. spider plant / strawberry 2. Tubers – e.g. potato plant Asexual Reproduction - tubers • Tubers are underground stems or roots that are swollen with food. • Each tuber can grow into another plant the next year, using food stored in the tuber to start it off. New potato plant growing from one of last year’s tubers. New tubers will form on underground stems. tuber Asexual Reproduction -Runners • Some plants produce plantlets at the end of long stems that ‘run’ along the ground. • The plantlets will get food and water from the ‘parent’ plant until they have grown roots into the soil. • Then the stem will wither away and the plantlet will grow on its own. Spider plant runner runner plantlet Artificial Propagation • Artificial propagation is the production of plants by humans • It involves asexual reproduction and so the new plants are genetically identical • There are two methods of artificial propagation • Cuttings e.g. geranium / busy lizzie • Grafting e.g. fruit trees / rose trees Artificial Propagation -Cuttings • Gardeners can take cuttings from plants. • The plants will regrow roots if the cut end is put in moist compost or water for a couple of weeks. • Rooting powder can be put onto the cut end to encourage root growth. • Then the cutting can be planted in soil or compost. Stem cutting placed in water. Two weeks later it has grown roots. Reducing water loss • A new cutting loses water through its leaves but doesn’t have any roots to take up more water. • So gardeners often remove lower leaves from a cutting to reduce water loss. • Cuttings can be kept under a plastic bag. This reduces water loss too because it makes the air around the plant humid (damp). Artificial propagation - grafting • Grafting is a method of propagating fruit trees and rose bushes. • A cutting (scion) is taken from a delicate cultivated variety • The scion is grafted onto the root stock of a hardy variety • The join is bound together with tape Cutting (scion) Root stock Grafting scion Root stock join Advantages of Artificial propagation (C) • Once a new variety of plant has been produced by sexual reproduction it can be artificially propagated • Advantages of artificial propagation • Rapid production of new plants • All plants will have the same desirable characteristics • Sterile / weak varieties of plants can be reproduced • Rare plants can be conserved Asexual reproduction (C) • Advantages – when a plant reproduces asexually there are the following advantages • There is no variation – offspring are genetically identical (a clone) • Vulnerable stages of sexual reproduction are avoided e.g. pollination • Rapid colonisation / growth • Offspring obtain food and water from parent Clone (C) • All plants produced by asexual reproduction or artificial propagation form a clone • A clone has no genetic variation • Offspring and parent in a clone are genetically identical • Disadvantages of asexual reproduction • Overcrowding • Bad characteristics passed on • Not widely dispersed Advantages of sexual reproduction (C) • Sexual reproduction involves the fusion of gametes resulting in new genetic combinations. It has the following advantages • New varieties can be produced • Can survive a change in conditions • Seed dispersal allows plants to spread to new habitats Disadvantages of sexual reproduction (C) • Sexual reproduction can be considered to have the following disadvantages • Has vulnerable stages e.g. pollination, germination and seed dispersal which are not guaranteed to take place • Produces variation – a plant grower may want the new plants to have guaranteed uniformity ( all the same)