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C40: Sexual Reproduction in Flowering Plants
Mr. E Murphy
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Objectives Introduction Structures and functions of a flower
Formation of sex cells or gametes Pollination Fertilisation Fruit and Seed Dispersal Dormancy Germination Stages in seedling growth
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Introduction The ability to produce offspring of the same species as the parent is one of the characteristics of life Reproduction ensures that the traits of the parent and species are transmitted to succeeding generations
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Introduction Asexual and sexual reproduction Asexual reproduction
Asexual reproduction involves only one parent Does not require meiosis Sexual reproduction Sexual reproduction involves two parents Each parent typically produces sex cells called gametes Gametes are haploid cells capable of fusion Two gametes fuse to form a diploid cell called a zygote Meiosis is essential for sexual reproduction
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Structures of a flowering plant
Sketch this diagram into your notes
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Activity/homework P 257 Q 2 a-h
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Solutions P 257 Q 2 a-h Sexual Reproduction: Flower produces gametes which fuse together to produce a new individual Asexual reproduction: Does not involve gametes. Individuals are produced from one parent plant. (clones)
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Solutions P 257 Q 2 a-h Sepal: Green coverings that protect the flower while it is still a bud Petal: brightly coloured, they attract animals to carry their pollen to other flowers Stamen: Male reproductive part, anther produces pollen Stigma: Tip of the carpel
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Solutions P 257 Q 2 a-h Ovule: Where egg develops, fertilisation occurs and seeds mature Ovary: Swollen base of the carpel, contains the ovule Pollination: Transfer of pollen grains from an anther to a stigma Fertilisation: Uniting of a sperm nucleus with an egg nucleus
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Solutions P 257 Q 2 a-h Self-pollination: Pollen is transferred to a stigma of the same flower, or another flower on the same plant Cross pollination: pollen reaches the stigma of a flower on a different plant (of same species)
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Solutions Zygote: What is formed when gametes fuse together
P 257 Q 2 a-h Zygote: What is formed when gametes fuse together Embryo: The growth of a zygote results into an embryo Seed: A miniature plant embryo) and its food store Fruit: Mature ovary or modified floral part that contains seeds
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Structures and functions of a flowering plant
Receptacle – part which the flower grows from Sepals – Green, leaf-like structures, protect flower when it is a bud Petals – Attract animals through smell, (absent) in wind-pollinated Stamens – Male part of the flower Carpels – Female part of the flower
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Formation of sex cells (gametes)
Male gamete formation Inside of anther is diploid Meiosis takes place in some of these cells producing haploid pollen grains Each pollen grain divides by mitosis to form two haploid sperm nuclei (male sex cells or gametes) (40.3) Each pollen grain has a thick outer wall called the exine Pollen grains are formed on the inside of the anther(40.4, 40.6) When they are fully developed, the pollen grains are exposed to the outside of the anther
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Formation of sex cells (gametes)
Male gamete formation Sketch into your notes
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Formation of sex cells (gametes)
Male gamete formation
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Homework P 246 c 28 Read p
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Formation of sex cells (gametes)
Male gamete formation Anther consists of four chambers called pollen sacs Inside each pollen sac are a number of diploid microspore mother cells Cells divide by meiosis to produce a cluster of four haploid cells called a tetrad Each tetrad breaks up to form four separate haploid pollen grains The pollen may divide by mitosis to produce two haploid nuclei , the tube and degenerative nuclei The tube nucleus will form the pollen tube and will then degenerate Degenerative nucleus will form the male gametes When the pollen grains have matured, the walls of the anther become dry and shrivel Results in splitting of the anther walls The pollen grains are then exposed on the outside of the anther
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Formation of sex cells (gametes)
Female gamete formation Each ovule is made up of a number of egg cells One will divide by meiosis to form a single haploid cell Cell undergoes mitosis three times to form a single large cell, containing eight haploid nuclei (embryo sac) Five of the 8 will later degenerate One of the nuclei forms a haploid egg cell and 2 of them form haploid polar nuclei in the centre of the embryo sac Egg cell and polar nuclei = female gametes
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Formation of sex cells (gametes)
Female gamete formation
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Formation of sex cells (gametes)
Development of the embryo sac Each ovary contains one or more ovules Ovule has two walls, called integuments, through which a pollen tube can enter One cell, in the ovule is called the megaspore mother cell Cell is diploid and divides by meiosis to form four haploid cells Three degenerate, the remaining one is called the embryo sac Haploid nucleus of the embryo sac divides by mitosis three times to form 8 haploid nuclei Of the eight, 5 degenerate, the three remaining form the female gametes Two of the female gametes form the polar nuclei in the embryo sac, the remaining gamete becomes the egg cell When the embryo sac is mature it forms the carpel, as shown on the next slide...
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Formation of sex cells (gametes)
Development of the embryo sac
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Formation of sex cells (gametes)
Carpel with mature embryo sac
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Pollination Pollination is the transfer of pollen from an anther to a stigma of a flower from the same species Self-pollination involves the transfer of pollen from an anther to a stigma on the same plant Self-fertilisation Cross-pollination involves the transfer of pollen from an anther to a stigma on a different plant of the same species Cross-fertilisation
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Pollination Methods of pollination Wind Animal (insect)
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Hay fever Allergic reaction to the inhalation of particles of certain harmless substances Most common allergens are pollen grains, animal skin, house dust and dust mites Symptoms include inflammation of the mucous membrane in the nose, sneezing etc. Hay fever affects up to 10 % of the population Treatments include decongestant drugs, antihistamines
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Fertilisation Fertilisation is the union of the male and female gametes to form a diploid zygote When a pollen grain lands on a stigma it is stimulated to grow A pollen tube grows down through the style towards the ovule Growth of a pollen tube is controlled by a nucleus, which degenerates when the pollen tube reaches the opening of the ovule Chemotropism The haploid generative nucleus divides by mitosis as it moves down the pollen tube, forming two haploid sperm nuclei (male gametes) Two haploid sperm nuclei move down through the pollen tube Presence of a pollen tube means that the male gametes of flowering plants can move towards the egg without the need for external water Adaptation for life on dry land
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Fertilisation Growth of a pollen tube
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Fertilisation Double fertilisation
One sperm nucleus (n) joins with the egg nucleus (n) to form a diploid (2n) zygote. Zygote will develop into an embryo (young plant) The second sperm nucleus (n) joins with the two polar nuclei (both n) to form a triploid (3n) endosperm nucleus
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Fertilisation Seed Formation
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Fertilisation Seed Formation Fertilised ovule becomes the seed
Walls of the ovule (integuments) dry up to become the wall of the seed (testa) The zygote grows by mitosis giving rise to the embryo or young plant Embryo consists of the future root (radicle) or shoot (plumule) Some embryo cells grow to form the seed leaves (cotyledons), which can store food The endosperm nucleus divides repeatedly by mitosis to produce many endosperm cells, which act as a food store, storing fats and starch Cotyledons continue to grow absorbing the endosperm Non-endospermic (broad bean) and endospermic (maize)
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Fertilisation Seed Formation Non-endospermic seed
Endospermic dicot seed
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Monocots and dicot seeds
Monocots have one cotyledon (cereals and grasses) Dicots have two cotyledon seeds Monocots differ in their method of storing food
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Fertilisation Fruit formation
As the seed develops, the surrounding ovary becomes fruit (auxins) Wall of the ovary becomes the wall of the fruit Fruits are designed to protect the seed and to help dispersal Once the fruit forms the rest of the flower parts die away and fall away
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Fertilisation False fruits
False fruits develop from other parts of a flower besides the ovary Apple is formed when the base of a flower, join together and swell with stored food Core of the apple is the ovary Strawberry is also a false fruit, as it develops from a swollen receptacle
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Fertilisation The development of a fruit without a seed is called parthenocarpy This is the form of virgin birth, as the egg is not fertilised seedless fruit can be formed genetically, either naturally or by special breeding programmes Spraying with growth regulators can also produce seedless fruit These growth regulators also cause fruits and vegetables to grow larger
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Fruit and seed dispersal
Dispersal is the transfer of a seed or fruit away from the parent plant
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Fruit and seed dispersal
Dispersal is necessary to: Avoid competition Increase chance of survival for the plants Find new areas for growth Increase number of the species Types of dispersal Wind Water Animal Self
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Dormancy Onset of dormancy
Dormancy is a resting period when seeds undergo no growth and have reduced cell activity or metabolism Onset of dormancy Growth inhibitors The testa may be impermeable to water or oxygen The testa may be too tough to allow the embryo to emerge There may be lack of suitable growth regulator needed to stimulate growth
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Dormancy Advantages of dormancy Allows plant to avoid harsh conditions
Gives embryo time to develop fully Provides time for the seed to be dispersed Maximises the growing season for the young seedling Helps survival of the species because the duration of dormancy varies
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Germination Germination is the regrowth of the embryo, after a period of dormancy, if the environmental conditions are suitable Conditions Water Oxygen Suitable temperature Dormancy must be complete Light may be required
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Germination Events in seed germination
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Germination When weighing plant material, dry weight is normally used
Changes in dry weights of germinating seeds When weighing plant material, dry weight is normally used This is weight without water Dry weight is measured by placing the plant in an oven at 100 degrees until the weight remains constant
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The Stages in Seedling growth
Cotyledons remain below soil
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The Stages in Seedling growth
Cotyledons move above the soil
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Asexual reproduction Vegetative reproduction is asexual reproduction, using part of the parent plant to produce a new individual Propagation means reproduction and vegetative means the non-flower parts of the plant New roots and shoots grow directly from part of the parent plant This occurs through mitosis, offspring are identical
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Organs of Vegetative reproduction
Stem Stem tuber e.g. potato Runner e.g. strawberry Root Root tuber e.g. dahlia Bud Bulb e.g. onion
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Organs of Vegetative reproduction
Leaf Small detachable plantlets form along the leaf
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Artificial propagation
Cuttings Layering Grafting Tissue culturing
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Comparison of Seed and vegetative Reproduction
Advantages Produces offspring similar but not identical Seeds are dispersed Seeds can remain dormant Disadvantages Long, complicated series of events necessary to produce adult plant Plants grown from seeds take many year to reach maturity
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Comparison of Seed and vegetative Reproduction
Advantages Rapid spread over short distances Simple and more reliable than reproduction by seed Useful to gardener Identical plants Quick growth at spring Disadvantages Dispersal is limited and offspring grow in clumps near parent plant All plants identical, may be susceptible to the same diseases
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Activity Revision worksheet
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Solutions 2010 HL Q13
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Solutions 2010 HL Q13
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Solutions 2009 HL Q15 a)
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Solutions 2007 HL Q14 a)
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Solutions 2006 HL Q14 a)
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Experiments Mandatory Activity 20: Investigate the effect of water, oxygen and temperature on germination Mandatory Activity 21: Investigate digestive activity during germination using starch agar or skimmed milk plates
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Experiments Mandatory Activity 20: Investigate the effect of water, oxygen and temperature on germination Will complete next week
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Experiments Mandatory Activity 21: Investigate digestive activity during germination using starch agar or skimmed milk plates Today’s class
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Experiment
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Experiments
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Experiments
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Experiments
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Revision Test Topics Nervous System The Senses
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Activity/Homework 30.3.11 Write notes on: Pollen grain development (H)
Development of embryo sac (H) Pollination
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Experiment Questions HL 2012 Q 7b v
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Experiment Questions HL 2006 Q 7b iv
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Experiment Questions HL 2012 Q 7b iii,iv
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Experiment Questions HL 2009 Q 8
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Experiment Questions HL 2006 Q 7 bii
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Solutions a) to produce pollen, reproduction
b) a-filament, b- anther, c-stigma, d-ovary, e-stamen c) wind: no bright colours, reproductive organs are on the outside d) anther, ovary
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Solutions P410 a) pollen, ovary
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