2Assessment Statements 9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower Distinguish between pollination, fertilization and seed dispersal Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed Explain the conditions needed for the germination of a typical seed Outline the metabolic processes during germination of a starchy seed Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.
3Flowers Reproductive structures of angiospermophytes Dependent upon animals for pollinationCan grow as large as 3 feet in diameter and weigh as much as 14.5 lbs.Rafflesia arnoldiiWhen mature, this flower smells like rotting meat thus attracting flies that transfer pollen from the male reproductive structures to the female structures
4Flower structure and function Flower partFunctionSepalsProtect the developing flower while in the budPetalsOften are colorful to attract pollinatorsAntherPart of stamen which produces the male sex cells, pollenFilamentStalk of stamen that holds up the antherStigmaSticky top of carpel on which pollen landsStyleStructure of the carpel that supports the stigmaOvaryBase of carpel in which the female sex cells develop
5Carpel (entire female part) Stamen (entire male part)Complete – contain sepals, petals, stamen, and carpalIncomplete – lack at least one partStaminate – have only stamensCarpellate – have only carpels
6Alternation of generations All plants show two different generations in their life cycle:Gametophyte generation which is haploidSporophyte generation which is diploidGametophyte generation produces plant gametes by mitosisSporophyte generation produces spores by meiosisFor example, a cherry tree is in the sporophyte form (it grew from a zygote and produces new cells by mitosis). When the cherry tree produces flowers, haploid spores are formed and develop into haploid bodies referred to as gametophytes. Sperm form within the male gametophytes, and eggs form within the female gametophytes.
7PollinationProcess by which pollen (containing male sex cells) is placed on a female stigmaFirst step towards fertilization and the production of seedsCommon vectors: wind, insects, birds, water, and other animalsMeans of attractionRed flowers are conspicuous to birdsYellow and orange flowers are noticed by beesHeavily scented flowers are easily found by nocturnal animalsPlants that rely on wind have inconspicuous, odorless flowers
8Types of pollination Self-pollination Cross-pollination Pollen from the anther of the same plant falls onto its own stigmaForm of inbreeding and results in less genetic variation within a speciesPollen is carried from the anther of one plant to the stigma of a different plantIncreases variation and may result in offspring with better fitnessProblem: distance
9FertilizationPollen grain adheres to the stigma, which is covered by a sticky, sugary substancePollen germinates to produce a pollen tubePollen tube grows down the style of the carpelWithin the growing pollen tube is the nucleus that will produce the spermPollen tube completes its growth by entering an opening at the bottom of the ovarySperm moves from the tube to combine with the egg of the ovule to form a zygoteZygote develops with the surrounding tissue into the seedAs the seed is developing, the ovary around the ovule matures into a fruitThe fruit encloses and helps to protect the seed
11The seed (means by which an embryo can be dispersed to distant locations) Seed partFunctionTestaTough, protective outer coatCotyledonsSeed leaves that function as nutrient storage structuresMicropyleScar of the opening where the pollen tube entered the ovuleEmbryo root (radicle) and embryo shoot (epicotyl)Become the new plant when germination occursPlumule will become first leaves.Hilum is where the seed was attached to the ovary.Endosperm provides nutrition for growing embryo.
12MaturationDehydration until water content of the seed is about 10% - 15% of its weightSeed enters dormancy (low metabolism, not growth or development)Adaptation to overcome harsh environmental conditionsConditions needed for germination:WaterOxygen for aerobic respirationAppropriate temperature for enzyme actionOther (testa disrupted, fire exposure)Most will not become a functional plant so plants produce large numbers of seeds
14Seed metabolism during germination Uptake of waterGibberellin is releasedGibberellin (growth hormone) triggers the production of the enzyme amylaseAmylase causes the hydrolysis of starch into maltose. The starch is present in the seed’s endospermMaltose is further hydrolyzed into glucose that can be used for cellular respiration or may be converted into cellulose by condensation reactions.Cellulose is then used to produce the cell walls of new cells being produced
15Control of flowering in angiosperms Photoperiodism – plant’s response to light involving the relative lengths of day and night (a very important factor in the control of flowering)A plant must flower when pollinators are available and when necessary resources are plentiful.Plant-typeFlowering and lightExamplesLong-day plantsBloom when days are longest and nights shortest (midsummer)Radishes, spinach, lettuceShort-day plantsBloom in spring, late summer, and autumn when days are shorterPoinsettias, chrysanthemums, astersDay-neutral plantsFlower without regard to day lengthRoses, dandelions, tomatoes
16PhytochromePhytochrome is a photoreceptor, a pigment that plants use to detect light.There are two forms: Inactive (Pr) and active (Pfr)When red light (wavelength of 660 nm) is present in available light, the inactive form Pr is converted into the active form Pfr which has the ability to absorb far-red light (wavelength of 730 nm).This Pfr is rapidly converted back to the inactive form in daylight.However, in darkness, the conversion is very slow.It is thought that this slow conversion of Pfr back to Pr allows the plant to time the dark period.
17In long-day plants, the remaining Pfr at the end of a short night stimulates the plant to flower. In this case, Pfr acts as a promoterIn short-day plants Pfr appears to act as an inhibitor of flowering. For these short-day plants, enough Pfr has been converted to Pr to allow flowering to occur.Even though the names refer to day length, it is actually the length of night that controls the flowering process.