9.3 Reproduction in Angiospermophytes

Transcription

1 9.3 Reprductin in Angispermphytes Draw and label a diagram shwing the structure f a dictylednus animalpllinated flwer Sepal Petals Cver the flwer structure while the flwer is develping Smetimes mdified int petals surrund the male and female flwer parts functin is t attract animal pllinatrs Anther Where meisis ccurs t prduce haplid pllen Filament a stalk that supprts the anther Stamen male reprductive structure cnsists f the anther and filament Pistil, r carpel Stigma Ovary Style female reprductive structure cnsists f the stigma, style and vary the surface n which pllen lands receives pllen frm the anther the pllen grws dwn t the vary where meisis ccurs t prduce haplid vules pllen grws in a tube dwn thrugh the style cnnects the stigma t the vary

2 Distinguish between pllinatin, fertilisatin and seed dispersal Pllinatin The transfer f pllen grains frm the mature anther t the receptive stigma Fertilisatin The fusin f the male gamete with the female gamete t frm a zygte Seed Dispersal Seeds are mved away mved away frm the vicinity f the parental plant befre germinatin t reduce cmpetitin fr limited resurces. Mechanisms fr this include fruits, winds, water and animals Draw and label a diagram shwing the external and internal structure f a named dictylednus seed Brad Bean - Vicia faba Testa - seed cat t prtect the plant embry and the ctyledn fd stres. Frmed frm the vule wall. Radicle - the embrynic rt. Attached t and sandwiched between the ctyledns Plumule - the embrynic stem. Ctyledns - cntain fd stre fr the seed. Tw in the seed Micrpyle - a hle in the test frm pllen tube fertilisatin, thrugh which water can enter the seed prir t germinatin. A hand lens is needed t see it. Scar - where the vule was attached t the carpel wall, r vary/ fruit.

3 Explain the cnditins needed fr the germinatin f a typical seed Many seeds have a drmant perid, in which they d nt germinate as sn as they are dispersed. This happens fr a number f reasns, including: incmplete seed develpment - the embry is immature, which is vercme in time presence f a plant grwth regulatr - such as abscisic acid, which inhibits develpment, and disappears with time impervius seed cat - eventually made permeable by abrasin with carse sil r the actin f micrrganism requirement fr pre-chilling - under mist cnditin, befre the seed can germinate, smetimes belw 5 C fr 50 days (the equivalent f winter in temperate climates Once drmancy is vercme, germinatin will ccur sme certain essential external cnditins are met water - uptake ccurs s that the seed is fully hydrated and the embry is able t be physilgically active xygen - must be present in high enugh partial pressure t sustain aerbic respiratin. Grwth requires cntinuus supply f metablic energy in the frm f ATP that is best generated by aerbic cell respiratin in all the cells suitable temperature - clse t ptimum temperature fr the enzymes invlved in the mbilisatin f stred fd reserves, translcatin f rganic slutes in the phlem, and the synthesis f intermediates fr cell grwth and develpment. Seeds als may require fire, freezing, passing thrugh the digestive system f a seed dispersing animal, washing t remve inhibitrs, light r the ersin f the seed cat Outline the metablic prcesses during germinatin f a starchy seed 1. Water absrptin, causing the testa t split, cmbined with adequate xygen and favurable temperature. Ctyledn cells are activated 2. Gibberellic acid (GA) is frmed by the embry in the embry's ctyledn

4 3. GA passes t the fd stred in the ctyledns, and stimulates the prductin f amylase 4. Starch is brken dwn int maltse, which is then brken dwn int glucse 5. Glucse is released fr energy t sustain respiratin and grwth. It may als be plymerised int cellulse fr cell wall frmatin Explain hw flwering is cntrlled in lng-day and shrt-day plants, including the rle f phytchrme Flwering Cues The blue-green pigment called phytchrme is present in very lw cncentratins, which is a highly reactive prtein. It is a phtreceptr pigment in the leaves, able t absrb light f a particular wavelength, and changes its structure as a cnsequence. Frms f Phytchrme P R is a blue pigment that mainly absrbs red light, which has a wavelength f 660nm. P FR is a blue-green pigment that mainly absrbs far-red light, with a wavelength f 730nm. This inhibits flwering in shrt day plants, and prmtes flwering in lng day plants. P R is cnverted int P FR when expsed t light (r just red light). It is cnverted back int P R in the dark, r just far-red light

5 Lng-Day Plants These blm when days are lngest and nights are shrtest, such as midsummer. They include radishes, spinach, lettuce, barley, wheat and clver. They need sufficient expsure t light. In daylight, P R is cnverted int P FR, but during the shrt night, the P FR des nt have a lng time t cnvert back int P R. At the end f the night perid, the cncentratin f P FR is high. The high P FR cncentratin is the trigger fr flwering. The shrt night is the critical element. Shrt-Day Plants These nly flwer if the perid f darkness is lnger than a certain critical length. They typically flwer in the spring r autumn when day length is shrt. In daylight r red light, P R is cnverted int P FR, which nly requires brief expsure. At the end f the night perid the cncentratin f P FR is lw, which is the trigger fr flwering. The lng night is the critical element.