4[1].5 FORM 5


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4[1].5 FORM 5

  2. 2. LEARNING OUTCOMES• Identify male & female structure in a flower;• Describe the formation of pollen grains;• Describe the formation of the embryo sac in the ovule;• Describe the formation of pollen tube;• Describe the formation of zygote;• Describe the formation of triploid nucleus;• Conceptualise double fertilisation;• Relate the structure of a fruit to the flower parts;• Explain the importance of double fertilisation for the survival of flowering plants.
  3. 3. TH E G E N E R A L S TR U C TU R E O F A F L O WE R• FLOWER = a modified shoot which is the reproductive structure of angiosperms.
  4. 4. Petal AntherStamen Stigma Filament Style Ovary Ovul Sepal Th e S tru c tu re s O f F lo w e r
  5. 5. • Each part of the flower serves a certain function : – the pedicel supports the flower in the best position for pollination; – The petals are usually big & brightly coloured to attract insects @ birds for pollination; – The sepals protect the flower when it is still a bud.
  6. 6. • The male structure = stamen (consists of a filament & an anther).• The anther functions in producing pollen grains & is supported by the filament.• The male gametes are found in the pollen grain.
  7. 7. • The female structure = pistil (consists of stigma, style & ovary).• Inside the ovary, one @ more ovules can be found.• The female gametes @ egg cell is found in the ovule.• Pollen grain are received by the stigma.
  8. 8. THE FORMATION OF POLLEN GRAINS• Are formed in the anther.• Each anther contains 4 chambers called pollen sacs in which pollen grains are formed.• The tapetum provides nourishment to the developing pollen grains.
  9. 9. A Cross Section Of Anther
  10. 10. • Each pollen sac contains many diploid pollen mother cells  meiosis  a tetrad of 4 haploid cell  separate & become the pollen grain.• The haploid nucleus divides by mitosis to produce a generative nucleus & a tube nucleus.• Pollen grain is a microspore & not a gamete.• Male gamete are form when the generative nucleus divides.
  11. 11. Th eF o r m a t io n O f P o lle n
  13. 13. THE FORMATION OF EMBRYO SAC• Embryo sac = a structure containing the egg cell found in the ovule.• Initially, the ovule contains similar diploid cells, nucellus  one of the cells enlarges to become the embryo sac mother cell.• Embryo sac mother cell  meiosis  4 haploid cells, 3 disintegrate.
  14. 14. • The remaining cell (which represents the young embryo sac) will undergo mitosis thrice to produce 8 nuclei.• 2 of the nuclei will move to the middle of the embryo sac  polar nuclei.• Other 6 nuclei are enveloped with cytoplasm & become cells 3 antipodal cells, 2 synergids, 1 egg cell  mature embryo (megaspore containing the female gamete)
  15. 15. • Only the egg cell & the 2 polar nuclei are important in fertilisation  the other will disintegrate.• The ovule becomes enveloped by 2 layers of integuments, leaving a small opening (micropyle)  connected to the ovary by funicle.  megaspore (embryo sac containing the female gamete).
  16. 16. The Formation Of Embryo Sac
  17. 17. T h e F o r m a t io n O f
  18. 18. THE FORMATION OF POLLEN TUBE• POLLINATION = the transfer of pollen from the stamens to the stigma• Self-pollination / cross pollination• The stigma secretes a sugary liquid which stimulates germination.• The pollen germinates  a pollen tube is produces through the tissues of the style into an ovule.• The generative nucleus divides by mitosis to produce 2 male nuclei.
  19. 19. FERTILISATION• When the pollen tube arrives at the embryo sac, the tube nucleus disintegrates.• 1 of the male nuclei fuses with egg cell to form a diploid zygote  develops into embryo which consist of the radicle, plumule, & 1 @ 2 cotyledons.• The other male nucleus fuses with the 2 polar nuclei to form a triploid nucleus (3n)  endosperm (store food for the developing embryo).
  20. 20. • The ovary becomes a fruit  pericarp & the ovules become seeds.• The outer integument becomes the seed coat @ testa (to protect the seed)• The inner integument becomes tegmen, a thin membrane underneath the testa.• All parts of the flower wither away.
  21. 21. PERI CARP M ODE OF FRUI T DI SPERSAL F l e s h y, Eat e n b y an i mal s  s uccul e nt ; s e e d s ar e t h e n ed i bl e d i s c ar d e d , f ar f r o m Ho o k / s p i n e s S t i tchkes ptar efnutr. o f o p as s i n g an i mal sW n g - s h ap e d ; d r y i Eas i l y c ar r i e d b y & l i gh t ; wi n d . f e at h e r y h ai r s Fi b r ou s t i s s u e Car r i e d b y wat e r . wi t h man y ai rUn e ve s p ac e s n g o f n d r yi Se e d s d i s pe rs e d by f r u i t wal l e x p l o s i ve me c h an i s m c au s i n g s u d d e n
  22. 22. D o u b le F e r t ilis a t io n In F lo w e r in g P la n t s
  23. 23. THE IMPORTANCE OF DOUBLE FERTILISATION FOR THE SURVIVAL OF FLOWERING PLANTS• Double fertilisation is important for two reasons : • By formation of the 3n nucleus  endosperm, the parent plants provide an important nutrient store for the developing plant. • It is ensure that the nutritive tissue formed is not wasted because it will be used by the growing embryo  the endosperm only develops if the ovum has been fertilised.
  24. 24. • The provision of food for the embryo is important for the survival of flowering plants.• The presence of food enables the embryo to live for a long period of time even when conditions are unfavourable such as dry & cold conditions.• When favourable  the food in the endosperm will be broken down into simple molecules such as sugar, amino acids, glycerol & fatty acids  absorbed by the embryo to build tissues for germination.