Angiosperms

  • Flowering plants; seeds are enclosed

  • Two Greek words: 

    • Angeous - vessel

    • Sperma - seed

  • Flowers - reproductive organs

  • Monocotyledons - smaller and simpler, making the structures easier to observe

  • Sepal - structure that supports the petals and protects the flower as a bud

  • Stamen - male reproductive structure of the flower

    • Parts of the stamen:

      • Anther - sac that contains the microsporangia

      • Filament - stalk that supports the anther and extends it to reach the female reproductive structure

      • Tapetum - structure that protects the microsporangia

  • The microsporangia contains diploid sporocyte cells

  • Cellulose is then replaced by the callose

  • The diploid sporocyte cells undergoes meiosis twice, producing four haploid microspores (tetrad) each having a pair of chromosome 

  • The callose is then removed, and on the surface of the cell, the sporopollenin forms

  • The tapetum releases sporopollenin, 1 area remains smooth, called the sulcus

  • These cells (microspore) then mature, and are now called the pollen grain

  • The haploid microspore undergoes mitosis, producing 2 cells; 1 separates as the generative cell and one turns into the tube cell

  • Pollen grain accumulates nutrient reserves, loses water, and goes into the resting state

  • Endothecium, which are thickened walls, form before the anther releases pollen

  • When the anther and pollen mature and dry out, the endothecium shrink, tearing open the anther and releases the pollen

  • Ovary - female reproductive structure flowers

  • Carpel - located in the center of the flower

  • Style - extends the stigma

  • Stigma - located at the tip of the style

  • Style has a central canal and the base is the ovary

  • In the young carpel, there are small outgrows that appear on the ovary walls known as the megasporangia

  • Integument - protects the megasporangia

  • Micropyle - opening; not covered by the integument

  • Megasporangia, integument, micropyle all together are known as the ovule

  • In the megasporangium,  there is 1 diploid megasporocyte that divides via meiosis, forming 4 haploid nuclei, each having a pair of chromosomes

  • These 4 cells sometimes form walls around them, forming 4 megasporocytes

  • 3 of these cells degenerate; the remaining functioning cell divides via mitosis thrice, forming 8 haploid nuclei

  • 2 of these nuclei move to the center, which are known as polar nuclei, the remaining forming 7 cells

  • These seven cells are known to be:

    • 1 egg cell

    • 2 synergid cells

    • 1 central cell (formed by the 2 polar nuclei)

    • 3 antipodial cell 

  • These cells are known as the embryo sac (female gametophyte) and are contained in the megasporangium


Pollination: happens with the help of wind, insects, or other animals; the pollen sticks to the carpel 

  • Pollen grains absorb water, making them swell

  • Pollen tube grows, containing the tube nucleus and a generative cell

  • This generative cell divides, forming two sperm cells

  • Pollen tube grows along the transmitting tissue (moist tissue inside the canal; path to the ovary) at a rate of several micrometers per minute

  • Growth is localized on the tip of the pollen tube

  • Vesicles containing wall material are in the tip

  • Cytoplasmic streaming - behind the vesicles; the sperms and the tube cells move along the cytoplasm

  • Callose - boundaries so that the cytoplasm stays close to the tip

  • The moving tube enters the base of the style and moves to one of the three ovaries

  • The tube locates the two rows of ovules, entering each ovule via the micropyle, penetrating the microsporangium

  • Tube grows into 1 of the synergid cells, releasing both sperms

  • One sperm fertilizes the egg cell forming a diploid zygote cell

  • The other sperm fuses to the two polar nuclei, forming a primary endosperm cell

  • This double fertilization is a characteristic of all angiosperms


Seed and fruit

  • Parts start to wither, then is shed

  • The ovary remains as the healthy part and is firmly attached to the stem

  • Ovules: containing 2 fertilized cells; nucleus of the primary endosperm cell divides,, forming a tissue with no cell wall

  • Zygote divides; basal and apical cells

  • Basal cell - large; produces a chain of cells (suspensor)

  • Apical cell - gives rise to the embryo

  • Suspensor transports nutrients to the young embryo

  • In monocotyledon, a single seed leaf forms (cotyledon)

  • As it enlarges, the embryo also receives nutrients from the endosperm

  • Wall slowly form on the endosperm tissue

  • Shoot tip from one side of the embryo

  • Below: stem (hypocotyl), base of the hypocotyl, there is a root protected by the root cap

  • Nutrient accumulation starts in the endosperm, when complete, water is removed, and the embryo enters a state of dormancy

  • Dicotyledons: the growing seed accumulate nutrients and absorb all of the endosperm

  • In both: integument turns into a seed coat, the ovule is now a seed

  • At the same time, the embryo releases hormones, stimulating the ovule, making it expand, making room for the enlarging ovule

  • Ovary wall expands, transforming into a fruit

  • In plant, reproduction by flower is the most efficient way