Page 156 - Biology_F5

Comparative studies of natural groups of organisms

Reproduction of Pinus Once the pollen grain has landed on the
Task 3.10 female cones, the nucleus within the pollen
Watch simulations or videos showing grain divides mitotically to form a pollen
the life cycle of Pinus. tube nucleus and a generative nucleus,
which later divides by mitosis to form two
sperm nuclei. The pollen tube is formed
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The sporophyte generation is dominant, and grows, carrying the two male sperms
more pronounced, and varies in form to the archegonium and penetrate the ovule
or habit. They include shrubs and trees, via a small hole called micropyle. In female
consisting of roots, stems and leaf- cones inside the ovule, the megasporocyte
bearing branches. The gametophyte is produces four haploid nuclei through
highly reduced (only a few cells). The meiotic division. One of these cells develops
sporophyte is heterosporous, producing into megaspore and three degenerates. The
microspores, which are pollen grains nucleus of megaspore undergoes mitotic
(male gametophyte) and megaspores division to form a small female gametophyte
(female gametophyte). Male cones bear (megagametophyte) whereby two or three
microsporangium with microsporocyte, archegonia are present; each with one egg
that produce microspores by meiotic cell. During fertilisation, one of the sperms
division to produse light winged pollen fertilises the egg to form a zygote, while the
grains (microspores). These pollen other sperm degenerates. The zygote later
grains are transferred to mature female develops to form a seed embryo, which is
cones, mainly through the process called a sporophyte in resting condition (Figure
pollination. 3.28).

Seed
Stored food
Ovule
Seed coat Seed cone scale
Embryo Wing

Sporophyte Megasporangium
Microsporangium Megasporocyte
Zygote
Integument
Microsporocyte
Fertilisation Meiosis
Microspore
Microgametophyte Pollen grain
Sperm Pollen tube

Pollination
Megaspore
Archegonium
Megagametophyte

Figure 3.28: The life cycle of Pinus plant

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