Reproduction in Plants Flashcards
A flower consists of
an expanded stem tip, the receptacle, which usually bears four whorls (rings) of modified leaves, sepals, petals, stamens,andone or more carpels in the centre.
female parts
carpels; produce one or more ovules which contain the female gametes
male parts
stamens; these produce the pollen grains which contain the male gametes
honey guides
markings or
patterns on petals to guide
insects to the nectar
anther
produces pollen grains containing
male gametes
filament
– holds the
anther where it can best deliver pollen
stamen –
male part of the flower
composed of the anther and the filament
sepal
usually green. Protects the flower when in bud
pedicel
pedicel – the flower stalk
petal
– provides colourand scent to attract insects and birds for pollination
stigma
sticky end of the style. Catches pollen grains
style
– holds the stigma where it can best catch pollen
ovary
contains ovules
ovule
conatins an ovum, the female gamete
nectary
– at the base of the petal.
Contains nectar to attract insects and birds for pollination
receptacle
bears the flower parts
carpel
the female part of the flower
consists of the stigma, style and ovary and ovules
flower- wind pollinated vs insect polinated
- Usually small and inconspicuous.
*Usually large and conspicuous
petals- wind pollinated vs insect pollinated
- Often absent. If present they are small, green or dull coloured and have noscent, nectar or honey guides. There are no pollinating agents to attract.
*Usually relatively large, brightly coloured and scented, and have nectaries and honey guides to attract insects.
pollen grains- wind pollinated vs insect pollinated
- Small, smooth and light so they areeasily carried by the wind.
- Large quantities are produced as many are lost
*Relatively large, sticky or spiky to stickonto the body of insects.
* Smaller quantities are produced asfewer are lost
stigmas(anthers) wind pollinated vs insect pollinated
- Long, branched and feathery and hang outside the flower to provide a large area to catch the pollen grains.
- Flat or lobed and sticky, and are usually situated inside the flower sothe insect brushes against them as itgoes to get nectar and deposits pollen onto them.
wind pollinated plants
Guinea grass, maize, sugar cane.
insect pollinated plants
Pride of Barbados, flamboyant, allamanda.
mechanism of fertilisation in flowerings plants after pollination occurs
STEP 1
A pollen grain lands on the stigma.It absorbs nutrients present, swells and develops a pollen tube.
STAGE 2
The pollentube, withtwomale nuclei and a tube nucleus in its tip, grows down Through the style by secreting digestive enzymes that digest a pathway.
STAGE 3
The pollen tube grows through the ovary wall and through the micropyle of the ovule and bursts.The tube nucleus degenerates, and one male nucleus fuses with the female gamete to form the zygote. The other male nucleus and the two polar nuclei fuse to form the endosperm.
Seed development
After fertilisation, each ovule develops into a seed:
* The zygote divides by mitosis forming the embryo which develops into three parts
:the plumule or embryonic shoot
the radicle or embryonic root
one cotyledon/seed leaf in monocotyledonous seeds
or two cotyledons in dicotyledons
seed development continued
- The endosperm remains in endospermic seeds, e.g. maize and castor oil, but is absorbed by thecotyledons in non-endospermic seeds, e.g. green bean and pigeon pea. In endospermic seeds, theendosperm stores food; in non-endospermic seeds, the cotyledons store food.
- The integuments become dry and develop into thetesta, and the micropyle remains in the testa.
- Water is withdrawn from the seed and it becomes dormant
fruit development
After fertilisation, the ovary wall develops into the fruit. A fruit contains one or more seeds; thenumber depends on the number of ovules in the original ovary that were fertilised. The shape and structure of many fruits is very similar to the original ovary.
The stigma, style, stamens and petals wither and drop off. The sepals may drop off or they may remain, e.g. in eggplant.
male reproductive system- humans
The male gametes are called sperm or spermatozoa and they are produced in the testes which form part of the male reproductive system. Unlike the ovaries which are inside the female body, the testesare located outside the body in a sac called the scrotum. This keeps the sperm at a slightly lower temperature than body temperature which is essential for their proper development.
production of ova
ovary- secretes hormones and produces female gametes
At birth, each female ovary contains many thousand immature ova. Each is surrounded by a fluid filled space which forms a primary follicle. Each month between puberty at about 11 to 13 years old, and menopause at about 45 to 50 years old, one immature ovum will develop into a mature ovum. About 450 immature ova will ever mature. To produce a mature ovum, the immature ovum undergoes meiosis (see page 147). One of the four cells produced develops into a mature ovum which is released during ovulation.
Production of sperm
Sperm cells are produced continuously from puberty in the seminiferous tubules of the testes. Cells inthe tubule walls undergo meiosis andall the cells produced develop into mature sperm. These are stored in the epididymis until ejaculation
