sexual reproduction in flowering plants gr.11

8/2/2019 Sexual Reproduction in Flowering Plants Gr.11

http://slidepdf.com/reader/full/sexual-reproduction-in-flowering-plants-gr11 1/23

Sexual reproduction in flowering

plants



Objective

• To explain the advantage and disadvantage of

sexual reproduction



Flowering plants reproduce sexually as well as

asexually.

Sexual reproduction is by means of flowers.

Flowers make gametes. Some flowers make

both male and female flowers, that is , a large

number of flowers are hermaphrodites.



Parts of a flower



• Pedicel – flower stalk.

• Sepals- protect the flower while it is a bud. Normally

they are green. Sepals make the calyx. In flowers like

Hibiscus an outer whorl of epicalyx is also present.

• Just inside sepals are petals. Form corolla of the flower.

They are often brightly colored. Petals of some flowers

have lines running from top to bottom. These lines arecalled guide-lines, because they guide the insects to

the base of the petal. Here, there is a gland callednectary. Nectary makes a sugary liquid called nectar,which insects feed on.



• Inside petals are stamens. These are the male

parts of the flower. Each stamen is made up of a

long filament, with an anther at the top.

• The anthers contain pollen grains, which contain

the male gamete.

• The female part of the flower is in the centre. It

consists of one or more carpels.• A carpel contains an ovary. Inside the ovary are

many ovules, which contain the female gametes.



• At the top of the ovary is the style, with a

stigma at the tip.

• The function of stigma is to catch pollen

grains. The female parts of different kinds of

flower vary. One main difference is the

arrangement of the ovules in the ovary.



Advantages

• There is variation in the offspring ,so

adaptation to the changing environment islikely.

• Enabling the survival of the species-newvarieties can be created which may be

resistant to disease.

•

In plants seeds are produced which allowdispersal away from the parent plant ,reducing

competition.



Disadvantages

• Two parents are needed.

• Growth of a new plant to maturity from a

seed is slow.



Objective

• Can explain fertilization in flowering plants.



• In flowering plants, the male gamete is in the pollen grainand female gamete is in the egg cell or ovule.

• The pollen grain absorbs liquid from the stigma and growspollen tube.

•

This tube grows down in to the ovary where it enters in to asmall opening called micropyle.

• The nucleus of the pollen grain travels down in to thepollen tube and enters the ovule where it combines withthe nucleus of the egg cell.

• Each ovule needs its own pollen grain and pollen tube tobe fertilized.

• Chemical signals released by the stigma make sure thatpollens landing on the stigma is of same species.



Fruit and seed formation

• The zygote divides many times and produces aminiature plant called embryo.

• The sepals and petals wither away and may falloff.

• The stamens, style and stigma wither away sothat only the ovaries remain on flower stalk.

• The ovary is now called a fruit. The ovary walldevelops in to a fruit which may be fleshy oredible. Example-plum or it may becomehardened or dry.[green peas]

• The ovule forms the seed.



Pollination

ObjectiveCan define pollination and the agents of

pollination.



Pollination

It is the transfer of pollen from the anther to the stem.

Types of pollination

1] Self pollination involves the transfer of pollen from theanther to the stigma of the same plant. Small numberof pollen grains need to be produced because there is

great chance of successful pollination. This increases

the chance of fertilization and seed formation but

reduces the variation in the offspring. Self pollinatedplants can not cope well with adapting to

environmental change.



2] Cross pollination involves the transfer of

pollen from the anther of a flower to the

stigma of a flower on a different plant of the

same species. This reduces the chances of

fertilization [wind pollinated flower produces

large amount of pollen because of wastage

involved], but increases variation and theability to adapt to environmental change.



Agents of Pollination

Parts of flower Insect pollination Wind pollination



Parts of flower Insect pollination Wind pollination

1. Petals Usually colored,

large, scented often

with nectaries,

guidelines etc.

Small, green or dull

in color. No scent or

nectaries

2. Anthers Stiff, firmly

attached and

positioned where

insects might brush

against them.

Anthers are held at

the middle and

hang loosely on

long thin filaments.

3. Pollen Small amounts of large, sticky grains

or covered in spikes

to attach to the

bodies of insects.

Light and producedin huge quantities.

Has tiny wings to

help the transfer

by wind.

4. Stigma Usually flat or

lobed, small

surface area inside

the flower.

Large & feathery to

give a large surface

area for the pollen

to land on, hanging

outside the flower

to catch pollen

carried by the

wind.

sexual reproduction in flowering plants gr.11

Documents