Reproduction in

Flowering Plants

Principle Parts of Flowers

• Reproductive organs are in structures called Flowers

• Many Flowers contain male and female parts - hermaphrodite

Male Organs ♂• Male Organs are the Stamen

– Each Stamen made up of a stalk – Filament– The filament bears the Anthers– The Anthers are lobed and contain 4 Pollen

Sacs where pollen is formed

♀ Female Organs

• The Female Organs are called Carpels

– Carpels consist of Stigma, receptive to pollen– A Style connecting the Stigma to the Ovary– In the ovary, one or more Ovules develop

Where are these organs?

• Male and female organs develop at the top of the flower stalk – receptacle

• Surrounding the organs you may get:– Sepals– Petals– Nectaries

Generalised Dicot Flower

Page 4 of Sex HOP

Insect Pollinated

Wind Pollinated (Grass)

Page 6 of Sex HOP

Compare wind vs insect

Gametogenesis

Microspores Pollen

Egg Cells – megagamates

Pollination & Fertilisation

Pollination

• Before fertilisation, mature pollen needs to be transferred to the receptive Stigma

– That is POLLINATION

Pollen Germination

• After pollination Stigma secretes sucrose solution stimulating pollen to germinate

• A pollen tube grows out of a pore in the pollen grain

• Rapidly penetrates the style tissue

• Pollen tube growth is controlled by tube nucleus – located at tip of the tube

Pollen Germination

• Secretes digestive enzymes to allow penetration

• Pollen tubes are:– Positively hydrotropic– Negatively aerotropic

– When approaching ovule it becomes positively chemotropic

to a substance produced by the micropyle

Pollen Germination

Fertilisation

• The tip of the pollen tube enters the ovule through the micropyle

• Comes into contact with the embryo sac

• Male nuclei are released through a pore in the pollen tube tip

Double Fertilisation• One male nucleus fuses with egg

nucleus to form diploid zygote– Gives rise to the embryo

• Other male nucleus fuses with the 2 polar nuclei (2n fusion/diploid nucleus) to make a triploid nucleus (3n) –primary endosperm nucleus– Gives rise to the endosperm nutritive tissue

Fertilisation

Candidates should be able to draw a diagram of a broad bean (internal and external)

and label; micropyle, testa, position of radicle, plumule, cotyledons.

Candidates should be able to describe the germination of the broad bean, includingthe uptake of water and mobilisation of food reserves.

Mobilisation of food reserves during germination

• Food reserves in seeds are mainly _____

which is insoluble (why?)• The reserves must be broken down to

simpler soluble substances• They can then be transported to the

growing apex of the shoot (plumule) or root (radicle)

• Firstly, water is taken up by the seed causing tissues to swell

• The seed coat (testa) ruptures as the radicle pushes through

• Amylase hydrolyses starch

Proteases hydrolyse proteins• During germination, the cotyledons stay

underground

the plumule is bent over (hook shaped) as it pushes through the soil, protecting the tip

http://www.youtube.com/watch?v=TJQyL-7KRmw