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Part VII : Reproduction in Flowering Plants

Flowers and Reproduction Summary (useful for revision)
Flowers and Reproduction : Questions
Laboratory work relating to this chapter

Flowers and Reproduction
Pollinating Mechanisms
Wind-pollinated flowers
Fruits and Seeds
Other Methods of Dispersal
Seed Germination
Conditions necessary for Germination
Development of the Embryo

Topic Chapters Index

 

A daisy flower head, Bristol, UK © Shirley Burchill 

The daisy is pollinated by a variety of animals
attracted by its bright yellow center and white petals

 

A passion flower, Bristol, UK © Shirley Burchill

The Passion flower has a complicated structure

 

An ornamental sweet pea flower, Bristol, UK  © Shirley Burchill

The Sweet Pea's flower structure allows only
the bee to enter

 

REPRODUCTION IN PLANTS

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The Structure of insect-pollinated Flowers

Some of these flowers have a simple structure and can be pollinated by many different types of animals. Other flowers have a more specialized structure and depend on one type of insect, or another type of animal, to pollinate them.

 

Simple Flower Structure

 Buttercup flower as seen under the binocular microscope © Shirley Burchill

Buttercup flower showing nectary as seen under the binocular microscope © Shirley Burchill

Buttercup stamens as seen under the binocular microscope © Shirley Burchill

A buttercup ovule as seen under the binocular microscope © Shirley Burchill

 

The buttercup is a good example of simple flower structure. The petals are shiny yellow and have lines on them which lead the insects towards the nectaries. These lines are called `guidelines" because they guide the insect towards the nectar.

Each buttercup flower has many stamens. When these are mature they stand upright with the anthers open. Each pollen grain is sticky and spiky which makes it easier for it to be picked up by the hairy bodies of the insects as they walk over the flower. In the center of each buttercup flower there is a large number of carpels. These are the female parts of the flower. Every carpel contains one egg (ovule). The top of the carpel is slightly pointed and covered with short, thick hairs. This is called the stigma and it is this part of the carpel which collects the pollen from insect bodies.

 

The daisy : A composite flower

The daisy is pollinated by a variety of animals which are attracted to it by its bright yellow centre and white petals. The daisy, however, is not one flower. It is made up of two types of small flowers which are arranged to give the impression of being a single flower. This makes the group of small flowers more conspicuous.

 

Complicated Flower Structure

There are many different types of complicated flowers which depend on a particular insect or another animal to pollinate them. In return the insect receives nectar and pollen, since the flower produces enough pollen for its own needs and those of' the visiting insect.

 

The Sweet Pea Flower

Many flowers have complicated structures which allow them to be pollinated by only one type of insect. The sweet pea is an excellent example. Its flower structure allows only the bee to enter because other insects do not have the correct size or mass. The petals of the sweet pea flower are not all alike. There is a large petal at the top, called the standard, and two side ("wing') petals. At the bottom of the flower there are two petals joined together to form a boat shape, called the keel.

It is inside the keel petal that the stamens, stigma and style are to be found. The nectar is stored just over the filaments of the anthers. When the bee enters the flower, its mass pulls down the keel and the anthers or the stigma move up and touch the underside of the bee's body. In this way the bee gains access to the nectar and also carries the pollen from one sweet pea flower to another.

 

Orchids

Orchid, Queensland, Australia © Shirley Burchill

 

The petals of some orchids are arranged to look like a female bee. The petals even take the shape of the antennae and wings of the insect. The flower even smells like a female bee. The male bees are fooled enough to try to mate with the orchid flower. As they do so they transfer pollen from one orchid to another.

 

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