SEXUAL REPRODUCTION IN PLANTSCAPE BIOLOGYUNIT 1MODULE 3

OBJECTIVES You should be able to: Describe the structure of the anther and the formation of

pollen grains. Make annotated diagrams of the anther. Describe the structure of the ovule and the formation of

the embryo sac. Make annotated diagrams of the ovule and embryo sac. Make drawings of the anther and embryo sac from

prepared slides. Explain how cross fertilization is promoted through non-

synchronous maturation of stamens (protogyny) and carpels (protandry), separate sexes (dioecy), insect pollination, self incompatibility and sterility.

Discuss the genetic consequences of sexual reproduction including self fertilization and cross fertilization.

GENETIC CONSEQUENCES OF SEXUAL REPRODUCTION

THE LIFECYCLE OF FLOWERING PLANTS

FLOWER STRUCTUREThe following structures are found from the outside of the flower to the inside. Sepals – small green structures, these protect the bud and are often seen

at the bottom of mature flowers. The ring of sepals forms the calyx. Petals – usually brightly coloured and scented. The ring of which is called

the corolla. Nectaries - may or may not be present. They produce a sugary substance

called nectar. Stamen or androecium is the male part of the flower. Stamens are made

up of anthers and filaments. Filament – stalk which attaches the anther to the flower. Anther – structure at the top of the stamen which produces pollen grains

(they contain male sex cells)  Carpel or gynoecium is the female part of the flower. It has three

components: Stigma – slightly swollen structure situated at tip of the carpel – this is

where pollen grains land during pollination Style – slender hollow stalk that attaches stigma to ovary Ovary – contains ovules which in turn contain female gametes.

 

FLOWER STRUCTURE – NON REPRODUCTIVE STRUCTURESThe following structures are found from the

outside of the flower to the inside.

Sepals – small green structures, these protect the bud and are often seen at the bottom of mature flowers. The ring of sepals forms the calyx.

Petals – usually brightly coloured and scented. The ring of which is called the corolla.

Nectaries - may or may not be present. They produce a sugary substance called nectar.

REPRODUCTIVE STRUCTURES – ANDROECIUM (STAMEN)Stamen is the male part of the

flower. Stamens are made up of anthers

and filaments. Filament – stalk which attaches

the anther to the flower.Anther – structure at the top of

the stamen which produces pollen grains (they contain male sex cells)

REPRODUCTIVE STRUCTURES - GYNOECIUMCarpel or gynoecium is the female part

of the flower. It has three components:Stigma – slightly swollen structure

situated at tip of the carpel – this is where pollen grains land during pollination

Style – slender hollow stalk that attaches stigma to ovary

Ovary – contains ovules which in turn contain female gametes.

DEVELOPMENT OF POLLEN GRAINS

DEVELOPMENT OF POLLEN GRAINS

Each anther has four pollen sacs. Each pollen sac has pollen mother cells. The pollen mother cells undergo meiosis to form four pollen grains.

This group of four is called a tetrad. Each grain forms a thick patterned outer wall characteristic of the species.

The outer wall or exine is made of sporopollenin which is waterproof, resistant and long lasting. They are capable of lasting millions of years and have been found in peat bogs.

The pollen grain nucleus divides into two by mitosis to form a generative nucleus and a pollen tube nucleus.

DEVELOPMENT OF OVULE 1Each ovule is attached the ovary wall at

the placenta by a funicle which is a small stalk. It is through the funicle that the ovule receives food and water.

The main body of the ovule is the nucellus.The nucellus is enclosed and protected by

integuments.There is a small hole at one end of the

ovule called a micropyle.In the nuclellus, near the micropyle, a

spore mother cell develops this is called the embryo sac mother cell.

DEVELOPMENT OF OVULE 2The embryo sac mother cell is diploid and

undergoes meiosis to produce four haploid cells. One of these haploid cells develops to form the

embryo sac. The embryo sac grows and its nucleus

undergoes mitosis until there are eight nuclei formed. Four at each end of the embryo sac.

One of the eight nuclei is the female gamete.Two nuclei go to the centre of the embryo sac

and fuse to become a single diploid nucleus.The remaining six nuclei, three at each end

become separated by thin cell walls. Five disintegrate.  

DEVELOPMENT OF OVULE - OVERVIEW

REVIEW QUESTIONS

1. With the aid of a diagram, describe the functions of the parts of a flower.

2. Make a large annotated diagram of the pollen grain sac and the carpel.

3. Describe with the aid of diagrams, the development of pollen grains and ovules.