LAPORAN AMALI

SB0034: GENETICS AND DEVELOPMENT

(PRACTICAL 1: DISSECTION AND OBSERVATION

OF PLANT REPRODUCTIVE ORGANS)

NAME

NURSAKINAH NAJWAH BINTI SUHAIMI

MATRIK NO.

FS11110003

DATE

05/03/2012(Isnin)

PUSAT PERSEDIAAN SAINS DAN TEKNOLOGI

UNIVERSITI MALAYSIA SABAH

Introduction

There are four main groups of terrestrial plants namely: bryophytes, pteridophytes,

gymnosperms and angiosperms. Bryophytes and pteridophytes are cryptogamic plants,

meaning they are seedless and reproduce through spores. Gymnosperms and angiosperms, on

the other hand, reproduce through seeds.

Angiosperms are also known as flowering plants and are the dominant group of plants

on Earth which reproduces by sexual means. The dominance of angiosperms on Earth today is

because of many traits that contribute to their success. These traits include the evolution of

flower for sexual reproduction, double fertilisation of gametes and the enclosure of the ovule

within a fruit (Alters and Alters, 2009).

Other than for visual pleasure, the flower is the reproductive structure of the plant that

functions as devices of sexual processes and subsequent production of propagules. Propagules

refer to structures that are involved in the propagation of a plant. The flower is the site where

gametes unite and develop into an embryo within a seed. Moreover, one of the modes of

pollination is by animals so flowers also function to attract animal pollinators by the advent of

colourful petals, sweet aromas and nectaries. Other than that, they also serve as to provide

protection to the gametes (Endress, 1996).

Flowers are categorised as hypogynous perigynous and epigynous based on their ovary

position. Hypogynous flowers have superior ovaries in which the gynoecium occupies the

highest position while the other parts are situated below it. If the gynoecium is situated in the

centre and other parts of the flower are located on the rim of the receptacle almost at the same

level, the flower is perigynous and the ovary is said to be half inferior. In epigynous flowers, the

overies are inferior, meaning that the receptacle grows upward enclosing the ovary while the

other parts of flower arise above it (Endress, 1996).

Objectives1. To explore and examine the reproductive structure and function of flowering plants.

2. To distinguish type of flowers (epigynous, hypogynous, perigynous) according to ovary

position.

Materials

Bunga Raya (Hibiscus sp.)

Bunga Tapak Kuda (Bauhinia sp.)

Bunga Kemboja (Plumeria sp.)

Apparatus

Sharp razor blade/dissecting scalpel

Method

1. The flowers provided were dissected and the structures namely the sepals, stamens and

pistils were examined. The stamens were divided into filaments and anthers. The pistils

were divided into the style, stigma and carpel.

2. The type of flower was determined based on their ovary position.

3. The observations of the dissected plants were drawn and labelled. The characteristics of

the observed flowers was compared and tabulated.

Results (Observation)

Table 1: Comparison of characteristics of flowers observed

Hibiscus sp. Bauhinia sp. Plumeria sp.

Number of petals 5 5 5

Number of sepals 5 5 5

Number of stamens Numerous 6 0

Number of carpels 1 1 0

Bilateral or radial symmetry Radial Bilateral Radial

Discussion

Flowers are complicated plant parts that have differentiated into regions with different

structures and functions. They are actually modified leaves. A typical flower has four different

kinds of whorls of modified leaves that are arranged successively on the receptacle. These are

the calyx, corolla, androecium and gynoecium. Calyx and corolla are accessory organs and are

also termed as sterile parts, while androecium and gynoecium constitutes the essential

reproductive organs (Gray, 1853).

The calyx is the outermost whorl or ring of modified leaves comprising of sepals. They

surround and enclose the growing flower parts as they mature. Structurally, they are thick,

tough and waxy to offer protection to flower buds against bacterial and fungal spores. At the

same time, they maintain a high humidity inside flower buds to deter or put off insects from

eating them (Alters and Alters, 2009). Above the sepals is the corolla, referring to the whorl of

petals. Petals are flat, thin and come in a variety of shapes and sizes. They are usually prominent

and colourful to attract pollinating animals, especially insects. The calyx and the corolla form the

perianth but for flowers in which the calyx and corolla are not distinct, they are termed as tepal

(Beentje, 2010). It was observed that all the flowers had 5 petals and that the petals of the

Hibiscus sp. was bright red, the Bauhinia sp. had bright purple petals and the Plumeria sp. had

attractive pink petals. The number of sepals is equivalent to the number of petals for all three

flowers.

Inside and above the petals are the essential floral parts are made up of gynoecium and

androecium. The floral parts where the microspores form is the androecium. It consists of the

male reproductive functional organs called the stamen, also termed as microsporophyll, which

has two main parts that is: the filament that holds up the anther and the anther that contains the

pollen ( Endress, 1996). The anther usually is made up of four pollen sacs called microsporangia

in which microspores develop into male gametophytes by gametogenesis to form pollen grains

(Mishra, 2009). The gynoecium constitutes the seed bearing, female parts of the flower where

megasporogenesis occurs and is located at the centre or summit of the flower. Its basic unit is

the carpel which is commonly referred to as the megasporophyll and consists of the stigma,

style and ovary. The style is a narrow stalk arising from the top of the ovary that bears the

stigma. The stigma is the top most structure in the carpel and forms the receptive surface for

pollen grains. At the lower part of the carpel is the ovary, which is the enlarged basal part that

bears the ovules (Alters and Alters, 2009).

The number of stamens observed on the Hibiscus sp. was numerous and was attached

directly to the stigma while the Bauhinia sp. had six free stamens and the Plumeria sp. had no

observable stamens. Both the Hibiscus sp. and Bauhinia sp. had one carpel while the Plumeria sp.

had no observable carpels. However, the carpel of the Hibiscus sp. had 5 stigmas, different from

the Bauhinia sp. that only had 1 stigma. The evolution of this structure developed by the Hibiscus

sp. is probably to increase the chances of pollination and ensure the success of its propagation.

In theory, the Plumeria sp.’s reproductive parts are located at the bottom of a very deep trumpet

inside the flower. The five petals unite into a tube with epipetalous stamens and the style is

expanded at the apex into a massive clavuncle just below the stigma with the ovaries being

superior (Rapanarivo et al., 1999). Yet, these structures could not be identified when the flower

was dissected. Since the Plumeria sp.’s reproductive parts are located deep inside the tube of the

flower, it can be concluded that the mode of pollination for the Plumeria sp. would most

probably be little bugs crawling down into the core of the flower (Haber, 1984). Both the female

and male reproductive parts are on all the flowers dissected and so they are classified as

perfect, bisexual flowers.

During the dissection of the flowers, other characteristics could be observed. The stigmas of

the Hibiscus sp. and Bauhinia sp. were sticky. This was probably the due to a substance that

contains sugar, similar to nectar which is produced by the egg cell when the plant is ripe or

ready for reproduction. After fertilisation, the production of the substance is stopped. It is

secreted by papillous cells of the pistil’s epidermis and allows pollen to stick on the stigma and

not to be blown away from a breath of wind or carried away by other insects. Moreover, it

benefits germination of pollen tube and feeds it.

In terms of symmetry, a flower may be actinomorphic (radial symmetry) or zygomorphic

(bilateral symmetry). When a flower can be divided into two equal radial halves in any radial

plane passing through the centre, it is said to be actinomorphic. When it can be divided into two

similar halves only in one particular vertical plane, it is zygomorphic. A flower is asymmetric

(irregular) if it cannot be divided into two similar halves by any vertical plane passing through

the centre ( Endress, 1996). Hibiscus sp. was observed to have radial symmetry with 5 planes.

The petals overlap, so the symmetry could not be readily seen but could be observed after closer

examination. The Plumeria sp. also had radial symmetry with 5 planes and could be observed

readily since the petals did not overlap. However, the Bauhinia sp. is zygomorphic because it had

only one plane of symmetry.

Moreover, the flowers can be classified based on the position of the calyx, corolla and

androecium in respect of the ovary on the receptacle. Flowers are described as hypogynous

perigynous and epigynous. In the hypogynous flowers the gynoecium occupies the highest

position while the other parts are situated below it. The ovary in such flowers is said to be

superior. If the gynoecium is situated in the centre and other parts of the flower are located on

the rim of the receptacle almost at the same level, it is called perigynous. The ovary here is said

to be half inferior. In epigynous flowers, the margin of receptacle grows upward enclosing the

ovary completely and getting fused with it, the other parts of flower arise above the ovary.

Hence, the ovary is said to be inferior (Mishra, 2009). Based on the definitions, the Hibiscus sp.,

and Bauhinia sp. can be classified as epigynous flowers because the ovaries of both of these

flowers are inferior. Meanwhile, the Plumeria sp. is hypogynous since its ovaries are superior

and the gynoecium occupies the highest position.

Conclusion

After the dissection practical, the reproductive structures of flowers were examined.

The functions of each structure were also explored. Based on the ovary positions with respect to

the calyx and corolla, the type of flowers was determined. Two of the flowers (Bunga Raya and

Bunga Tapak Kuda) were observed to be epigynous whereas one of the flowers (Bunga

Kemboja) were observed to hypogynous.

References

Alters, S. and Alters, B. 2009. Biology Understanding Life. (1st edition). NJ: Wiley.

Beentje, H.J. 2010. The Kew Plant Glossary. Surrey: Royal Botanic Gardens

Endress, P.K. 1996. Diversity and Evolutionary Biology of Tropical Flowers. UK: Cambridge

University Press.

Gray, A .1853. The Botical Text-Book. Michigan: University of Michigan.

Haber, W.A. 1984. Pollination by Deceit in a Mass-Flowering Tropical Tree Plumeria rubra L.

(Apocynaceae). Biotropica, Vol. 16, No. 4, pp. 269-275. Washington D.C., The Association

for Tropical Biology, Blackwell Pub. Hoboken, NJ : Wiley.

Hassan Abdullah, Shakinaz Desa and Zulkaflee Ali. 2009. College Matriculation Biology. Shah

Alam: IPTA Publication.

Mishra, S.R. 2009. Understanding Plant Reproduction. New Delhi: Discovery Publishing House

Pvt. Ltd.

Rapanarivo, S. H., Lavranos, J. J., Leeuwenberg, A. J. M., Roosli, W. 1999. Pachypodium

(Apocynaceae): Taxonomy, Ecology & Cultivation. Netherlands: Balkema.