Lorraine Kuun, July 2011. The stamens are the male organs and produce pollen that contain the male gametes The pistil with the stigma, style and

FLOWERS AS REPRODUCTIVE

STRUCTURES

Lorraine Kuun, July 2011


The Angiosperm flower

Male and female whorls

The stamens are the male organs and produce pollen that contain the male gametes

The pistil with the stigma, style and ovary is the female organ of the plant. The ovulums are found in the ovule.


POLLEN, BEARERS OF MALE GAMETES

Stamens consist of an anther with a filament.

The anther produces pollen in the pollen sac.

The pollen grains contain the male gametes.



POLLINATION is the transfer of ripe pollen from the anther to a receptive stigma of a flower of the same species




1. Self pollination 2. Geitonogamy 3.Cross-pollination

POLLINATORS Most pollinators are

insects e.g. Bees, moths, butterflies, beetles.

Some vertebrates also pollinate flowers e.g. Bats, mice, birds (mainly).

Many flowers are pollinated by wind.



Bright colours (bees cannot see red), white for night pollinators e.g. moths

Often sweet scent (attracts moths and butterflies)

Reward of nectar and pollen Contrasting markings on petals to locate

centre of flower (usually not visible to human eye – ultraviolet)

Pollen cling to hair on insect bodies

Flower adapted for insect pollination



Adaptations of Salvia for insect pollination by bees

Landing platform

Nectar guides

Tubular shape, contains nectar

Stamens form “lever”

Pistil overhanging landing platform

Bees attracted to blue and yellow flowers


High yield of dilute nectar Bigger than most insect-pollinated flowers Open in daytime, often red Sturdy against rough feeding of birds Little or no scent – birds have poor sense of

smell Protect ovary against beaks by being inferior or

by partition Pollen sticks together in clumps Often erect or with landing platform for birds

that do not hover

Adaptations of flowers for bird pollination


Adaptations of Strelitzia for pollination by birds

Bright colours

Nectaries

Sturdy landing platform

Stigma close to pollen

Stamens fused in tube to fit beak





Flowers do not have scent, nectar or brightly coloured petals – no need to attract pollinators.

Flowers high on plant to be exposed to wind.

Flowers usually small and reduced, lacking calyx or corolla (sepals and petals).

Anthers large and well-exposed. Masses of light, non-sticky pollen produced. Stigmas long and feathery with large area

for trapping pollen.

Adaptations for wind pollination



The pollen grain germinates Meiosis occurs in the

pollen grain.

The male gametes are haploid.

When the ripe pollen grain lands on a receptive stigma, it will germinate.

The pollen grain germinates and form a pollen tube.



The germinated pollen grain is the male gametophyte

The female pistil The ovary contains

the ovule(s) with female gametes (n).

The pollen tube grows down the style, through the micropyle and into the embryo sac.

Double fertilisation occurs.



The female gametophyte: germ sac with 8 nuclei


The ovary develops into the fruit, the ovule into the seed.

The fruit develops from the following layers:

• Fruit wall from ovary wall.

• Seed from ovule.


A SEED … A seed

consists of a

1. Seed coat – outer layer of ovule (pericarp).

2. Embryo – from fertilisized egg cell (zygote undergoes mitosis).


A SEED …Endosperm – result of double fertilization. Endosperm is food for embryo – also why we eat seeds for food.


When a seed germinates The cotyledons

contain food for the embryo in some seeds.

In beans the cotyledons are responsible for photosynthesis after germination before first leaves are formed.



Plants can be dicots or monocots

MONOCOTYLEDON


Plants can be dicots or monocots

DICOTYLEDON

Resistant to unfavourable conditions as they have seed coat.

Can be dispersed effectively (see later). Can remain viable in dormant state for long

periods. Seeds have stored food reserve in endosperm

or cotyledons; includes starch, oils and or protein.

Important to man as they are cheap form of plant propagation, way to store plants and are a store of food.


Significant features of seeds


Dormancy is a state of rest. Embryo inactive, seed will not germinate.

Some plants have obligatory period of dormancy – seed will not germinate even if conditions are favourable.

Dormancy prevents seeds from hatching in wrong season when seedlings would be exposed to unfavourable conditions. Allows seeds to survive unfavourable conditions.

Allows for seed dispersal agents to act.

Why is dormancy important?


Wind – seeds are light with plumes or wings.

Animals – hooks and thorns – cling to wool, stick in paws.

Animals – edible fruit – seeds egested in different position.

Water – seeds contain oil or air bubbles – float away.

Self-dispersed – fruit dry, dehiscent.

Agents for seed dispersal


SEEDS NEED TO BE DISTRIBUTED BY DIFFERENT AGENTS


SEEDS NEED TO BE DISTRIBUTED BY DIFFERENT AGENTS

COCO DE MER drifts along ocean currents

SEEDS AND FRUIT PROVIDE US WITH FOOD


Most important plant source of food for humans.

Practical form of food – easy to transport and store for long periods of time.

Grains – wheat, maize (mealies), sorghum, rice, oats; mainly starch

Pulses (legumes) – beans, peas, soy beans, peanuts, lentils, plant proteins

Nuts – oily seeds in hard shells e.g. walnuts, cashews, pecans etc.


Seeds as a source of food


Many plant species under threat. Seed bank stores seeds of wild plants and crops. UK – conserves seeds of about 10% of wild plant

species at Kew – Millennium Seed Bank Project. Swedish International Seed Vault – reinforced

concrete tunnel – 4,5 million seed samples – will remain viable for 1000’s of years.

MSBP working with SA National Biodiversity Institute – contributing 2500 indigenous species – endangered, endemic, over-exploited

Use of seed banks to maintain biodiversity


Offer protection against loss of species in wild due to:

1. Habitat loss – agriculture, development of cities, building of dams, large-scale ecological disasters etc.

2. Climate change3. Over-exploitation of certain species

How do seed banks contribute to maintain biodiversity?


Can be used to 1. re-establish damaged, lost

habitats and ecosystems2. re-introduce extinct,

endangered or threatened species

3. provide research material

SEED BANKS ...

CONFUSION ABOUT FRUIT AND VEGETABLES, AND SEED


Documents

Lorraine Kuun, July 2011. The stamens are the male organs and produce pollen that contain the male gametes The pistil with the stigma, style and