R2101 3.1 – 3.2 Functions of Flowers and Seeds Flashcards
What is fertilisation?
What is needed for process to be successful?
Fertilisation: Fusion of a male gamete from pollen with a female gamete in the ovule to produce the embryo.
For success:
- Pollen needs to be ripe to be released from the anther for pollination
- Stigma needs to be at the right stage of growth
- The pollen and stigma need to be compatible
What is a flower?
- A shoot modified evolved for the purposes of sexual reproduction
- Female sex cells are contained in the egg (ovule) – female gametes
- Male sex cells contained in the sperm – male gamete
What does moneocious mean?
Give examples.
Unisexual, having male and female organs on separate flowers on the same plant. (Male flowers are generally more conspicuous.)
- Corylus avellana*
- Betula pendula*
- Zea mays*
- Begonia rex*
What does dioecious mean?
Give examples.
Separate male and female flowers, but these occur on different plants.
- Skimmia japonica*
- Ilex aquilfolium*
- Salix alba*
- Silene dioica* (Red Campion)
What is a hermaphrodite flower?
Give examples.
Has both male and female reproductive parts in the same flower, i.e. it is bisexual.
- Rosa rugosa*
- Ranunculus repens*
What is pollination?
The transfer of pollen from the anther of the male reproductive structure to the stigma – the tip of the female reproductive structure.
What is the anther?
- Made up of four elongated lobes called pollen sacs.
- The pollen grains within ripen and the anther splits open.
What are the advantages and disadvantages of self pollination?
Advantages:
Not dependent on pollinating agents.
If a given genotype is well-suited for an environment, self-pollination helps to keep this trait stable in the species.
Disadvantages:
Lack of variation so no adaptation to the changing environment/pathogens.
Genetic defects in self-pollinating plants cannot be eliminated.
What are the advantages and disadvantages of cross pollination?
Advantages:
Increases the variation in the progeny after genetic recombination
Increases adaptability of the offspring to environmental changes
Disadvantages:
Requires agent of pollination – insect or bird/wind
Requires plant to produce structures to attract pollinators
What are the features of wind-pollinated plants?
Pollen grains are small and light
Petals small and green
Anthers tall, exposed to the wind, hinged at the mid-oint so that pollen is readily shaken out
Stigma long, and large feathery surface area to catch wind-blown pollen
No scent or nectary
How do flowers attract pollinators?
Honey guides and nectar
Scent – when their pollen is ripe many flower species secrete volatile compounds that broadcast aromas
Colour
Long anthers
Some plants have developed complex structures which prevent all but specific insects species from reaching the nectar and getting pollen deposited on them.
How do insects pollinate?
Pollen is deposited on the insect from the stamens when it visits the flower to collect or drink the nectar
It is then deposited on the stigma of the next flower it visits
Compare the adaptations of wind- and insect- pollinated plants.
Wind pollinated:
Small, inconspicuous flowers which often have green petals.
No scent or nectar.
Anthers are larger, on long filaments and loosely attached to the filament. To release pollen more easily.
Flower structure often dangles loosely, as in catkins, and stamens hang out of the flower.
Large quantities of pollen made, which is light and smooth and easily carried by wind.
Stigmas are feathery and hang outside flower to catch passing pollen grains.
Insect-pollinated:
Larger flowers with brightly coloured petals.
Scented, with nectaries and sometimes with honey guides.
Anthers normally smaller and firmly attached to the filament. Usually within the flower.
Smaller quantities of pollen produced as more efficient than wind pollination. Often rough, sticky or spiky so sticks to insects well.
Stigmas are flat or lobed and are within the flower.
How is stamen adapted for wind and bee pollination?
Wind pollination:
- huge amounts of non-sticky pollen
- anthers hinged mid-way so pollen readily shaken out
- filaments long and flexible so that anthers maybe held out in exposed position
Bee pollination:
- pollen has sticky projections to ensure contact with body of insect
- filaments stiff, to resist buffeting by insects; short, keeping anther within the corolla
How is petal adapted for wind and bee pollination?
many flowers packed into an inflorescence (to increase success rate)
a large and showy calyx or corolla (to attract bees), or smell, or scent
