Why Do flowers…?

Why do flowers...

Why Do Flowers Smell Fragrant, Have Bright Colours & Pollen?

Quick Answer:- To attract birds and insects which carry their pollen for fertilisation.

Perhaps the best place to start when answering this question is to clarify that a flower is part of a plant that has no other purpose than to ensure pollination. A plant, that, like all over living things from bacteria to complex life such as ourselves, wants to reproduce. Pollination is the process which enables fertilisation, the plant world’s version of sexual reproduction.

20070612-2adq8001-1However, unlike us, plants can’t simply uproot, pop down to the local bar and search for a willing mate. Instead they have evolved various methods of ensuring transportation of their pollen from male to female.

While some plants rely on the wind, or water to carry their pollen, other have evolved to attract other carriers such as insects and birds. The pollen itself is rich in protein and within the flower, nectaries secrete sweet, sugar rich nectar. Two things that birds and insects are very fond of.

20070410-IMG_5673Of course with millions and millions of flowers producing both pollen and nectar clearly they need to employ further methods to attract their preferred pollinators. Whilst we may advertise, offer coupons, discounts and special offers plants have evolved other methods.

One of these methods is the production of scent which can attract pollinators from far away and hence the reason that flowers smell. Of course they don’t always smell nice to us, they only have to smell nice to the pollinator that evolution has deemed the most successful for any given plant.

IMG_51292006As the pollinators gorge on pollen or nectar, the pollen itself sticks to the pollinators’ bodies, and in a further crafty move, the nectaries are usually located deep within the flower to ensure the pollinators have to brush past as much pollen as possible.

Thus, now laden with pollen the pollinator will travel to the next flower and when it reaches a female of the species some of the pollen it has carried with be deposited and hopefully begin fertilisation allowing the plant to reproduce.

Incidentally, wishing to avoid being eaten by animals, many plants will give off unpleasant aromas, tastes or even toxins if their leaves and stems are broken.



Why do flowers have leaves?

Quick Answer:- Flowers are parts of plants which in turn have leaves to absorb energy from the sun to produce food.

20070524-2ADQ7214When answering this question it’s important to clarify that leaves and flowers are both parts of plants. Therefore the question really should be why do plants have leaves?

The answer to this question is that leaves are designed to absorb sunlight and through the process of photosynthesis create food for the plant in the form of starch which is synthesised from water and carbon dioxide.

Leaves are therefore often broad and flat in order to absorb as much available sunlight as possible. However, water is also lost through the leaves via transpiration therefore a balance needs to be struck to ensure the plant doesn’t simply dry up and die.

20070524-2ADQ7210Leaf sizes and shapes have therefore evolved to ensure plants can flourish in their given habitats. Pine needles for example are thin and covered in a waxy substance to minimise transpiration, the wax also helps to avoid snow accumulation. Pine trees can therefore grow in areas of low water supply such as rocky mountain sides with shallow soil.

20070430-IMG_5879Plants that grow on the rainforest floor with limited amounts of available sunlight but plentiful water supply often have very broad leaves in order to absorb as much sun as possible with little fear of drying out.

Why are most leaves green? Chlorophyll is the green pigment present in leaves which absorbs light during photosynthesis.

Why do flowers droop/wilt?

Quick answer:- Because they need water and nutrients to maintain their rigidity.

It’s the turgor. Plant cells contain vacuoles which are membrane bound compartments containing water and nutrients. Turgor or turgidity describes the pressure of the contents of the cell, up to ninety percent of which can be taken up by a vacuole, pushing on the plant cell wall.

20070603-IMG_7150Whilst water can move freely in and out of the vacuole, nutrients can only move in and are then trapped. They are pushed or pumped in by molecular pumps. Through the process of osmosis water will move into the vacuole providing the concentration of nutrients is higher inside the vacuole than out. As the water enters the vacuole it increases the hydrostatic pressure, or turgor giving the plant its rigidity.

Flowers or plants that have been cut no longer receive enough energy to power their molecular pumps to replace the nutrients within the vacuole. The existing nutrients within the vacuole are exhausted, the solution becomes no more concentrate than that outside the vacuole and water no
longer enters the vacuole through osmosis. The pressure within the cell (turgor) drops and the plant loses its rigidity and droops and wilts.

So whilst a cut flower may be in a vase with plenty of water, once the nutrients are consumed water will no longer enter the cells of the flower. Using flower food in the water will replace some of those nutrients, prolonging the flower’s vase life.

Why do some flowers bloom at night?

Quick Answer:- Their preferred pollinators are nocturnal.

The flowers of some plants will only open at night as they have evolved to attract particular pollinators, usually flying insects, which are nocturnal (only active at night) such as moths.

For an explanation of a plant’s desire to attract pollinators, go to the section on ‘Why do flowers smell?’

Why do some flowers close at night?

Quick Answer:- To protect their reproductive organs.

There is no definitive answer to this one, botanists are still theorising as to the exact reasons.

The most common theories center around the idea that the plant is protecting its reproductive organs and conserving energy.

Flowers that emit scent for instance need only do so during the day if their pollinators are diurnal (active during the day.) Therefore closing their flowers will preserve scent for the following day.

Some flowers are also vulnerable to nocturnal, plant eating creatures which can damage the internal structures of the flower. Closing the flower may therefore give added protection.

Protection from cold nights and dew has also been postulated. Damage from the cold or dampness may inhibit the plant’s ability to reproduce.

The actual mechanism employed by most plants to close their flowers at night is known as nyctinasty, driven by a combination of change in light, temperature and the plant’s internal clock.