9.4 (Plant Biology) Flashcards
Compare the vegetative and reproductive phases of the angiospermatophyta life cycle.
When a seed germinates, a young plant is formed that grows roots, stems and leave. These are called vegetative structures and plant is in the vegetative phase. This can last for weeks, months or years, until a trigger causes the plant to change into the reproductive phase and produce flowers. The change from the vegetative to the reproductive phase happens when meristems in the shoot start to produce parts of flowers instead of leaves.
State that flowers are produced from a shoot apical meristem.
Flowers are produced from a shoot apical meristem and are therefore a reproductive shoot. They are structures that allow for sexual reproduction, thereby increasing variety.
State two abiotic factors that may trigger flowering.
Temperature and day length
Compare the timing of flowering in short-day plants and long-day plants.
The length of the dark period is the main trigger for transforming a leaf-producing shoot into a flower-producing shoot. Some plants such as the poinsettia are categorized as short-day plants because they flower when the dark period becomes longer than a critical length, for example in the autumn. Other plants, such as red clover are long-day plants because they flower during the long days of early summer when nights are short.
Outline the process by which changes in gene expression trigger flowering.
Light plays a role in the production of either inhibitors or activators of genes that control flowering. For example in long-day plants, the active form of the pigment phytochrome leads to the transcription of a flowering time (FT gene). The FT mRNA is then transported in the phloem to the shoot apical meristem where it is translated into FT protein. The FT protein binds to a transcription factor. This interaction leads to the activation of many flowering genes which transform the leaf-producing apical meristem into a reproductive meristem.
State the role of the pigment phytochrome.
Leaves use the pigment phytochrome to measure the length of dark periods.
Describe the conversions between the two forms of phytochrome.
Phytochrome is unusual because it can switch between two forms, PR and PFR. During periods of light the active form of phytochrome (PR). During periods of dark the active form of phytochrome slowly reverts back to the inactive form (PFR).
Describe role of phytochrome in controlling flowering in long and short day plants.
In long-day plants, large enough amounts of PFR remain at the end of short nights to bind to the receptor, which then promotes transcription of genes needed for flowering. In short-day plants, the receptor inhibits the transcription of the genes needed for flowering when PFR. Binds to it. However, at the end of long nights, very little PFR. Remains, so the inhibition fails and the plant flowers.
Define pollination, fertilization and seed dispersal.
Pollination: pollen carried from anther of one flower to stigma of another
Fertilization: the pollen grain germinates to produce a pollen tube that carries down the two male nuclei
Seed dispersal: he scattering of seeds using other animals or mother nature (wind) to scatter the seeds
State the changes to the ovule and ovary that result from fertilization.
The fertilized ovule develops into a seed and the ovary develops into a fruit.
List mechanisms of seed dispersal.
Seeds cannot move themselves, but nonetheless they often travel long distances from the parent plant. This is called seed dispersal and it reduces competition between offspring and parent and helps to spread the species.) The type of seed dispersal depends on the structure of the fruit - dry and explosive, fleshy and attractive for animals to eat, feathery or winged to catch the wind, or covered in hooks that catch onto the coats of animals.
Define mutualism.
Both species involved in the relationship benefit from it
Explain an example of mutualism between a flowering plant and its pollinator.
Almost 3/4 of plants are pollinated by animals. The plant and animal have a mutualistic relationship which both of them benefit from. Plants receive pollen and have their pollen transferred to other plants by pollinators. Most pollinators receive nectar and pollen, forms of nutrition for them. (approximately 1/3 of the food humans eat relies on insect pollinators.)
State how plants can be manipulated to force flowering out of season.
Flower forcing is a procedure designed to get flowers to bloom out of season or at a specific time such as during holiday time. Growers can manipulate the length of the days and nights to force flowering. An example of a short day plant is chrysanthemum which flowers when nights are long, late Summer and Autumn. They can be covered to achieve longer periods of darkness (at least 12 hours) during the summer to stimulate the day and night periods of autumn. The plants will then flower in the summer.
State the function of the different parts of the seed.
Testa – an outer seed coat that protects the embryonic plant
Micropyle – a small pore in the outer covering of the seed, that allows for the passage of water
Cotyledon – contains the food stores for the seed and forms the embryonic leaves
Plumule – the embryonic shoot (also called the epicotyl)
Radicle – the embryonic root
