22) Plant reproduction Flashcards
Define daily heat unit
the amount of heat a plant experiences in a day
What is the growth and development of a plant usually dependent on and why?
temperature
a set number of daily heat units are required between developmental stages
Define vernalisation
an extended period of exposure to low temperatures that stimulates flowering
What does vernalisation promote?
transcription of genes associated with flowering
What can plants measure to ensure they only flower when it is favourable to do so?
changes in the length of night and day
Describe long-day plants
flower during late spring when day length rises above a critical value
Describe short-day plants
flower as nights grow longer and day length drops below a critical value (but length of dark period is more important)
Define phytochrome
photoreceptor (light-sensitive protein) that enables plants to measure changes in day length
The conversion between two isomers enables plants to measure day length. Name these two isomers
Pr and Pfr
Describe the conversion between Pr and Pfr
Pr absorbs red light (660nm) -> Pfr
Pfr accumulates during the day, absorbs far red light (780nm) -> Pr at night
What do the relative proportions of Pr and Pfr dictate?
flowering time
Name the 7 key parts of a flower
stigma style anther petal filament sepal ovary
Where are the male gametes found in a plant?
within pollen grains
Where are the female gametes found in a plant?
in ovules
What must happen for a plant to reproduce?
pollen from the anthers on one plant must be transferred to the stigma of another plant
State 2 adaptations of insect-pollinated flowers
nectar
colourful + fragrant - attract pollinators
State 3 adaptations of wind-pollinated flowers
light pollen grains - carried easily by wind
many pollen grains produced
anthers + stigma with a large surface area hand outside the flower exposed to air currents
Name the 3 parts of an endospermic seed
embryo - formed by successful fertilisation
endosperm - food source surrounding the embryo (primarily starch)
seed coat - testa, protective outer layer
Some seeds lack an endosperm, what do they use as a food source?
cotyledons (seed leaves) which during the development of the seeds absorb food reserves from the endosperm
Describe the 4 steps of fertilisation and seed formation
- pollen grain lands on the stigma of another plant
- pollen tube grows from the grain towards the ovule
- double fertilisation: pollen tube delivers two sperm cells to the ovary at the same time
- one fertilises an egg cell forming an embryo
- nucleus of the other fuses with the two polar nuclei at the centre of the embryo sac forming the endosperm - the ovules develop into seeds and the surrounding ovary into a fruit
Define seed germination
the process by which a plant grows from a seed
Describe what happens at the beginning of germination
after a seed has been exposed to water, starch in the endosperm is hydrolysed to glucose
gibberellins initiate the breakdown of starch by inducing the synthesis of amylase
Define gibberellins
plant hormones which act as cell signalling molecules
What is seed germination dependent on?
internal and external environmental conditions which differ between species e.g. temperature, water, oxygen, and light levels
How are cereals a staple food?
the endosperm within a seed can act as a source of nutrition / carbohydrate
Suggest the implications of the increasing use of cereal crops e.g. wheat, maize and rice
global consumption may exceed production (remaining stock is utilised from previous years)
as the world’s population increases, food demand increases however, less land is available, water is limited and fertilisers and fuel costs increase
