Sexual reproduction in plants Flashcards
What are the male reproductive parts of a plant called?
Stamen which is made up of the anther and filament.
What are the female reproductive parts of a plant called?
Carpel which is made up of the stigma, style and ovary (ovules inside ovary)
Where are pollen grains formed?
Inside anther
What are the small leaves under a flower called?
Sepal
What is the stem called?
Peduncle
What is the function of the petals?
Colourful to attract insects, inner whorl of the flower
What is the corolla?
Collective term for all petals
What is the function of the sepals?
Protect flower when budding
What is the calyx?
Collective term for all sepals
What is the function of the receptacle?
Basal portion of a flower to which all floral parts are attached
What is the function of the stamen?
Male reproductive part and consists of anther and filament
What is the function of the anther?
Male. Pollen produced by meiosis. 4 pollen sacs which split and release pollen
What is the function of the filament?
Male. Supports the anther and transports sucrose and amino acids for pollen grain formation
What is the carpel?
Female reproductive organs of a flower. Consists of stigma, style and ovary
What is the function of the stigma?
Female. Receive pollen
What is the function of the style?
Female. Holds stigma, tube produced by pollen which goes through style to the ovary
What is the function of the ovary in plants?
Female. Contain ovules and develop into fruit.
What is the function of the ovules?
Female. Contain egg cell and after fertilisation forms seeds
What is the function of pollination?
Transfer pollen from anther to the stigma
What is the structure of wind pollinated flower?
Lots of very small, light pollen to be carried by wind
Long anther exposed to wind to blow pollen
Long stigma to catch pollen
Small green petals as no need to attract insects
No scent
No nectar
What is the structure of an insect pollinated flower?
Few large sticky pollen grains
Shorter anther and stigma within flower. Sticky stigma to collect pollen
Big and colourful petals
Has scent and nectar
What is the main energy cost of a wind pollinated flower?
Producing a lot of pollen
What is the main energy cost of an insect pollinated flower?
Colourful petals, nectar, scent
Why may wind pollinated flowers be considered more effective?
Don’t have to rely on insects. Wind is mostly present
Why may insect pollinated flowers be considered more effective?
Insects actively seek flowers
How do plants avoid self fertilisation?
Chemical/genetic incompatibility
Stigma above anther
Separate male and female plants
Reproductive organs mature at different times
Male and female reproductive organs in separate flowers on the same plant
Why would plants try to avoid self fertilisation?
Would reduce genetic variation
What is dehiscence of an anther?
When pollen is mature, the outer layers dry up and split open which releases mature pollen grains
What is the function of the tapetum in the structure of an anther?
Food store. Provide food and energy to maturing pollen
What is the function of the epidermis and fibrous layer in the structure of an anther?
Protective layers
How are pollen grains formed?
Mitosis –> Pollen mother cell (2n) –> meiosis –> 4 haploid microspores (m) –> separate and harden –> 4 x pollen grains –> mitosis –> two haploid nuclei per pollen grain (generative nuclei - male gamete and tube nuclei)
What is a tetrad?
4 haploid microspores
What is the order of ovule production?
Mitosis –> megaspore mother cell (2n) –> meiosis –> 4 x haploid nuclei –> 3 degenerate –> 1 x haploid nuclei –> mitosis (x3) –> 8 x genetically identical haploid nuclei
What is the arrangement of the 8 haploid nuclei in the embryo sac inside the ovule?
3 at the top - antipodal cells
2 in the middle - 2 x polar nuclei
3 at the bottom - egg in the middle and 2 synergids either side
What is the structure of an ovule?
Micropyle - entry point for pollen tube
Integuments - walls of ovule
Nucellus - cells provide nutrients for growth of ovule
Embryo sac contains the haploid nuclei
What is the first stage of double fertilisation?
Pollen lands on stigma of same species plant. A sugary solution causes pollen to germinate and form a pollen tube
What is the second stage of double fertilisation?
The pollen tube secretes hydrolytic enzymes (cellulase and protease) as it grows. Digest and gain nutrients from style. Tube nucleus codes for enzyme production
What is the third stage of double fertilisation?
Pollen tube grows down the style following a gradient of chemoattractants secreted by the ovule (GABA)
What is the fourth stage of double fertilisation?
Behind the tube nucleus, the generative nucleus divides by mitosis to produce two male haploid nuclei. Tube nucleus precedes the growth of the two male haploid nuclei and controls growth of pollen tube
What is the fifth stage of double fertilisation?
Pollen tube reaches ovary through micropyle. Tube nucleus disintegrates and the tip of the pollen tube bursts releasing the two male gametes into the embryotic sac
What is the sixth stage of double fertilisation?
One male gamete fuses with egg nucleus to form a diploid zygote
What is the final stage of double fertilisation?
One male gamete fuses with polar nuclei to form a triploid endosperm nucleus which then divides by mitosis to form the endosperm tissue (food source)
What happens to the ovule after fertilisation?
Turns into a seed
What happens to the zygote after fertilisation?
Divide by mitosis to become an embryo
What happens to the ovary after fertilisation?
Develop into seeds
What happens to the integuments after fertilisation?
Become the testa (seed coat)
What happens to the micropyle after fertilisation?
Becomes a hole in testa
What is the radicle?
Embryo root
What is the plumule?
Embryo shoot
What is a cotyledon?
Food store for seed
How have plants/seeds adapted to disperse via wind dispersal?
Seeds have attachments to catch wind e.g. integuments in sycamore or feathery attachments in dandelion seeds
How have plants/seeds adapted to disperse via water dispersal?
Seed contains air so are buoyant e.g. coconut
How have plants/seeds adapted to disperse via animal dispersal?
Seeds surrounded by fruit so are eaten and secreted e.g. blackberries
OR
Have attachments like hooks to latch onto animal e.g. burrs
How have plants/seeds adapted to disperse via mechanical dispersal?
Plants have explosive dispersal methods to shoot seeds away from parent plant e.g. squirting cucumbers
What is the difference between pollination and dispersion?
Pollination is pre fertilisation
Dispersion is post fertilisation
What are monocotyledons?
Have one cotyledon. Main food store is the endosperm. Ovary wall still present so technically fruit though referred to as grains e.g. cereal, maize, rice
What are dicotyledons?
Have two cotyledons which act as a food store. Some are able to photosynthesise. No endosperm e.g. broad bean
What conditions are needed for germination?
- Water to rehydrate seeds. Crack open seed coat so roots can grow and allows hydrolytic enzymes to work
- Oxygen. Respiration for ATP - metabolism and growth
- Optimum temperature for enzymes that are involved with germination
What are the stages of germination in a broad bean?
- Water triggers hydrolysis of food reserves which pass to growing tips
- Tissue swells and testa splits
- Aerobic respiration of sugars allow radicle (root) to grow
- Once radicle has emerged it channels minerals and water to plumule. Plumule is bent in a hook so the tip isn’t damaged when pushing up through the soil
- Plumule breaks through soil and unfurls, beginning photosynthesis. Cotyledons remain underground
What is the aleurone layer?
The outer endosperm layer of a seed
How is gibberellin used in plant germination?
Water imbibed through micropyle. Cotyledons swell and testa splits allowing more O2 in for aerobic respiration
Rehydration activates a gene in the embryo that codes for gibberellin synthesis. The gibberellin diffuses into the aleurone layer which contains proteins
Gibberellin induces synthesis of amylase (hydrolytic enzymes)
Amylase breaks down starch in the endosperm into maltose
Maltose converted to glucose
Glucose used in respiration to allow growth of radicle and plumule
What does imbibed mean?
Absorbed/taken in
What is gibberellin?
A plant hormone that induces the synthesis of amylase
