Reproduction of Flowering Plants Flashcards
what is reproduction
it is the ability of organisms to produce a new generation of themselves
what are the two types pf reproduction
asexual - production of a new generation of the same species by one parent
sexual - production of a new generation of the same species by bringing together the genetic material of two parents
what is the similarity between sexual and asexual reproduction
- they both produce the same kind of organisms in order to prevent their species from dying out and becoming extinct
- they both result in food being produced, which is vital to feed the worlds growing population
what are the differences between sexual and asexual reproduction
number of parents:
a - 1 (all individuals can produce offspring)
s - 2 (with different genders)
processes:
a - 1 stage (mitosis, no fusion of cells, is quicker)
s - 2 stages (meiosis and fertlisation with fusion of two cells)
gamete formation:
a - no gametes formed
s - gametes formed
end result:
a - offspring are genetically identical to the parent (no variation because alleles aren’t shuffled)
s - offspring are genetically different to parents (there is variation because alleles are shuffled during meiosis and during fertilisation)
value:
a - in unchanging environments well adapted individuals are preserved and reproduction is possible where there are few or no mates
s - in changing environments individuals can adapt to new conditions
rate of reproduction:
a - faster (all individuals can reproduce)
s - slower (half of the population are males that don’t reproduce)
energy input:
a - no energy input needed, more efficient
s - energy input needed to produce gametes and find a mate, less efficient
outside agents:
a - none needed
s - pollinators needed for pollination
adaptability:
a - no
s - yes
possibility of evolution:
a - low (usually no genotype variation)
s - good (genotype variation)
what are the advantages of asexual reproduction
- all individuals can reproduce (no energy expenditure for producing gametes)
- simple and fast process (only involves mitosis)
- useful in unchanging/stable condition (if parent is well adapted then children will be too)
- favourable mutations can spread rapidly (this enables the population to adapt quickly to new environmental conditions)
what are the disadvantages of asexual reproduction
- no variation in offspring unless there is a mutation (no recombination of alleles, the population may be unable to adapt to new environmental conditions and could die out)
- overcrowding can occur (resources such as food might then be in short supply)
what are the advantages of sexual reproduction
- its the basis of evolution
- organisms have a better chance of survival (they’re able to adapt to new conditions in a unstable environment)
- can prevent the spread of disease (offspring can be genetically resistant to a particular disease)
- reduces the chance of inheriting a disease from the parent
what are the disadvantages of sexual reproduction
- high energy expenditure (special organs of reproduction need to be produced)
- reproduction process is slower (gamete production and the meeting of the gametes takes time)
- unfavourable mutations and recessive genes may be expressed in the offspring
- outside agents may be needed (like pollenators to transfer pollen in plants)
how does sexual reproduction take place
- the diploid parent produces gametes in the gonads by meiosis (the gametes are haploid - they contain half the number of chromosomes)
- the male and female gametes are brought together by pollination or mating
- the gamete nuclei then fuse (fertilisation)
- the new cell called the zygote is diploid (has both sets of chromosomes)
- the zygote grows by mitotic division into a new individual
what is the difference between the male and female gamete
male - small, and motile in animals
female - quite large and not motile
what are the gametes known as in animals
male - sperm
female - ovum or eggs
what are the gametes in plants
male - a nucleus in a pollen grain
female - an egg cell in an embryo sac
draw a diagram on sexual reproduction
page 58
what is an angiosperm
plants with flowers which produce their ovules enclosed in an ovary
what is a gymnosperm
plants with their ovules naked on a cone scale
where are angiosperms found
almost every habitat, except the open ocean, where the algae are found
what is a flower
the organ of sexual reproduction, containing the reproductive organs and often will attract pollinators
what are hermaphrodite plants
bisexual plants - they produce both male and female gametes
where are male and female gametes found
male - inside pollen grains (produced by the anthers)
female - inside ovules (found enclosed by the ovary)
label a flower
page 60 NB!!!!!!!!!!!!!
what does the carpel (female part) of the flower consist of
an ovary, style and stigma
what does the ovary contain, elaborate
the ovary contains the ovules
- each mature ovule contains a female gamete
- once the female gamete is fertilised by the male gamete the ovule will develop into a seed and the ovary will develop into a fruit
what is the style
the slender section connecting the stigma to the ovary, the style holds the stigma in the most favourable position to receive pollen.
where does the pollen tube grow
along the style towards the ovary
what is the stigma
the sticky part that receives pollen
what does the stamen (male part) of the flower consist of
the anther and the filament
what is the anther
the structure that forms pollen grains (in which male gametes are found)
what is the filament
it holds the anther in the best position for pollen to be released
what is the difference between pollination and fertilisation
pollination is the transfer of pollen from an anther to a stigma which then enables fertilisation to occur
how is pollen spread
when the anther is mature it splits open and discharges the pollen, then pollen is then carried to the stigma by various natural mean (wind and insects is most common, in plant breeding the pollination is carefully controlled y humans)
what are the two types of pollination
cross-pollination
self-pollination
explain cross-pollination
in cross-pollination the pollen is transferred from the anther of a flower of one plant to the stigma of a flower of another plant (of the same species)
cross pollination results in genetic variation in the offspring
explain self-polliantion
in self-pollination the pollen is transferred from the anther to the stigma of the same flower or to another flower of the same plant
self-pollination will not result in genetic variation in the offspring
how can self-pollination be prevented
in nature:
- in bisexual flowers the anthers ripen at different time, the anthers ripen first more often
- flowers are unisexual, they therefore cannot pollinate themselves
- the stigma is positioned above the anthers
plant breeders will remove anthers to prevent self-pollination
what is fertlisation
the joining of two haploid cells (the make gamete & female gamete to form a diploid zygote)
when does fertilisation take place in flowering plants
after pollination
explain the fertilisation process
- the pollen grain lands on the stigma
- the stigma develops a pollen tube
- the pollen tube grows along the style and into the ovule
- the pollen tube carries the male gamete
- once the male gamete enters the ovule, fertilisation can occur
- after fertilisation the development of the embryo and the seed can begin
label the pollination to fertilisation diagram
page 62
how is a seed formed
- the zygote divides multiple times due to mitosis, developing into a embryo consisting of:
- cotyledons or seed leaves
- a radical (embryonic root)
- a plumule (embryonic shoot) - the rest of the ovule develops into endosperm tissue, this is the stored food (starch, oil)
- The outer covering of the ovule thickens and hardens (forming the seed coat or testa)
how is fruit formed
while the seed is growing the ovary is too, it grows into a fruit
what are the functions of fruit
- to contain and protect the fruit
2. to help disperse the seeds from the parent plant
how many plants to humans eat
out of the 75000 edible plants, we eat 7000
what does the domestication of plants lead to
- great phenotypic changes (altered genotypes) which results in vastly improved food crops
- new varieties developing
what are wild plants
plants that grow in nature with no aid from humans (very few wild plants are now used for food source)
how did asexual reproduction improve crops
Techniques include division, grafting, using storage organs and cuttings
plants that have mutations causing a superior trait and reproduced asexually so that more plants with the superior trait can be grown
repeating the selection and elminiation of plants without the superior trait the food crop would eventually consist solely of the superior plant
explain grafting
a technique whereby the tissues of one plant are inserted into those of another so that the two sets join together
- one plant is selected for its roots (rootstock)
- the other is selected for its fruits (scion)
how does sexual reproduction improve crops
sometimes the offspring have better traits than their parents , so breeders selected these plants and planted their seeds while eliminating the seeds of inferior plants
explain cross-pollination of individuals of a species to improve crops
by cross-pollinating plants of a species new crop varieties with improved traits are produced
eventually all seeds from the plant species will produce plants with the desirable plant
what are cultivars
a plant or a grouping of plants selected for desirable characteristics that can be maintained by propagation
explain how self-pollination is used to improve crops
when a crop plant shows a new, desirable trait, to perpetuate this trait plants grown from the seeds are self-pollinated, therefore the next generation of plants will all have the desired trait
how are engineering techniques and asexual reproduction used to help solve the food crisis
plant breeders use asexual/vegetative propagation and genetic engineering techniques
what challenges does future food security pose for plant breeders
the new varieties need to be:
- even higher yielding than at present
- resistant to pests and disease
- drought resistant or regionally adapted to different environments and growing conditions
- able to use soil nutrients more efficiently
how could asexual reproduction benefit future crop production
- propagation is faster (no gamete formation)
- all plants are consistently of superior quality
- large quantities of plants can be produced cheaply
- using grafting technique fruit tress will grow more quickly (producing fruit faster)
- micro-propagation can lead to numerous identical plants being produced
why is micro-propagation favoured over traditional crop breeding
- commercially important crops can be mass propagated quickly
- disease free plants can be propagated
- propagation can take place all year round
- it may be used together with genetic engineering to propagate transgenic plants from genetically modified cells
define micro-propagation (tissue culture)
a process whereby a small amount of plant tissue is cultured in a growing medium to produce a callus and then plantlets
What is genetic engineering
the process of taking a gene (transgene) out of one organism and putting it into the DNA of another organism resulting in genetically modified organisms (GMO’s)
why is genetic engineering beneficial
- the production of a new variety with a desired trait in this way is achieved in a much shorter time compared to conventional breeding
- all organisms use the same genetic code so there aren’t any real interspecies barriers when using this type of production
what is a possible issue with genetic engineering
proteins produced by transgenes are identical to those produced in the original species because the genetic code is universal, however, the signals needed to express these genes are not universal so modifications must be made to the signals that control gene expression
give two examples of GMO’s
- Bt maize - a soil bacterium called bacillus thuringiensis that produces a protein that kills many insect pests and (especially the maize earworm) is transplanted into maize and gives them resistance to pests
- roundup ready soybeans - roundup is the bran name for a herbicide called glyphosate. A bacterial gene that is resistant to this herbicide has been transplanted into many crops, the farmer sprays the crop with glyphosate virtually all the weeds without killing the crops
what traits are biotechnologists trying to incorporate into food crop plants
- resistance against certain diseases and herbicides (eg. virus resistant sweet potato and maize in Kenya)
- increased tolerance to insect pests (white maize which has been made resistant to the stalk borer in SA)
- nutrient content enrichment (eg. proteins, vitamins, iron, zinc, carotenoids)
- increases tolerance to environmental pressure (eg. droughtguard maize is the 1st drought resistant maize)
- flood tolerance (eg. a flood tolerant rice cultivar in Asia)
- longer storage life of harvested crops (eg. strawberries)
- improved flavour
how can sexual reproduction be used to improve food crop varieties
crop breeders hybridise plants, hybrid crops are crops produced by cross-pollinating two inbred plants of dissimilar genotypes
- as the crossing results in genetic variation, the hybrid plant will express new desirable traits
- they’re not genetically modified
what improvements have been brought about by hybridisation
- plants are more vigorous (less agricultural land is needed to produce the same amount of food)
- improved disease resistance (eg. hybrid tomatoes have resistance to Fusarium wilt, a common fungal infection)
- earlier maturity and extended growing season (eg. tomatoes and strawberries)
- increased yield (eg. hybrid rice which shows a 17% yield increase over the best inbred rice varieties)
- quality improvement (eg. hybrid watermelons which have a crispy taste)
what is a polyploid plant
polyploid plants are those containing more than two homologous sets of chromosomes
how can a diploid plant develop into a polyploid
by:
- a disturbance in mitosis or meiosis during crossing of two hybrids
- its seeds being treated with the chemical colchicine
give an example of polyploidy
wheat - after millennia of hybridisation ad modification by humans what went from being diploid, to tetraploid and hexaploid
polyploidy is especially common in cultivated plant species
what are the advantages of polyploidy in agriculture
- polyploidy forms seedless varieties of fruit such as watermelons, bananas, grapes and apples
- compared to the diploid plants, polyploidy can make the:
- plants bigger and more robust
- flowers larger
- fruits bigger
what is mutation breeding
the process of exposing seeds to mutagens in order to generate mutants with desirable traits
- these plants are called mutagenic plants/seeds
where is mutagenesis most valuable
in crops with restricted genetic variability
how many plant species are currently under threat and why
60 000 to 100 000
- human population growth
- socio economic fcators
what is a seed bank
a facility used to store seeds of various wild plants and crop sin an effort to maintain biodiveristy
name two seedbanks and briefly explain them
- Kew’s Millennium Seed bank Project (in the UK) - they aimed to have conserved 10% of the worlds seed plants, mainly from dry lands by 2010. it holds seeds thought to be extinct in the wild. South Africa’s aim is to contribute 2500 of its indigenous species to MBSP focusing on: endangered species, endemic species and species that may become endangered
- The Swedish International Seed Vault (on the Svalbard Islands about 620 miles from the North Pole) - this seed bank is in a reinforced concrete tunnel, 70m into a mountain, and aims to store 4.5 million seed samples from every country in the world. the seeds are stored at -180 degrees celcius and will be viable for thousands of years
how do seed help to maintain biodiversity
they offer protection against loss of species in the wild because plant diversity has been negatively affected by factors such as:
- habitat loss
- climate change
- over-exploitaion of certain species
so to help maintain the diversity seed banks can be used to produce plants for the:
- re-establisment of damaged or destroyed habitats or ecosystems
- re-introduction of newly extinct, endangered or threatened species back into the environment
- production of plant material as a source for research of over-exploited plants
how do they esnure that genetic diversity is not lost
by storing the seeds of wild and less productive crop species as well
what is the most important source of human food in terms of plants
seeds,
the other five majors: roots, stems, leaves, flowers and fruits
whats cool about seeds
they:
- have great food value
- are very practical source of food as they’re easy to transport and store well for a long time
what 3 categories do plants with edible seeds fall into
- grains - grass like plants (maize, wheat)
- pulses - pea and bean plants (lentils, peanuts)
- nuts - any large, dry, oily seed found within a hard shell
what can the food stored in these seeds be used for
- directly as food
- for the manufacture of human food products
why are grains and pulses so important
- they form the staple diet of most of the worlds population
- they have a high nutrional value
- they are cheap
what is the value of each seed group
grains
- rich store of starch (good energy source)
- fibre (healthy bowel, preventing constipation and protecting against colon cancer)
- B Vitamins and many minerals from seed coat
- small amount of proteins and fats
pulses
- very good source of protein, minerals and vitamin B’s
- help regulate blood sugar levels
Nuts
- very good source of energy
- are rich in monounsaturated or polyunsaturated fatty acids
- supply vitamin E
Oil seeds
- rich in polyunsaturated fatty acids
- can contain omega-3 fatty acids (soya beans)
explain growth regulators
plant growth regulators are for controlling and improving the natural plant growth process to increase crop productivity
- they can either be synthetic or natural
- they can be growth promoters or inhibitors
- they include:
- auxins
- gibberellins
- cytokinin
- ethylene
- abscisic acid
- flowering hormone
how is productivty improved by plant growth regulators
- they bring about successful propagation
- increase the size of the fruit
- induce early flowering and increasing the number of flowers
- break the dormancy of some seeds
- increase the yield and oil contents of seeds and nuts
- control the ripening of some fruits
