chapter 17: reproduction in plants Flashcards
what is asexual reproduction?
- it is the process resulting in genetically identical offspring from one parent, without the fusion of gametes
> involves mitosis - offspring genetically identical to the parent are called clones
what are the advantages to asexual reproduction?
- only one parent is required
- the fusion of gametes is not required
- all the beneficial qualities are passed down to the offspring
- faster method of producing offspring as compared with sexual reproduction
- since organisms are already in a suitable habitat, they can colonise the area rapidly
what is the disadvantage of asexual reproduction?
- there is no genetic variation in the offspring
> species are not well adapted to the changes in the environment
what is sexual reproduction?
- is a process involving the fusion of two gametes to form a zygote
> produces genetically dissimilar offspring
what are the advantages of sexual reproduction?
- offspring may inherit the beneficial qualities from both parents
- there is a greater genetic variation
> species that are better adapted to changes in the environment
what are the disadvantages of sexual reproduction?
- two parents are required ( except in plants with bisexual flowers)
- fusion of gametes is required
- slower method of producing offspring as compared with asexual reproduction
what is inflorescence?
- a cluster of flowers borne on the same stalk
what are the parts a complete flower consist of?
- pedicel
- receptacle
- sepals
- petals
- stamens
- carpels (pistil)
what are petals?
(parts of a flower)
- petals are modified leaves forming the most conspicuous (obvious) part of the flower
> all petals together make up the COROLLA
in insect-pollinated flowers, petals:
- are brightly coloured to attract insects for pollination
- provide a platform for insects to land
what are sepals?
(parts of a flower)
- sepals are modified leaves which enclose and protect the other parts of the flower in the bud stage
> all sepals together are called CALYX
> sepals are usually the outermost layer of floral leaves
> some flowers have another layer outside the sepals
EPICALYX
eg. hibiscus
what is the pedicel?
(parts of a flower)
- the flower stalk
what is the receptacle?
(parts of a flower)
- receptacle is the enlarged end of the flower stalk
> which bears the other parts of the flower
what is the stamen?
- the male part of the flower
> consists of an anther and a filament
what it an anther?
(stamen)
- the anther consists of two lobes
- each lobe contains two pollen sacs
> in the pollen sacks are pollen grains produced by the anther - when the anther matures, it splits open to release the pollen grains
> anther also contains a vascular bundle
what does the carpel consist of?
- an ovary
- a style, above the ovary
- one or more stigmas
what is a stigma?
(a part of the carpel)
- it is a swollen structure at the end of the style
- receives the pollen grains
- the mature stigma secretes a sugary fluid that stimulates the pollen grains to germinate
what is a style?
(a part of the carpel)
- the stalk that connects the stigma to the ovary
> holds the stigma in a suitable position to trap pollen graisn
what is an ovary?
(a part of the carpel)
- the ovary is a structure that will develop into a fruit after fertilisation
> produces and protects one or more ovules - the ovule is the structure that will develop into a seed after fertilisation
( if carpel produce more than one ovule, more than one seed will be produced) - the ovule produces a female gamete or ovum by meiosis
> ovum is haploid - the ovule is attached to a region in the ovary called the placenta by a stalk called FUNICLE
What is pollination?
- it is the transfer of pollen grains from the anther to the stigma
> self-pollination or cross-pollination
What is self pollination?
- the transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant
What are the features favouring self-pollination?
- flowers are bisexual with anthers and stigmas maturing at the same time
- the stigma is situated directly below the anther
- in some plants with bisexual flowers, some flowers never open
> only self-pollination can occur in these flowers
What are the advantages of self-pollination?
- only one parent plant is required
- offspring inherits its genes from the parent plant
> beneficial qualities are more likely to be passed down to the offspring - does not depend on external factors
> like insects and wind for pollination - since the anthers are close to the stigmas of the same flower
> higher probability that pollination will occur as compared with cross pollination - less pollen and energy is wasted in self-pollination as compared to cross-pollination
what are the disadvantages of self-pollination?
- less genetic variation in the offspring as compared to cross-pollination
> species less well adapted to the changes in the environment - the probability of harmful recessive alleles being expressed in the offspring is higher as compared with cross pollination
- continued self pollination may lead to the offspring becoming weaker, smaller and less resistant to diseases
what is cross-pollination?
- it is the transfer of pollen grains from one plant to the stigma of a flower in another plant of the same species
what are the features favouring cross-pollination?
- plants that cannot undergo self-pollination
> DIOECIOUS PLANTS
> eg. papaya, bear either male or female flowers - in many plants with bisexual flowers, the anthers and stigmas mature at different times
- the stigma of plants with bisexual flowers may be situated some distance away from the anthers so that
> self-pollination is unlikely
what are the advantages of cross-pollination?
- offspring produced may inherit beneficial qualities from both parents
- more varieties of offspring can be produced
> greater genetic variation
> increases the chance of the species surviving changes in the environment
> any changes in the environment is less likely to destroy all the varieties in a species - increased probability of offspring being heterozygous
> the likelihood of harmful recessive alleles being expressed in offspring is lower compared with self-pollination - more viable seeds are produced
> seed are capable of surviving longer before germination
what are the disadvantages of cross-pollination?
- two parent plants are required
- it depends on external factors such as insects or wind for pollination
- since the pollen grains have to be transferred from the anther of one plant to the stigma of another plant
> lower probability that pollination will occur
> compared to self-pollination - more energy and pollen are wasted as compared with self-pollination
8 structures
what are the structures of clitoria?
(an insect polinated flower)
- CALYX
- the calyx consists of 5 green sepals - EPICALYX
- the base of the calyx is enclosed by the epicalyx
> consisting of 2 green leaves - COROLLA (region)
- the corolla consists of five brightly-coloured petals of different shapes and sizes - STANDARD PETAL
- the large, deep blue standard petal has lines on it that guide the insects to where the nectar is located
> lines are called nectar guide - WING PETALS
- two deep blue wing petals are enclosed by the standard petal - KEEL PETALS
- two small, yellowish-green keel petals are enclosed by wing petals
> the keel petals enclose the reproductive organs - STAMENS
the ANDROECIUM consists of 10 stamens with long filaments
- the filaments of 9 of the stamens are fused along most of their length to form a trough (hollow tube)
> the trough encloses the carpel
> nectar secreted by the flower, collects at the bottom of the stamens trough
> nectar can only be reached by an insect with a long tubular mouth/ PROBOSCIS (eg. bee or butterfly)
- the tenth stamen is free - CARPEL
consists of:
- stigma: the stigma is small and compact
> located at the end of the style
- style: a long, curved, hairy structure
- ovary: long and narrow with a single row of ovules
describe the pollination of clitoria.
- when an insect (eg. bee) visits a flower, it lands on the standard petal
- the insect follows the nectar guide into the flower
- the insect forces its way between two wing petals and moves in to collect the nectar
- the insect’s back forces the keel petal upwards to expose the stigma and the anthers
> the stigma and anthers brush against its hairy back
> some pollen grains from the anther sticks to the hairy insect’s back
> pollen grains on the insect’s back ( from another flower which the insect had visited earlier) are transferred to the sticky stigma - when the insect leaves the flower, the keel petals springs back to its original position
>to enclose the stamens and stigma again
- self pollination may also occur
what is the structure of ischaemum muticum?
( a wind-pollinated flower)
- pair of flowers
- the flowers occur in pairs
- each ischaemum muticum flower is enclosed by two transparent flowering bracts - upper flower (bisexual)
- it consists of an ovary with 2 long feathery stigmas, 3 stamens
>and 2 tiny structures called LODICULES at the base of the ovary
- when the ischaemum muticum is ready to reproduce,
> the lodicules swell and force the 2 flowering bracts slightly apart so that the stigmas and anthers can emerge - lower flower ( male)
- it is unisexual
> consists of only 3 stamens with long filaments and two lodicules
> male flower - spikelet
- each pair of flowers, together with a short stalk forms a SPIKELET
> at the base of each spikelet is a pair of non-flowering bracts
> they protect the two flowers in the spikelet
describe the pollination of ischaemum muticum.
- the mature stamens have long filaments that hang downwards and can swing freely (pendulous)
- the filaments hand out of the bracts, exposing the mature anthers to the wind
- when the filaments sway in the wind, dust like pollen is shaken free and dispersed in the by the wind
- the mature stigmas do not had freely
> project out of the bracts
> they are large, extended and feathery
> provide a large surface area to receive any pollen that is floating around in the wind
what are the characteristics of insect-pollinated flowers?
petals: flowers are usually large with brightly-coloured petals
> to attract insects
nectar: present
scent: flowers are usually fragrant or sweet smelling
stigmas: usually small, compact and do not protrude out of the flowers
stamens: are not pendulous and usually do not protrude out of the flower
pollen: fairly abundant
> pollen grains are usually larger with rough surfaces so that they can readily cling onto the body of insects
nectar guide: may be present on the petals to guide insects towards the nectar
what are the characteristics of wind-pollinated flowers?
petals: flowers are usually small and dull-coloured, without petals
nectar: absent
scent: flowers are odourless
stigmas: stigmas are large, feathery and usually protrude out of the flower to provide a large surface area to trap pollen
stamens: have long pendulous filaments and protruding anthers
> pollen grains are hence easily shaken out from the anthers
pollen: is more abundant
> pollen grains have smooth surfaces and are tiny and light
> easily blown about by the wind
nectar guide: it is absent
how does fertilisation take place?
- after pollination, the pollen grains germinates after it comes into contact with the stigma
> in response to the sugary fluid secreted by the mature stigma - a pollen tube grows out from each pollen grain
> the male gametes enter the pollen tube - as the pollen tube grows, it secretes enzymes to digest the surrounding tissue of the stigma and style
> pollen tube grows down the style into the ovary - the pollen tube enters the ovule through an opening in the ovule wall called the MICROPYLE
- within the ovule, the tip of the pollen tube absorbs sap and bursts, releasing the two male gametes
- the nucleus of one male gamete fuses with the nucleus of the ovum to form the zygote
> fertilisation
