chapter 17: reproduction in plants Flashcards
1
Q
what is asexual reproduction?
A
- 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
2
Q
what are the advantages to asexual reproduction?
A
- 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
3
Q
what is the disadvantage of asexual reproduction?
A
- there is no genetic variation in the offspring
> species are not well adapted to the changes in the environment
4
Q
what is sexual reproduction?
A
- is a process involving the fusion of two gametes to form a zygote
> produces genetically dissimilar offspring
5
Q
what are the advantages of sexual reproduction?
A
- 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
6
Q
what are the disadvantages of sexual reproduction?
A
- 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
7
Q
what is inflorescence?
A
- a cluster of flowers borne on the same stalk
8
Q
what are the parts a complete flower consist of?
A
- pedicel
- receptacle
- sepals
- petals
- stamens
- carpels (pistil)
9
Q
what are petals?
(parts of a flower)
A
- 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
10
Q
what are sepals?
(parts of a flower)
A
- 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
11
Q
what is the pedicel?
(parts of a flower)
A
- the flower stalk
12
Q
what is the receptacle?
(parts of a flower)
A
- receptacle is the enlarged end of the flower stalk
> which bears the other parts of the flower
13
Q
what is the stamen?
A
- the male part of the flower
> consists of an anther and a filament
14
Q
what it an anther?
(stamen)
A
- 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
15
Q
what does the carpel consist of?
A
- an ovary
- a style, above the ovary
- one or more stigmas
16
Q
what is a stigma?
(a part of the carpel)
A
- 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
17
Q
what is a style?
(a part of the carpel)
A
- the stalk that connects the stigma to the ovary
> holds the stigma in a suitable position to trap pollen graisn
18
Q
what is an ovary?
(a part of the carpel)
A
- 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
19
Q
What is pollination?
A
- it is the transfer of pollen grains from the anther to the stigma
> self-pollination or cross-pollination
20
Q
What is self pollination?
A
- the transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant
21
Q
What are the features favouring self-pollination?
A
- 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
22
Q
What are the advantages of self-pollination?
A
- 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
23
Q
what are the disadvantages of self-pollination?
A
- 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
24
Q
what is cross-pollination?
A
- it is the transfer of pollen grains from one plant to the stigma of a flower in another plant of the same species
25
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
26
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
27
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
28
# 8 structures
what are the structures of clitoria?
| (an insect polinated flower)
1. CALYX
- the calyx consists of 5 green sepals
2. EPICALYX
- the base of the calyx is enclosed by the epicalyx
> consisting of 2 green leaves
3. COROLLA (region)
- the corolla consists of five brightly-coloured petals of different shapes and sizes
4. 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
5. WING PETALS
- two deep blue wing petals are enclosed by the standard petal
6. KEEL PETALS
- two small, yellowish-green keel petals are enclosed by wing petals
> the keel petals enclose the reproductive organs
7. 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
8. 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
29
describe the pollination of clitoria.
1. when an insect (eg. bee) visits a flower, it lands on the standard petal
2. the insect follows the nectar guide into the flower
3. the insect forces its way between two wing petals and moves in to collect the nectar
4. 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
5. 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
30
what is the structure of ischaemum muticum?
( a wind-pollinated flower)
1. pair of flowers
- the flowers occur in pairs
- each ischaemum muticum flower is enclosed by two transparent flowering bracts
2. 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
3. lower flower ( male)
- it is unisexual
> consists of only 3 stamens with long filaments and two lodicules
> male flower
4. 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
31
describe the pollination of ischaemum muticum.
1. the mature stamens have long filaments that hang downwards and can swing freely (pendulous)
2. the filaments hand out of the bracts, exposing the mature anthers to the wind
3. when the filaments sway in the wind, dust like pollen is shaken free and dispersed in the by the wind
4. 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
32
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
33
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
34
how does fertilisation take place?
1. 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
2. a pollen tube grows out from each pollen grain
> the male gametes enter the pollen tube
3. 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
4. the pollen tube enters the ovule through an opening in the ovule wall called the MICROPYLE
5. within the ovule, the tip of the pollen tube absorbs sap and bursts, releasing the two male gametes
6. the nucleus of one male gamete fuses with the nucleus of the ovum to form the zygote
> fertilisation
