Reproduction in Plants

Question 1

what are flowering plants known as?

Answer 1

angiosperms

Question 2

give the labels of an insect-pollinated flower

there are 14 to label and briefly describe

Answer 2

stigma (sticky to trap pollen)
style (holds the stigma)
petal (brightly coloured/scented to attract insects)
anthem (produces pollen - male gamete)
filament (thin, contains vascular tissue to provide anther with nutrients)
ovules (female gamete)
ovary (protects ovule)
nectaries
receptacle (part of the stalk where flower is attached)
sepal (protects flower when in bud - often green to aid photosynthesis)
carpel (female reproductive parts of a plant)
stamen (male reproductive parts of a plant)
the collective name for the sepals is the calyx
the corolla is all the petals on a flower

Question 3

give the labels of a wind-pollinated flower

Answer 3

stigma, style and ovary (carpel)
filament and anther (stamen)

Question 4

describe the features of an insect-pollinated flower in terms of petals, locations of anther and stigma and type and quantity of pollen

Answer 4

petals: often scented, large brightly coloured conspicuous petals, nectar present

anther: anthers fixed to filaments and positioned inside flower to come into contact with visiting insects

stigma: small stigma enclosed within the flower and positioned to come into contact with visiting insects

pollen: less pollen produced, grains are larger, barbs for hooking onto insects

Question 5

describe the features of a wind-pollinated flower in terms of petals, locations of anther and stigma and type and quantity of pollen

Answer 5

petals: no scent, small inconspicuous petals and sometimes absent and if present then not brightly coloured, no nectar

anther: anthers outside of flower so pollen easily dispersed

stigma: large stigma, often branched and feathery, hanging outside the flower to trap pollen

pollen: pollen produced in large quantities, light, smooth pollen grains

Question 6

give the labels of an anther of a plant

Answer 6

epidermis
fibrous layer
pollen sac
tapetum
pollen mother cells (2n)
pollen

filament (contains vascular bundle supplying water and sucrose to the anther)
groove is where the anther splits to release pollen

Question 7

how is a pollen grain (male gamete) formed?

Answer 7

pollen grains are formed in the anther by mitosis and meiosis

mitosis occurs to produce large numbers of diploid pollen mother cells

the mother cells undergo meiosis to produce a tetrad (four) haploid cells
these cells form pollen grains that contain the male gamete

the tapetum is a layer of cells around the pollen sac
it provides nutrients to the developing pollen grains and produces a waterproof coat for the pollen grain

Question 8

what happens next after the pollen grains are formed?

Answer 8

inside each pollen grain the haploid nucleus undergoes mitosis to produce two nuclei: a generative nucleus and a pollen tube nucleus

the generative nucleus will later undergo mitosis to give rise to two male nuclei

Question 9

describe and name the pollen cell wall

Answer 9

exine

it is tough and resistant to chemicals
it resists desiccation - drying out

Question 10

what is pollen also resistant to?

Answer 10

UV radiation
meaning pollen can be carried at high altitudes without DNA mutation occurring

Question 11

what type of pollen dispersal method is being resistant to UV radiation particularly important in?

Answer 11

wind pollination

pollen can be carried to high altitudes by the wind

Question 12

describe the process of dehiscence

Answer 12

the outer layers of the anther dry out, causing tension

dehiscence occurs - tension pulls the walls of the anther apart and the edges of the pollen sacs curl away (creating the stomium)

an opening called the stomium exposes the pollen grains and they are carried away by insects or the wind

Question 13

what does open grooves mean in the anther?

Answer 13

the pollen grain has matured

Question 14

describe the process of developing the ovule

Answer 14

the ovule contains the female gamete and is formed in the ovary by mitosis and meiosis

the megaspore mother cell in the nucellus undergoes meiosis to produce four haploid megaspores

three of the megaspore cells degenerate and only one grows and develops

this one megaspore undergoes three mitotic divisions to produce eight haploid nuclei within the embryo sac of the ovule

Question 15

give the labels of the female gamete

Answer 15

wall of ovary (funicle)

integuments

nucellus (may provide nourishment to the developing embryo)

embryo sac (megaspore mother cell 2n)

micropyle

Question 16

describe embryo sac devlopement

Answer 16

the eight haploid nuclei inside each embryo sac includes one female gamete, two polar nuclei, two synergids and three antipodal cells

Question 17

what do the antipodals and synergids provide?

Answer 17

antipodals - provide nourishment to the fertilised egg

synergids - are involved in pollen tube guidance

Question 18

define micropyle

Answer 18

a gap in the integuments for the male nuclei to enter the embryo sac

Question 19

define integuments

Answer 19

protect the embryo sac

Question 20

define funicle

Answer 20

attaches the ovule to the ovary wall

Question 21

define polar nuclei

Answer 21

fuse with a male nucleus in double fertilisation to form a triploid endosperm

Question 22

define female gamete

Answer 22

fuses with a male nucleus to form a zygote

Question 23

define pollination and why is it necessary

Answer 23

it is the transfer of pollen grains from the anther to the stigma

necessary so that the pollen grains containing the male gametes are brought into contact with the female part of the flower so that fertilisation can be achieved

Question 24

what is self-pollination?

Answer 24

transfer of pollen grains from an anther to a stigma of the same plant

some genetic variation through crossing over and independent assortment

Question 25

what are advantages of self-pollination?

Answer 25

only one parent needed can help maintain genotypes which are well adapted to the current environments

Question 26

disadvantages of self-pollination

Answer 26

reduces genetic variation - offspring may be less likely to survive changes in the environment increases the chance of offspring being homozygous for recessive alleles, which could lead to genetic diseases (many genetic diseases are caused by mutations resulting in defective recessive alleles)

Question 27

describe cross-pollination

Answer 27

transfer of pollen grains from an anther to a stigma of a different plant of the same species increased genetic variation through crossing over, independent assortment and mixing of parental genotypes when haploid gametes fuse cross pollination is of greater evolutionary significance than self-pollination because it increases genetic variation, so a species can adapt to environmental change through natural selection

Question 28

how could cross-pollination be prevented during plant reproduction experiments?

Answer 28

prevent the transfer of pollen from one flower to another by enclosing or isolating the flower in a bag

Question 29

where do insect-pollinated flowers have their nectaries located? why is this an advantage?

Answer 29

below the anther/stigma this promotes insects transferring pollen grains as they will brush past the anther/stigma when going down to the nectaries

Question 30

what process ensures that cross pollination occurs?

Answer 30

1) the stamen and stigma ripen at different times even if pollen produced by the anther lands on the stigma it will not germinate and form a pollen tube no pollen will fall onto the ripe stigma as it is not being produced by the anther 2) the anther is below the stigma so that pollen cannot fall from the anther onto the stigma 3) genetic/chemical incompatibility e.g. red clover pollen is unable to germinate on the stigma of the flower which produced it 4) separate male and female plants (unisexual) e.g. holly the plant does not have both make and female sex organs so can't self pollinate

Question 31

describe the process of fertilisation in a plant

Answer 31

when a compatible pollen grain lands on a stigma, the stigma secretes a sugary solution the pollen grain then germinates, and the pollen tube nucleus controls the growth of a pollen tube the pollen tube nucleus codes for hydrolytic enzymes that digest through the tissues of the style the products of digestion are used by the pollen tube the pollen tube nucleus is at the tip of the pollen tube with the two male nuclei behind the pollen tube enters the embryo sac through the micropyle the pollen tube nucleus now disintegrates, and the tip of the pollen tube opens, releasing the two male nuclei into the embryo sac

Question 32

are you able to map out the path of the pollen tube to the embryo sac?

Answer 32

page 11 in booklet

Question 33

describe double fertilisation

Answer 33

both male gametes are involved in separate fertilisation events: one male gamete fuses with the female gamete to produce a diploid zygote the second male gamete fuses with the two polar nuclei to form a triploid primary endosperm (3n) nucleus

Question 34

what are the similarities and differences between fertilisation in humans and fertilisation in flowering plants?

Answer 34

similarities: both involve the fusion of haploid gametes to form a zygote both involve internal fertilisation in the female both involve secretion of digestive enzymes to digest a path for the male gamete to reach the female gamete differences: double fertilisation occurs in plants pollen tube formation in plants/acrosome reaction in humans meiosis is not followed by mitosis in humans but it is in plants

Question 35

describe briefly the formation of the seed and fruit

Answer 35

the ovule becomes the seed the ovary becomes the fruit - a fruit is a mature ovary that may contain seeds

Question 36

how does each structure in an ovary transform into the structures of a seed? there are 6

Answer 36

diploid zygote -> mitosis -> diploid embryo, consisting of plumule (developing shoot), radicle (developing root) and one or two cotyledons triploid endosperm nucleus -> mitosis -> endosperm tissue, an important food storage tissue in cereal grains, e.g. wheat & maize ovule -> seed ovary wall -> develops into a fruit wall enclosing the seeds integuments -> develop into the testa (seed coat) micropyle -> remains as a pore in the testa

Question 37

give the labels of the seed

Answer 37

ovule wall plumule funicle - forms a scar on the seed called the hilum micropyle radicle cotyledon testa

Question 38

what is a cotyledon? and describe the different types

Answer 38

cotyledon = a seed leaf seeds with one cotyledon are called monocotyledons, e.g. maize & wheat seeds with two cotyledons are called dicotyledons, e.g. broad beans

Question 39

describe maize/monocotyledons and give labels

Answer 39

the endosperm acts a food store therefore maize is endospermic testa and ovary wall fused endosperm plumule sheath plumule radicle cotyledon funicle

Question 40

describe broad beans/dicotyledons

Answer 40

broad beans have the embryo lying between the two cotyledons broad beans use the cotyledons as food storage tissue this means they do not have an endosperm (its been absorbed into the cotyledons) so are non-endospermic (labels: seed coat, cotyledon)

Question 41

what have seeds evolved as?

Answer 41

as a survival strategy for a terrestrial mode of life

Question 42

give the seed adaptations for life on land

Answer 42

the testa is chemically resistant, so seeds survive adverse chemical conditions, it also provides physical protection endosperm/cotyledons provide a supply of nutrients until photosynthesis can occur dormant seeds have a low metabolic rate so they can survive over winter in time for higher temperatures in spring/summer very low water content to survive dry conditions

Question 43

plants have developed different mechanisms to enable the dispersal of seeds why is seed dispersal important for plants?

Answer 43

reduces competition with the parent plant and other offspring plants allows for colonisation of new areas

Question 44

why are fruit important in seed dispersal?

Answer 44

seeds from fruit eaten by animals pass through the digestive system and out non edible fruits have other adaptations for dispersal e.g. hooks to attach to animals

Question 45

state three seed dispersal mechanisms and how it works

Answer 45

water - coconut seeds can float as air cavities make them buoyant wind - light seeds that can be easily carried by the wind, may have parachute-like or feathery structures animals - spikes means seeds attach to animals

Question 46

when will seeds germinate?

Answer 46

after a period of dormancy and when environmental factors are favourable, stored food will mobilise and the seed will germinate

Question 47

what are the three main requirements for successful germination?

Answer 47

suitable temperature - optimum for the enzymes, differs between species water - needed for mobilisation of enzymes, vacuolation of cells and transport oxygen - aerobic respiration releases ATP energy required for metabolism and growth

Question 48

what do the first steps of germination involve?

Answer 48

water is imbibed (taken in) through the micropyle the tissues then swell, splitting or softening the testa, allowing entry of more oxygen oxygen can then be used in aerobic respiration to produce ATP energy for metabolism

Question 49

the graph shows changes in the dry mass of seeds as they are germinating, the dry mass of the endosperm (food reserve), embryo as it develops into a seedling and the total for. the seed (page 16) explain the relative changes in the dry mass of the embryo, seedling and endosperm

Answer 49

embryo - uses the glucose for growth seedling - as first leaves produced, starts to photosynthesise, increasing in mass endosperm - decreases as food reserves are hydrolysed by enzymes (starch -> maltose/glucose) and used in respiration (CO2 lost)

Question 50

describe the process of germination in non-endospermic seeds

Answer 50

mobilised enzymes hydrolyse large, insoluble food stores: amylase hydrolyses starch into maltose lipase hydrolyses lipids into fatty acids and glycerol protease hydrolyses proteins into amino acids these soluble products are transported to the plumule and the radicle for use in respiration aerobic respiration can then produce ATP energy for mitosis and growth the plumule grows upwards the radicle grows downwards the plumule emerges from the soil, the leaves unfurl and begin to photosynthesise the plant is now independent of food stores in the seed

Question 51

what hormone is involved in germination of endospermic seeds and what does the endosperm contain?

Answer 51

gibberellin endosperm contains starch, proteins and fats

Question 52

describe the process of germination in endospermic seeds

Answer 52

following imbibition of water, gibberellin is released by the embryo and diffuses to the aleurone layer gibberellins cause transcription and translation to occur, producing hydrolytic enzymes e.g. protease protease digests the proteins in the aleurone layer to form amino acids, these can be used in further enzyme synthesis e.g. amylase amylase diffuses into the endosperm and hydrolyses the starch stored there into maltose proteins and fats in the endosperm are also hydrolysed into amino acids, fatty acids and glycerol maltose, glucose and other nutrients diffuse to the embryo where they are used in aerobic respiration to provide ATP for the growth of the plumule and radicle

Question 53

describe the breakdown of starch and proteins into soluble products including the enzymes used

Answer 53

starch -> amylase (+maltase) -> maltose (+glucose) proteins -> protease -> amino acids

Question 54

in what vessels are the soluble products transported in the plumule and radicle

Answer 54

phloem

Question 55

give examples of the uses of the soluble products, produced in germination, in plant cells

Answer 55

maltose hydrolysed to glucose for respiration, or converted to cellulose for cell wall protection amino acids for protein synthesis

Question 56

as maize seeds germinate, they produce the enzyme amylase which hydrolyses starch in the endosperm into maltose this can be demonstrated in the laboratory using the following method: maize seeds are soaked in water seeds are cut in half and placed onto starch agar after 24 hours the seeds are removed and iodine solution added to the starch agar clear zones around the position of seeds indicate amylase activity, boiled then cooled seeds are set up as a control describe how you would develop and refine this practical procedure to determine whether treatment of seeds with a 1.0 mmol dm^-3 solution of gibberellic acid increased production of amylase

Answer 56

independent variable - some seeds soaked in gibberellic acid and water and some soaked in just water dependent variable - measure clear are/compare size of clear zone control variable - any two from: same type/variety/age/size/mass of seed soaked for same time same concentration/depth of starch agar same temperature/light

Question 57

the plumule is positively phototropic and negatively geotropic the radicle is negatively phototropic and positively geotropic explain this statement

Answer 57

plumule grows towards light and against gravity radicle grows away from light and towards gravity