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A Level Biology > Sexual reproduction in plants. > Flashcards

Sexual reproduction in plants. Flashcards

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1
Q

Plants that have flowers are called?

A

Angiosperms

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2
Q

The flower contains what structures of a plant?

A

the reproductive structures

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3
Q

What’s produced from meiosis in reproductive structures?

A

Haploid spores, which contain the gametes.

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4
Q

name the male and females spores in plants and where they are produced.

A

male- pollen grains produced in the anther

female- the embryo sac produced in the ovule in the ovary

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5
Q

What do you call a flower that contains both male and female parts?

A

hermaphrodite

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6
Q

Define a flower.

A

Four sets of modified leaves arising from the receptacle at the base of the flower.

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7
Q

What is the calyx and what is it comprised of?

A

It is the outermost ring structure of a flower and is comprised of the sepals.

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8
Q

Describe the sepals of a flower.

A
  • they are usual green

- they protect the flower in bud

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9
Q

Whats located inside the sepals?

A
  • The corolla- a ring of petals which can be small or large and pale green or brightly coloured.
  • At the base of the corolla there may be a nectary, which is scented to attract pollinators such as insects.
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10
Q

What’s located inside the petals of a flower?

A

The male parts of a flower- the stamens

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11
Q

What does each stamen consist of?

A

A filament supporting an anther.

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12
Q

What does the filament contain?

What does the anther contain?

A

Filament- contains vascular tissue that transports sucrose, mineral ions and water which produces pollen grains.
Anther- Each anther contains four pollen sacs arranged in two pairs side by side.

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13
Q

What happens when pollen sacs mature?

A

They dehisce- they open and release the pollen

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14
Q

What’s located in the centre of a flower?

A

One or more carpels.

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15
Q

Describe the carpel of a flower.

A
  • The female parts of the flower.
  • Each carpel is a closed structure in which one or more ovules develop
  • The lower part of the carpel surrounding the ovule is the ovary.
  • At the tip of the ovary is the style.
  • At the end of the style is the stigma.
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16
Q

Describe cross pollination by insects.

A
  • Pollinators like bees are attracted by the large coloured petals, scent and nectar.
  • They use their long tongues to reach the sugary nectar at the base,
  • When entering the flower the anther brushes agains the bee leaving sticky pollen attached to it.
  • when the bee enters another flower it brushes some of the pollen against the ripe stigma of that other flower.
  • cross pollination has taken place.
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17
Q

Describe cross pollination by wind.

A
  • wind pollinated flowers do not need to attract insects so do not have the bright petals.
  • their anthers hang outside the flower so that the wind can blow away the pollen- which is small, smooth and light to aid this
  • feather stigmas hang outside the flowers and provide a large surface area for catching pollen grains that are blown into their path.
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18
Q

Describe the key features of insect pollinated flowers.

A
  • colourful petals- sometimes have nectar guides
  • scent and nectar- mainly sucrose
  • anthers within the flower
  • stigma within the flower
  • small quantities of sticky, sculptured pollen
  • produces large pollen grains
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19
Q

Describe the key features of wind pollinated flowers.

A
  • petals are usually absent or small, green and inconspicuous
  • no scent or nectar
  • anthers hang outside the flower
  • large, feather stigma hang outside the flower
  • large quantities of smooth pollen
  • produces smaller pollen grains
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20
Q

How are the hoary plantain pollinated and why?

A
  • older flowers are at the top so mature carpels are above mature stamens.
  • pollen cannot fall onto the carpels and so they are wind pollinated.
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21
Q

What is dehiscence?

A

the opening of the anther, releasing pollen grains

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22
Q

Describe how the male gamete of a flower develops.

A
  • in the pollen sacs of each anther diploid pollen mother cells undergo meiosis
  • each forms a tetrad containing four haploid cells- these become four pollen grains
  • The tapetum surrounds the pollen sac and provides nutrients and regulatory molecules to the developing pollen grains- it also has a role in the formation of the pollen cell wall.
  • Inside the pollen grains the haploid nucleus undergoes mitosis
  • two nuclei are produced- a generative one and a tube nucleus
  • the generative nucleus produces two male nuclei by mitosis
  • the pollen is now mature
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23
Q

what occurs once the pollen is mature and how?

A
  • once mature the anthers dry out
  • this causes tension in lateral grooves
  • dehiscence occurs- the tension pulls the walls of the anther apart and at the edges the pollen sacs curl away. an opening called the stomium exposes the pollen grains and they are carried away by insects or the wind.
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24
Q

Describe the functions of the tapetum in flowering plants.

A

It is a layer of cells surrounding the pollen sac it…

  • provides nutrients and regulatory molecules to the developing pollen grains
  • has a significant role in the formation of the pollen cell wall which is tough and resistant to chemicals
  • resists desiccation so the pollen grains can be transferred from one flower to another without drying out
  • cannot be penetrated by UV light so that the DNA in the pollen that is carried to a high altitude is protected from mutation
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25
Q

Describe the development of the female gamete in flowering pants.

A
  • the ovary may contain one or more ovules
  • in each ovule there is a megaspore mother cell which is surrounded by the cells of the nucellus
  • the megaspore mother cell undergoes meiosis making four haploid cells
  • three of these cells disintegrate
  • the remaining cell undergoes three rounds of mitosis- this produces eight haploid nuclei
  • one of the haploid nuclei is the female gamete
  • two of the other haploid nuclei fuse to make a diploid nucleus called the polar nucleus.
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26
Q

What does an embryo sac in a mature ovule contain?

A
  • 3 antipodals- haploid
  • 2 synergids- haploid
  • 1 oosphere- haploid
  • 1 polar nucleus- diploid
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27
Q

What are the nuclei in a mature ovary surrounded by and what are the features of this structure?

A
  • These nuclei are in the embryo sac surrounded by the nucellus.
  • The nucellus is a layer of cells which provide nutrients.
  • Around the nucellus are two layers of cells called the integuments.
  • A gap in the integuments is called the micropyle.
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28
Q

What’s another name for the female gamete?

A
  • oosphere
  • ovary
  • oocyte
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29
Q

What’s a funicle?

A

The stalk that attaches an ovule or seed to the wall of the ovary.

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30
Q

Define pollination.

A

The transfer of pollen grains from the anther to the mature stigma of a plant of the same species.

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31
Q

What does pollination do?

A

Brings the pollen grains containing male gametes into contact with the female part of the flower, which can result in fertilisation.

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32
Q

Define self pollination.

A

The pollen of the anthers of a flower is transferred to the mature stigma of the same flower or another flower on the same plant.

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33
Q

Define cross-pollination.

A

Most angiosperms use cross-pollination, in which pollen is transferred from the anthers of one flower to the mature stigma of another flower on another plant of the same species.

34
Q

Describe some of the genetic consequences of self pollination (also known as inbreeding.)

A
  • self fertilised species depend only on independent assortment and crossing over during meiosis and mutation to bring about genetic variation in the genomes of their gametes- hence they display less genetic variation than cross-fertilised species.
  • There is a greater chance of two harmful recessive alleles being brought together at fertilisation.
  • an advantage of inbreeding is that it can preserve those successful genomes that are suited to a relatively stable environment.
35
Q

Describe some of the genetic consequences of cross-pollination (also known as outbreeding.)

A
  • outbreeding combines gametes from two individuals in addition to events from meiosis and mutations, hence more genetic variation occurs than during inbreeding.
  • Outbreeding reduces the the chance of producing harmful allele combinations.
  • outbreeding is of evolutionary significance- the most suited combination of alleles to the environment (which can change) will allow that organisms to go on to survive and breed- natural selection.
36
Q

Name some of the methods used by plants to insure cross pollination occurs.

A
  • Dichogamy- when the stamen and stigma ripen at different times.
  • The anther is below the stigma so the pollen cannot fall onto it.
  • Genetic incompatibility- pollen cannot germinate on the stigma of the flower which produced it.
  • Separate male and female flowers on the same plant.
  • Separate male and female plants.
37
Q

Define Dichogamy.

A

When the stamen and stigma ripen at different times.

38
Q

What is protandry?

A

When the stamens of a flower ripen before the stigmas.

39
Q

Define fertilisation.

A

The fusion of a female and male gamete producing a zygote.

40
Q

What is the female gamete in flowering plants and what is the male gamete?

A

female- ovule- protected by the ovary

male- nucleus- contained in the pollen grain

41
Q

How is the male gamete delivered to the female gamete during double fertilisation.

A

By a pollen tube.

42
Q

Describe the process of double fertilisation in flowering plants.

A
  • When a pollen grain lands on the stigma it germinates in the sucrose solution secreted by the stigma producing a pollen tube.
  • the pollen tube nucleus is at the tip of the tube, followed by the two male nuclei.
  • The pollen tube grows out of the pollen grain through a gap in the cell wall called a pit.
  • It then grows down the style, up a gradient of chemoattractants- like GABA from the ovule
  • The pollen tube nucleus codes for the production of hydrolyses (including celluloses and proteases) and it digests its way through the tissues of the style- the products of digestion are used by the growing pollen tube.
  • The pollen tube grows through the gap in the integuments, the micropyle and passes into the embryo sac.
  • The pollen tube nucleus disintegrates.
  • The tip of the pollen tube opens, releasing the two male gametes into the embryo sac.
  • The male and female gametes are haploid so when one of the male gametes fuses with the female gamete (the oosphere) a diploid zygote is formed.
  • The other male gamete fuses with the diploid polar nucleus to form a triploid nucleus- also knowns as an endosperm nucleus.
  • Two fusions have occurred, one to form the zygote and one to form the endosperms- this is double fertilisation
43
Q

What is double fertilisation unique to?

A

flowering plants

44
Q

How is the endosperm tissue generated?

A
  • One of the male gametes fuses with the diploid polar nucleus to produces a triploid nucleus.
  • The triploid nucleus is the endosperm nucleus.
  • When it divides repeatedly by mitosis it generates endosperm tissue
  • this tissue takes over from the nucellus in providing nutrition for the developing embryo.
45
Q

What does a seed develop from?

A

The fertilised ovule and contains an embryonic plant and food store.

46
Q

Describe the development of the fruit and seed in a plant.

A

□ The ovule comprising the embryo, endosperm and testa become the seed…

  • The diploid zygote divides by mitosis becoming an embryo which consists of a plumule, a radical and one or two cotyledons.
  • The triploid endosperm nucleus develops into a food store, providing food for the developing embryo.
  • the outer integument dries out and hardens becoming waterproof with deposits of lignin- it is known as the seed coat or testa.
  • the micropyle remains as a pore in the seed.
  • The ovule

□ The funicle/ stalk of the ovule becomes the funicle of the seed attaching to the seed at the hilum

□ The ovary becomes the fruit.

  • In some species the fruit becomes sweet, juicy and pigmented.
  • In other species the ovary wall becomes dry and hard.
47
Q

Describe the following…

  • a pumule
  • a radicle
A
  • a pumule- the developing shoot

- a radicle- the developing root

48
Q

What is a cotyledon?

A

Seed leaves

49
Q

Define fruit.

A

The structure developing from he ovary wall, containing one or more seeds.

50
Q

Define seed.

A

The structure developed from a fertilised ovule containing an embryo and food store enclosed within a testa.

51
Q

Describe the ovary of a broad bean flower.

A
  • It contains several ovules.
  • after fertilisation the ovary elongates into a pod which is the fruit
  • the ovules mature into seeds which are the broad beans
52
Q

Define dicotyledon and give an example of a plant that has this.

A

A plant thats seeds have two seed leaves/cotyledon for example the broad bean.

53
Q

What happens to the endosperm in broad beans?

A

It was the food store for the early embryo, but is now absorbed into the cotyledon so that the broad bean has a non-endospermic seed.

54
Q

Give an example of a monocotyledon plant.

A

Maize

55
Q

What happens to the endosperms in maize?

A

the endosperm remains as the food store in maize so the seeds are considered endospermic

56
Q

What happens to the testa of grasses and cereals like maize?

A

The testa fuses with the ovary wall so maize has a one -seeded fruit.

57
Q

Explain what is meant by a seed being dormant.

A
  • The seed’s active growth is suspended.
  • Germination will only occur when specific conditions are met.
  • seeds become dormant when their water content level falls below 10% resulting in their metabolic rate reducing.
58
Q

Describe the feature of monocots.

A
  • one cotyledon in seed
  • leaf veins are parallel
  • sepals, petals and stamens in multiples of threes
  • vascular bundles scattered in stems
  • vascular bundles scattered in roots
59
Q

Describe the feature of dicots.

A
  • two cotyledons in seed
  • leaf veins form a network
  • sepals, petals and stamens in multiples of four or five
  • vascular bundles in a ring in stems
  • vascular bundles in the centre of roots
60
Q

Why is seed dispersal so important?

A
  • seed dispersal is the movement of seeds away from the parent plant
  • if a seed were to germinate close to its parent, the parent plant would be more successful at obtaining water and mineral from the soil. It would also cast shade over the seedling preventing it from photosynthesising adequately.
  • the seedling would be outcompeted
61
Q

Name the six dispersal methods of seeds.

A
  • wind
  • transport
  • rolling
  • bursting
  • water
  • carrying
62
Q

Describe the following seed dispersal methods…

  • wind
  • transport
  • rolling
A

wind:

  • ash/sycamore fruits have sails
  • dandelions have a parachute of stiff hairs
  • the fruit of the poppy has pores which the seeds are shaken out of when the stem is blown in the wind

transport:
- birds eat seeds that pass through the digestive system and are dispersed in the faeces- a process called scarification occurs which is the only way the seeds of some species can germinate.

rolling:
- horse chestnut tress breaks open and the conker (the seed) falls to the ground and rolls away from the tree.

63
Q

Describe the following seed dispersal methods…

  • bursting
  • water
  • carrying
A

bursting:
- legume pods dry and they split causing the seeds to scatter- in many species they rotate as they burst open sending the seeds in many different directions

water:
- coconut palms grow by water so that when the coconuts (the seeds) fall into the water they are carried away- they are buoyant because of their air cavities.

carrying:
- hooked seeds attached to animal coats and are carried away- for example burdock

64
Q

What is scarification?

A

When the digestive system weakens the testa by physical attack- by acid and enzymes and the seeds of some species can only germinate when this has happened.

65
Q

Explain how seeds are adapted.

A
  • dormant seeds have a low metabolic rate so can survive very cold weather
  • dormant seeds have a water content level below 10% so so can survive very dry conditions
  • the testa is chemically resistant and so the seeds survive adverse chemical conditions
  • the testa can protect the embryo physically
  • the endosperm or cotyledon provide nutrients which last until the emerging seedlings can photosynthesise adequately.
  • seeds can be dispersed away from the parent plant so do not compete with it
  • dispersal allows the colonisation of new habitats
  • inhibitors only allow germination at certain times of the year
66
Q

Explain how inhibitors only allow germination at certain times of the year.

A

Inhibitors are broken down in very cold weather in a process called ‘vernalisation’ so that the seeds can germinate in the spring.

In cabbages the inhibitors are in the seeds and the tomatoes they are in the fruits.

67
Q

Define germination.

A

The biochemical and physiological process through which a seed becomes a photosynthesising plant.

68
Q

How does germination begin and end?

A
  • It begins with very vigorous biochemical and and developmental activity.
  • It lasts until the first photosynthesising leaves are produced- by which time all the food stored in the endosperm or cotyledons will be used.
69
Q

Describe the germination sequence in a broad bean.

A
  • seed imbibes water
  • testa splits
  • radical emerges
  • plumule emerges
  • elongation pushes shoot above ground
70
Q

What are the three main requirements for successful germination?

What factor varies between species?

A
  • a suitable temperature- the optimum temperature for germination is the optimum for the enzymes involved in the process- it is usually between 5-30 degrees celsius
  • water- to mobilise enzymes for transport in the xylem and phloem- also to vacuolate cells making them turgid.
  • oxygen- aerobic respiration releases energy which fuels metabolism and growth

The effect of light varies between species- e.g. daisy seeds need light to germinate, but ivy seeds need darkness, whereas geranium can germinate in either

71
Q

What does it mean when a seed imbibes water and what does this result in?

A
  • When conditions are suitable water is taken up (imbibed) rapidly by the seed through the micropyle.
  • The water causes the tissues to swell and provides suitable conditions for enzyme activity.
72
Q

How does a seed imbibing water result in the radicle and pumule emerging?

A

The water causes the tissues to swell and provides suitable conditions for enzyme activity…

  • food reserves are insoluble in water so cannot be transported to the embryo- they are broken down by enzymes to more soluble molecules- e.g. amylase hydrolyses starch to maltose and proteases hydrolyse proteins to amino acids
  • the soluble products are carried in the phloem to the atypical meristems of the pummel and radicle where rapid cell division occurs- some sugars are converted to cellulose (for a cell wall) or used in aerobic respiration (to release energy for the synthesis of new proteins).
  • the swollen tissues ruptures the testa so that the radicle emerges from the seed, followed by the pumule.
73
Q

How come the radicle grows downwards?

A

It is positively geotropic and negatively phototropic.

74
Q

How come the pumule grows upwards?

A

It is positively phototropic and negatively geotropic.

75
Q

Describe how the pumule of a broad bean develops during germination.

A
  • the cotyledons of the broad bean remain below ground.
  • the part of the pumule above the join between the embryo and the cotyledon elongates rapidly pushing the pumule upwards
  • the pumule is bent over in the shape of a hook as it pushes its way up through the soil- this protects the tip from soil abrasion
  • if planted at the correct depth in the soil when the pumule emerges the hook straightens and leaves unfurl to allow for photosynthesis to occur- by this point the food reserves of the cotyledons will have been depleted.
76
Q

Describe how the mass of a seed changes during germination.

A
  • as a seed germinates its dry mass increases.
  • the dry mass of the embryo increases as it develops into a seedling
  • the dry mass of the cotyledon decreases
77
Q

Describe a use of gibberellin.

A

It is a plant hormone used in the brewing industry to speed up germination so that barely seeds need to be kept warm for less time and more malted barely can be produced.

78
Q

Describe the effect of gibberellin on a barley seed.

A
  • the barley embryo secrets gibberellic acid which diffuses through the endosperm to the aleuron layer
  • the gibberellic acid acid switches on genes in the cells of the aleurone layer, resulting in transcription and translocation- producing enzymes including protease and amylase
  • the proteases hydrolyse protein in the aleuron layer to amino acids which are used to make amylase
  • the amylase diffuses out of the aleuron layer and hydrolyses the starch stored in the endosperm cells
  • the maltose and glucose produced diffuse back through the endosperm to the pumule and radicle of the embryo
  • they are respired for energy which fuels biosynthesis and cell division which brings seeds out of dormancy.
79
Q

What is gibberellic acid?

A

a plant growth regulator

80
Q

What is the aleuron layer of a seed?

A

a layer of cells towards the outside of a seed which has a high protein content

A Level Biology (10 decks)

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