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Biology A-level (Unit 4) > Biology Unit 4.2 - Sexual Reproduction in Plants > Flashcards

Biology Unit 4.2 - Sexual Reproduction in Plants Flashcards

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1
Q

What is the flower?

A

Organ of reproduction in plants containing both male and femal gametes

Top-bottom:
* Petal
* Stigma
* Stamen consisting of the anther and filament
* Sepal
* Style
* Ovar containing one or more ovules

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2
Q

What is the function of the petal?

A

Brightly coloured, which may have a scent and produce nectar to attract insects

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3
Q

What is teh function of the stigma?

A

Receptive surface that receives pollen during pollination when matured

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4
Q

What is the function of the anther?

A

Structure that produces pollen grains and contains the male haploid gamete

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5
Q

What is the function of the filament?

A

Supports the anther, and has vascular tissue that transports food (phloem) and water (xylem)

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6
Q

What is the function of the sepal?

A

Usually green and protect the flower in bud

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7
Q

What is the function of the style?

A

Stalk like structure that supports the stigma

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8
Q

What is the function of the ovary?

A

Surrounds the ovules is the lower part of the carpel, and contains the femal haploid gamete

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9
Q

What is pollination?

A

Transfer of pollen grains from the anther to the mature stigma, so they can be brought into contact with the female part of the flower

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10
Q

What is self-pollination?

A

Pollen is transferred to the stigma of the same flower, or another flower on the same plant

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11
Q

What is cross-pollination?

A

Transfer of pollen from the anthers of one flower to the stigma of another flower on a different plant of the same species

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12
Q

What is insect pollination?

A

Bees feed on sugary nectar using long tongues to reach the nectaries, where anthers brush against the back of the bee, leaving behind sticky pollen, which burhs against a ripe stigma

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13
Q

What is wind pollination?

A

Petals are absent or small and insignificant

Anthers hang outside the flower; allow wind to blow away the small, smooth and light pollen

Feathery stigmas hang outside the flowers; provide a large surface area

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14
Q

Compare insects pollinated and wind pollinated flowers…

A

Insect pollinated:
* Colorful petals with nectar guides
* Scent and nectar - mainly sucrose
* Anther and stigma within the flower
* Small quantities of sticky sculptured pollen
* Produces large pollen grains

Wind pollinated:
* Petals ususally absent or small, green or insconspicuous
* No scent or nectar
* Anthers hanging outside the flower
* Large, feathery stigma hang outside the flower
* Large quantities of smooth pollen
* Produces smaller pollen grains

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15
Q

What are the genetic consequences of self-pollination?

A
  • Leads to self-fertilisatio; results in inbreeding
  • Variation can only be achieved by mutation by crossing over during prophase I and the random assortment of chromosomes/chromatids
  • Less genetic variation
  • Inbreeding can preserve good genomes suitable to a stable environment
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16
Q

What are the genetic consequences of cross-pollination?

A
  • Leads to cross-fertilisation; results in outbreeding
  • Variation achieved by fusion of gametes from diffeent plants of the same species in addition to mutation: crossing over during prophase I and random assortment of chromosomes/chromatids
  • More genetic variation
  • Outbreeding has evolutionary significance as some genomes are more successful than others; allow species to survive better in a changing environment
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17
Q

What are the anthers?

A

Contain male haploid gametes produced by meiosis

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18
Q

Explain pollen production…

A
  • Diploid pollen mother cells divide by meiosis, where each forms a tetrad, containing haploid cells
  • Haploid nucleus divides by mitosis forming two haploid nuclei per pollen grain
  • One is the tube nucleus, while the other is generative nucleus
  • As pollen matures tension in the lateral grooves occurs
  • Dehiscence occurs, causing tension to pull the walls of the anther apart, while the edges of the pollen sacs curl away
  • Opening called the stomium exposes the pollen grains and are carried away by insects or wind
19
Q

Explain ovule development…

A
  • Ovules develop in the ovary
  • In each ovule a megaspore mother cell undergoes meiosis to form four haploid cells
  • Three degenerate, while the remaining haploid cells divides by mitosis three times, producing eight haploid nuclei
  • Two polar nuclei fuse forming a mature embryo sac
  • Oosphere is the haploid female gamete
20
Q

Explain double fertilisation…

A
  • Male gamete is delivered by a pollen tube
  • When a compatible pollen grain reaches a ripe stigma pollination occurs
  • Pollen absorbs water, germinating it, producing a pollen tube, which grows out of the pollen grain through a gap in the cell wall called a pit
  • Tube pushes down through the tissues of the style up a gradient of chemo-attractents
  • Pollen tube nucleus produces hydrolases which digest through the style tissues
  • Generative nucleus divides into two male nuclei
  • Tio of the pollen tube enerts the ovule via the micropyle and releases the two male gametes into the embryo sac
  • One fuses with the oosphere, forming a zygote which divides by mitosis
  • Other male nucleus fuses with the diploid polar nucleus forming a triploid nucleus called the endosperm nucleus
21
Q

Where do different fruit/seed structures develop from?

A
  • See - The ovule
  • Embryo plant - Diploid zygote
  • Endosperm - Triploid endosperm nucleus
  • Test - Integument
  • Fruit - Ovary
22
Q

Explain the embryo plants, cotyledons, and endosperm…

A
  • Embryo consists of a plumule, radicle, and one or two cotyledons
  • Flowering plants are either monocotyledons (Maize) and dicotyledons (Broad bean)
  • In the broad bean the endosperm is absorbed into the cotyledons
  • In maize the endosperm surrounds the cotyledon
23
Q

What is seed dispersal?

A

Movement of seeds away from the parent plant, where if germination occurs close to the parent the parent will be more successful

These methods are subject to natural selection

24
Q

How evolutionary developments led to the success of Angiosperms?

A
  • Dormant seeds have low metabolic rate to survive in very cold weather
  • Testa is chemically resistant
  • Water content of dormant seeds is reduced to 10% to survive in very dry conditions
  • Test physically protect the embryo
  • Endosperm and cotyledons supply nutrients
  • Seeds can be dispersed great distances, allowing colinisation of new habitats
  • Inhibitors only allow germination at suitable times of year
25
Q

What is germination?

A

Process in which the plant grows from a seed, where the dormant seed will undergo vigorous biochemical and developmental activity, which lasts until the first photosynthesising leaves are produced

26
Q

What are the optimum conditions for germination?

A
  • Temperature - optimum for enzyme activity, usually between 5 and 30 degrees celsius
  • Water - needed to mobilise enzymes, for transport in the xylem and phloem
  • Oxygen - needed for aerobic respiration for ATP production, fueling metabolism and growth
27
Q

Explain mobilisation of food reserves and germination…

A
  • Begins with rapid absorption of water
  • Tissues swell providing suitable conditions for enzyme activity
  • Insoluble food stores must be hydrolysed, using amylase and proteases
  • Products are transported to the embryo and carried in the phloem to the apical meristems
  • Swelling causes the testa to split, causing the radicle and plumule to emerge
  • Plumule elongates rapidly and pushes its way up through the soil
  • Plumule emerges, hook straightens, leaves unfurl and photosynthesis begins while food reserves have been depleted
28
Q

How does dry mass change during germination?

A

Dry mass of the seed and embryo increases, while the dry mass of the cotyledon decreases

29
Q

Describe germination a broad bean…

A
  • Endosperm has been absorbed by the cotyledon
  • Amylase digests starch into maltose
  • Proteins are broken down into amino acids
  • Fats are broken down into fatty acids and glycerol
  • Products are transported to the embryo for mitosis
30
Q

Describe germination in barley seed…

A
  • Endosperm is present (not within the cotyledon)
  • Starch, proteins, and fats are present in the endosperm
  • The embryo produces gibberellic acid, which diffuses into the aleurone layer causing the break down of proteins into amino acids
  • Amino acids used to synthesis enzymes e.g., amylase to break down starch into maltose
  • Maltose is transported to the embryo
31
Q

What is the effect of gibberellin?

A

Speeds up germination so seeds need to be kept warm for less time, so more malted barley can be produced

32
Q

What is gibberellic acid?

A

Plant growth regulator which triggers the processes necessary for germination

33
Q

Summarise germination using gibberellic acid…

A
  • Embryo produces GA which diffuses into the aleurone layer
  • Enzymes hydrolyse proteins into amino acids
  • Amino acids form the enzyme amylase
  • Amylase diffuses into the endosperm, where starch is hydrolsyed into maltose
  • Maltose is transported to the embryo
  • Maltose is hydrolysed into glucose for respiration, while ATP provides energy for mitosis
34
Q

How is wind used as a dispersal method?

A

Different species have mechanisms which enable pollen/spores to be dispersed by the wind

35
Q

How is transport used as a dispersal method?

A

Organisms eat seeds which pass through the digestive system, where carification weakens the testa by the actions of enzymes and stomach acid

36
Q

How is rolling used as a dispersal method?

A

Seeds of plants roll away from the parent tree

37
Q

How is bursting used as a dispersal method?

A

Seeds scatter after the plant dries and splits

38
Q

How is water used as a dispersal method?

A

Seeds float in the water due to air cavities making them buoyant, where they can be carried away

39
Q

How is carrying used as a dispersal method?

A

Seeds attach to animal coats and are carried away

40
Q

What is chemical incompatibility?

A

Gametes from the same parent plant fail to fuse to form a zygotre, or the embryo plant does no develop if the zygote is formed

41
Q

What is irregular flower sturcture?

A

Stigmas and anthers are at different levels, within the flower, which makes it less likely self-pollination can occur

42
Q

What is dichogamy?

A

Anthers and stigmans mature at different times

43
Q

What are monoecious plants?

A

Plants which have seperate male and female flowers on the same plant

44
Q

What are dioecious plants?

A

Plants that have seperate male and female plants

Biology A-level (Unit 4) (8 decks)

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