Plant Reproduction

Question 1

What is an angiosperm?

Answer 1

Flowering plant
Insect pollinated

Question 2

What are the female parts of a flower?

Answer 2

Carpal = collective name
- stigma = sticky to trap pollen on the surface
- style = holds the sticky stigma where it can come into contact with insects
- ovary = protects the ovule
- ovule = female gamete (meiosis)

Question 3

What are the male parts of the plant?

Answer 3

Stamen = collective term
- filament = thin, stalk like, contains vascular tissue to provide another with nutrients
- anther = produces pollen (with male gametes inside by meiosis)

Question 4

What are the other parts of the plant?

Answer 4

Nectary = secretes nectar
Petal = brightly coloured/scented to attract insects
Sepal = protects the flower when in bud, green to aid photosynthesis
Receptacle = part of the stalk where the flower is attached

Question 5

What is the collective name for the sepals?

What is the corolla?

Answer 5

Calyx

All of the petals on the flower

Question 6

Is there petals, scent, and nectar on insect and wind pollinated plants?

Answer 6

Insect pollinated = petals are brightly coloured, produce scent and nectar to attract pollinating insects

Wind pollinated = absent or small petals, dull in colour - often green, no scent or nectar

Question 7

Where are the anthers on both insect and wind pollinated plants?

Answer 7

Insect pollinated = anthers within the flower so it is more likely to brush past an insect

Wind pollinated = anthers hang outside flower, so they can be blown in the wind

Question 8

Where are the stigma on both insect and wind pollinated flowers?

Answer 8

Insect pollinated = within the flower, sticky to trap pollen, can secrete chemicals to stimulate pollen tube growth

Wind pollinated = large and feathery, large surface area to catch pollen grains in the wind outside the plant

Question 9

What type of pollen and in what quantities is it present in both insect and wind pollinated plants?

Answer 9

Insect pollinated = small quantity, pollen has barbs/hooks on its surface to attach to the insect

Wind pollinated = large quantity as there is a lower probability of successful pollination, small smooth and lightweight

Question 10

What is the tapetum?

Answer 10

A layer within the anther that releases proteins, nutrients, and lipids that nourish the developing pollen. It also provides a waterproof coat for the pollen grain

Question 11

How are pollen grains formed?

Answer 11

• formed in the anther by mitosis and meiosis
• mitosis occurs to produce large numbers of diploid pollen microspore mother cells
• the microspore mother cells undergo meiosis to produce a tetrad of haploid cells
• the haploid cells form young pollen grains the contain the male gamete

Question 12

How does a young pollen grain mature?

Answer 12

The haploid nucleus inside the young pollen grains undergoes mitosis to produce two nuclei: a generative nucleus and a pollen tube nucleus

If pollinated, the generative nucleus will divide by mitosis to form two male nuclei

Question 13

What is the pollen cell wall formed of?

Answer 13

The intine (thin inner coat) and the exine (thick outer coat)

The exine is tough, resistant to chemicals, resists desiccation (drying out), is UV resistant (pollen can be carried at high altitudes without DNA mutation), and has barbs and hooks in a characteristic pattern

Question 14

What method of pollen dispersion can the qualities of exines be particularly important for?

Answer 14

Wind pollination
Pollen can be carried to high altitudes by the wind, so they must be able to resist higher UV radiation levels and resist drying out

Question 15

How is pollen released from the anther?

Answer 15

• the outer layers of the mature anther dry out, causing tension
• dehiscence occurs, and the tension pulls the walls of the anther apart and the edges of the pollen sacs curl away as the lateral groove ruptures
• the stomium (opening) exposes the pollen grains and they are carried away by insects or the wind

Question 16

How does the ovule develop in the ovary?

Answer 16

• the megaspore mother cell in the nucellus undergoes meiosis to produce four haploid megaspores
• three of the four megaspore cells degenerate and only one grows and develops
• this one megaspore undergoes tree mitotic divisions to produce eight genetically identical haploid nuclei within the embryo sac of the ovule - three antipodal cells, two synergids, two polar nuclei, and one female gamete
• the antipodal and the synergids degenerate, leaving three haploid nuclei, forming the egg cell

Question 17

What is the micropyle?

Answer 17

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

Question 18

What are integuments?

Answer 18

Structures that surround and protect the embryo sac, and eventually form the testa (seed coat)

Question 19

What is a funicle?

Answer 19

Attaches the ovule to the ovary wall

Question 20

What is pollination?

Answer 20

the transfer of pollen grains from the anther to the stigma

It is necessary so that the pollen grains (male gamete) come into contact with the female part of the flower so fertilisation can be achieved

Question 21

What is self pollination?

Answer 21

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

Some genetic variation through crossing over and independent assortment

Question 22

What are the advantages of self-pollination?

Answer 22

• only one parent is needed
• can help to maintain genotype which are well adapted to the current environment

Question 23

What are the disadvantages to self pollination?

Answer 23

• reduces genetic variation = offspring may be less likely to survive changes in the environment
• increases the chance of offspring being homozygous for recessive allele (don’t code for functional protein) , which could lead to genetic diseases (many genetic diseases are caused by caused by genetic mutations resulting in defective recessive alleles)

Question 24

What is cross pollination?

Answer 24

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

Increases genetic variation through crossing over, independent assortment, and mixing of parental genotypes when haploid gametes fuse

Question 25

Why is cross pollination of greater evolutionary significance than self pollination?

Answer 25

It increases genetic variation so a species can adapt to environmental change though natural selection

Question 26

How can cross pollination be prevented during plant reproduction experiments?

Answer 26

Prevent the transfer of pollen grains from on flower to another by enclosing or isolating a flower in a bag

Question 27

Where are nectaries located in insect pollinated flowers, and why is this advantageous?

Answer 27

- below the anther/stigma - it promotes insects transferring pollen grains s they will brush past the anther/stigma when going down to the nectaries

Question 28

How have plants evolved to ensure that cross pollination occurs?

Answer 28

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 = pollen is unable to germinate on the stigma of the flower which produced it (e.g. red clover) 4- separate male and female plants (unisexual) = the plant does not have both male and female sex organs so cannot self pollinate (e.g. holly)

Question 29

What is the process of fertilisation?

Answer 29

- when a compatible pollen grain lands on a stigma, the stigma secretes a sugary solution - the pollen grain germinates, the generative nucleus undergoes mitosis to form two male gamete nuclei, and the pollen tube nucleus controls the growth of the pollen tube - the pollen tube nucleus codes for hydrolytic enzymes that digest through the tissues of the style, the products of digestion are then used by the pollen tube - the pollen tube nucleus is at the tip of the pollen tube with the two male gamete 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 two male nuclei into the embryo sac of the ovary - one male gamete fuses with the female gamete to produce a diploid zygote - the other male gamete fuses with the two polar nuclei in the embryo sac to form a triploid primary endosperm nucleus (double fertilisation)

Question 30

What are the similarities with fertilisation in humans, and fertilisation in plants?

Answer 30

- both involve the fusion of haploid gametes to form a diploid zygote - both involve internal fertilisation in the female - both involve the secretion of digestive enzymes to digest a path for the male gene to reach the female gamete

Question 31

What are the differences between fertilisation in humans, and fertilisation in plants?

Answer 31

- double fertilisation in plants, single fertilisation in humans - pollen tube formation in plants, but acrosome reactants in humans - male gamete is able to swim in humans (has flagellum) towards the secondary oocyte, but pollen grain must form a pollen tube through which the male gamete moves

Question 32

What does the diploid zygote form in a mature plant?

Answer 32

it divides by mitosis to form a diploid embryo, consisting of the plumule (developing shoot), and a radicle (developing root) and one or two cotyledons

Question 33

What does the triploid endosperm cell (central) form in a mature plant?

Answer 33

It divides by mitosis to form endosperm tissue, which is an important food storage tissue (starch = amylose/amylopectin) in cereal grains e.g. wheat and maize

Question 35

What does the ovary wall and the ovule form in a mature plant?

Answer 35

Ovary wall = develops into the fruit wall, to enclose the seeds Ovule = seed (embryo is within the seed)

Question 36

What do the integuments and the micropyle form in a mature plant?

Answer 36

Integuments = develops into the testa (seed coat = prevents drying out, resists frost) Micropyle = remains as a pore in the testa (allows water to enter - needed for the germination of the seed)

Question 37

What is the hilum?

Answer 37

A scar on the seed left by the funicle

Question 38

What is a cotyldon?

Answer 38

The part of the embryo that absorbs starch from the endosperm in monocots In dicots = food storage tissue

Question 39

What is a monocotyledon?

Answer 39

- a seed with only one cotyledon - contains endosperm (is endospermic) - maize and wheat

Question 40

What is a dicotyledon?

Answer 40

- a seed with two cotyledons with the embryo lying between them - do not have an endosperm (non-endospermic) as they use the cotyledons as food tissue

Question 41

What are the adaptations of a seed for life on land?

Answer 41

- testa is chemically resistant, so seeds survive adverse chemical conditions, and provides physical protection - endosperms/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 42

Why is seed dispersal important for plants?

Answer 42

- reduces intraspecific competition for nutrients (nitrates/phosphates/oxygen) with the parent plant, and the other offspring plants - allows for colonisation of other areas

Question 43

Why are fruit important in seed dispersal?

Answer 43

- fruit is ingested by animals, the seed passes through the animals digestive system and is then egested. This disperses the seeds - fruit may be adapted for a specific mode of dispersal

Question 44

What are some adaptations for seed dispersal?

Answer 44

- buoyancy = coconut seeds float on water and is distributed away from the parent - lightweight = lightweight seeds can easily be carried by the air/wind currents - spikes/barbs = the seeds can attach to animal fur

Question 45

What are the three main requirements for successful germination and why?

Answer 45

Water = mobile enzymes for transport, enters cells by osmosis (down WP gradient) to make them turgid = important in growth Oxygen = aerobic respiration in the cells of embryos to produce ATP = more cell division (mitosis) Temperature at optimum for enzymes = higher temperatures means higher kinetic energy which means more enzyme-substrate complexes form

Question 46

How are non-endospermic seeds germinated?

Answer 46

- water is imbibed through the micropyle - tissues swell, splitting and softening the testa and allowing the entry of more oxygen - oxygen can then be used in aerobic respiration to produce ATP energy for metabolism - mobilised enzymes hydrolyse large, insoluble food stores (amylase -> starch into maltose etc) - the soluble products are transported to the plumule and radicle for use in aerobic respiration to produce ATP energy for mitosis and growth - the plumule grows upwards whilst the radicle grows downwards - the plumule emerges from the soil, the leaves unfurl and begin to photosynthesise meaning the plant is now independent of the food stores in the cell

Question 47

How are endospermic seeds germinated?

Answer 47

- water is imbibed through the micropyle - the tissues swell, splitting or softening the testa to allow entry of more oxygen - oxygen can be used in aerobic respiration to produce ATP energy for metabolism - gibberellin is releases by the embryo and diffuses to the aleurone layer - in the aleurone layer, gibberellins stimulate aleurone cells to produce proteases to hydrolyse the protein stores (releases amino acids) - amino acids from protein hydrolysis are now used in translation to form amylase from aleurone cells - amylase diffuses into the endosperm and hydrolyses the starch there into maltose - maltose is absorbed by the embryo to be used in respiration to produce ATP energy for cell division and the growth of the plumule and the radicle