22 Plant reproduction

Question 1

what is the definition of pollination?

Answer 1

the transfer of pollen grains from male reproductive structures to female reproductive structures (of another plant) prior to fertilisation

Question 2

what is self-pollination?

Answer 2

pollen is transferred to a stigma of the same flower/another flower on the same plant

Question 3

what is the advantage of self-pollination?

Answer 3

more reliable than cross-pollination

Question 4

what is the disadvantage of self-pollination?

Answer 4

less genetic variation –> inbreeding –> disadvantageous recessive characteristics more likely to be passed on

small gene pool makes population susceptible to disease

Question 5

how is self-pollination avoided?

Answer 5

male and female parts mature at different times (protandry and protogyny)

physical separation of male and female parts

some flowers are monoecious (i.e. only male/female)

chemicals on stigma prevent pollen grains from same plant producing pollen tube (self-incompatibility)

Question 6

what is cross-pollination?

Answer 6

pollen is transferred from one plant’s anther to another plant’s stigma

Question 7

what are the features of plants that are pollinated by insects?

Answer 7

colourful, scented petals (can mimic female insects)

nectar produced

short stamen with firmly attached anthers

small, sticky pollen grains

small, sticky stigma

Question 8

what are the features of plants that are pollinated by the wind?

Answer 8

small and inconspicuous petals

long stamen with loosely attached anthers

large, smooth, light pollen

large, feathery stigma

Question 9

what are the advantages of cross-pollination?

Answer 9

increases variation and widens gene pool

more heterozygous plants ∴ allele frequency of advantageous genes increases

population less susceptible to epidemic disease

better chance of adaptation to environment

Question 10

what are the disadvantages of cross-pollination?

Answer 10

requires a pollinating agent

waste of energy

transmission of disease more likely

takes longer

fewer offspring produced

Question 11

outline the first stage of fertilisation in angiosperms (flowering plants) (4)

Answer 11

pollen grain lands on stigma, completes development and matures

pollen tube grows a cytoplasmic extension down the style (chemotropism), controlled by tube nucleus

pollen tube enters the ovule through the micropyle

tube tip bursts to release male gametes

Question 12

outline the second stage of fertilisation in angiosperms (4)

Answer 12

double fertilisation:

• one sperm nucleus fuses with ovum –> zygote
• one sperm nucleus fuses with 2 polar nuclei within embryo sac –> 3n endosperm tissue –> embryo food supply

ovules develop into seeds (containing embryo and endosperm)

ovary develops into fruit

Question 13

what is the genetic advantage of fertilisation in angiosperms?

Answer 13

restores chromosome number to diploid

increases genetic variation

Question 14

what are the features of a seed’s embryo?

Answer 14

plumule = shoot

hypocotyl = simple stem

radicle = root

1 or 2 cotyledons

Question 15

what are the three main features of an endospermic seed?

Answer 15

embryo

endosperm

testa

Question 16

why might a seed lack an endosperm?

Answer 16

to prevent it from germinating in the autumn/winter by reducing its metabolic rate

Question 17

what would a seed have instead of an endosperm?

Answer 17

seed leaves - absorb nutrient reserves from the endosperm

Question 18

what is the function of the micropyle?

Answer 18

to allow the entry of water and nutrients to the seed

Question 19

what is the definition of germination?

Answer 19

plant growth from a seed, including the growth of an embryo root and shoot

Question 20

what are gibberellins?

Answer 20

plant ‘hormones’ required for germination as growth regulators and cell signalling molecules

Question 21

outline the process of germination (5)

Answer 21

exposure to water causes rehydration of the seed

water washes out enzyme that was inhibiting growth

metabolic rate reactivated

insoluble starch in endosperm hydrolysed to maltose by a-amylase and then to G/S by maltase

gibberellins induce synthesis of amylase –> initiates break down of starch

Question 22

how does water affect germination?

Answer 22

enters by osmosis and softens testa to allow it to rupture

mobilises food reserves in the endosperm

activates enzymes

required for hydrolysis and as a solvent

washes out germination/growth inhibitors

Question 23

how does temperature affect germination?

Answer 23

increased metabolic rate

enzymes reach optimal temp

food reserves can be digested

respiration and growth are therefore moderated

Question 24

how does oxygen affect germination?

Answer 24

required for aerobic respiration

required for oxidation of glucose and lipids as respiratory substrates

Question 25

what are the three vegetative structures?

Answer 25

root

stem

leaves

Question 26

what are triggers for development to the reproductive phase?

Answer 26

temperature

duration of dark period

Question 27

what is unique in each flowering plant that causes it to flower?

Answer 27

the proportions of Pr and Pfr

Question 28

what are the two isomers of phytochrome?

Answer 28

Pr - 660nm

Pfr - 730nm

Question 29

what is photoperiodism?

Answer 29

the reactions of Pr Pfr that occur in daylight and darkness

Question 30

which phytochrome accumulates in darkness?

Answer 30

Pr

Question 31

how is day length measured by the plant?

Answer 31

the conversion rate of Pr –> Pfr

Question 32

how is the apical meristem triggered to its development phase?

Answer 32

active form of phytochrome

causes transcription of flowering time gene

FT mRNA transported in phloem to shoot apical meristem

translated to FT protein

protein binds to transcription factor

activation of flowering gene –> reproductive meristems

Question 33

give an example of a cereal

Answer 33

rice

maize

wheat

Question 34

why are cereals used as a source of food by humans?

Answer 34

rich in starch

Question 35

what is the definition of global supply?

Answer 35

the annual production of a specific crop, plus stockpiles of it carried over from previous years

Question 36

what is the effect of the increasing human population on cereal production?

Answer 36

increasing use

demand exceeding supply

Question 37

why is sustainability of food increasingly more difficult?

Answer 37

population increasing

BUT available land and water decreasing

+ increasing costs