Download Growth of pollen tubes (micrometres)

Knowing how pollination leads to
fertilisation
Aseel Samaro
 It is a pollen grain from a sunflower.
 Pollen comes in a variety of shapes and sizes
 The variety means that you might be allergic to one
type but not another.
 The world’s chocolate supply depends on midges.
 These tiny flies are the only insects that can pollinate the cacao plant.
 Once fertilised, the plant produces seeds, which are used to make
coffee and chocolate.
Fertilising Plant
 Pollen contains the male sex cell.
 The female sex cell, the egg cell, is found in the ovule.
 The pollen travels down the style to reach the ovule by growing a long
tube.
 Once it has reached the ovule, the nucleus of the male sex cell joins
with the nucleus of the egg cell – this is fertilisation.
 The result is a new seed, which will eventually become a new plant.
Describe how pollination and fertilisation
differ.
Pollination is the transfer of pollen; fertilisation is the nucleus of a male cell fusing with an egg cell in the ovary.
VIDEO
Pollen tubes
 When a pollen grain lands on the stigma of another plant, the tube
cell uses stored nutrients and sugars to grow a pollen tube down to
the ovule.
 The concentration of sugar affects the ability of the pollen grains to
grow tubes.
The effect of sugar on the growth of pollen tubes
5
Sugar
concentration (%)
growth of pollen
tubes
(micrometres)
250
10
15
20
350
450
200
As the sugar concentration increases, the growth of the pollen tube
increases; up to a concentration of 15%; after which any increase in
sugar concentration inhibits the growth of pollen tubes.
Factors affecting the growth of pollen tubes
 Many factors affect the growth of pollen tubes.
 The pollen grain is dry when it lands on the stigma.
 Chemicals in the stigma enable water to enter the pollen grain so it can
grow.
 These include sugar.
 In some plants, if pollen lands on the stigma of the same plant, chemicals
prevent it from growing pollen tubes so it cannot fertilise itself.
 If the temperature is hotter  pollen tubes grow faster.
 Once the tube has formed, chemicals in the stigma direct the pollen
tube to the ovule.
 Only one pollen cell fertilises the egg.
The growth of pollen tubes in different sugar concentrations
5
Sugar
concentration (%)
10
15
20
Growth of pollen
tubes
(micrometres) –
experiment 1
225
345
200
213
Growth of pollen
tubes
(micrometres) –
experiment 2
250
350
450
207
Growth of pollen
tubes
(micrometres) –
experiment 3
275
355
450
250
The effect of temperature on pollen tube growth
Temperature
(°C)
15
0
Growth of
pollen tubes
(micrometres)
20
25
30
35
40
200
420
700
800
100
Which has the bigger effect on pollen tube growth, from these data?
Why do you think this?
Temperature has the greater effect; longer growths are recorded.
Which data would you trust more – explain why.
The data in the effect of sugar concentration experiment is more reliable; the experiment has
been carried out three times for each concentration.
Did you know ?
 Pollen that does not land on a stigma remains in the environment.
 It is the primary cause of hay
fever and allergies.