2.21 Processes of Pollination and Fertilisation

Question 1

Self Pollination

Answer 1

Where pollen from the same plant is used (identical genetic material)
Pros:
Identical to parent
Does not depend on pollinators or presence of other plants of same species
Plants which are not normally self-fertile can utilise their own pollen in extreme circumstances.

Question 2

Cross Pollination

Answer 2

Where pollen from different plants is used
Pros:
Provides variation in offspring /enables evolution.
hybrid vigour
improved seed fertility
Cons:
Energy used in attracting pollinators
Requires pollination, even if human

Question 3

Self Fruitful

Answer 3

Capable of fertilisation with its own pollen

Question 4

Self Unfruitful

Answer 4

Do not become fertilised when self pollinated

Question 5

Cross Fruitful

Answer 5

Become fertilised when cross pollinated

Question 6

Cross unfruitful

Answer 6

Non compatible when cross fertilised

Question 7

Process of Pollination

Answer 7

Pollen grain has to be accepted by stigma (must be of correct species and from different plant (for x pollination)
Pollen grain sticks to stigma
Intine (internal strata) absorbs moisture from stigma, swells and ruptures the extine (outer strata)
Intine grows into aperture and forms pollen tube
Pollen tubule grows rapidly down style canal to ovary
Tube carries 2 sperm cells.
Penetrate ovary through micropile and sperm are released
One of the sperm fuses with the female sex cell to form a zygote
The other fuses with the other nucleus in the ovule (primary endosperm nucleus) which produces a structure that divides and developes into a food store (endosperm) which nourishes the developing plant
If pollen not same species = rejected
Gameteophytic incompatibility
N.B Germination is the development of a plant from a seed (i.e. a later stage)

Question 8

Pollination - definition

Answer 8

The transfer of pollen by an agent (honeybee)

from anther to receptive stigma

Question 9

Fertilisation - definition

Answer 9

The fusion of a male gamete (from pollen) with female gamete (in the ovule/egg) to produce a single cell (zygote) with the full compliment of chromosomes with the potential to grow into a plant

Question 10

Process of Fertilisation - IOTTE

Answer 10

1. Inside ovary 2 sperm cells released from pollen tubule
2. One fuses with egg cell nucleus
3. The other fuses with pollen nuclei to form endosperm
4. Together these form the seed
5. Enclosed in receptacle which grows to protect the seeds within it

Question 11

To prevent self fertilisation

T
S
H
Mono
Dio

Answer 11

1. Timing - Pollen ripens before the stigma is receptive (protandry) chamerion angustifolium, rosebay willow herb, or stigma receptive before pollen ripe (protogyny).
2. Self-incompatibility stigma will not accept pollen from same plant (sporophytic incompatibility)
3. style and stamens at different Heights in different plants so pollen is on different part of pollinators body. Primula vulgaris has two forms thrum-eyed and pin-eyed with stamens of different lengths and pollen grains of different size.
4. Monoecious plants - separate male and female flowers on same plant – corylus avellana, hazel.
5. Dioecious plants - separate male and female flowers on different plants - ilex aquifolium, holly.

Question 12

What attracts bees to flowers?

ACSTT (All Come Sit To Talk)

Answer 12

The following are in order of decreasing distance from the flower that the signals become effective.
Aroma - The bees’ sense of smell is better than their vision and will detect flowers from further away.
Colour - Bees have poor vision at the red end of the spectrum but are sensitive to UV light
Shape - many flowers have veins along the petals which show up in the near UV to guide the bees to the nectaries.
Texture - the texture of the petals may influence the readiness of bees to land
Taste - higher sugar contents will be more attractive to bees and will encourage them to visit similar flowers.

All five are liable to change once the flower has been fertilised signalling to the bees that their services are no longer required.

Question 13

What makes bees good pollinators?

Answer 13

Surviving en masse over winter in clusters
Emerge in Spring en masses
Can be moved onto crops en masse
Faithful flower type/foraging visit
Pollinates non stop (except in bad weather/cold
During daylight (sp spraying at night is possible)
Possibly mark sources with nasonov and direct other bees to it
Hairy - covered in plumose hairs that trap pollen to be deposited on next flower
Waggle dance - communicate sources to other bees

Question 14

Development of the Female Gamete

Answer 14

1. Carpel comprises ovary surmounted by a slender style which terminates in a small swelling called the stigma
2. Ovary is hollow and contains one or more ovules. Ovules begin as a protuberance projecting into the cavity
3. Initially a uniform mass of cells called nucleus. Undergoes meiosis to form 4xhaploid cells
4. 3 x haploids die, remaining one undergoes 3 x mitotic divisions making 8 daughter nuclei, 4 at each end of the embryo sac
5. One nucleus will move from each group into the middle to form polar nuclei. One of the cells at the micropyle end becomes the functional egg (female gamete) the other two are called synergids. The three cells at the other end of the embryo sac are called antipodal cells.

Question 15

Development of the Male Gamete

Answer 15

1. Anther contains 4 x pollen sacs in which pollen grains develop
2. Each mother cell is diploid
3. Divides by meiosis to give 4 haploid cells which will develop into a pollen grain
4. Thick outer wall (extine) thin inner wall (intine)
5. Each haploid nucleus divides mitotically into 2 nuclei - one the generative nucleus, one the tube nucleus
6. When pollen is ripe the outer layers of the anther dihisce