reproduction in plants

Question 1

define sexual and asexual reproduction

Answer 1

-fusion of haploid nuclei of two gametes to form a genetically unique zygote
-process resulting in the production of a genetically identical offspring from one parent, without the fusion of gametes

Question 2

state the function of sepal, petals, anthers, filament, stigma, style ovary and ovule

Answer 2

-modified leaf that protects the flower during bud stage
-modified leaf that forms the most obvious part of a flower that in insect pollinated flowers, is brightly coloured to attract insects for pollination and provides a landing platform for insects
-filament holds the anther in a suitable position to disperse pollen grains
-anthers produce pollen grains
-stigma is a swollen structure to achieve pollen grains, matured one secretes sugary fluid to stimulate the germination of pollen grains
-style connects stigma to ovary, holding the stigma in a suitable position to trap pollen grains
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Question 3

process of self pollination

Answer 3

-transfer of pollen grains from the anther to the stigma of the same flower of different flower of the same plant
-flowers are bisexual with anthers and stigma developing at the same time, stigma is situated directly below anther

Question 4

advantages and disadvantages of self pollination

Answer 4

-beneficial qualities are passed down to offspring
-less pollen and energy is wasted
-not dependent on external factors
-more likely to occur since stigmas are close to anthers
-only one parent is required
-offspring produced are genetically similar to parents causing fewer varieties of offsprings
-probability of harmful recessive alleles being expressed in offspring is higher compared with cross-pollination

Question 5

process of cross-pollination

Answer 5

-transfer of pollen grains to the flower of another plant
-dioecious plants bear either only male or female flowers, making self pollination impossible
-can occur in bisexual plants when stigma and anthers occur at different times, or when stigmas are situated a distance away from anthers

Question 6

advantages and disadvantages of cross pollination

Answer 6

-probability of harmful recessive alleles being expressed in offspring is lower compared with self pollination
-offspring can inherit beneficial qualities from both parents
-more varieties of offspring can be produced which leads to greater genetic variation
-increased probability of offspring being heterozygous
-seeds produced are able to survive longer before germination
-two different parents are required
-less likely to occur
-more energy and pollen wasted
-dependent on external factors

Question 7

describe fertilisation in plants

Answer 7

-after pollination, the pollen grain germinates in response to the sugary fluid secreted by the matured stigma
-pollen tube grows out of the pollen grain, and it is controlled by the pollen tube nucleus
-cytoplasm and two nuclei passes into the pollen tube, secreting enzyme to digest the surrounding tissue stigma and style
-pollen tube enters the ovule through the micropyle
-generative nucleus divides into two male gametes while pollen tube nucleus disintegrates
-when pollen tube reaches the ovule, it absorbs the sap and burst, releasing two male gametes
-one male gamete fuses with the ovum to form the zygote, the other male gamete fuses with the definitive nucleus to form the endosperm nucleus
-zygote divides and develops into an embryo, and endosperm nucleus gives rise to endosperm

Question 8

what is seed dispersal

Answer 8

seed dispersal is the movement or transport of seeds away from parent plant to colonise new areas, avoid overcrowding and competition for limited resource