2- sexual reproduction in plants

Question 1

pollen formation

Answer 1

1) diploid microsphere mother cells (anther) undergo meiosis to form 4 haploid microspores
2) in each microspore, the nucleus undergoes mitosis to form 2 haploid nuclei: the tube cell nucleus, the generative nucleus (male gamete)
3) the microspore (single cell containing 2 nuclei) is now called a pollen grain

Question 2

ovum formation

Answer 2

1) diploid megaspore mother cells (ovule) undergo meiosis to form an ootid and 3 polar bodies
2) the ootid undergoes 3 mitotic divisions to form an embryo sac which contains: egg cell which forms the zygote, 2 polar nuclei which form the endosperm, 2 synergids which help the generative nucleus reach the egg cell, 3 antipodal cells, and a protective coating

Question 3

pollen grain germination

Answer 3

the pollen grain containing the tube cell nucleus and generative nucleus, adheres to the stigma of the flower. this triggers the pollen grain to germinate

Question 4

pollen tube growth

Answer 4

the tube cell nucleus guides the growth of a structure called the pollen tube down the style of the flower. this growth is facilitated by the secretion of digestive enzymes that break down surrounding tissue for nutrients

Question 5

pollen response to stimuli

Answer 5

the pollens tube growth direction is influenced by various stimuli such as water, gravity and certain chemicals

Question 6

entry into the embryo sac

Answer 6

the pollen tube grows through the micropyle (a tiny opening) into the embryo sac of the ovule

Question 7

generative nucleus division

Answer 7

inside the pollen tube, the generative nucleus divides by mitosis to form two haploid sperm nuclei

Question 8

delivery of sperm nuclei

Answer 8

these two sperm nuclei are then delivered to the embryo sac through the pollen tube. one sperm nucleus will fertilise the egg cell to form a zygote while the other will combine with two polar nuclei to form the endosperm, a nutrient rich tissue that feeds the developing embryo

Question 9

flowering plant fertilisation diagram

Answer 9

Question 10

double fertilisation inside the embryo sac to form a triploid endosperm and zygote

Answer 10

1) pollen tube- the pollen tube reaches the ovule, grows through the micropyle and enters the embryo sac
2) pollen tube breakdown- its tip breaks down, leading to the disintegration of the pollen tube nucleus
3) diploid zygote- one male nucleus fuses with the female gamete, forming a diploid zygote
4) triploid endosperm- the other male nucleus fuses with 2 polar nuclei, forming a triploid endosperm
5) degeneration of other nuclei- the remaining 5 nuclei within the embryo sac degenerate