Question

20. Describe the characteristics of, and relationship between, the following: Auxin, geotropism,

phototropism, gravitropism, cytokinins, gibberellins, abscisic acid, ethylene, apical dominance.

16. Explain double fertilization and how it differs from a conifer life cycle.

17. Describe the relationship between the following terms: embryo, plumule, cotyledon, scutellum, endosperm, radicle, epicotyl, hypocotyl, root, and shoot.

18. What are characteristics of monocots and dicots?

12. How are a conifer seed and flowering plant seed different?

13. Describe the following types of flowers: perfect, imperfect, complete, incomplete, regular,

irregular.

14. Describe the flower characteristics: sepal, receptacle, petal, stamen, anther, filament, carpel,

pistil, stigma, style, ovary, ovule, seed.

10. Describe the characteristics of, and relationship between, the following: Gymnosperms,

Angiosperms, Coniferophyta, Ginkgophyta, Cycadophyta, Gnetophyta, Anthophyta, Monocots, Eudicots (Dicots).

8. What is the evolutionary importance of pollen grains?

6. Describe the characteristics of, and relationship between, the following: Bryophytes,

Bryophyta, Hepatophyta, Anthocerophyta, Lycophyta, Pterophyta, vascular, avascular, gametophyte dominant, sporophyte dominant.

please answer those questions as many as you can

Answer 1

Q20)

Describe the characteristics of, and relationship between, the following: Auxin, geotropism,

phototropism, gravitropism, cytokinins, gibberellins, abscisic acid, ethylene, apical dominance.

Answer-

Auxin helps in the growth of stem, and inhibits growth of lateral buds, this helps in apical dominance. It goes towards the darker side of plant and causes the cells to grow larger than the lighter side of the plant as a result there appears a curvature in plant, causing the stem tip grow towards light by which phototropism or bending of stem towards light occurs. Helps in gravitropism, that is growth of roots towards gravitation or soil, or geotropism.

Cytokinin promotes cell division, they are produced in growing areas like tip of shoot.

Plant growth depends on the ratio of auxin to cytokinin, when auxin alone present plants only grow but do not divide, but when cytokinin is added it, it grows and divide. When auxin and cytokinin are present in equal amount the parenchyma cells form an undifferentiated callus tissue or hard tissue, if auxin amount is more it causes root formation, if cytokinin is more it causes shoot formation or (growth of stem, leaf, flowering parts etc.)

Gibberlins helps in stem elongation, germination, flowering. Effect of auxin is stronger in presence of gibberlin for cell elongation.

Abscisic acid promotes seed dormancy and delays seed germination, inhibits shoot growth, also plays an important role in opening and closing of stomata.

Auxin induces shoot apical dominance, that is the axillary buds are inhibited by auxin, due to high concentration of auxin in plant, it stimulates synthesis of ethylene in axillary buds, by which there is inhibition of their growth and apical dominance takes place. When the apex of the plant is removed, the inhibitory effect is removed and the growth of lateral buds increases.

Q16)Explain double fertilization and how it differs from a conifer life cycle.

Answer:- In Flowering plants two male gametes are discharged from the pollen tube into embryo sac or megagametophyte. Of the two gametes one fuses with the egg-cell and gives rise to embryo and the other fuses with the diploid secondary nucleus to produce the endosperm nucleus. As the process of fertilization occurs twice in an embryosac, it is called double fertilization.

In conifers the pollen grain develops an outgrowth called pollen tube, it penetrates the egg cell within an archegonia, sperm cells via pollen tube goes to fertilize the egg. When fertilization is over, embryo develops within the female gametophyte and ovule becomes seed. It is complete with its food source, the gametophyte tissue and seed coat the integument. Embryo becomes a new sporophyte.

In angiosperms ovule has an egg cell and a diploid fusion nucleus, due to fusion of two polar nuclei in the ovule. When pollen grain comes in contact with stigma, it sends pollen tube down into the ovary at the pistil base. When pollen tube enters ovule it releases two sperm cells, one fuses with egg cell to form a diploid zygote other joins with fusion nucleus to form a triploid nucleus. This triploid nucleus converted into endosperm and nourishes the developing embryo.

In conifers ovule becomes a seed enclosing the embryo and endosperm in seed coat but in angiosperm ovary containing ovule develops into a fruit after fertilization. Fruit protects the embryo from dessication and also helps in dispersal when animals eat them