Chapter 5 Flashcards
what is asexual reproduction?
method that does not involve the fusion of gametes.
There are many types:
binary fission, multiple fission, budding, vegetative propagation, spore formation (sporogenesis), fragmentation, parthenogenesis, and cloning.
binary fission
means splitting in two. the simplest asexual repro method, found in bacteria, protozoa, some invertebrates. Remarkably fast under ideal conditions, some bacteria split every 20 mins.
In the process, bacterium duplicates its chromosomes and then divides into two cells. The daughter bacteria grow and divide again. In protozoa, mitosis of parent organisms produces daughter cells of equal size. They are identical to their parent cell.
Some invertebrates like planaria reproduce through this method by splitting in halve.
Multiple fission
mitosis that requires the formation of a spindle and a mitotic apparatus. Does not occur in bacteria (prokaryotes).
under unstable conditions, cells divide rapidly. In this, a protective cyst is formed, inside which the nucleus divides rapidly to produce many daughter nucleoli. Cytoplasm surrounds each nucleus forming multiple spores, each of which develops its own tough resistant wall, forming more cysts. The parent cell breaks up and the spores are liberated.
Each spore develops into a tiny organism when ideal conditions are available.
Fragmentation
Aka regeneration, it is the process in which a lost body part is regenerated or a new organism grows from a piece of the organism. It is common in echinoderms and flat worms.
Budding
Budding in yeast: parts of cells soften and bud outwards, allowing cytoplasm to flow into it. The nucleus divides by mitosis into two nuclei, one of which enters the bud, which then separates once organelles like the mitochondria fill its increasing size. Sometimes bud remain attached to the parent cell, forming a chain and subchain of yeast cells.
budding in hydra: a small outgrowth on the parent body, which grows into a new individual. Hydra buds elongate rapidly, developing mouth and tentacles while still attached to the parent body for sometimes until it detaches and becomes independent.
spore formation (in rhizopus)
seen generally in fungi like the rhizopus. It bears saclike structures called sporagia, which is spherical in shape with large numbers of spores contained inside. Spores are tiny cells surrounded by a thick cell wall, when the sporangium bursts and spores are released, they fall in a suitable place and their cell wall ruptures. A new rhizopus is formed.
parthenogenesis
unfertilized eggs develop into new offspring. example, queen bee of a bee hive lays two eggs, one type develops into haploid males (drones), while the other develops into diploid females (worker and new queen bees).
Cloning
Clones are groups of people having the same genetic makeup. Produced by a single parent using artificial propagation using tissue culture.
describe different types of asexual reproduction in plants
aka vegetative propagation. New plant is formed from a vegetative part of a parent plant.
natural v propagation: occurs by means of root, stem, and leaves. Types are:
A) Creeping stem: two types, runners and suckes.
Runners are thin, long and week stems which creep along the surface of the ground and produced adventitious roots and lateral buds at the nodes. Internodes often die, leaving new plants independent of one another. When internodes dont die, plants are linked together by the runner. (grasses, strawberry)
Suckers are underground stems and shoots which contain stored food and numerous buds which grow into new plants by stored food (ginger, corn, potato, and onion)
B) Leaves; in plants such as bryophyllum, a series of buds develop on the leave at the end of the vein. When a leave falls, the bud develops into a new plant.
describe artificial propagation
Growing of new plants from the cut portions of a vegetative body. two types, Grafting and Stem cutting.
stems are cut diagonally, with necessary nodes and buds with at least two nodes being close to the end that is inserted into the soil. removal of the leaves is crucial to avoid transpiration (rose and sugar cane)
grafting includes a shoot piece of one type of plant being attached to the stem of another of the same variety. The piece is called stock while the stem it’s attached in is called scion which are typically of higher quality than the stock. (fruit trees)
advantages and disadvantages of fruit artificial propagation
Advantages: desired characteristics are retained in the offspring. Large number of identical plants are gown. New plants take less time to mature.
Disadvantages: new varieties are not produced. Plants are less resistance to diseases and environmental changes. Plants become localized.
structure of a flower
four main whorls known as calyx, corolla, androecium and gynoecium.
the outmost whorl has green leafy structures known as sepals, collectively called calyx which protect the closed bud.
second whorl is usually brightly colored petals called the corolla.
third whorl has male reproductive structures androecium which consists of stamens, each stamen having filament and anther.
Innermost structure is gynoecium, female repro component. carpel is its individual unit and has a stigma, style, and ovary inside which there are many ovules.
flowering plants reproduce by seeds.
Life cycle of flowering plants
consists of two generations: Sporophyte and gametophyte.
Lifecycle of angiosperms follows alternate generations. The haploid gametophyte alternates with the diploid sporophyte during the sexual reproduction process of angiosperms. Flowers contain repro structures.
Sporophyte is the plant body, a multicellular diploid generation. It produces haploid spores, produced by meiosis. Male spores are produced in the anther. Female spores are produced in ovules.
Gametophyte is the part that produces gametes. Small, multicellular, haploid generation. Spores divide mitotically to form gametophyte of two types, male and female.
female gametophytes
Micropyle is an ovule’s opening. some ovule cells are called megaspore mother cells that undergo meiosis to produce four haploid cells out of which only one survives. Its nucleus divides by mitosis three times to produce eight nuclei.
Ovule’s center has embryo sac, which gets all eight nuclei. wall formation takes place here, converting nuclei into cells. this eight cells structure is the female gametophyte.
male gametophytes
anther contains sacs of pollen. when anther is developing, mitosis division produces microspore mother cells. a diploid mother cell produces four haploid microspores. Microspore divides mitotically to produce pollen, each grain of which produces pollen tubes which grow until it reaches the ovule. during this process, two pollen nuclei, which are generative and pollen tube nucleus, move into the pollen tube.
generative nucleus divides to form two sperms (male gametes). with the grain having pollen tube, tube nucleus, and two sperms, it is a male gametophyte.
