Chapter 38: Angiosperm Reproduction and Biotechnology

Question 1

Key Features of Angiosperms

Answer 1

Flowers, Double Fertilization, and Fruits, dominant sporophytes

Question 2

Flowers of Angiosperms

Answer 2

The reproductive shoots of angiosperms that contain four types of floral organs: carpels (first/innermost whorl), stamens, petals, and sepals (last/outermost whorl)- all of which are attached to a part of the stem called the receptacles. Flowers are determinate shoots that cease growing after the flower and fruit is formed.

Question 3

Carpel (reproductive organ of flowers)

Answer 3

Contains the ovary at its base, followed by a long, slender stalk called the style, at the top of which is a sticky structure that captures pollen known as the stigma. Within the ovary, ovule are found that become seeds when fertilized. A flower may have one or more carpels and the number of ovules depends on species . Carpels may fuse to produce a single structure containing one ovary with 2 or more chambers, each of which has one or more ovules.

Question 4

Pistil

Answer 4

refers to a single carpel or two or more fused carpels

Question 5

Stamen (reproductive structure of a flower)

Answer 5

Consists of a stalk called the filament and a terminal structure called the anther, within which are chambers called microsporangia which produce pollen.

Question 6

Petals and Sepals

Answer 6

Petals advertise the flower to pollinators and are more brightly colored. Sepal protect the flower buds and resemble leaves.

Question 7

Complete Flowers/ Incomplete flowers

Answer 7

Complete Flowers are those that have all four basic organs while incomplete flowers lack one or more of these 4 organs. Incomplete flowers may be sterile or unisexual as they lack either the stamen or the carpel.

Question 8

Inflorescences

Answer 8

Showy clusters of flowers. Example: Sunflowers are inflorescences consisting of a central disk surrounded by sterile and incomplete flowers.

Question 9

Gametophyte development in Angiosperms

Answer 9

They are microscopic and are the smallest gametophytes out of those of all plants. They are highly reduced and dependant on sporophyte for nutrients.

Question 10

Development of a Female Gametophyte (Embryo sac)

Answer 10

embryo sac is a female gametophyte that develops within each ovule in a tissue called the megasporangium. Megasporocyte or the megaspore mother cell undergoes meiosis to produce 4 megaspores, only one of which survives. Then, the nucleus of the surviving megaspore undergoes mitosis 3 times without cytokinesis to produce a multinucleate structure, which is then divided by membranes to form the embryo sac. Cell fates of nuclei is determined by a gradient of the hormone Auxin that originates near the micropyle.

Question 11

2 integuments

Answer 11

2 layers of integuments, tissues that will become the seed coat, surround the megasporangium within the ovule except at a gap called the micropyle.

Question 12

Synergids (2)

Answer 12

2 cells that are at the micropyle edge of the embryo sac and that flank the egg and help attract and guide the pollen tube to the embryo sac

Question 13

Antipodal cells (3)

Answer 13

3 antipodal cells are at the opposite end and their functions are unknown.

Question 14

Polar nuclei (2)

Answer 14

2 nuclei that share the cytoplasm of the large central cell of the embryo sac

Question 15

One egg cell

Answer 15

haploid and has one nuclei

Question 16

Nuclei and Cells within the embryo sac

Answer 16

Embryo sac contains 8 nuclei within 7 cells. Eventually, the ovule, which will become the seed, consists of the embryo sac within the megasporangium (which will wither), all of which is surrounded by 2 integuments.

Question 17

Development of male gametophyte in pollen grains

Answer 17

Each anther contains 4 microsporangia, each of which is called a pollen sac.

Question 18

microsporocytes

Answer 18

Diploid cells within the microsporangia in the pollen grain that undergo meiosis to produce 4 microspores, each of which gives rise to a male gametophyte containing 2 cells through mitosis.

Question 19

generative cell and tube cell and spore wall

Answer 19

Generative and tube cells are the 2 cells of a male gametophyte that, along with the spore wall, form a pollen grain. During maturation, generative cell passes into the tube cell. Spore wall has material produced from the anther and the microspore.

Question 20

pollination

Answer 20

When a pollen grain is transferred to a receptive surface of a stigma.

Question 21

pollen tube

Answer 21

a long cellular protuberance that delivers sperm to the female gametophyte. The generative cell´s nuclei divided by mitosis as it passes through the pollen tube to produce 2 sperm cells. Tube nucleus guides the sperm towards the micropyle as the pollen tube is attracted to the chemical signals released by the synergids. One of the synergids die when the pollen tube arrives at the micropyle, allowing the sperm to enter.

Question 22

Fertilization

Answer 22

the fusion of gametes. One sperm forms a zygote and the other forms a triploid nucleus with the 2 polar nuclei of the large central cell, which will become the endosperm

Question 23

endosperm

Answer 23

food storing tissue of the seed.

Question 24

double fertilization

Answer 24

the union of 2 sperm cells with the 2 different nuclei of a female gametophyte

Question 25

Ovule and ovary after fertilization

Answer 25

Ovule becomes seed and the ovary becomes the fruit, which aids in seed dispersal.

Question 26

Sporophyte formation

Answer 26

Sporophyte embryo develops from zygote. Initially, nutrients are stored in the endosperm but later, the seed leaves called cotyledons may take over this function.

Question 27

Methods of Pollination

Answer 27

Pollination can occur by wind, water or animal

Question 28

Coevolution

Answer 28

the joint evolution of 2 interacting species, each in response to selection imposed by the other.

Question 29

Endosperm development

Answer 29

Endosperm develops before embryo. The triploid nucleus divides to form a multinucleate supercell with a milky consistency. Individual cells form when membranes form between the nuclei. These cells secrete a cell wall and become solid.
Grains and other monocots have an endosperm that can store nutrients for the seedling even after germination . In others, all endosperm nutrient is transferred to the cotyledon and the mature seeds lack cotyledon.

Question 30

Embryo Development

Answer 30

Mitosis of zygote produces 2 cells: basal and terminal cell. Terminal cell gives rise to most of embryo and the basal cell produces a thread of cells called the suspensor which anchors the embryo to the parent plant. The suspensor transfers nutrients from endosperm or parent plant to the embryo. Terminal cells gives rise to proembryo after mitosis. Cotyledons form as bumps on proembryo.

Question 31

Shoot and Root apex

Answer 31

embryonic shoot apex is cradled between the two cotyledons and the embryonic root apex is located at the opposite end where the suspension attaches. Apices of roots and shoots sustain growth for the rest of the plant´s life.

Question 32

Structure of Mature Seed

Answer 32

Seed dehydrates at the end of its maturation and the embryo enters dormancy. The seed is surrounded by a seed coat that may impose dormancy when intact.

Question 33

dormancy

Answer 33

seed stops growing and its metabolism nearly ceases.

Question 34

embryonic axis

Answer 34

an elongate structure that is attached to the cotyledons

Question 35

hypocotyl

Answer 35

the embryo axis below where the 2 cotyledons are attached

Question 36

Radicle or embryonic root

Answer 36

where the hypocotyl terminates. It is the first organ to emerge from a germinating seed

Question 37

epicotyl

Answer 37

the embryonic axis above where the cotyledons are attached below the first pair of miniature leaves.

Question 38

plumule

Answer 38

the epicotyl, young leaves, and shoot apical meristems are together called the plumule.

Question 39

scutellum

Answer 39

a specialized cotyledon present in grasses like maize and wheat.

Question 40

Coleoptile and coleorhiza

Answer 40

coleoptile is protective sheath that covers the young shoot of grasses while the coleorhiza is the protective sheath that covers the young root. Both aid in soil penetration.

Question 41

Imbibition

Answer 41

the uptake of water due to low water potential of the dry seed. Causes the seed coat to rupture and the embryo to resume growth. In germination, nutrients from endosperm and cotyledons are used up in growing regions of the embryo

Question 42

Germination of the seed

Answer 42

1. Water is absorbed
2. The radicle emerges
3. the shoot tip breaks ground
4. In garden beans and eudicots, the hypocotyl forms a hook which is pushed upwards
5. epicotyl is exposed and it grows true leaves
6. Cotyledons shrivel away
   7 Vegetative growth, including primary and secondary growth, arises from activity of meristems.
7. Reproduction phases follows

Question 43

flowering

Answer 43

Flowers occur simultaneously at specific times of the year, which promotes outbreeding.
Flower forms when the shoot apical meristem switches from a vegetative to a reproductive growth mode. This transition forms a floral meristem that is triggered by environmental cues and internal signals.

Question 44

Fruit formation

Answer 44

As the ovules of a flower become a seed, the ovaries become the fruit, which enclose seeds and aid in their dispersal. This change is triggered by hormonal hormonal changes due to fertilization. As the fruit develops, the other parts of the flower wither and die

Question 45

Pericarp

Answer 45

the thickened wall of the fruit that forms from the ovary wall. They ovary wall may dry out or remain fleshy. In peaches, the inner ovary becomes stony and the outside remains fleshy.

Question 46

Simple Fruit

Answer 46

fruits derived from a single carpel or many fused carpel. Example: Pea Fruits

Question 47

Aggregate Fruit

Answer 47

fruits that result from a single flower with more than one separate carpels, each of which form a small fruit.
Example: Raspberry fruit

Question 48

Multiple Fruit

Answer 48

fruit that develops from an inflorescence, a group of flowers clustered together. As the wall of many ovaries thicken, they fuse and become a single fruit.
Example: Pineapple

Question 49

Accessory Fruit

Answer 49

fruits that develop when other floral parts contribute to it.
Example: In apples, the ovary is embedded in the receptacle and the fleshy part of the apple is derived from an enlarged receptacle. Only the apple core is from the ovary.
Strawberry is an aggregate fruit consisting of an enlarged receptacle with many embedded fruits that each bear a seed.

Question 50

Ripening of fruit

Answer 50

In dry fruit, ripening involves aging and drying of the fruit tissue. In fleshy fruit, hormonal interactions produce an edible fruit that entices animals. In these, the enzymes digest cell walls and the pulp becomes softer. There is also a color change from green to a more overt color. Organic acids and starch are converted to sugar, making the fruit sweeter

Question 51

asexual reproduction

Answer 51

A type of reproduction where offspring are derived from a single parent without the fusion of an egg and a sperm.. This results in a clone.

Question 52

Mechanisms of Asexual Reproduction

Answer 52

A. reproduction in plants is an extension of indeterminate growth which occurs in meristems, regions of undifferentiated and dividing cells.
Parenchyma cells throughout plant can develop into more specialized cell types, enabling regeneration of lost parts.

Question 53

Fragmentation

Answer 53

a type of asexual reproduction in which the separation of parent plant into parts that can develop into whole plants. Detached vegetative fragments can develop into offspring. Seeds are not formed.

Question 54

Apomixis

Answer 54

the asexual reproduction of seeds that occurs without pollination or fertilization where there is no production or joining of sperm and egg. This is found in dandelions. Here, a diploid cell in the ovule gives rise to an embryo , the ovule becomes a seed, which is distributed by windblown fruits.

Question 55

Advantages and disadvantages of Sexual and Asexual Reproduction

Answer 55

Advantages of Asexual Reproduction:
There is no need for a pollinator. All the genetic info can be passed on to the progeny, which is advantageous when the plant is well suited to its environment. Progeny are stronger than seedlings produced by sexual reproduction since offspring arise from mature vegetative fragments of parent plant. This is why A. reproduction in plants is also known as vegetative reproduction. Seed germination produced fragile seedlings that are not likely to survive due to risk by the environment (which is why many seeds are produced)
Advantages of Sexual Reproduction:
In unstable environments, it is favorable because it produces genetic variation where evolving conditions affect survival rate. Seeds allow dispersal to more distant locations and allows for dormancy to be sustainable till the environment improves.

Some plants self fertilize because it ensures that every ovule develops into a seed.

Question 56

Dioecious

Answer 56

Species whose plants cannot self fertilize because different individuals have either staminate flowers or carpellate flowers. Others may have carpels and stamens that mature at different times or are structurally arranged in a different way that ensures that pollinature will not transfer pollen to the carpel of the same plant.

Question 57

Self-incompatibility

Answer 57

an anti selfing mechanism where where the plant has the ability to reject its own pollen and the pollen of closely related individuals. This is the most common. Biochemical block prevents pollen from completing development and fertilizing the egg. Self pollen is recognized based on S genes of which there are many alleles. If the alleles of the pollen grain match the allele of the stigma , the pollen tube fails to germinate or fails to grow through the style to the ovary.

Question 58

Gametophytic Self-incompatibility

Answer 58

This governed by the S allele in the pollen grain. An S1 pollen grain from S1S2 sporophyte cannot fertilize an S1S2 flower but can fertilize an S2S3 flower. If the alleles are the same, then the style produces RNA hydrolyzing enzymes that enter the pollen tube and destroy its RMA.

Question 59

Sporophytic Self-incompatibility

Answer 59

This is when fertilization is blocked by the S allele gene products in tissues of the parental sporophyte. Example, neither an S1 or an S2 pollen grain from an S1S2 flower can fertilize an S1S2 flower or an S2S3 flower because of of the S1S2 parental tissue attached to the pollen wall. This incompatibility involves a signal transduction pathway in epidermal cells of the stigma that prevent pollen germination.

Question 60

Totipotent

Answer 60

a quality of a cell that can divide and asexually generate a clone of the original organism. This is usually associated with meristematic plants but other plant cells can de-differentiate and become totipotent.

Question 61

Vegetative Propagation

Answer 61

The process where vegetative reproduction is facilitated or induced by humans.
In house plants, shoot cuttings are used. Callus develops at the cut end and gives rise to adventitious root. If shoot includes a node, roots form without a callus

Question 62

Callus

Answer 62

a mass of dividing undifferentiated totipotent cells.

Question 63

Modification of vegetative reproduction

Answer 63

A twig or bud from one plant can be grafted to another plant of related species or different variety of the same species. This combines best qualities of both plants. A callus first forms between the joining cut ends of the scion and stock, cell differentiation then unites the grafted individuals.

Question 64

Stock

Answer 64

the plant that provides the roots

Question 65

scion

Answer 65

the twig that is grafted onto the stock

Question 66

Test-tube Cloning and Related Techniques

Answer 66

whole plants can be obtained by culturing small samples of tissues from a parent plant on an artificial medium that has nutrients and hormones.All tissues can be cloned, but the growth rate depends on the type of tissue. In media, a callus of undifferentiated totipotent cells may form and manipulation of the hormones and nutrients can allow the sprouting of roots and shoots with fully differentiated cells.
Test tube culture allows regeneration of genetically modified plants from a single plant cell into which the foreign DNA has been incorporated.

Question 67

Maize

Answer 67

Maize cannot spread its seeds because maize kernels are permanently attached to the central axis and are protected by tough overlapping leaf sheaths. This arose due to artificial selection over time.

Question 68

Wheat

Answer 68

The wheat species used by us today formed through the natural hybridization between different species of grass.

Question 69

Plant Breeding

Answer 69

Beneficial traits that breeders look for usually arise through mutation but natural mutations rate are usually slow. Due to theis, breeders often treat large batches of seeds or seedlings with radiation or chemicals. If a wild plant with a beneficial trait is identifies, it is crossed with a domesticated variety. Offspring often inherit the beneficial trait as well as the undesirable traits of the wild parent. The offspring are continuously crossbred with a domesticated plant until an offspring arises which has both, the beneficial trait and well as the domesticated plants traits.
Plants from different species can also be crossbred- this usually results in abortion of the hybrid seed during development or the endosperm does not develop while the seed does. Hybrid embryos can be rescues by removing the embryo and culturing it in vitro.

Question 70

Plant Biotechnology

Answer 70

Refers to the use of plants to make products that are useful to humans or more specifically, the use of GM organisms in agriculture and industry.
Plant biotechnologists can use techniques of genetic engineering to transfer genes between plant that are not limited to be closely related species or genera.

Question 71

transgenic

Answer 71

organisms that have been engineered to express a gene from another species.

Question 72

Reducing malnutrition and world hunger

Answer 72

transgenic crops can increase the yield of crops over a certain area of land. Examples include hybrids of cotton, maize, and potatoes that contain genes from the bacterium Bacillus thuringiensis. These transgenes encode a protein Bt toxin that is toxic to insect pests. This reduces the need for chemical pesticides and the Bt toxin is only activated by alkaline conditions like the guts of insects. It is harmless to humans because humans and vertebrates have highly acidic stomachs.
Transgenic plants can be made resistant to herbicides so that other plants can be weeded through herbicides without the transgenic crops being harmed. Weeding is a supplement toi soil tillage which causes soil erosion. Transgenic plants can also be engineered to resist certain diseases.

Question 73

Golden rice

Answer 73

a transgenic variety supplemented with trangenes that enable it to produce grain with increased levels of beta Carotene, a precursor of Vitamin A, without which many children go blind.

Question 74

Biofuels

Answer 74

fuels derived from living biomass. Biofuels from the plant biomass can be used as a replacement to fossil fuels because it would reduce the net amount of CO2 release. This is because biofuel crops resorb the CO2 released by the burning of fossil fuels through photosynthesis.

Question 75

Biomass

Answer 75

the total mass of organic matter in a group of organisms in a particular habitat.

Question 76

Biofuel crops

Answer 76

Biofuel crops can be made from wil precursors that are fast growing such as switchgrass and poplar, that grow on soil too poor for soil production. Plants would not be directly burned. Rather, cellulose and hemicellulose- the most abundant organic compounds on earth- will be broken down into sugars by enzymatic reactions. The sugars would be fermented to alcohol and distilled to yield biofuels. Reducing lignin content of the plant cell walls through genetic engineering will lower the cost of biofuel production

Question 77

Issues of Human Health

Answer 77

genetic engineering may transfer allergens, a molecule to which some people are allergic, from one species that produces it to a plant used for food. Removal of genes that code for allergenic protein sis underway. Some transgenic plants may be healthier than the normal plant- Bt maize has 90% less fungal toxin called fumonisin, which is found in many processed maize products. Fumonisin is produced by a fungus that infects insect damaged c=maize and since Bt maize suffers less insect damage, it has less fumonisin.

Question 78

Possible effects on non target organisms

Answer 78

Larvae of monarch butterflies responded adversely after eating milkweed leaves dusted with pollen from transgenic Bt maize. Research found that it was the floral parts and not the pollen that contained Bt toxin in high concentration which killed the larvae. Since only pollen is carried from plant to plant, this would not affect the butterflies naturally. Only one Bt maize line produces pollen with high concentrations of the Bt toxin. Spraying of non Bt maize with pesticides is even more harmful to the monarch populations.

Question 79

Addressing the problem of transgene escape

Answer 79

introduced genes may escape from transgenic crops into their weed relative through crop to weed hybridizations.. This may cause weeds to gain selective advantage towards other wild weeds. Likelihood of transgene escape depend son the ability of crop and weed to hybridize and on how the transgene affects the fitness of the hybrids. A dwarf phenotype may be advantageous for for crops and disadvantageous for a weed in the wild. Wild relatives may not be available ( soybean has no wild relatives in the US)
Example: Transgenic variety of creeping bentgrass that was engineered to resist the herbicide glyphosate escaped during a windstorm. All the Argotis plants found nearby in the next three years were of the glyphosate variety

Question 80

Strategies to prevent transgene escape

Answer 80

1. Male sterility would allow transgenic plants to produce seed and fruit is pollinated by pollen from nearby plants but they themselves would not produce an viable pollen.
2. Genetically engineering apomixis into transgenic plants would prevent transgene escape since in apomixis, the embryo and the endosperm develop without fertilization. this would reduce transgene escape via pollen since plants could be male sterile and still be able to produce seed and fruit.
3. Transgene may be imbedded into the chloroplast DNA which is inherited strictly from the egg, which prevents transfer of transgenes via pollen.
4. Flowers may be engineered so that they develop normally but fail to open, promoting self pollination and inhibiting the escape of pollen.