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Selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.
Alternation of generations
- Life cycle in which there is both a multicellular diploid (2n) form, the sporophyte, and a multicellular haploid (n) form, the gametophyte.
- 1.Sporophytes are the dominant generation.
- a) Larger than gametophytes.
- b) More conspicuous than gametophytes.
- c) Longer-lived than gametophytes.
- 2.Gametophytes are reduced in size and completely dependent on the sporophyte for nutrients.
Flower that has all four basic flower organs: petal, sepal, carpel, stamen.
- Flower in which one or more of the four basic floral organs are either absent or non-functional.
- a)Grass flowers lack petals.
- b) Flowers lacking carpels or stamen are sterile.
Gametophyte (pollen grains)
- 1.Each anther contains four microsporangia.
- 2.Each microsporangia hold many microsporocytes.
- 3.Each microsporocyte undergoes meiosis forming four haploid microspores.
- 4.Each haploid microspore undergoes mitosis producing a male gametophyte consisting of pollen grains.
consists of only two cells
- 1.generative cell: Divides and produces two sperm.
- 2.tube cell: Produces the pollen tube which delivers the sperm to the female gametophyte.
Divides and produces two sperm.
Produces the pollen tube which delivers the sperm to the female gametophyte.
- 1.The ovule contains one megasporangium.
- 2.The megasporangium holds one megasporocyte.
- 3.The megasporocyte undergoes meiosis forming four haploid megaspores.4. Only one megaspore undergoes mitosis 3X producing a multicellular female gametophyte – the embryo sac.
- Transfer of pollen from to the part of a seed plant containing the ovule; process required for fertilization.
- wind/water: Enormous quantities of pollen released for random dispersal.
- animals: Direct transfer of pollen from one plant to another by insects, birds, etc.
- Joint evolution of two interacting spp, each in response to selection process required for fertilization.
- a) Insects, birds, etc. with uniquely adapted structures to pollinate specific plants.
- 1. After a pollen grain lands on the stigma, it absorbs water and germinates by producing a pollen tube.2. The pollen tube grows down the style towards the ovary.
- 3. The nucleus of the generative cell divides by mitosis, forming 2 sperm.
- 4. In n response to chemical attractants, the pollen tube grows toward the micropyle.
- 5. The he sperm are discharged from the pollen tube and find their way into the embryo sac.
- 6. Upon reaching the female gametophyte, one sperm fertilizes the egg, forming the zygote.
- 7. The second sperm combines with the 2 polar nuclei, forming a triploid nucleus.
- 8. This large central cell (3n) will produce the endosperm.
- 9. Double fertilization: Mechanism of fertilization in angiosperms in which 2 sperm cells unite with 2 cells in the female gametophyte (embryo sac) to form the zygote and endosperm.
- 10. Endosperm: Nutrient tissue formed by the fusion of a sperm with two polar nuclei during double fertilization; provides nourishment to developing embryo in angiosperm seeds.
- a) Usually develops before the embryo.
- b) Begins as a liquid mass that eventually becomes solid.
- c) Stores nutrients to be used by the seedling after germination.
- a) First mitotic division splits the zygote into a basal cell and a terminal cell.
- b) Terminal cell gives rise to most of the embryo.
- c) Basal cell produces the suspensor which anchors the embryo while transferring nutrients from the parent cell or endosperm.
Seed Dormancy: Adaptation to Tough Times
- a) Seed dehydrates until water is 5 – 15% of its weight.
- b) Embryo enters dormancy – stops growing and nearly ceases all metabolic activity.
- c) Hard protective seed coat protects the embryo and its food supply.
- d) Some seeds break dormancy as soon as they are in suitable environmental conditions.
- e) Other seeds require specific nvironmental cues in addition to suitable conditions to break dormancy.
- f) Specific environmental cues include:
- i.Substantial rainfall in desert regions.
- ii.Intense heat in areas prone to wildfires.
- iii.Light for seeds buried in shallow soil.
- iv.Chemicals for seeds that pass through an animal’s digestive system.
Mechanism of fertilization in angiosperms in which 2 sperm cells unite with 2 cells in the female gametophyte (embryo sac) to form the zygote and endosperm.
Nutrient tissue formed by the fusion of a sperm with two polar nuclei during double fertilization; provides nourishment to developing embryo in angiosperm seeds.
Seed Germination and
- a) Imbibition: The physical absorption of water onto the internal surface of structures (seeds).
- i. Causes the seeds to expand, rupturing seed coat.
- ii. Enables the embryo to resume growth.
- iii. Nutrients are transferred from the endosperm to the growing regions of the embryo.
- b) Germination: Initiation of growth in seeds.
Fruit Form and
- Fruit: Mature ovary of the flower;
- protects dormant seeds and
- often aids in their dispersal (wind or animals).
- a) If flower hasn’t been pollinated, fruit doesn’t develop.
- b) As fruit grows, the flower withers and falls away.
- 1. simple: Derived from a single or several
- fused carpels.
- 2. aggregate: 1 flower , multiple carpels,
- multiple fruits.
- 3. multiple: Multiple flowers (inflorescence),
- multiple carpels, multiple fruits.
- 4. accessory: When other floral parts contribute to fruit.
Derived from a single or several fused carpels.
1 flower , multiple carpels, multiple fruits.
Multiple flowers (inflorescence), multiple carpels, multiple fruits.
When other floral parts contribute to fruit.
Mechanisms of Asexual
- Asexual reproduction: Generation of offspring from a single parent without fusion of gametes.
- a) Offspring are usually genetically identical to parents.
- b) Common in angiosperms; in some spp, predominant mode of reproduction.
- c) Vegetative reproduction.
Generation of offspring from a single parent without fusion of gametes.
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