The Perpetuation of Life
Earth and Life Science...
PERPETUATION OF LIFE The Reproduction of Plants Angiosperms, also called flowering plants, have seeds enclosed within an ovary whilegymnosperms have unenclosed or "naked" seeds on the surface of their leaves or scales. How do angiosperms and gymnosperms reproduce? Reproduction in Angiosperms Flowers are the sexual reproductive organs in angiosperms. They consist of the androecium (male reproductive structure) and gynoecium (female reproductive structure). Male Reproductive Parts of the Flower Androecium is the male reproductive structure of the plant that consists of a whorl of stamens. The stamen is comprised of the filament and the anther. The filament is a long, slender stalk that holds the anther while the anther produces the pollen grains (male reproductive cells).
(a) Stamen (b) a cut section of the anther Female Reproductive Parts of the Flower Gynoecium is the female reproductive structure of a flower. It may consist of a single pistil (monocarpellary) or may have several pistils (multicarpellary).
The pistil is made up of the stigma, the style, and the ovary. The style is a slender stalk that supports the stigma while the stigma is the sticky part that receives the pollen. The ovary is the basal sac that contains the ovules (female reproductive cells).
Both the male and female gametes of the flowers are non-motile. They are brought together by pollination. Pollination Pollination unites the male and female reproductive cells or gametes. It takes place when the pollen grains from the male anther are transferred to the female stigma. Types of Pollination Autogamy is a type of pollination where pollen grains are transferred to the stigma of the same flower. Geitonogamy is a type of pollination where pollen grains are transferred to the stigma of another flower of the same plant. Xenogamy, also called cross-pollination, is a type of pollination where pollen grains are transferred to the stigma of a different plant. Agents of Pollination Abiotic agents are nonliving things that aid in the transfer of pollen grains from the anther to the stigma. They include wind and water. Biotic agents are living things that aid in pollination. They include animals and even humans. Example A bee, which sips nectar from flowers, transfers the pollen grains from one flower to another. It is an example of a biotic agent. Fertilization Fertilization takes place when the sperm (germinated pollen) unites with the egg (ovule) forming a fertilized egg called a zygote.
Process of Fertilization 1. The pollen grain attaches to the stigma. 2. Each pollen grain becomes a part of the pollen tube, which grows down the neck of the style and reaches the ovary. 3. Sperm cells are discharged into the embryo sac, fertilizing the egg cell.
Double Fertilization During double fertilization, the pollen grain enters the ovary and releases two sperm cells. One sperm cell unites with the egg cell forming a diploid cell or zygote. The other sperm cell bonds with two polar nuclei forming a triploid endosperm nucleus. Post-fertilization During post-fertilization, the zygote develops into an embryo while the endosperm nucleus develops into the endosperm. Also, the ovule, which contains the embryo and endosperm, matures into a seed while the ovary forms the pericarp of the fruit. The seed is the beginning of the next generation. It grows into a seedling and then into a mature plant. The mature plant then produces flowers that contain the reproductive cells.
Reproduction in Gymnosperms Unlike angiosperms, gymnosperms do not have flowers and fruits. Their ovules, which become seeds, are on the surface of a scale or modified leaf. Examples of gymnosperms include cycads and conifers.
Most gymnosperms have reproductive parts called cones. They produce two kinds of cones: the male and the female cones. The male cones produce the pollen while the female cones contain at least one ovule. Pollination In gymnosperms, the main pollinating agent is wind. Wind carries the pollen from the male cones to the female cones. A sticky substance secreted by the ovule collects the pollen. Fertilization After pollination, the ovule closes and seals in the pollen. One sperm cell fertilizes the egg cell forming a zygote. Post-Fertilization The fertilized egg develops into an embryo, and the other parts of the ovule mature into the seed coat and food store.
Angiosperms have seeds enclosed within an ovary while gymnosperms have unenclosed or "naked" seeds on the surface of their leaves or scales. The flower consists of the gynoecium (female reproductive structure) and androecium (male reproductive structure).
Most gymnosperms have reproductive parts called cones. The male cones produce the pollen while the female cones contain at least one ovule.
Pollination unites the male and female reproductive cells or gametes.
Fertilization is the union of pollen grain and ovule in the ovary.
During double fertilization, one sperm cell fertilizes the ovule forming the zygote (diploid) while the other sperm cell unites with the two polar nuclei to form the endosperm (triploid).
In angiosperm fertilization, the zygote matures into an embryo while the rest of the ovule develops into a fruit.
In gymnosperm fertilization, the zygote matures into an embryo while the rest of the ovule develops into a seed.
DNA: Its Role in Inheritance and Protein Synthesis What do you observe in this diagram?
Deoxyribonucleic acid (DNA) contains the genetic information of almost all living organisms. It contains nucleotides composed of a five-carbon sugar deoxyribose and a phosphate group. There are four nucleotides in a DNA: adenine (A), thymine (T),guanine (G), and cytosine (C).
The nucleic acid sequence indicates the order of nucleotides in a DNA or RNA strand. The nucleotides or nucleotide bases (A, C, T, G) of a DNA strand or a sequence can be complementary to another sequence. Cytosine pairs with guanine, and adenine pairs with thymine in the complementary DNA strand. The sequence of the DNA strand contains codes of information that provide instructions for making proteins needed by organisms in order to grow and live. In our diagram in the previous lesson chapter, the recipe was transcribed into English for one to make the recipe. The same with DNA, if not transcribed, it will not give instructions to make proteins needed by our cells. Role of DNA in Inheritance Genes are short segments of DNA that are the basic units of heredity. Every individual has two copies of each gene, one from the father and the other from the mother. They are responsible for all the traits that an individual inherits from their parents. The sperm and egg cells carry 23 chromosomes each. When they unite, a total of 46 chromosomes will be produced. The only thing that makes us unique from each other is the slight variations in the genes. For example, most of us have black eyes, some have brown eyes. We all have genes for eye colors, but the differences in the genes dictate whether a person will have black or brown eyes. Role of DNA in Protein Synthesis The DNA plays an important role in the synthesis of proteins. Proteins play an important role in the cells’ functions and structures. There are three processes involved in the production of proteins: replication, transcription, and translation.
Replication Replication refers to the process of copying one DNA to produce two identical DNA molecules. During this process, the DNA unwinds, and both strands of the double helix will serve as templates for producing new strands of DNA.
Transcription Transcription is the process by which the genetic information in the DNA strand is transcribed to the messenger RNA (mRNA). This RNA is called the messenger RNA because it carries the message copied from the DNA to produce proteins. In this process, RNA uses complementary coding where the bases are matched up, similar to how DNA forms a double helix. The difference between RNA and DNA is that instead of thymine, RNA makes use of uracil.
Translation Translation is the process wherein protein molecules are assembled from the information encoded in mRNA. As a whole, the synthesis of proteins is made possible by the DNA which provides the information needed to create proteins in the body.
DNA contains the genetic information of almost all living organisms. The nucleotide consists of deoxyribose and a phosphate group.
There are four nucleotides in a DNA: adenine (A), thymine (T), guanine (G), andcytosine (C).
Genes are short segments of DNA that are the basic units of heredity.
Replication refers to the process of copying one DNA to produce two identical DNA molecules.
Transcription is the process by which the genetic information in the DNA strand is transcribed to the messenger RNA (mRNA).
Translation is the process wherein protein molecules are assembled from the information encoded in mRNA. Genetic Engineering and Its Applications in Reproduction
Have you ever heard of genetically modified organisms? Genetic Engineering and Biotechnology Genetic engineering means modifying genes in a living organism to produce genetically modified organisms (GMOs) also known as transgenic organisms. It is a modern type of genetic modification. In this process, the gene of interest is physically removed and placed in an organism to be modified. This method is more rapid and specific than the traditional plant breeding because a gene coding for a specific trait could be transferred to an organism. Genetic engineering is an application ofbiotechnology which uses biological systems, processes, or organisms to create products intended to improve the quality of human life.
How is genetic engineering done?
As shown in the illustration above, copies of the recombinant plasmid— a circular, doublestranded DNA molecule, will be isolated and transferred to other organisms. Depending on the gene of interest, genetic engineering has various applications in the field of medicine, environment, and agriculture. To help you describe the processes involved in genetic engineering, let us use Bt corn, a genetically modified pest resistant plant as an example. This plant was grown in the Philippines against Asian corn borer, a major pest in corn. DNA Isolation (isolating plasmid and gene of interest) The first step in creating a pest-resistant plant is isolating the plasmid of Agrobacteriumand pestresistant gene from a bacteria, Bacillus thuringiensis (Bt).
Agrobacterium tumefaciens, a gram-negative soil bacteria cause crown gall disease in plants but its tumor-inducing plasmid is usually used in genetic engineering because of its ability to integrate its DNA into a plant’s genome. The resistant gene would be obtained in the DNA of Bacillus thuringiensis. This bacterium produces a protein known as Cry1Ab toxin that is lethal to the larval stage of lepidopterans (moth family).
Ligation (gene insertion to the plasmid) When the resistant gene is inserted into the isolated plasmid, they are cleaved using the same restriction enzyme before they are combined using DNA ligases. Restriction enzymes are also called restriction endonucleases. Once they recognize a specific nucleotide sequence, they cleave the strands.
Transformation (plasmid is placed back into bacterial cell) The recombinant plasmid would then be placed back to the bacterium in a process called transformation.
Selection (identification of the desired clone) The nutrient media with X-gal (special galactose sugar) are used to select the transformed bacteria containing the recombinant plasmid with the gene of interest. The selected bacteria would then infect the cell of corn and integrate the gene into the plant’s DNA. When the plant cell divides, each daughter cell receives the new gene. The transformed corn plant is now pest-resistant.
The inserted gene producing the toxin in the genetically modified crop is only lethal to specific target pests. Current Uses of GMOs The genes of bacteria, plants, and animals are being modified to improve the quality of human life. Depending on the gene of interest, GMOs have many uses in agriculture, medicine, and the environment. Uses of Genetically Modified Bacteria Escherichia coli creates a synthetic human insulin. Cyanobacteria is used to yield polyhydroxybutyrate to produce bioplastic. Uses of Genetically Modified Plants Bt corn is a pest-resistant plant against corn-infesting larvae. Banana vaccine is an edible vaccine against hepatitis virus.
Golden rice is a genetically modified rice that produces beta-carotene.
Uses of Genetically Modified Animals Bioluminescent animals are used to identify different types of cells to detect diseases. Some bioluminescent animals such as glofish became novelty pets to humans.
Fast-growing salmon are genetically modified salmon to continually produce growth hormones.
Advantages of GMOs The GMOs offer many benefits to mankind such as:
Increased productivity. This enables farmers to have higher crop yields and reduced pesticide use. (e.g. Bt corn) Reduced pesticide use. Since GM crops are modified for a specific pest, the use of pesticide against that pest is reduced or removed.
Improved nutrition like the high beta carotene content of Golden Rice. GM crops such as Golden Rice with improved nutrition (high in beta carotene) reduces eye-related problems like blindness due to malnutrition.
Aided disease detection. Diseases can be identified because of protein trackers in bioluminescent animals.
Disadvantages of GMOs GMOs also raised concerns from people because of its possible harm to the environment and mankind such as:
Reduced biodiversity of non-damaging insects. Pest resistant crops (e.g. Bt corn) lead to unintended harm to non-crop damaging insects such as larvae of Monarch butterflies when affected by pollen of Bt corn. Decreased pesticide effectivity. Pest resistant crops seem to reduce the need for pesticide at first but it would increase later on.
Produced allergic reactions. Some people develop an allergic response to GM crops when exposed to them.
Led to a higher cost for GM seeds. Farmers buy new seeds every year. Farmers using second generation seeds would lead them to Supreme Court with a charge of patent infringement.
Genetic engineering means altering genes in a living organism to produce a Genetically Modified Organism (GMO). Biotechnology is a technology using biological systems, processes, or organisms to create products intended to improve the quality of human life.
The following are the steps in genetic engineering: DNA isolation, ligation, transformation, and selection.
DNA isolation is isolating the plasmid and gene of interest.
Ligation involves sealing the gene of interest into the plasmid after they are both cut with the same restriction enzyme.
Transformation is a process wherein cells ingest foreign DNA from the surroundings.
Selection is the process where the bacteria containing the recombinant plasmid with the gene of interest is selected and will be used to integrate the gene of interest in the host organism.
Depending on the gene of interest, GMOs have many uses in agriculture (e.g. pest resistant plants), medicine (e.g. edible vaccines), and environment (e.g. butanol production).
GMOs offer many benefits to mankind such as increased productivity, improved nutrition, disease detection, and cheaper medicines.
Possible risks about GMO such as reduced biodiversity, decrease pesticide effectivity, allergic reactions, and high cost for GM seeds posed concerns to many people.