Required Minerals
In addition to these three elements, a number of minerals twelve to be exact are essential to the welfare of plants. The majority of these are found dissolved in water in the soil phosphorus, sulphur, calcium, potassium, magnesium, iron, zinc, manganese, copper, boron, and molybdenum are all taken into the plant through the roots. Nitrogen, the twelfth mineral, may be supplied by the atmosphere, yet it is taken in through the roots in a changed form. Because plants must take in minerals through...
Root Hairs
Figure 33-2 shows a longitudinal section of the growing tip of a root. Meristematic activity, which increases the length of the root, occurs only at the tip. When the cells here divide, they produce both new root cells and root cap cells. The root cap cells are sloughed off as the root grows through the soil. The epidermal cells produce root hairs a short distance above the tip. Root hairs are part of epidermal cells. Figure 33-2 shows a longitudinal section of the growing tip of a root....
Notes Diffusion
Consider some substances in true solution. Substances tend to diffuse, that is, move from a region where they are in greater concentration to a region where they are in lesser concentration. This is simply because molecules are in constant motion. If a cell membrane is involved, water can pass readily through but dissolved material may or may not be able to pass through. Whether or not dissolved material is able to pass through a cell membrane depends in part on the size of the molecules....
Zygomycetes
There are no flagellated cells in Zygomycetes. Rather, there is an extensive coenocytic mycelium within the substrate as well as an aerial mycelium that produces sporangia. The walls are chitinous. Black bread mold Rhizopus nigricans is the most common form of Zygomycetes and demonstrates both Notes the vegetative production of mitospores and a sexual process called conjugation whereby zygospores are produced. If a piece of bread is placed in a moist container, a cottony, white mycelium will...
Yeasts
The classification of yeasts as Ascomycetes is surprising because the yeasts are known for reproducing by budding. The yeast cell typically develops a bud on the side, the nucleus divides, and a daughter nucleus migrates into the bud. The cells may either divide to form two separate cells or remain attached to each other. This asexual process of budding can occur when the nuclei are haploid or when they are diploid. Under certain circumstances, ascus formation is noted in yeasts, however....
Cell Membrane
All cells are bounded by cell membranes, which are similar in all cells. In pro-karyotic cells, the membranes appear to be much-folded, the convolutions extending to the interior of the cell and having the effect of increasing surface area. Plant and animal cells are alike in this respect however, a significant difference between the two is found in the cell wall. In plants, cell walls are secreted by plant cells and lie outside of the cell membrane. Animal cells for the most part do not...
Golgi Bodies
Eukaryotic cells regularly contain numerous flattened, saclike structures, which under an electron microscope appear as a stack of pancakes. These are the Golgi bodies. They derive their name from Camillo Golgi 1843-1926 , an Italian physician who discovered these structures in 1883, while examining nerve cells of a barn owl. Although they are present in all kinds of cells, Golgi bodies appear to be more prominent in cells that produce secretions and they are always found in association with...
c c c
I I magnesium-containing C head portion Figure 9-7 Top chlorophyll bottom hemoglobin. that the reactions were temperature sensitive led Blackman to conclude that such reactions are governed by enzymes. Chlorella, a one-celled green protist, is a favored organism in studies of photosynthesis. Laboratory experiments with Chlorella show that photosynthesis efficiency increases when light is alternately turned on and off. Figure 9-8 The Engelmann experiment. A filamentous alga such as Spirogyra is...
Questions for Review Notes Vap
1. Approximately when was it suggested that organisms might vary and undergo changes, which led, in time, to the idea of evolution 2. Among the several tenets to the concept of evolution is survival of the fittest what are the others 3. Hugo DeVries contributed to our understanding of the concept of evolution through his theory of_, which may explain the abrupt 4. Who demonstrated that genes are located on the chromosomes 5. If life had only one beginning, every species is derived from__ 6....
Symptoms of Improper Nutrition
What happens when an essential element is lacking When nitrogen is lacking, the leaves become yellow and are unable to form chlorophyll. When phosphorus is lacking, the leaves turn dark green. One may infer, then, that elemental deficiency can be determined solely by looking at the plant and observing the symptoms. While this is true to a certain degree, experience is also required to accurately assess such deficiencies. For example, plants turn yellow when nitrogen is lacking. But they also...
Leaves and Plant Classification and Identification
Plants can be classified into two groups according to whether the leaves are shed in the fall deciduous or retained through the winter evergreen . While angiosperms are mostly deciduous and gymnosperms are mostiy evergreen, there are some exceptions. Figure 34-5 Cross section of a leaf. Stomates appear on both upper and lower surfaces. What causes leaves to fall in autumn While it might be supposed that diminishing temperature is the cause, the true cause is diminishing number of daylight...
Endoplasmic Reticulum
The endoplasmic reticulum ER, endo meaning inner, reticular meaning net was an unknown constituent of cells until early in the 1950s when the electron microscope brought it into view. It is now known that the endoplasmic reticulum is present in all eukaryotic cells. It appears as a system of paired, parallel membranes running through the cytoplasm and taking the form of flattened tubes or bags. The bags are called cisternae. It has been suggested that the endoplasmic reticulum divides the...
The Tenets of Darwinian Theory
Darwinian theory is based on several tenets 1. Species tend to produce more individuals than can be accommodated. 2. Variations occur among offspring. Some variations yield a greater capacity to adapt to the environment and, thus, to survive. Such variations are significant when they are inheritable. 3. Certain forms are thus better able to survive than are others. This is referred to as natural selection, or survival of the fittest. Variations that are inheritable make evolution inevitable.
Pyrrophyta
Two classes are recognized in the phylum Pyrrophyta Dinophyceae dino-flagellates and Cryptophyceae cryptomonads . Because all are unicellular, they are classified in the kingdom Protista. There are approximately one thousand mostly marine, mostly motile species. A few are colonial or filamentous. Chlorophylls a and c are present, as are carotenoids and xanthophylls. Peridinin, a reddish-brown pigment, is largely responsible for the color of these organisms. The product of photosynthesis is...
Variations in Flowers
There is great variation in flowers. Some flowers are so small that they can scarcely be seen without a lens. One example is duckweed, Lemna minor, an aquatic plant found floating on water. At the opposite extreme is a plant of the Figure 35-3 Cross section of an anther, showing pollen grains. Figure 35-3 Cross section of an anther, showing pollen grains. Figure 35-4 Two species of duckweed, minute flowering plants that float on water. amp Notes amp Malay peninsula. Rafflesia produces flowers...
Other Plant Hormones
Since the discovery of auxin, a number of other plant-growth regulators have been uncovered ethylene, gibberellins, cytokinins, abscisic acid, florigen and photoperiodism , phytochrome, and wound hormone are examples. While ethylene certainly exhibits hormonal properties in its effects on plants, its simple molecular structure and the fact that it is a gas seem incompatible with our concept of hormones. Thus, it may be better to refer to ethylene as a hormone-like substance. Ethylene's effect...
Organic Acids
If the terminal carbon atom of such a series bonds with an oxygen atom and an -OH group, as shown in figure 4-8, an organic acid is created. The group -COOH is called a carboxyl group figure 4-9 . Note that in all cases the carbon atom always has four bonds, the hydrogen atom always one bond, and the oxygen atom always two bonds. TWo organic compounds of this type can react together to form a longer chain, as shown in figure 4-10. Because hydrogen is removed to create these compounds, this is...
Empirical and Structural Formulas
Organic chemistry can be simply defined as the chemistry of carbon compounds. Inorganic chemistry, then, is all the rest. In inorganic chemistry, empirical formulas for compounds utilize the appropriate atomic symbols. For example, ammonia has one atom of nitrogen and three atoms of hydrogen in its molecule. Its empirical formula, therefore, is NH3. In organic chemistry, however, structural formulas are necessary. In organic chemistry, ammonia an inorganic compound would thus be represented as...
Grafting
Among horticultural plants, there are numerous times when a desired shoot system does not develop well on its own root. In such situations, great improvement can be achieved by grafting the desired shoot to a root of higher quality, a root system that is more disease resistant. European varieties of grapes are regularly grafted to American-type root stock. A graft is made by fusing a scion twig of one variety to the base of a stem bearing the desired root system of another variety. When the two...
Aberrations in Mitosis and Cellular Composition
Aberrations in mitosis can be induced by altering the environment. Alternating hot and cold as well as treatment with certain chemicals such as mustard gas, naphthalene acetic acid, and colchicine can cause changes in mitosis. The normal events at anaphase result in chromatids separating and moving to opposite poles. However, a process called nondisjunction can occur. In nondisjunction, both members of a pair go to the same daughter cell. This results in aneuploidy one daughter cell will have...
The Basics of Mitosis
In mitosis, the daughter nuclei each retain the same number of chromosomes as the parent nuclei in meiosis, by reduction division, the daughter nuclei each have half the chromosome number of the parent. We thus speak of the diploid number and the haploid number of chromosomes. Common practice is to represent the haploid number with the letter n. The diploid number, therefore, is 2n. In a general sense, all nonreproductive cells in a body have the same number of chromosomes that is, the diploid...
The Functions of DNA
What does DNA do The answer is twofold DNA can provide a pattern for the structuring of more DNA, which it must do when a cell divides and DNA can provide a pattern for the making of RNA. To accomplish either of its functions that is, self-replication or the patterning of m-RNA the helices of DNA must uncoil. This is accomplished by the breaking of the hydrogen bonds that join the paired bases. In becoming uncoiled, each helical strand forms a companion strand, and the two strands again become...
Cell Walls
The presence of a wall secreted by the cell is a characteristic of plant cells. Animal cells do not produce walls. Many, but not all, protista have cell walls. Fungi and bacteria produce cell walls. The distinction between the cell membrane and cell wall is an important one. The cell membrane is a part of the cell and is a living structure. The cell wall is not part of the cell rather, it is secreted by the cell, lies outside of it, and is not living. The cell wall may appear homogeneous when...
Physical Properties of Protoplasm
here are great differences among living organisms, yet all Notes organisms are made of cells. When the most minute organelles of cells are examined, even of very diverse life forms, the differences disappear. Mitochondria, Golgi bodies, ribosomes, endoplasmic reticulum, centrioles all seem to be the same wherever they are found. This is also largely true of chemical composition. All cells have proteins, fats, carbohydrates, nucleic acids, minerals, and enzymes. This living substance is called...
Fungi Classification
How should the fungi fungus be characterized While it is a concern in classification to put together those organisms that are related to one another by descent from a common ancestor, this is certainly not the case with fungi. While these organisms do share certain traits, this does not imply kinship. All fungi lack chlorophyll. They can be unicellular, multicellular, or acellular. The cell walls often have chitin similar to the chitin found in insects and crustacea. Cellulose may also be...
Contributors to Root Growth
Like stems, roots grow in length only at the tips. Although they grow where moisture occurs, moisture is not the only requirement for their growth. Sugar produced in the leaves by photosynthesis is also necessary, as are hormones, which are also produced in the leaves. Hormones must be transported from the leaves to the roots in order to influence root growth. Temperature the presence of minerals and fungi and acidity or alkalinity are other important factors in both root and plant growth. In...
Chloroplasts
Nearly all life on Earth runs on sunlight and, thus, depends on the processes that occur in chloroplasts. It is therefore fitting that these structures be examined in depth. The most significant distinction between animal cells and plant cells is the presence of chloroplasts in plant cells. Under a light microscope, chloroplasts appear as uniformly green, often lens shaped, and commonly about 6 microns in diameter. A single leaf cell may contain 20 to 100 chloroplasts each cell of a spinach...
The Search for the Substance of Heredity
There are several types of molecules in chromosomes. One such molecule is protein. For a long time, protein molecules were thought to be the bearers of heredity, the reason being that heredity appeared very complicated, and proteins are certainly also complicated. It seemed logical to suppose that protein bore the secret of heredity. While logic is a laudable process, it can serve only as a basis for directing investigation in science. In 1868 Friedrich Miescher 1844-1895 separated nuclear...
The Basics of Meiosis
Recall that in fertilization a male gamete having a haploid chromosome number unites with a female gamete also having a haploid number. The union of gametes reestablishes the diploid condition. Each chromosome of an egg cell pairs with a like, or homologous, chromosome in the sperm cell the union of gametes brings homologous chromosomes together. The chromosomes of the 2n condition occur in pairs. Because the coming together of gametes results in a doubling of chromosome number, it follows that...
Bacterial Growth
Bacteria divide by fission and may do so every twenty minutes in favorable living conditions. This suggests that in a given day, a given bacterium could come to weigh 2,000 tons. This, of course, does not happen. Because bacteria divide by fission, they are known as Schizophyta, or Schizomycetes a term introduced by von Naegeli in 1857 . The cytoplasmic membrane grows inwardly, the cell wall splits from the outside toward the center, and the cell divides into two daughter cells. Bacteria grow...
The Anaerobic and Aerobic Pathways
Although the events of respiration may be thought of as the reverse of the events of photosynthesis, they are not altogether the same events in the reverse order. The first stage of respiration, called glycolysis, is an anaerobic process of the initial breakdown of sugar. The 6-carbon glucose is broken down into two 3-carbon molecules of pyruvic acid. In order for this to occur, however, the glucose must first be linked to phosphate groups a process known as phosphorylation . The molecule is...
Myxomycetes
The organisms of Myxomycetes present a challenge in classification because during one part of the life cycle they exhibit animal-like characteristics, and during another part, they exhibit plantlike traits. A large, naked, noncellular mass of protoplasm possibly several inches in diameter and called a Plasmodium can be found growing on damp forest debris. It may be variously colored yellowish, brown, green, and orange. It is capable of amoeboid movement and can glide slowly to get away from...
Mosses
Mosses are low plants that produce dense mats. They occur mostiy in moist places, but some forms can be found in the desert. Approximately 14,500 species have been described. Mosses provide an elegant example of alternation Figure 24-4 Anthoceros. At left, an egg cell in the center of the archegonium and to its right an antheridium. At right, the sporophyte generation growing in the remnant of the archegonium. It produces a foot, which grows into gametophyte tissue and may continue into the...
The Cell Doctrine
The doctrine that all living things are made up of cells was published in 1839. This doctrine is credited to two men Matthias Schleiden 1804-1881 , a botanist, and Theodor Schwann 1810-1882 , an anatomist. Though working independently, Schleiden and Schwann came to this conclusion at nearly the same moment. As it turns out the doctrine that all living things are composed of cells is not tenable. Some things do not have a cellular organization. Yet, most organisms, both plant and animal, are...
Cilia
Many microscopically sized plants and certain fungi contain hairlike structures that project out from the cell surface. These structures are used to propel the cells through the water and are called cilia or flagella. In many plants, cilia or flagella are found only in sperm cells. There is little difference between cilia and flagella except for length flagella tend to be longer , and method of movement. An electron microscope reveals the same structure for both. A cross-sectional view of a...
The Calvin Cycle
Recall now what F.F. Blackman observed in 1905 in certain situations, the rate of photosynthesis is governed by temperature, indicating that the chemical changes of photosynthesis are controlled by enzymes. Such reactions are the so-called dark reactions of photosynthesis. Carbon is converted to carbohydrate during the dark reactions. Melvin Calvin 1911- used a radioactive isotope of carbon, C'4, to trace the carbon of carbon dioxide as it went through several intermediate changes. He very...
Notes Ginkgo biloba
Gymnosperms are generally and correctiy considered to be coniferous trees having needle-shaped leaves commonly retained on the plant for several years. They are thus called evergreens. An exception is Ginkgo biloba, which has many traits of a hardwood angiosperm. Ginkgo biloba is the only remaining survivor of the Ginkgophytes, which were extensive in the late Paleozoic period. Their ancestors are unknown, but they seem to have arisen from more than a single precursor. In past times, there were...
Nuclear Membrane
The nuclear membrane is a double membrane much like the double membrane of the endoplasmic reticulum. An electron microscope reveals a light line sandwiched between two dark lines. This double-membrane system is called the nuclear envelope, and each unit membrane is believed to be composed of a central lipid layer sandwiched between layers of protein. Numerous pores can be seen in this envelope see figure 2-8 perhaps one-third of the surface is taken up by these perforations. The holes of the...
Club Mosses
Lycopodium is an example of club mosses. These plants are often seen in the woods and may be mistaken for pine seedlings. In fact, they go by the vernacular name ground pines. The sporophytes produce upright stems, which bear minute leaves, called microsporophylls, each having a single, central vein without branches. Stomates can be found on both surfaces of the leaves. The leaves arise without forming leaf gaps an advanced characteristic found Enlarged View of Leaf Underside Showing Sori...
The Monocot Stem
Monocots are mostly annuals, meaning they live for only a single season. They are most readily recognized by their leaves although there are exceptions, most monocot leaves exhibit parallel venation. A cross section of a monocot stem figure 32-13 shows vascular bundles scattered in parenchyma. There may be a layer of sclerenchyma beneath the epidermis. Figure 32-13 Cross section of a monocot stem. Notes Although this arrangement of vascular bundles represents the simplest organization of stem...
Casparian Strip
Close examination of the endodermis reveals closely packed cells having thickened walls and lacking intercellular spaces. There is also a strip of suberin called the Casparian strip see figure 33-6 . This strip lies on radial and transverse walls. Suberin is a waxy material that inhibits the passage of water. The positioning of the Casparian strip appears to block the lateral movement of water, both in and out, through the cell wall. Because the secondary wall does not exert selectivity, and...
Cuttings
Because stems are able to produce adventitious roots, cuttings of stem pieces are commonly planted. This is in fact the preferred method of vegetative propagation. Both herbaceous and woody cuttings are successfully used. The new roots grow on the cut surface of the stem piece. A root-growth promoting substance such as indole acetic acid, naphthalene acetic acid, or a phenoxyacetic acid compound is commonly used. The cut surface of the stem piece is dipped in a powder containing such a...
Notes Fruiting Bodies
The fruiting body in Pyronema is the apothecium. Other fruiting bodies occur in other species. In some species, the fruiting body containing the asci and the paraphyses may be entirely closed. This is called a cleistothecium and is shown in figure 19-4a. In one genus, Exoascus, there is no evident fruiting Figure 19-4 Several ascocarps a a cleistothecium b a perithecium c an apothecium and d an ascostroma. body. Rather, the asci and paraphyses develop on an open surface. A fruiting Notes body...
Euglenophyta
Students of botany as well as those of zoology often are required to study the organisms of Euglenophyta because these organisms possess both animal and plant characteristics. These organisms are currently if temporarily considered part of the Protista kingdom. Yet, they are still called algae. The number of Euglenophyta species is estimated to range from 450 to 800. Notes A classic example of the group is Euglena, a single-celled, flagellated, gen erally green although several forms are...
The Woody Dicot Stem
First, consider the woody dicot stem. As explained earlier, cells are either meristematic or permanent. Meristematic cells are those that retain the ability to divide, whereas permanent cells are those that have lost this ability. Cells at the growing tip of a stem are meristematic. A cluster of young leaves is generally present at the apex of the stem so as to protect the young point. This apex is the terminal bud. Growth in length is accomplished by both divisions of the cells lying under the...
Meristematic Tissue
Meristematic tissues are further divided into two groups apical meristem and cambium. Apical meristems are found at the tips of stems and roots. These cells increase the length of shoot and root, and are responsible for primary first growth. The cambium is of two kinds vascular cambium and cork cambium. Vascular cambium produces two kinds of tissues xylem, which is deposited central to the cambium, and phloem, which is deposited peripheral to the cambium. Cork cambium also produces two kinds of...
Chrysophyta
The Chrysophyta are characterized as unicellular and have the pigments chlorophyll a, sometimes chlorophyll c, and perhaps chlorophyll e, carotenes, diadinoxanthin, and fucoxanthin. The products of photosynthesis are oils and the polysaccharide leucosin. Cell walls, if present, may have silica, calcium, and some organic material, but little or no cellulose. A student of algae soon comes to appreciate the uncertainties researchers face in attempting to classify these organisms. Some algae are...
Acetabularia A Green Alga
While working with the green marine alga Acetabularia in the early 1930s, Joachim Hammerling observed that the cell continued to produce a particular protein for up to two months after the nucleus had been removed. This seemed to indicate that the mechanism of control of protein synthesis resided in the cytoplasm. Hammerling wanted to determine the extent to which the nucleus controlled cellular functions. Acetabularia, romantically called the mermaid's wineglass, can reach a height of two to...
Notes Root Growth
When the root cambium produces secondary xylem and secondary phloem, the secondary xylem, formed medial to the cambium, lies in contact with the primary xylem. The secondary phloem, deposited peripheral to the cambium, pushes all tissues external to it outward, until the small patches of primary phloem are soon pushed quite away from their original positions between the points of primary xylem see figure 33-7 . Another cambial layer, the cork cambium, develops in the pericycle cells this layer...
Structure of a Root
Figure 33-4 shows a cross section of a root in a region where only primary growth has occurred. All tissues here derive from apical meristem. The innermost, star-shaped tissue is the primary xylem. Between the points of the primary xylem are areas of primary phloem. Immediately outside of these primary vascular tissues is a zone of parenchyma cells, called the pericycle. This is bounded by a layer of suberized cells one cell in thickness and called the endodermis. Peripheral to the endodermis...