Unit 2: PLANTS The move to land Chapter 16 P. 315-327 Chapter 28 P. 604-613 and P. 616-620
Outcomes 2.1 The Move onto Land 2.2 Plant Structure 2.3 Plant Life Cycles
2.1 Move on to Land - What is a Plant? P. 316-317 Plants evolved from a group of green algae known as Charophytes. Molecular science has shown that these 2 groups of organisms are most similar by comparing pigments, chloroplasts and DNA structure, etc. Vast differences have placed plants in their own kingdom separate from algae --- MAIN DIFFERENCE plants live on land and this habitat has resulted in structural differences such as division of labour
https://www.y outube.com/ watch?v=4l4l KCq2eJs How did plants evolve? Problems from water to land. Aquatic plants that were upright in buoyant water go limp on land and soon shrivel up in the drying air. In addition the aquatic algae are not equipped to obtain the carbon dioxide needed for photosynthesis from the air.
P. 316-317 Plant Terrestrial Adaptations 1. Vascular Tissue Tissues, organs and organ systems(division of labour) were among the first evolutionary change that plants acquire separate from green algae. Life on land was harsh temperature ranges extreme, wind and rain and a less dense atmosphere than the buoyant nature of water ---- plants needed structure and shape to allow them to grow and reach sunlight for photosynthesis. Then as population increased on land, competition for sunlight meant that plants trying to increase in height and overpower smaller plants again needed more support and structure. Vascular tissue was one of the first tissues to evolve! https://www.youtube.com/watch?v=dgpp HrLF-5M
Vascular tissue main function is for support and transport. (found in all parts of the plant. Two types of vascular tissue: 1) xylem tissue composed of hollow cells joined together to carry water and nutrients up the plant from the roots to the leaves. 2) phloem tissue composed of live cells joined together to carry sugar produced by photosynthesis in leaves down the plant to be stored in the roots. https://www.youtube.com/watch?v=9szoaemnd8u
2) Organ: Stem The stem was the first organ to evolve with the function of support and transport. Within the stem is tissue that contains specialized cells that provide support and structure. They achieve this function by growing and acquiring cell walls that contain lignin a very hard substance that results in the structure and support for the entire oranisms. Lignin cells sole function was ro produce lignin, and therefore, empty internally.
3) Organ: Root Function primarily to absorb water and nutrients and secondarily to provide anchorage for support. To ensure maximum water uptake, roots are designed to have maximum surface area to volume ratio by having numerous roots and root hairs underground. They also lack any protective laying that may inhibit water uptake.
4) Organ: Leaves Leaves were one of the last organs to evolve. Its function is for photosynthesis and tissues making up the leaf will contain cells that contain active chloroplasts. It is for this reason that leaves appear green in color. For photosynthesis, leaves require carbon dioxide, water and sunlight to produce sugar and oxygen. Water is acquired by the xylem as sugar is released into the phloem. Sunlight is acquired by the thin, broad and maximum exposed surface area of a leaf. The uptake of carbon dioxide and release of oxygen, however, is especially important. For this reason, leaves evolved specialized 'pores' known as stomates where carbon dioxide can enter the leaf and oxygen may leave.
Leaf structure however perfect for photosynthesis, poses a problem for water loss or dehydration. Water can easily exit the stomates as well as the tissue themselves because of the large surface area exposed to a drying atmospheric environment. As a result, the nonliving waxy cuticle has been instrumental in the success of plants to a terrestrial environment.
5) Reproduction Reproduction also required changes to adapt to land. Sperm need water to swim to an egg which is plentiful in an aquatic habitat for algae. In plants, a new mechanism had to evolve which we will discuss later. (sporophyte vs gametophyte) Besides mechanism, it was important to prevent the sperm and eggs from drying out. They therefore evolved 'little jackets around the sperm and egg known as gametangia.
C. Plant Evolution P. 318-327 Four main periods of evolution occurred in the plants that resulted in different kinds of plants and different structures. The main periods below go from earliest in time (most primitive plant) to the latest in time (most advanced plants). 1)bryophytes 2) Ferns 3) Gymnosperms 4) Angiosperms The algal ancestors of plants carpeted the fringes of lakes and coastal salt marshes. Periodically these habitats were subjected to periods of drying. Natural selection would have favoured algae that could survive periodic droughts charophytes https://www.youtube.com/watch?v=yl1o49yghtm
https://www.y outube.com/ watch?v=8rvn jphglio
1) Bryophytes Division (Phylum) Bryophyta includes the mosses, which are the most primitive terrestrial plants and the most closely related to the green algae ancestor. They have some tissue differentiation that lead to them belonging to the Plant Kingdom; however they still rely a great deal on an aquatic environment.
Their close ties to an aquatic habitat is again required for their reproduction in keeping sperm and egg moist and to have sperm swim to egg, as well as their prevention of dehydration or desiccation. 1) Bryophytes continued.. They have no vascular tissue therefore they are small in size since no vascular tissue means no internal transport system of water, nutrients and sugar. Nor do they have true roots, stems or leaves. Another reason they are extremely small in size and found in quite boggy or water saturated habitats is because they do not have any cuticles to prevent dehydration or gametangia to protect egg and sperm.
2) Ferns Vascular tissue evolved as did stems, roots and leaves which allowed plants to grow taller, have support and to move to a slightly dryer environment. These evolutionary changes define the ferns. Ferns, in comparison to mosses, are much larger in size and found in much dryer environments than mosses. However, ferns still prefer darker, shadier and moister conditions than most truly terrestrial plants. The reason is the lack of evolution and adaptation in relation to reproductive structures.
2) Ferns continued. Ferns still contain sperm that must swim to an egg to achieve fertilization. Because of this and since, of course, reproduction is a necessity of life; ferns must have contact with water for survival. The changes to occur in evolution after this point deal with reproduction only and the adaptation to make plants truly terrestrial.
3) Gymnosperms This group includes the conifers. They have all the same adaptations of the fern AS WELL AS the lack of reliance on water for reproduction. This is because the gametes, egg and sperm, are well protected in the plant body. Sperm are no longer flagellated or 'swimmers but nonflagellated and protected within pollen during their development. The pollen no longer will swim but will depend on wind (and other adaptations) to achieve fertilization.
3) Gymnosperms continued. Once fertilization (fusion of sperm with egg) is complete, the developing embryo is protected within a seed. These seeds are housed in cones. All aspects of the plant reproduction cycle are well protected within the gymnosperms. This has led to these plants moving farther inland into drier and drier soils, losing their ties to water and their aquatic ancestors.
4) Angiosperms This group includes the flowering plants and is the most successful plants in terms of their independence of water. Like gymnosperms, all aspects of the reproductive cycle are extremely well protected. The difference, however, is that angiosperm seeds are housed within an ovary (rather than naked in a cone). This provides even further protection than the gymnosperms. As well, the ovaries of flowering plants develop into fruit which is sweet and tasty to many animals. This allows for increase dispersion of seeds by animal ingestion rather than simply having cones fall from a tree.
4) Angiosperms continued Flowers also increase pollination rates and thus fertilization rates because the flowering structure and color attracts animals (pollinators) to carry the pollen for dispersal rather than simply relying on abiotic factors such as wind. It is because of this that not only are they no longer dependent on water but they also have the greatest success in terms on numbers and reproductive success.
https://www.youtube.com/watch?v=493weysyf-8 P. 617
gametangium. Plural gametangia. An organ or a cell in which gametes are produced, such as those of fungi, algae, mosses, and ferns.
2.2 Plant Structure A. Introduction - Basic Review P. 607-609
Recall from Essential Biology I that plants belong to Domain Eukarya and Kingdom Plantae. As a result of this taxonomy, it should be understood that plants are multicellular organisms that are photoautotrophic. In short, this means they use inorganic carbon dioxide and light energy in the form of sunlight to produce organic sugar and ATP. Also, the cells making up this multicellular organism are eukaryotic cells (one of the two types discussed in the previous course). These cells, recall, are greater than 10 μm in size and contain membrane bound organelles such as a nucleus, endomembrane system, and vacuoles and in the case of plants, chloroplasts and a cell wall composed of cellulose.
P. 611
Also recall that plants are not only multicellular but are organisms that display division of labor. Therefore, cells produce tissues and tissues produce organs - all with unique functions. Because the functions are different, the structure of tissues and cells must be adapted to perform its function at its optimum. For this reason, the cells making up a plant, although eukaryotic, may at times be slightly different than typical eukaryotic cells. They may lack some organelles or, in some cases, may be dead and therefore hollow. Regardless, they are classified as eukaryotic because of their size.
Flowering Plant Structure Introduction A flowering plant will have all the basic characteristics as discussed above. Perhaps the best way to introduce Flowering Plants is to discuss its taxonomy. (In brackets, is the information that characterizes the particular taxon)
P. 606
Root Organ System of Flowering Plants The primary function of the underground root organ system is to absorb water and minerals for transport to the rest of the plant. Secondary function is to provide anchorage and support for the portion of the plant that is growing above ground. Depending on the specific root type, the organ structure maintains these functions. No matter how different particular root structures may be, however, all roots are designed to increase surface area to volume ratio which increases the amount of water and minerals that can be absorbed. This is usually achieved with the presence of root hairs.
Root Types The Underground Organ System is obviously composed of the organ known to many as the root. There are various root types however. They all perform the same function, but their different structures means that some functions are more important than others or they may have additional functions we have not yet mentioned. Recall that roots evolved after stems, therefore in some plants underground stems remain and perform the function of roots. Because their function is that of a root, but structurally similar to stems, they are known as modified stems. There are 4 types of modified stems\roots: 1) Runners 2) Rhizomes 3) Tubers 4) Tendril
1) Runners Runners: found in Strawberry plants, runners are a horizontally growing stem that is below ground and above ground. Above ground, the runners can sprout into new plants and of course contain a cuticle for protection from the dry environment. Runners often become matted, therefore in growing strawberry plants, to reach maximum yield, it is important to untangle and 'train' runners.
2) Rhizomes Rhizomes: horizontal underground stem of greater diameter than the runners. It is used mainly for anchorage and support yet it is not deeply planted. Roots usually grow from a rhizome to perform the function of water and mineral absorption.
3) Tubers Tubers: Examples are potatoes. Tubers are large circular structures that develop from rhizomes. They are designed to store sugar or the photosynthetic products of the plant and are also able to develop into a new plant.
4)Tendril Tendril: Tendrils are popular on climbing plants and vines. They may be modified stems or leaves that are above ground. Tendrils are not roots at all but they function for support and anchorage. They are threadlike in structure and they wrap around some physical structure giving the plant support as it climbs.
Monocot's Fibrous Roots The fibrous root system of monocots is relatively shallow and contain many tiny roots. For this reason, it has a large surface area for maximum absorption of water and minerals that are close to the grounds surface. Anchorage and support is a minor function. Dicot's Taproots Anyone who has ever tried to pull a complete dandelion weed from their lawn knows what the primary function of this root system. It is one large vertical root primarily for anchorage and support. It is also used for water and mineral absorption however; it obtains its water and nutrients from much deeper in the ground. The large vertical root does not provide a lot of surface area for water absorption and therefore taproots often have numerous and very fine root hairs that are easily removed. Another example would be carrots. Another function associated with taproots is storage of photosynthetic products which also explains the size of the root structure.
Shoot Organ System
Plant Tissues P. 610-611 Although each organ is of a very different make-up as a result of their different functions, there is some consistency within the entire plant. This is known as the tissue systems of the plant of which there are three found in roots, stems and leaves. It is perhaps the change in arrangement of these tissue systems that relates more to the function of each organ. 3 major types of tissue systems in a plant.. Dermal Tissue System Vascular Tissue System Ground Tissue System
P. 610-612
Water-Conducting Cells: Vessel Elements Xylem tissue which functions for water transport is made up of cells known as vessel elements. These cells are joined together in a chain-like manner and run from the root (one xylem per numerous roots) into the stem (several xylem per stem) and into the leaf. Because water is traveling upwards against the force of gravity, the vessel elements are hollow and dead cells. They are similar to pieces of pipe joined together where water inside uses the hydrophilic property of the cell walls with hydrogen bonding of water to creep up the sides of the vessel elements and make its way to the leaves for photosynthesis and transpiration. The property of cohesion, keeps the water molecules in a continuous chain within the vessel elements rather than one water molecule moving at a time. As long as water is present and hydrogen bonding keeps the water molecules together, water lost by transpiration through the leaf allows for the continuous pull of water up the plant rather thanwater remaining stagnant inside the vessel elements.
Sugar-Conducting Cells: Sieve Tube Members Phloem tissue is composed of cells known as sieve tube members. These cells are responsible for carrying the sugar produced in the palisade mesophyll of the leaf down the phloem of the stem and roots where it is stored in the cortex. Because the sugar is flowing downwards, these cells are alive with cytoplasm. The cells are again like pipes joined together, however between the cells are sieves or 'filters' that screen and purify the sugar as it moves down the plant. The sieve tube members, although living, function only for sugar transport and thus it lacks a nucleus and other organelles. Surrounding the sieve tube members however are parenchyma cells called 'companion cells' that do exactly as their name suggest. As companions or friends, they help maintain and load the sugar into the sieve tube members.
Summary of Plant Structure and Function Root Organ System Root Organ: Water and mineral uptake, support and anchorage, storage (from outside to center)
Shoot Organ System Stem Organ: Transport, support and anchorage(from outside to center)
Leaf Organ: photosynthesis, transpiration (from top to bottom)
Read P. 614-615 to help with assignment
P. 618-620 2.3 Plant Life Cycles A. Typical Plant Life Cycle: Alternation of Generations Introduction All plants reproduce in a life cycle known as Alternation of Generations. This means that plants display two body forms (or generations) which they alternate back and forth. The generations are known as the sporophyte generation and the gametophyte generation. Therefore, Alternation of Generations is the alternating between the multicellular sporophyte generation and the multicellular gametophyte generation.
Depending on the particular plant, one generation is usually more dominant. If the plant is gametophyte dominant, then the plant spends a majority of its time as a gametophyte, however it will still alternate with its sporophyte form. Plants that are gametophyte dominant are plants that are closely related to their algae ancestors and still largely rely on water for their reproduction. The reason is because gametophyte, which means 'making of gametes', produces unicellular gametes which are egg and sperm. Because sperm must swim to egg for fertilization, water is extremely important in a gametophyte dominant plant. Mosses are gametophyte dominant. Plants that are sporophyte dominant spend a larger portion of their life cycle as a sporophyte. Sporophyte, which means 'making of spores', produces unicellular spores that can be carried by air. These plants are less dependent on water for reproduction; however they still alternate and have a gametophyte generation which normally relies on water, again for the sperm to swim to the eggs. (The exception will be the flowering plants which will be discussed later). The gametophyte generation of a sporophyte dominant plant will normally be below ground where water is available.
Flowering Plant Life Cycle https://www.youtube.com/watch?v=hlypm2idste
As discussed in the previous unit, the flower is composed of four parts: 1. sepals, 2. petals, 3. male stamen and female pistil. Considering this is reproduction, the male stamen and female pistil is often discussed as the sporophyte generation.
Sporophyte Produces Spores Male microsporangium (2n) will undergo meiosis and produce haploid (n) spores called microspores. The female megasporangium (2n) will undergo meiosis and produce haploid (n) spores called megaspores.
Pollination and double fertilization P. 619
Zygote Grows into the Sporophyte
Once the seed is released, it is still protected by its outer shell or jacket. Environmental factors, such as warm, dark and moist conditions trigger the little embryo to rupture through the seed coat and continue its mitotic growth into the sporophyte generation. Notice how the conditions to trigger the emergence of the seed are that of the soil and not of a harsh environment. Also, once emergence occurs, the embryo will rely on the nutrients of the soil rather than the now expired endosperm to continue growth. Before long, this once protected embryo will develop into a large flowering plant with all its organs and systems, producing its own seed within its own flowers.
Lab #2