Week 4 Part 2 (Introduction to Plantae)
Collenchyma cells
-Abundant in young, developing shoots -Stretchy, capacity to bend -Remain alive -Thick cellulose wall
Dermal tissue system
-Barrier to distinguish between internal and external environment -Important for protection, retention of water, gas exchange, defense -Main component is epidermal cells, but also has guard cells and trichomes
What are the distinctive features of land plants?
-Bodies composed of tissues (close associations of cells) -Tissues arise from one or more actively dividing cells that occur at growing tips, forming apical meristems -Life cycle with alternation of generations -Have embryos (young, multicellular sporophytes that are produced by mitosis following fertilization of an egg cell that depend on maternal tissues for food during early development) -Sporic life cycle with tough walls made of sporopollenin -Specialized structures called gametangia generate, protect, and disperse land plant gametes; tough sporangia likewise produce, protect, and disperse the spores of land plants
Identify organelles and structures of a plant cell.
-Cell wall: rigid layer that is found outside the cell membrane and surrounds the cell. The cell wall contains cellulose and protein -Large central vacuole: Aside from storage, the main role of the vacuole is to maintain turgor pressure against the cell wall -Plastids such as chloroplasts: closely related membrane-bound organelles that carry out many functions. They are responsible for photosynthesis, for storage of products such as starch, and for the synthesis of many types of molecules that are needed as cellular building blocks
Identify and describe the synapomorphies that are shared by both green plants and land plants
-Chloroplasts containing chlorophyll a and b -Starch produced in plastids -Cell wall made of cellulose
Describe general characteristics of green plants (streptophytes).
-Chloroplasts with chlorophyll a and b -Starch produced in plastids -Cellulose-rich cell wall
Explain the egg retention in gametangia (i.e. archegonium) as an adaptation to terrestrial environment.
-Gametangia: Where gametes were produced. Complex structure that protected gametes from drying out. -Having an embryo retained with the mother, and being nourished by it. (Examples-gametophyte supports sporophyte)
Sclerenchyma cells
-More abundant in mature plant -More stiff/strong, rigid -Dead at maturity -Cellulose cell wall, secondary wall made of lignin
Explain challenges and benefits of transition from a freshwater to a terrestrial lifestyle experienced by ancestral plants.
-There are four major challenges to plants living on land: obtaining resources, staying upright, maintaining moisture, and reproducing. -abundant light, unfiltered by water -CO2 abundant, circulated more freely -initially there was no competition or herbivores
Describe a type of environment in which the most common ancestor of modern land plants evolved.
A billion years ago, Earth's terrestrial surface was comparatively devoid of life. Green or brown crusts of cyanobacteria most likely grew in moist places, but there would have been very little soil, no plants, and no animal life
Tissue
A group of similar cells that perform the same function.
Evolutionary Longhand Template
A long time ago, some individuals of [species] experienced a mutation that led to [trait]. The new trait of X was heritable because it ocurred in the sex cell of the multicellular organism Y (make sure it is multicellular). Individuals with this trait had greater fitness than those without because...(intentionally elaborate on fitness with focus on reproduction). Over generations, this trait became more abundant within a population, thus evolution took place as a result of the change in allele frequency.
Obtaining resources from two places at once
Algae and other aquatic organisms acquire the resources they need from the surrounding water. In contrast, the resources required by a photosynthetic organism growing on land are found in two very different environments: air and soil. Light and carbon dioxide are mainly available above ground, while water and mineral nutrients are found mainly in the soil. The bodies of most plants have specialized organ systems—shoots and roots—that provide access to these two environments. Below ground, a plant's roots absorb water and essential minerals from the soil. Above ground, shoots bear leaves. Leaves use sunlight as an energy source to make food from carbon dioxide. Most plants transport materials between their roots and shoots within vascular tissue, a system of tube-shaped cells that branches throughout the plant.
Explain the evolutionary relationships among protists, fungi, plants and animals with a phylogenetic tree (refer to the tree on the next page).
All are in the domain Eukarya. Protists diverged first, then plants, followed by fungi and finally animals
Identify and describe the major evolutionary innovations (synapomorphies) that define: nonvascular plants
Bryophytes (mosses) -Relatively small in stature and are most common and diverse in moist habitats; have dominant gametophyte generation -Stomata: pores that can open or close to take in CO2, release oxygen, and conserve water -Embryo retention -Alternation of generations -Complex gametangia
What are the two types of green algae?
Coleochaetes and stoneworts
Organ system
Different organs composing a functional unit
Organ
Different tissue systems composing a functional unit
Tissue system
Different tissues composing a functional unit
Identify and describe the major evolutionary innovations that define: seed plants
Divided into gymnosperms and angiosperms -Seeds: complex structures having specialized tissues that protectively enclose embryos and contain stores of carbohydrate, lipid, and protein that enable embryos to grow and develop -Pollen: small air or animal borne spores that contain and protect microscopic male gametophytes
Identify and describe the major evolutionary innovations that define: Angiosperms
Eudicots and monocots -Produce seeds and pollen but are distinguished by the presence of flowers, fruits, and a specialized seed tissue known as endosperm -Vessel elements (evolved independently) -Flower: short stem bearing reproductive organs that are specialized in ways that enhance seed production -Fruit: structure that develops from flowers, enclose seeds, and foster seed dispersal in the environment -Endosperm: nutritive seed tissue that increases the efficiency with which food is stored in the seeds of flowering plants
Staying "afloat" in air
If you have seen kelp or other seaweeds washed up on the beach, you know that these large algae are limp and flexible, yet they stay upright in water. In an aquatic environment, the buoyancy of water provides physical support for large algae. Air does not provide the same level of support as water. Plants can only stand upright because they contain strong and rigid support tissues. An important terrestrial adaptation of plants is the production of lignin, a chemical that hardens the plants' cell walls. A tree would collapse if it were not for its framework of lignin-rich cell walls.
Understand the basic sequence of alternation of generations in plants.
In most plants meiosis and fertilization divide the life of the organism into two distinct phases or "generations". -The gametophyte generation begins with a spore produced by meiosis. The spore is haploid, and all the cells derived from it (by mitosis) are also haploid. In due course, this multicellular structure produces gametes — by mitosis — and sexual reproduction then produces the diploid sporophyte generation. -The sporophyte generation thus starts with a zygote. Its cells contain the diploid number of chromosomes. Eventually, though, certain cells will undergo meiosis, forming spores and starting a new gametophyte generation. Two points revealed by plant life cycles: -Mitosis can occur in haploid cells as well as diploid ones. -A haploid set of chromosomes, and hence a single set of genes (one genome), is sufficient to control cell function in these organisms (but not in most animals). In fact, the gametophyte generation is the major stage in the life of mosses and an independent plant in ferns. However, the gametophyte is only an inconspicuous structure in angiosperms and other "higher" plants.
Be able to draw the cross section of a leaf and label the various components
Leaf mesophyll is composed of spongy and palisade parenchyma cells -Palisade: photosynthesis -Spongy: Provide structure, storage, wound repairs
Reproducing on land
Living on land also requires reproductive adaptations. For algae, the surrounding water ensures that released gametes (sperm and eggs) and developing offspring do not dry out. The aquatic environment also provides a means of dispersing the gametes and offspring to new locations. Plants, however, must keep their gametes and developing offspring from drying out in the air. Plants must also have some means for dispersal other than water currents. Several adaptations of plants meet these challenges. All plants produce their gametes in a "jacket" of protective cells. The protective jacket surrounds a moist chamber where gametes can develop without dehydrating. In most plants, sperm reach the eggs by traveling within pollen grains, which are carried by wind or animals. Eggs remain within the tissues of the female parent and are fertilized there. The zygote (fertilized egg) develops into an embryo while still inside the female parent. For most plants, the embryos are eventually dispersed as seeds, enclosed in protective coats.
Ground tissue system
Makes up bulk of plant body; composed of parenchyma, collenchyma, and sclerenchyma cells -Important for production of sugars and storage of starches
Identify the sister taxon to land plants.
Multicellular green algae (charophytes) -Biologists hypothesize that some ancient charophytes may have lived in similar shallow-water habitats that occasionally dried out. Natural selection would have favored individual algae that could survive these dry periods.
Identify and describe the major evolutionary innovations that define: Gymnosperms
Pinophytes (pine trees) and Ginkgophytes (conifers) -Seeds are not enclosed within fruits -Vessel elements
Stomata
Pores in the leaves allowing for gas exchange -Flanked by guard cells that open and close stoma
Identify and describe the major evolutionary innovations that define: seedless vascular plants
Pteridophytes (ferns) -Possess vascular system made up of stem, roots, and leaves which carry nutrients and other materials throughout the body -Relatively dry habitats; able to grow to larger sizes and remain metabolically active for longer periods -Vascular tissue -True leaves: ? -Roots: branching organs specialized for the uptake of water and minerals from the soil -Sporophyte-dominant life cycle -Tracheids: specialized conducting cell
Parenchyma cells
Responsible for photosynthesis -Have totipotency (ability to differentiate to various cell types) -Involved in wound repair
Elaborate on the timing of evolution of various innovative traits by identifying them on a cladogram.
See first worksheet
Compare and contrast the structures of a plant cell versus an animal cell.
Structurally, plant and animal cells are very similar because they are both eukaryotic cells. They both contain membrane-bound organelles such as the nucleus, mitochondria, endoplasmic reticulum, golgi apparatus, lysosomes, and peroxisomes. Both also contain similar membranes, cytosol, and cytoskeletal elements. The functions of these organelles are extremely similar between the two classes of cells (peroxisomes perform additional complex functions in plant cells having to do with cellular respiration), The main structural differences between plant and animal cells lie in a few additional structures found in plant cells: chloroplasts, the cell wall, and vacuoles.
Elaborate how various synapomorphies of each of the major plant group could be considered as adaptations to life on land.
There are four main ways that plants adapted to life on land and, as a result, became different from algae: 1. In plants, the embryo develops inside of the female plant after fertilization. Algae do not keep the embryo inside of themselves but release it into water. This was the first feature to evolve that separated plants from green algae. This is also the only adaptation shared by all plants. 2. Over time, plants had to evolve from living in water to living on land. In early plants, a waxy layer called a cuticle evolved to help seal water in the plant and prevent water loss. However, the cuticle also prevents gases from entering and leaving the plant easily. Recall that the exchange of gasses—taking in carbon dioxide and releasing oxygen—occurs during photosynthesis. 3. To allow the plant to retain water and exchange gases, small pores (holes) in the leaves called stomata also evolved (Figure below). The stomata can open and close depending on weather conditions. When it's hot and dry, the stomata close to keep water inside of the plant. When the weather cools down, the stomata can open again to let carbon dioxide in and oxygen out. 4. A later adaption for life on land was the evolution of vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. In algae, vascular tissue is not necessary since the entire body is in contact with the water, and the water simply enters the algae. But on land, water may only be found deep in the ground. Vascular tissues take water and nutrients from the ground up into the plant, while also taking food down from the leaves into the rest of the plant. The two vascular tissues are xylem and phloem. Xylem is responsible for the transport of water and nutrients from the roots to the rest of the plant. Phloem carries the sugars made in the leaves to the parts of the plant where they are needed.
What do sclerenchyma and collenchyma have in common?
They are both ground tissue system cells important for structural support
Maintaining moisture
Though most plants are exposed to dry air, their cellular processes must still take place in an aqueous environment. Plants (and other terrestrial organisms) have adaptations that maintain a watery internal environment. The waxy surfaces of a cactus or an apple are examples of such an adaptation. This waxy cuticle coats the leaves and other aboveground parts of many plants, helping the plant body retain water. However, the cuticle also slows down the exchange of carbon dioxide and oxygen between the surrounding air and the inside of photosynthesizing leaves. Gases are exchanged through stomata (singular, stoma). Stomata (STOH ma ta) are microscopic pores in the leaf's surface. Two surrounding cells regulate each stoma's opening and closing. Stomata are open at certain times of day, allowing gas exchange, and are closed the rest of the time, preventing water loss by evaporation.
Trichomes
Tiny, spikelike projections on some leaves -form cooling structure that reflects sunlight, water retention (trap moisture), provide defense, store chemicals to repel herbivores
Compare and contrast tracheids and vessel elements
Tracheids (thin) and vessel elements (wider/shorter) are both hollow with a mechanism to let water out (pits and slits, respectively) and both have a secondary cell wall made of lignin
Compare and contrast xylem and phloem
Xylem: -Water transport -Unidirectional flow from root to leaf -Tracheids or tracheids and vessel elements Phloem: -Sugar transport -Bidirectional flow -Sieve tube elements with companion cells
