Plant Structure, Reproduction, and Development

General Biology 2 - Quarter 4: Modules 1-4

Module 1: Plant Structure, Reproduction, and Development

• Vascular plants have three basic organs: roots, stems, and leaves.
• A root anchors a vascular plant in the soil, absorbs minerals and water, and stores food.
• Most eudicots and gymnosperms have a taproot system with one large vertical root producing many small lateral roots.
• Angiosperms' taproots often store food that supports flowering and fruit production later.
• Seedless vascular plants and most monocots, including grasses, have fibrous root systems with a mat of thin roots spreading below the soil surface.
• Fibrous root systems are shallower than taproot systems.
• Grasses make excellent ground cover for preventing erosion due to the concentration of their roots in the upper few centimeters of soil.
• Root hairs, extensions of individual epidermal cells on the root surface, increase absorption of water and minerals.
• Absorption is also increased by mutualistic relationships between plant roots and bacteria and fungi.
• Adventitious roots arise aboveground from stems or leaves.
• Some modified roots provide additional support and anchorage and store water and nutrients or absorb oxygen or water from the air.
• Stems consist of alternating nodes (where leaves attach) and internodes (stem segments between nodes).
• An axillary bud is located at the angle formed by each leaf and has the potential to form a lateral shoot or branch.
• A terminal bud inhibits the growth of axillary buds, which is called apical dominance.
• Modified shoots, including stolons, rhizomes, tubers, and bulbs, have diverse functions.
• Leaves are the main photosynthetic organs, generally consisting of a flattened blade and a stalk (petiole) connecting it to a stem node.
• Monocots have parallel major veins running the length of the blade, while eudicots have a multibranched network of major veins.
• Plant taxonomists use floral morphology, leaf shape, spatial arrangement of leaves, and vein patterns to identify and classify plants.
• Plants reproduce sexually or asexually. Sexual reproduction depends on pollinating agents, while asexual reproduction is independent of these agents.
• Flowers attract insects, birds, and animals for pollination with their bright colors, fragrances, and shapes.
• Other plants pollinate via wind or water, while some self-pollinate.
• Gymnosperms generate cones (rather than flowers) containing male and female gametophytes.
• Gymnosperm male cones contain microsporophylls where male gametophytes (pollen) are produced and carried by wind to female gametophytes.
• The megaspore mother cell in the female cone divides by meiosis to produce four haploid megaspores. One of the megaspores divides to form the female gametophyte.
• The male gametophyte lands on the female cone, forming a pollen tube to meet the female gametophyte.
• One sperm cell released by the generative cell fuses with the egg, forming a diploid zygote, which divides to form the embryo.
• Unlike angiosperms, gymnosperms lack ovaries. Double fertilization does not take place, and male and female gametophytes are present on cones.
• Pollination is the transfer of pollen from flower-to-flower or cone-to-cone, through self-pollination or cross-pollination.
• Cross-pollination is more advantageous, providing greater genetic diversity.
• Maturation of pollen and ovaries at different times and heterostyly are methods plants have developed to avoid self-pollination.
• Double fertilization involves two sperm cells, one fertilizing the egg to form the zygote, the other fusing with polar nuclei to form the endosperm.
• After fertilization, the fertilized ovule becomes the seed, and the ovary tissues become the fruit.
• In embryonic development, the zygote divides into two cells: one becomes the suspensor, the other the proembryo.
• In eudicots, the developing embryo has a heart shape. As the embryo grows, it begins to bend and fills the seed, ready for dispersal.
• Seed production in angiosperms begins with double fertilization, which doesn't occur in gymnosperms.
• Food reserves are stored in the endosperm in both monocots and dicots; in non-endospermic dicots, the cotyledons store the food.
• A seed consists of the plumule, radicle, and hypocotyl.
• In dicots, the extending hypocotyls give rise to the stem of the plant. In monocots, hypocotyls remain below ground.
• Roots grow downwards from dicot seeds to form the tap root, while lateral roots branch off to all sides.
• Germination in monocot seeds is marked by the production of a fibrous root system where adventitious roots emerge from the stem.
• Seed germination depends on size and favorable conditions.
• Seed dispersal depends on structure, composition, and size. Seeds dispersed by water are buoyant; those dispersed by wind have wing-like appendages.
• Animals disperse seeds by excreting or burying them; other fruits have structures (hooks) that attach to animals' fur.
• Humans disperse seeds by moving fruit and discarding inedible portions.
• Some seeds remain dormant and germinate when favorable conditions arise.
• Plants obtain nutrition from the soil and atmosphere. Using sunlight, plants make organic macromolecules necessary for them by modifications of the sugars they form by photosynthesis.
• Carbon, Hydrogen, and Oxygen are the essential elements. Nitrogen, Potassium, and Phosphorous are primary macronutrients obtained from the soil.
• Calcium, Magnesium, and Sulfur are secondary macronutrients.
• Micronutrients, needed in very small quantities, include Iron, Manganese, Copper, Zinc, Boron, and Chlorine, and are toxic in large quantities.
• A complete fertilizer provides all three primary macronutrients with some of the secondary and micronutrients. Fertilizer labels list numbers showing the percent by weight of the primary macronutrients. For example, for a 5-10-5 fertilizer, its contents consist of 5% Nitrogen, 10% Phosphorous and 5% Potassium.
• Soil is weathered, decomposed rock and mineral fragments mixed with air and water.
• Fertile soil contains readily available nutrients.
• Roots act as miners, moving through the soil to bring minerals into the plant, which are used in structural components (carbohydrates and proteins), organic molecules (Magnesium in chlorophyll, Phosphorous in ATP), enzyme activators (potassium), and maintaining osmotic balance.
• Plants need nitrogen for nucleotides and proteins but cannot use atmospheric nitrogen.
• Many plants have a symbiotic relationship with bacteria in their roots, exchanging organic nitrogen for space to live as rent.
• Plants with symbiotic bacteria tend to have root nodules where the nitrogen-fixing bacteria live.
• Some plants have an analogous system, the vascular system in vascular plants, trumpet hyphae in bryophytes.
• Root hairs are thin-walled extensions of epidermal cells that provide increased surface area for efficient water and mineral absorption.
• Water and dissolved mineral nutrients enter the plant via two routes: intracellular (apoplastic) and extracellular (symplastic).
• The intracellular route, water and selected solutes pass only through the cell membrane of the epidermis of the root hair and then through plasmodesmata on every cell until the xylem is reached.
• The extracellular route, ater and solutes enter the cell wall of the root hair and pass between the wall and plasma membrane until encountering the endodermis.
• The endodermis has the Casparian strip, a strip of waterproof material (containing suberin).

Module 2: Animal Reproduction, Nutrition, Digestion, and Respiration

• Animals produce offspring through sexual and/or asexual reproduction.
• Sexual Reproduction reproduction involves the union of gametes providing an important source of genetic variation.
• Species reproducing sexually must maintain two different types of individuals, males and females, which can limit the ability to colonize new habitats as both sexes must be present.
• Hermaphroditism occurs commonly in lower invertebrates in which one individual has a functional male and female reproductive parts.
• Hermaphrodites may self-fertilize or mate with others of their species.
• Coral and Hydra reproduce asexually through Budding.
• Sea stars reproduce asexually by Fragmentation.
• Another way of asexual reproduction is Parthenogenesis in invertebrates such as aphids, wasps, bees where an egg develops into a complete individual without being fertilized.
• Digestion breaks large molecules into smaller molecules. Digestive enzymes are chemicals that help break apart large molecules into nutrients.
• Gastrovascular cavity, is found in organisms with one opening for digestion.
• In the small intestine, nutrientas are absorbed through villi, while water is absorbed in the intestine.
• Animal diets need carbohydrates, protein and fat as well as vitamins and inorganic components for nutritional balance, and some vitamins differ from one animal to another.
• Respiration involves taking in oxygen, using it to release energy by burning food, then eliminating waste materials, CO2 and water.
• This process can occur through diffusion, or across outer membranes, or using spiracles and a specialized tracheal system for respiration.

Module 3: Circulation and Immune System

• The Circulatory System evolves over time in organisms to have efficient transporters of nutrients and waste throughout the body.
• A circulatory system has three main features: circulatory fluid (blood or hemolymph), blood vessels, and a heart.
• In open circulatory systems, hemolymph bathes body cells and is pumped into a cavity called a hemocoel.
• In closed circulatory systems, the circulatory fluid is confined to vessels and distinct from the interstitial fluid.
• Blood vessels are classified into three main types: arteries, capillaries, and veins.
• Arteries carry blood away from the heart, branching into arterioles and capillaries, which are microscopic vessels for gas exchange and converge into venules and veins to carry blood back to the heart.

Module 4: Nervous Control, Sensory and Motor Mechanisms

• The nervous system controls much of the body through somatic(voluntary) and autonomic(involuntary) functions.
• Neurons depend on glial cells, and include a cell body, nucleus, branched-extensions called dendrites and axons.
• A synapse, where axons transmit information to other cells are called synaptic terminals.
• Chemical messengers called neurotransmitters transmit information from the transmitting neuron to the receiving cell.
• In vertebrates, the central nervous system (CNS), integrates information, while the nerves of the peripheral nervous system (PNS) transmit sensory and motor signals between the CNS and the rest of the body.
• Afferent neurons carry sensory signals to the CNS.
• Efferent neurons function in either the motor system, or the autonomic nervous system regulate smooth and cardiac muscles.
• Taste and smell depend on stimulation of chemoreceptors by small dissolved molecules.
• The muscle cells of skeleton muscle contains myofibrils composed of thin filaments of actin and thick filaments of myosin, organized into repeating units called sacromeres.