Introductory Biology - Worksheet 2 Notes

2/15 Lecture Tophat Q: What plant organ (or part of an organ) is this? - Leaf Q: What plant organ (or part of an organ) is this? - Root Q: What plant organ (or part of an organ) is this? - Leaf Q: Where do you think this plant lives? - In a pond (has lot of vascular tissue) Q: where do you think this plant lives? - A desert (cells are tightly packed together – thick cuticle bc leaves are trying to conserve water & stomata is sheltered so the plant loses less water) How do plants grow v animals? 1. Growth is unrestricted in plants (if limb is cut off, it will grow back) 2. Plants are shaped by their environment (lots of sun & nutrients = large plant) & animals are determined by genes (inherited) Plant Structure Appearance of land plants - ~500 mya: Colonization of land - First true land plants - Associated w many adaptations (more later) - Set up for new radiations on land - Plants and animals - Animals can evolve and live on land bc they eat plants Challenges of moving to land - Communication between cells - Plasmodesmata - pores between cells - Desiccation - to dry out - Many adaptations - Gas exchange - Stoma - pores on leaves & stems – allow for entry of carbon dioxide - Open and close at certain times - Sexual reproduction - Alternation of multicellular generations (organism has both haploid and diploid multicellular stages) - Gametes cannot swim to each other anymore, at risk of desiccation What is a land plant? - A plant is a multicellular eukaryote that is often photosynthetic - Plants differ from all other organism by having - An apical meristem - A life cycle that exhibits alternation of multicellular generation - Thick-walled spores (1N) that grow into haploid plants (gametophytes) - Multiceullar sex organs What is an organ? (in plants) - Roots (usually bigger than shoots) - Shoots – includes leaves, stems, & reproductive parts Basic anatomy of a plant - Cells - Tissues - Tissue system - Organ systems Tissue systems - Three tissue systems - Dermal - protection (thornes, waxy cuticle on leaf, bark on tree) - Ground - storage (of sugars & water), support, photosynthesis - Vascular - transportation - Continuous in plant - Vary in appearance in different organs Plants display indeterminate growth - Unrestricted growth - Final body size/shape determined strongly by environment - Unlike animals (controlled stopping point) - Modular - Module = stem + axillary bud + leaf - Plant = repeated modules How do plants grow? Plant growth is indeterminate - Cell division is localized to special regions called meristems - Meristems = Non-permanent tissues that grows - 3 Locations of meristems: - Apical - Length - Lateral - Width - Intercalary – Where leaf meets stem - Developmental “fate” determined right after mitosis. - Dermal tissue, Vascular tissue or Ground Tissue Wrap Up - Plants have adaptations that allow them to survive on land - Plants are composed of two organs: roots and shoots - There are three tissue systems in plants: - Dermal tissue - Ground tissue - Vascular tissue - Plants have indeterminate growth, and grow in modules - Plants generate new growth from meristems W2 Tophat Q Q: where does the mass of a tree come from? - Carbon dioxide Q: How do you think this tree moves water all the way to the leaves at the very top? - Passive transport Q: Which of the following is/are true regarding water and plant physiology? - Most water is returned to the air via transpiration as a consequence of CO2 uptake Q: What type of bonds are responsible for water molecules ”sticking” to each other and nearby surfaces? - Hydrogen bonds Q: Why do plants transpire more water in dry environments compared to humid environments? - Lower water pressure in a dry atmosphere (how much water vapor is in the air) Q: How might a cell change its size? - Change the solute potential Plant Transpiration Water & Life (review) - Basics of water movement same for all - Water not actively pumped between cells - Moves passively by osmosis: diffusion of water across semi-permeable membrane - Diffusion: substance moves down its concentration gradient (high to low) - Semi-permeable membrane: water moves passively, often solutes do not - Osmosis describes the diffusion of water across a semipermeable membrane - High water concentration & low solute concentration → low water concentration & high solute concentration Why do hydrogen bonds form between water molecules? - Water molecules are polar - Oxygen more electronegative than the hydrogen - Electrons negatively charged - Oxygen partially negative & hydrogen partially positive - Only have hydrogen bonds between different molecules - Attraction between opposite charges (polar covalent bonds) - Hydrogen bonds can form between molecules other than water!!! → found in amino acids and side chains Water - Molecules (+) on one end, (-) on other - Form hydrogen bonds (relatively weak) - Cohesive - stick together - Surface tension - Adhesive - stick to hydrophilic surfaces - E.g., inner walls of tracheids & vessels - Allows water to move up the plant Solute Potential ψs - Solute potential: the tendency of water to move by osmosis - Water moves to areas of higher solute concentration (moving down concentration gradient) - Solute potentials are always negative because they are measured relative to the solute potential of water - Solutions with high concentrations of solutes have low solute potential - Water moves towards area of lower solute potential - Pressure Potential ψp - Pressure potential: the tendency of water to move in response to pressure - Physical pressure of water - Turgor pressure of the fluid on the cell wall - Wall pressure of the wall pushing back on the fluid - When pressure is negative it is called tension - Tension draws water up through a straw - Water moving via pressure potential is also called bulk flow - Water moves towards areas of lower pressure - Not just a plant thing – found in straws, kidneys, blood vessels, pipes of house Putting it together - Water potential or ψ = ψs + ψp (solute potential + pressure potential) → use to figure out which way water will move - Water moves to lower water potential & lower pressure Water potential of soil - Soil has few solutes and is under little pressure, therefore has higher pressure than water in the roots - Since water wants to favor movement of water to lower pressure, this favors movement into the roots - If water pressure drops in soil (e.g. a drought) this makes obtaining water difficult for the plant → plant solute potential drops during hot, dry months to increase greater difference of water potential (more water can enter) - Species in dry soils adapt by lowering the solute potential of their tissues Water potential in the air - Pressure exerted by water vapor in the atmosphere depends on temperature and humidity - The lower the pressure potential, the faster liquid water evaporates - Water that exists as vapor has no solute potential - Dry air → fewer water molecules → Less pressure exerted → Increased evaporation - Warm air → Molecules further apart → Lower pressure Water potential gradient - Water evaporates into air spaces from mesophyll, creating tension - Film of water on cell surface decreases - Tension on the water inside the mesophyll cells increases - Pull on water in the xylem vessels increases - Water moves up from root into xylem and up the plant Water Pressure in Plants - Top of plant has lowest water potential - Roots of plant have highest water potential - Water stays together bc of hydrogen bonds (how water moves from roots up into air) - Think of plant as a straw (constant pull on water) - Water goes from roots → stem → leaves → atmosphere (moving to LOWER water potential) How does plant structure facilitate transpiration? Vascular Tissue: a key innovation - Function: transport to all plant organs - 2 types – both contained in vascular bundle - Xylem: moves water & dissolved minerals → (smaller dark circles) - Phloem: moves food (photosynthate) → (larger area surrounding asylum) - Xylem Anatomy - Tracheids: product of a single cell - Multicellular: vessel - Grow, secrete lignin (reinforces cell wall w fibers), die leaving only cell walls behind - Water enters/exits through pits - xylem, plant vascular tissue that conveys water and dissolved minerals from the roots to the rest of the plant and also provides physical support. Stele contains vascular tissue - Xylem: conducts water - Phloem: conducts sugars → Xylem cells are wider in diameter and have thicker, waterproof cell walls → Phloem have cell walls of normal thickness and smaller diameter Where does water enter the roots of a plant??? → Endodermis - Layer of cells that surrounds stele - Contains waxy strip that forces incoming water through a selectively permeable membrane before it get to the xylem - “Filters” incoming water where the plant switches from diffusion to bulk flow (movement due to pressure gradient) → main factor that drives water up Buttercup stem cross section – Vascular Bundles - Vascular Bundle - Contains Xylem and phloem - Vascular bundles are surrounded by fiber to give it support (ex. celery) Anatomy of a Leaf - Epidermis - Lower epidermis contains stomata to help regulate gas exchange - Upper epidermis has a waxy cuticle to prevent water loss - Mesophyll - Areas of tightly-packed parenchyma cells help maximize light (where photosynthesis is happening) - Areas of loosely-packed parenchyma cells near stomata allow CO2 to diffuse through the leaf - Think “middle” - Must balance uptake of CO2 & loss of H2O - Stomata (on bottom): will open and close to let in CO2, but a consequence is water loss - Difference in CO2 concentration creates a gradient of CO2 that favors movement into the leaf Palisade Mesophyll: - Ground tissue - Contains many chloroplasts in each cells - Why on top of leaf on lily pad → bc do not need to take up water Lower Epidermis: - Thinner cuticle or no cuticle Guard Cells: - Regulate water & gas exchange Spongy Mesophyll - Loosely packed From top to bottom Cuticle → Upper Epidermis → Palisade Mesophyll → Veins → Spongy Mesophyll → Lower Epidermis → Stomata & Guard Cells Stomata & Guard Cells - Think of inner tube → more inflated, easier to get into - Uptake of solutes by guard cells causes water to be drawn into by osmosis. As the guard cells swell, they bow apart, opening the stoma - Release of solutes causes water to flow out of the guard cells, closing the stoma **Plants will absorb water through their roots and release water as vapor into the air through these stomata. To survive in drought conditions, plants need to decrease transpiration to limit their water loss. Some plants that live in dry conditions have evolved to have smaller leaves and therefore fewer stomata. **A stomate opens and closes in response to the internal pressure of two sausage-shaped guard cells that surround it. The inner wall of a guard cell is thicker than the outer wall. When the guard cell is filled with water and it becomes turgid, the outer wall balloons outward, drawing the inner wall with it and