Biology Study Guide Part 1: Cell Theory and Microscopes Biology: The scientific “study of life” extends from the microscopic scale of the molecules and the cells that make up organisms to the global scale of the entire living planet. Different levels of biological organization: Biosphere → Ecosystems → Communities → Populations → Organisms Organs and Organ Systems → Tissues(50µm) → Cells(10µm) → Organelles(1µm) → Molecules Processes of life: All living things must be able to carry out the following: 1. Organization: Being structurally composed of one or more cells 2. Metabolism: All of the reactions that occur inside the cell/organism 3. Growth: Increase in size of the organism 4. Reproduction: The ability to reproduce new individual organisms 5. Movement: The ability to move in their environment 6. Response: The ability to respond to environmental stimuli 7. Homeostasis: Maintaining a constant internal environment 8. Nutrition and Excretion: Take in nutrients and remove wastes History of Animal Development: Abiogenesis: Life could emerge spontaneously from nonliving matter ● Aristotle(384-322 BC) came up with the theory ● Abiogenesis = Spontaneous Generation ● It was not proven through experiments; it was accepted as true for over 2000 years. Francesco Redi(In 1668) ● Disproved of the theory ● Performed an experiment involving meat and maggots ● One of the first scientists to use an experiment to test his hypothesis ○ His hypothesis: Maggots only developed in rotting meat if flies were allowed to come into contact with it ● Spontaneous generation was still accepted despite the evidence ○ Only the open meat produced maggots Louis Pasteur(In 1859) ● Proved beyond reasonable doubt spontaneous generation does not occur ● Theory of Biogenesis ○ Thought that living organisms came from other living organisms ● Designed an experiment, where broth was boiled to force out air and kill microbes ○ Predicted that only flask that allowed dust to enter could grow mould ● He used the scientific method to prove his theory of Biogensis ● This evidence proved that microorganisms exist in the air and spontaneous generation cannot occur ● Led to the developments of microbiology, immunology and biochemistry Cell Theory: Robert Hooke(In 1665) ● The first person to observe and describe cells ● Looked at cork under a microscope ○ Examined think slices and saw many empty chambers which he called cells Antonie Van Leeuwenhoek(In 1674) ● ● ● ● Observed the first living cells and named them “animalcules” Made his own single-lens microscope(500x zoom) First to observe moving single-celled organisms Looked at blood, pond water, teeth scrapings, etc Schleiden & Schwann ● Matthias Schleiden(in 1838) stated that plants were made up of cells ○ Saw nuclei in young plant cells ● Theodor Schwann(In 1839) stated animals were made up of cells ○ Saw nuclei in developing animal tissues ● Together proposed the cell theory Rudolph Virchow(in 1855) ● Observed dividing cells in multicellular organisms ● Concluded that all cells come from preexisting cells Cell Theory: All plants and animals are composed of cells and cells are the basic unit of all organisms ● All living things are composed of one or more cells ● Cells are the smallest functional unit of life ● All cells are produced by the division of preexisting cells Microscopy: Microscope definition: A microscope is a scientific tool used to magnify tiny objects or organisms that are too small to be seen clearly with the naked eye Compound microscope: Uses more than one lens to magnify Quantative vs Qualitiative observations ● Quantitative: provides precise, measurable data that can be used in calculations or statistical analysis ○ Size of cell ● Qualitative: Offers detailed descriptions that help in understanding the characteristics and qualities of what is being observed ○ Colour of cell ○ Cell shape 3 important parameters in microscopy: ● Magnification: the increase in the size of an image compared to its actual size ● Resolution: clarity of image, the minimum distance between two points still be distinguished as two points ○ Human eye = 0.1mm ● Contrast: emphasizes differences in parts of the sample ○ Staining or labelling cell components ○ History of Microscopes: ● ~1600: Zacharias Janssen is credited with making one of the earliest compound microscopes ○ 20-30x zoom ● 16674: Antonie van Leeuwenhoek made own lenses ○ Good lenses can give up to 200x zoom ○ Go up for more information ● Early 1830s: Microscopes had 2 main issues: image blurring and colour separation ○ Joseph Jackson Lister and William Tulley ○ Issues solved = rapid growth in microscope popularity ● Just more discoveries using microscopes later on Light Microscope vs Electron Microscope ● Light Microscope ○ Visible light is passed through specimen and then through lens(1 or 2 lenses) ○ Specimen can be dead or alive ○ Max 2000x but resolution suffers beyond 400x ■ Resolution = 0.2um, 0.0002mm ● Electron Microscope ○ Uses a beam of electrons instead of light ○ Has better magnification and resolution compared to light microscopes ○ Max 1,000,000x magnification ■ Resolution = 0.001um, 0.0000001mm ○ Types Electron Microscope ■ Scanning Electron Microscope(SEM) ● Electrons reflect of specimen covered in electron-dense material(gold) and make 3D images ● Provides an image of the surface of the specimen ■ Transmission Electron Microscope(TEM) ● Electrons are passed through very thin section of the specimen ● Produces clear images of the interior of the specimen Advantages and Disadvantages of light and electron microscopes Light Microscope Electron Microscope Advantages ● Cheap ● Easy to use ● Can examine both alive and dead specimens ● Can see coloured images ● Good resolution ● Good zoom Disadvantages ● Not a lot of zoom ● Mediocre resolution ● Expensive ● Can only examine dead specimens ● Only see black and white ● Not widely accessible Summary of Microscopes Light Microscope SEM TEM Radiation Source Light Electrons Electrons Wavelength 400-700nm 0.005nm 0.005nm Lenses Glass Electromagnetic Electromagnetic Max Magnification 1500x - 2000x 100,000x 250,00x Maximum Resolution 200nm 10nm 1nm Specimen Status Dead or alive Dead Dead Type of Image Coloured Black and White Black and White Freeze Fracture 1. Specimen frozen at -190C and then fractured by steel blade 2. Vaporized platinum or carbon is sprayed onto a fractured surface to make a replica of the surface 3. Replica viewed under an electron microscope Cryogenic Electron Microscopy(Cyro-EM) ● Uses freeze fracture to study protein structure ● Allows scientists to understand how viruses duplicate Flourescence Microscope ● Uses UV light to pass through the specimens ● Specimen is covered in specific types of substances that emit different colours when hit with UV lights ○ Substances stick to one type of organelle ● Immunofluorescence uses dye to attach to antibodies ○ Antibodies target specific molecules ● Allows scientists to see where a specific protein is produced ○ Better understand of how viruses affect their target cells, replicate and damage the body Confocal Microscope ● Out-of-focus light in specimens is eliminated, improving the resolution ○ Multiple images are taken at different layers of specimen to make a 3D image Calculations on microscopes: ● Total magnification: Ocular lens x objective lense ● Field of View(FOV): ○ Low power: use ruler to measure ○ Medium and High Power ■ FOV(low) x Magnification(low)/Magnification(other) = FOV(other) ■ E.x FOV=4.5mm, magnification is 40x ● FOV medium = 4500um x 40/100 ● FOV medium = 1800um ● Actual size of specimen ○ FOV/# of objects that fit in FOV ● Scale: ○ Actual size of object/drawing size of object ○ 1cm = ● Magnification: ○ Drawing size/actual size ○ Not to be confused with scale ○ 150x bigger than organism, etc Part 2: Types of living things Dear King Philip Came Over For Good Soup Domain, Kingdom, Phylum, Class, Order, Family, Genesis, Species All living things can be classified into 3 domains, 2 are eukaryotic and prokaryotic Prokaryotic vs Eukaryotic ● Cells can either one ● Bacteria and archaea contain prokaryotic cells ● Organisms such as plants, animals, fungi, and protists contain eukaryotic cells Processes of life: All living things must be able to carry out the following: 1. Organization: Being structurally composed of one or more cells 2. Metabolism: All of the reactions that occur inside the cell/organism 3. Growth: Increase in size of the organism 4. Reproduction: The ability to reproduce new individual organisms 5. Movement: The ability to move in their environment 6. Response: The ability to respond to environmental stimuli 7. Homeostasis: Maintaining a constant internal environment 8. Nutrition and Excretion: Take in nutrients and remove wastes Eukaryotic Cells ● More complex compared to prokaryotic cells ○ Has a distinct, membrane-bound nucleus ■ Protects things in cytoplasm ● Includes domain Eukarya ● Evolved from prokaryotic cells ● Further classified into 4 kingdoms: animal, fungi, plant, and protists Organelles ● Little organs in cells that have specialized functions ● Cell wall, cytoskeleton, and cytoplasm are not considered organelles ● Structures and organelles can be grouped by function into 4 categories ○ Structure, support, and mobility ○ Genetic control ○ Endomembrane system ○ Energy makers Structure, support, and mobility 1. Cell wall: rigid and supports the cell’s structure a. Only in plants 2. Plasma membrane: the barrier between the inside of the cell and the surrounding environment 3. Cytoplasm: the jelly-like substance that fills in the cell a. Advantages of organelles separated from cytoplasm: i. Separation of reactions and enzymes ii. Small volumes within organelles increase the concentration of enzymes and substances to speed up reactions iii. pH can be held at optimum levels for reactions to happen quickly 4. Cytoskeleton: gives mechanical support within the cell(like cell wall but on the inside) 5. Centrioles/Centrosomes: tubed-like structure that help with splitting DNA during cell division a. Only in animal cells 6. Cilia: tiny hair-like structures on the outside of the cell to help propel the cell a. Only in animal cells 7. Flagella: long whip-like tail that helps with propelling the cell a. Only in animal cells Genetic Control 1. Nucleus: the main control center of the cell, where DNA and genetic information is stored in 2. Nucleolus: where ribosomes are created 3. Nuclear envelope: plasma membrane of the nucleus 4. Ribosomes: transporters for DNA information, translate genetic information into proteins a. 80s(svedberg units) 5. Rought Endoplasmic Rectum: Studded with ribosomes and transport proteins 6. Smooth Endoplasmic Rectum: synthesizes lipid and packages them to be transported to other parts of the cells a. Has no ribosomes 7. Vesicles: tiny sacs of membrane that are used to transport substances throughout the cell a. Doubled layered 8. Golgi Apparatus: Acts as the post office of the cell, packages from the rough/smooth ER arrive here to be repackaged and sent out to their destinations in the cell 9. Lysosomes: digest food particles, kill infectious organisms, and recycle dead/worn-out cell parts a. Only in animal cells 10. Vacuole: storage pace for water, minerals, and food a. Big in plants, smaller, and more spread out in animal cells 11. Mitochondria: the powerhouse of the cell 12. Chloroplast: the organelle for photosynthesis a. Only in plants Plant vs Animal cell In animals but not in plants: Centrosomes(2 centrioles), cilia, flagella, and lysosomes In plants but not in animals: Cell walls, chloroplasts, and central vacuole Animals Fungi Plants Cell wall Absent Present Present Vacuoles Small, temporary Large, permanent Large, permanent Chloroplasts Absent Absent Present Centrioles Present Absent Absent Cilia Present Absent Absent Flagella Present Present in some Rarely present Some cells don’t have a nucleus, while others have multiple ● Red blood cells do not have a nucleus to be flexible ● Muscle cells have many nuclei to make additional protein Prokaryotic Cells ● Smaller than eukaryotic cells ○ Typical size: 0.5-5um ● No membrane-bound organelles ● Includes domain bacteria and domain archaea ● Prokaryotes are the earth’s earliest inhabitants, before eukaryotes Structure of prokaryotes: 3 main shapes ● spherical(cocci) ● rod/pill shaped(bacilli) ● spiral/snake(spirilla) Parts of prokaryotes 1. Plasma membrane: enclosing the cytoplasm and acts as a barrier between the inside and outside of the cell 2. Cell wall: rigid structure outside the plasma membrane to provide shape, and protection, and stop the cell from bursting 3. Peptidoglycan a. Cell is often made up of this b. Sugar-protein complex c. Antibiotics can target the peptidoglycan to kill it 4. Capsule: stick, viscous layer of sugar outside the cell wall a. Helps stick to other cells or structures b. Can evade the host’s immune system c. Not present in many prokaryotes 5. Pili(fimbriae): short, thin hair that helps adhere to other cells or structures a. Not present in all prokaryotes 6. Flagella: like a tail in an animal cell and helps move a. Cells may contain one, none, or multiple flagella 7. Cytoplasm: watery solution filled in the cell a. No internally bound organelles in prokaryotic cells 8. Naked DNA: in a singular chromosome a. Not attached to any proteins 9. Nucleoid region: the area where the chromosome is located a. No nucleus b. Appears lighter in microscope c. Not membrane-bound 10. Ribosomes: structures in the cytoplasm that synthesize proteins a. 70s(svedberg units) - smaller than eukaryotic cells(80s) Ultracentrifugation ● Used to separate cell components 1. Cells are first broken open using a blender to release all components inside 2. The mixture is repeatedly centrifuged at increasing speeds, isolating the most dense components at each step 3. Each liquid(supernatant) is removed leaving behind a pellet of organelles Part 3: Plasma Membrane Plasma Membrane’s Components: ● Boundary that separates the living thing from the surrounding environment ● A bilayer of phospholipids ● Composed of phospholipids(and glycolipids), protein(and glycoproteins), carbohydrates and cholesterol ● 3 main functions: ○ Gives shape and strength to cell ○ Acts as a biological barrier between inside and outside the cell ○ Regulates movement of substances entering and leaving ■ The barrier is selectively permeable(semi-permeable), allowing certain substances in and excluding others Phospholipids: ● Is made up of 2 parts, a phosphate head and two fatty acid tails ● Are amphipathic ○ Has a hydrophobic and hydrophilic regions ○ Head is hydrophilic: water-loving ■ polar ○ Tail is hydrophobic: water-hating ■ Non-polar Phospholipid Bi-layer: ● Phosphate face outwards towards the outside and inwards towards the inside of the cell ● Lipids/tail are sandwiched between the 2 phosphate head Proteins: ● 2 types of proteins, integral and peripheral proteins ○ Integral have hydrophobic and hydrophilic regions and span the whole thickness of the membrane ■ Are an “integral” part of the membrane ○ Peripheral proteins are not embedded in the bilayer ■ Attached to the membrane ○ The proteins have a variety of function ■ Transport proteins ■ Cell-to-cell recognition ■ Enzymatic activity ■ Intercellular joining ■ Signal transduction ■ attachment Carbohydrates: ● Bonded to lipids(glycolipids) or proteins(glycoproteins) on the outside of the membrane ○ Different cell types have different distributions and types of proteins ■ Distinguishes one cell from another ○ Carbohydrates are involved in cell-to-cell recognition Cholesterol: ● Affects fluidity of membrane ○ If hot, cholesterol decrease the fluidity by restricting the movement of phospholipids ○ If cold, cholesterol increases the fluidity by preventing the close packing of phospholipids ■ Does not allow them to get close and stop moving Fluid Mosaic Model: ● Fluid: the components of the membrane are in constant motion ○ Evidence: fusion of mouse and human cell ● Mosaic: the scattered proteins are embedded in the phospholipid bilayer(like tiles in mortar) ○ Evidence: freeze fracture of membranes Membrane Transport: ● Nonpolar molecules: ○ Hydrophobic ○ Can easily cross the lipid bilayer of the cell membrane ○ Oxygen, carbon dioxide, hydrocarbons ● Polar molecules: ○ Hydrophilic ○ Have difficulty crossing the hydrophobic core of the membrane ○ sugar(glucose), water ● Charged molecules: ○ Have a sphere of water around them that prevents them from passing through the membrane ○ Na, K, Ca, Cl ● Large molecules: ○ Do not fit through the pores in the membrane ○ Proteins, polysaccharides Active Transport vs. Passive Transport: Passive Transport ● 2 types of passive transport, but branches into 3 types after ○ Diffusion ■ Osmosis ○ Facilitated diffusion Diffusion: ● molecules that make up substances are in constant random motion and disperse from high concentration to low contraction ● Molecules will disperse and spread out until they reach a state of equilibrium, where the molecules are equally distributed ● Several factors affect the rate of diffusion: concentration gradient, temperature, distance, area of the membrane, permeability of the membrane ● No energy is required for diffusion because the substances move down its concentration gradient ○ Always from high to low, if from low to high it is not passive transport ○ concentration gradient drives diffusion, because it represents potential energy Osmosis: ● The diffusion of water across a selectively permeable membrane ● Osmosis occurs when a concentration gradient of solutes(thing dissolved) exists but cannot diffuse ○ Instead of solute moving, water moves ● Water moves to balance out the concentration gradient of the solute Tonicity: ● The ability of a solution surrounding a cell to cause the cell to gain or lose water ○ Hypotonic: solution surrounding the cell has a lower solute concentration gradient than inside the cell, thus water goes into the cell ○ Isotonic: solution surrounding the cell has the same solute concentration gradient as inside the cell, thus nothing happens ○ Hypertonic: solution surrounding the cell has a higher solute concentration gradient than inside the cell, thus water leaves the cell ● Animal cells: ○ Animal cells are really sensitive to tonicity, as they don’t have rigid cell walls ○ In hypertonic solutions, they become shrivelled ○ In hypotonic solution, they become lysed(swelled) ○ Animal cells survive best in isotonic solutions ● Plant cells: ○ Depend on tonicity to push out on cell walls and to maintain structure ○ In hypertonic solution, the cytoplasm peels off from the cell wall, called plasmolysis ○ In isotonic solution, the cell becomes flaccid(limp) as there is no eternal pressure to push out the cell wall ○ In hypotonic solution, the cell becomes turgid and pushes out against the cell wall and keeps the plant cells firm Facilitated diffusion: ● The diffusion is the diffusion of solutes using the help of transport proteins ● Small, polar molecules and charged molecules(ions) can go through the transport proteins, which provide hydrophilic passageways. ● 2 types of transport proteins ○ Channel proteins: a passage through the cell membrane that is hydrophilic ○ Carrier proteins: takes in a solute and changes the shape and then goes through the membrane Active Transport: ● Uses energy to transport solutes against their concentration gradient ○ From low to high concentration ● Uses energy called ATP(adenosine triphosphate) ● Carrier proteins called “protein pumps” are the transport proteins involved in active transport ○ Proton pump ○ sodium-potassium pump is an important transport protein in the cell membrane ■ Removes 3 sodium ions(Na+) and moves 2 potassium(K+) ions into the cell ■ Keeps the inside of the cell more negative, which is crucial for nerves and muscles: ● Nerve signal ● Muscle contractions ● Heartbeat regulation ● Nutrient absorption in the kidneys Bulk Transport: ● Bulk transport = transport of large molecules, too big to fit through transport proteins or the pores in the cell membrane ● Large molecules are packaged in vesicles and moved through the membrane ● There are 2 types of bulk transport, where it branches into 5 ○ Endocytosis: the transport of material enters the cell ■ Phinocytosis: taking in liquid/water/dissolved solutes and liquid ■ Phagocytosis: taking in food/solid material ■ Receptor-mediated endocytosis: allows the cells to take in specific substances ● Proteins on the plasma membrane with specific receptors bind to specific substances(lock-and-key) ● Once bound to the receptor, the substances are brought into the cell ○ Exocytosis: the transport of materials out of the cell ■ Can be used to export waste ■ Can be used by secretory cells to export products Limitations on Cell Size: ● If cell is too big, food will take weeks to reach the inside of the cells to be used by organelles(cell get hungry) ● Wastes will take too long to leave the cell ● If cells die, the whole organism dies ● In order to survive, cells must be able to bring in nutrients and get rid of waste efficiently ○ Diffusion across the cell membrane is fast ○ Diffusion within the cell is slow ○ Difference in rate is due to the concentration gradient and distance ○ Cells must maximize surface area(cell membrane) and minimize volume(inside of cell) ○ surface area to volume ratio must be the biggest for most efficient cell diffusion ■ When cell small, the surface area to volume ratio is large ● Diffusion is effective ■ When cell is big, the surface area to volume ratio is small ● Diffusion is not effective ■ SA:V ratio is calculated with: ● Surface area/Volume:1 ○ Physical limit of cell size is controlled by the effectiveness of diffusion Cell Shape ● The cell shape can be modified to change the surface area to volume ratio ● A high SA:V ratio is especially important for cells that have to exchange a lot of materials such as ○ Plant roots ○ Intestinal cells villi and microvilli ○ Lung’s aveoli ○ Blood vessels’s capillaries ● When cells get grow, they split instead of getting bigger, maintaining the high SA:V ratio ○ Become multicellular organisms ● Multicellular organisms have different types of cells that perform different functions ○ Principle of complementarity: cell function reflects structure and cell structure reflects function ○ Different specialized cell types have different: ○ Shapes ○ Sizes ○ Number of different organelles ○ Over 200 different types of specialized cells in the human body ○ The division of labour allows cells to become more effective and efficient at performing one task ● multicellular organisms are organized in a structural hierarchy that relies on cooperation of individual cells ○ Specialized cells: each cell type has a different structure and function ○ Tissues: composed of groups of cells of similar structure that perform a particular, related function ○ Organs: structure of definite form and structure, comprising two or more tissues ○ Organ systems: an association of organs with a common function ○ Organism: a complex, functioning whole that is the sum of all its component parts Part 4: Plants ● Advantages to being multi-cellular ○ Division of labour: specialization of cells allows tasks to be performed more efficiently ○ Size: internal transport system allow organisms to grow to large sizes ○ Interdependence of cells: the life of an organism does not depend on one cell ● Cell → tissue → organ → organ system ○ Tissue: groups of cells performing same function together ○ Organs: tissues contributing to the same function ○ Organ system: set of interconnected organs working together Plant Structure: ● Plants have 2 main types of organ systems: root(below ground) and shoot(above ground) Organ System and Organs ● Root system: absorb water and minerals from below ground ○ Organ: roots. They anchor the plant in the soil, absorb minerals and water, and often store carbohydrate ● Shoot system: absorb CO2 and light from above ground ○ Organ: stem and leaves ■ Stem: supports leaves and reproductive structures ■ Leaves: the main photosynthetic organ of the plant Tissue ● 3 types of tissue: dermal, vascular, and ground ○ Dermal tissue(epidermis): the plants outer protective covering ○ Vascular tissue: carries out long-distance transport between shoot and root systems ○ Ground tissue: all the other tissues that aren’t vascular or dermal Leaf Structure: Cell Name Tissue Type Function Cuticle Dermal Waxy substances that coat epidermis cells. Prevents water lost Upper/Lower Epidermis Dermal On the upper and lower side of the leaf, it is a one-cell-thick layer of tightly packed and transparent cells that protect the leaf against physical damage and pathogens Palisade cell Ground Long, narrow cells are tightly packed together near the top of the cell. Where most of the photosynthesis occurs. Vascular Bundle Vascular Series of tubes that are like veins in the leaf. Contains xylem and phloem Xylem Vascular Made up of dead cells, transports water and minerals from the roots to the leaves. Tube like shape Phloem Vascular Tube shape that are made up of live cells and transport glucose(sugar) from leaves to everywhere else in the plant Spongy Tissue cell Ground Round, loosely packed cells underneath the palisade cells. Also carry out photosynthesis(less than palisade cells). Gaps between cells for gas exchange in leaf Stomata Dermal Small openings in the epidermis layers allow gas exchange. The opening sizes are controlled by guard cells. Photosynthesis and Cellular Respiration: Photosynthesis: 6H2O + 6CO2 + Light Energy → C6H12O6 + 6O2 ● Produces glucose(sugar) ● Occurs in chloroplasts ● Requires: ○ Light ○ CO2 ○ Water ● Light energy is converted into glucose ● Occurs only in plants ● Plants have chloroplasts in their cells which contain chlorophyll ○ Traps sun energy for photosynthesis ○ Chlorophyll doesn’t accept green light, but it reflects it instead ■ Hence why plants are green Cellular Respiration: ● ● ● ● C6H1206 + 6O2 → 6CO2 + 6 H2O + Energy Converts glucose into usable energy(ATP Energy) Reaction occurs in mitochondria ○ Occurs in both plants and animals Two reactions are inter-dependent Photosynthesis makes glucose and cellular respiration converts it to usable energy ○ Animals don’t do photosynthesis so they consume plants to get glucose Transport in Plants: ● 2 types of transport: ○ Water and minerals ○ Glucose Water and Mineral Transport: ● Transported by the xylem tissue from the roots to the leaves ● Xylem tissues are made up of 2 types of cells: ○ Vessel elements ○ tracheids ● Dead at functional maturity ● Pits in the tissue allows water to enter/exit ● Lignin in the xylem allows the walls to resist high-pressure ● Have no end walls to allow unimpeded water transport ○ Just a long tube ● Steps in transport through the xylem: 1. Absorption by roots and transported into the xylem a. Water enters the roots via osmosis while minerals are transported via facilitated diffusion or active transport(depending on the concentration gradient) i. Root hairs increase surface area, making transport more efficient 2. Bulk transport from roots to leaves a. Xylem sap(water and dissolved minerals) is transported upwards, against the force of gravity by 3 mechanisms i. Root pressure: pressure is created in the roots by the accumulation of water and ii. iii. minerals, thus pushing the xylem sap upwards 1. Only a minor mechanism for driving the sap up Transpiration pull: when water from the leaves evaporates, it pulls water from below to fill in the missing space left by them 1. Works how a syringe can pull water through a tube from a cup Cohesion and adhesion: properties of water help with the transport of the sap 1. Cohesion: the tendency of water to stick to other water molecules due to hydrogen bonding a. Pulls a column of water molecules up to the leaves 2. Adhesion: tendency of water molecules to stick to certain surfaces(hydrophilic) due to hydrogen bonding a. Prevents xylem sap from falling back to the roots Sugar Transport: ● Sugar is transported by phloem tissue from leaves to the rest of the plant ● Made up of 2 cells: ○ Sieve tube elements ○ Companion cells ■ Sieve tubes transport sugar ■ Companion cells transport sugar into sieve tubes and perform metabolic functions for phloem ● Alive at functional maturity ● Sugar is transported from a sugar source(where the sugar is produced) to a sugar sink(where the sugar will be used) ● Steps in Sugar transport 1. Loading sugar: sugars produced in the leaves are transported into the phloem vessels via ______ 2. Uptake of Water: water follows into the vessel by osmosis, thus increasing the pressure in the phloem 3. Bulk Transport: pressure and concentration gradients move the phloem sap(glucose and water) into the sugar sinks a. Passive transport 4. Unloading sugar: high pressure forces the phloem sap out of the vessel and into neighbouring cells Gas Exchange: ● Most gas exchanges occurs in the leaves through small pores in the epidermis layer called stomata ● The gas exchange happens through passive diffusion ○ The gas circulates through the space between the spongy tissue cells ● Some gas exchange occurs in special places like the stem and modified roots ○ Lenticles: lens-shaped openings in the bark of woody plants that enable gas exchange ○ Pneumatphores(air roots): modified roots produced by trees such as mangroves that absorb oxygen ● Transpiration is the loss of water through evaporation and diffusion from the leaves ○ Leaves have a high SA/V ratio and stomata. Even though those are important for photosynthesis, they also increase water loss ■ Approximately 95% of water a plant loses is through the stomata Controlling the Stomata: ● Opening: guard cells absorb water to become turgid and open ○ Stimulus to open: moist environment, light, CO2, circadian rhythms(internal clock) ● Closing: guard cells lose water and become flaccid and close ○ Stimulus to open: dry environment ● Generally, stomatas are open during the day but closed during the night, preventing water loss under conditions where photosynthesis cannot occur Tropisms: ● One characteristic of living things is their ability to change, or adapt, over a period of time in response to the environment ○ Animals respond to environmental stimuli mainly by behavioral mechanisms ○ Plants respond to stimuli by adjusting their individual patterns of growth and development ● Tropism(Greek for turn) = growth or movement of an organism to an external stimulus ○ Positive tropism: growth toward the stimulus ○ Negative tropism: growth away from the stimulus ○ Phototropism: photos mean light in Greek/ response to light ○ Gravitropism: reponse to gravity 3 experiments were conducted to help us understand phototropisms: ● Experiment on phototropism ○ Growth toward or away from light ● If a seedling is illuminated from one side, it grows toward the light ● Curves because cells on the dark side elongates faster than the cells on the bright side Darwin & Darwin Experiment: Problem: which part of the plant senses where light is coming from? Conclusion: Tip of the seedling detects light and sends a signal down the stem to control growth Boysen-Jensen Experiment: Problem: what type of signal controls stem growth?” Conclusion: The signal is a mobile chemical because it passes through a permeable barrier(gelatin) but not through an impermeable barrier(mica) Frits Went Experiment: Problem: What is the chemical signal? Method: ● Removed seedling tip and placed it on agar cubes to absorb the chemical ● Placed the cube on the decapitated stem in the dark Results: ● Center of stem: grew straight ● Off-center: grown away from the side of the cube ○ When placed on the left side, the plant will grow towards the right Conclusion: Went named the substance auxin and it causes the cells on the dark side to elongate Gravitropism: ● Plant’s growth in response to gravity ● Roots display positive gravitropism ○ Goes down ● Stems display negative gravitropism ○ Goes up ● Straitoliths are organelles in plants that contain dense starch grains to allow plants to detect gravity ● Ensures correct orientation of plants regardless of how the seed is oriented when it lands Mechanical Stimuli Plants have a variety of different responses to touch ● Thigmotropism: directional of growth of a plant in response to touch ○ Vines ● Rapid plant movement: type of nastic response due to rapid changes in tugor pressure ○ Nastic response is different than a tropism because the direction of the response is not dependent on the direction of the stimulus ■ Venus flytrap ● Mimosa pudira Day and Night: Sleep movements are plants responses to day and night. It follows a biological clock or circadian rhythm ● Plants lower their leaves in the evening and raise them in the morning ○ Happens due to tutor pressure at the base of stem ● Circadian rhythms can be altered by photoperiod, allowing plants to adjust their activities in synchrony with the seasons ○ Photoperiod = response to changes in daylight time due to changes in seasons Other tropisms: Many other tropisms also exist including: ● Hydrotropism: growth in response to water ○ Roots going to water ● Thermotropism: the tendency to turn away toward temperature/heat or cold ○ Some plants droop down or cul up in response to extreme heat or cold ● Chemotropism: growth in response to a chemical stimulus ○ Poolen tubes from pollen grains grow toward the female gametophyte
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