Botany Lecture Notes PDF

Botany Zoology: The science that covers animals and animal life. Chapter 1 Genetics: The study of heredity. SCIENCE...

Botany Zoology: The science that covers animals and animal life. Chapter 1 Genetics: The study of heredity. SCIENCE Medicine: The science of diagnosing, treating, A branch of knowledge or study dealing and preventing illness, disease, and with a body of facts or truths injury. systematically arranged Social Science Scientia – “Knowledge” - Sociology Natural Science - a branch of science that deals - History with the physical and natural world. - Political - Physical Science Applied Science ⮚ Physics: The study of matter - Agronomy and energy and the interactions - Agriculture between them. Physicists study - Education such subjects as gravity, light, and time. Theories of the Origin of Life ⮚ Chemistry: The science that Theory of Special Creation - created by God deals with the composition, o Hindu mythology, Christian belief, Sikh properties, reactions, and the mythology. structure of matter. - Earth Science Theory of Catastrophism – simply modification of the theory of Special Creation. ⮚ Geology: The science of the Several creations of life by God. French scientist origin, history, and structure of Georges Cuvier and Orbigney supporters of this the Earth, and the physical, theory. chemical, and biological changes that it has experienced Theory of Panspermia - Heavenly bodies; or is experiencing. Ritcher and Arrhenius proposed. ⮚ Oceanography: The exploration Theory of Chemical Evolution – Materialistic Theory or Physico-chemical Theory. and study of the ocean. ⮚ Meteorology: The science that Theory of Spontaneous Generation – Also known Abiogenesis. First believers were deals with the atmosphere and Aristotle, the Greek philosopher. its phenomena, such as weather and climate. - He believed dead leaves falling from tree into a pond would transform into fishes and those ⮚ Astronomy: The study of the failing on soil would transform into worms and universe beyond the Earth's insects. atmosphere. - Biological Science Theory of Evolution Botany: The study of plants. - Charles Darwin - Evolutions by means of natural selection - Animal cells do not have cell walls and have different structures than plant - more offspring are produced than can possibly cells. survive traits vary among individuals, leading to - Animals have a much more highly different rates of survival and reproduction developed sensory and nervous system. traits differences are heritable. Chapter 2 - Homo habilis, homo erectus, homo Neanderthalensis, Homo Sapien, Homo The Chemical Composition of Cells Characteristic of Living and Non-living Things Rinorea niccolifera Living Nickel-Eating Plant Discovered in Philippines ○ anything that is or has ever been alive Hyperaccumulator plant species Non-living Phytoremediation refers to the use of ○ anything that is not now nor has ever been hyperacccumulator plants to remove heavy metals in contaminated soils alive Phytomining is the use of hyperacccumulator Plants vs Animals plants to grow and harvest in order to recover Plants commercially valuable metals in plant shoots - They are rooted in one place and do not from metal-rich sites. move on their own. - Plants contain chlorophyll and can make The Chemical Composition of Cells their own food. Elements of Life - Plants give off oxygen and take in Chemical Bonds carbon dioxide given off by animals. Inorganic Compounds - Plants cells have cell walls and other Organic Compounds structures differ from those walls of animals. Atoms: - Plants have either no or very basic ability to sense. Proton - positive electric charge, small Animals mass - Most animals have the ability to move Neutron - uncharged, about same fairly freely. mass as proton - Animals cannot make their own food and are dependent on plants and other Electron - negative charge, extremely animals for food. small mass. Move around the nucleus at - Animals give off carbon dioxide which different energy levels. Allow elements to plants need to make food and take in combine chemically to form chemical oxygen which they need to breathe. compounds. Ions are atoms which tend to gain or lose electrons Electron Configurations A measure of the relative concentrations of H+ and OHin a solution Ionic Bond - An electrostatic attraction between A solution’s acidity or alkalinity is expressed in oppositely charged ions. terms of the pH scale Covalent Bond - A chemical bond involving one Carbohydrates or more shared pairs of electrons An organic compound containing carbon, Hydrogen Bond hydrogen, and oxygen in the approximate An attraction between a slightly positive hydrogen atom in one molecule and a slightly ratio of 1C:2H:1O negative atom (usually oxygen) in another Include sugars, starches, cellulose molecule Important fuel molecules, components of Water molecules (nucleic acids) and cell walls Has a strong dissolving ability Monosaccharides Molecules form hydrogen bonds with one another (cohesion) - simple sugars Molecules form hydrogen bonds to substances Disaccharides with ionic or polar regions (adhesion) - two monosaccharide units Adhesion & Cohesion are particularly Polysaccharides important for transport - many monosaccharide units All living things require water to survive Almost all chemical reactions that sustain life occur in aqueous solution High Boiling & Freezing Points Insulation Property after freezing (e.g., lakes) Acid and Base Acids dissociate in water to form hydrogen ions (protons, H+) Bases dissociate in water to yield negatively charged hydroxide ions (OH-) pH Scale  A large, complex organic compound composed of amino acid subunits A macromolecule composed of amino acids joined by peptide bonds Order of amino acids determines structure and function of a protein molecule Enzymes: Proteins that increase the rate of chemical reactions Lipids Any of a group of organic compounds that are insoluble in water but soluble in fat solvents. Have a greasy consistency, do not readily dissolve in water Important fuel molecules, components of cell membranes, waterproof coverings over plant surfaces, light-gathering molecules for photosynthesis A neutral fat or oil molecule is composed of a molecule of glycerol plus one, two or three fatty acids Nucleic Acid Proteins  Deoxyribonucleic acid (DNA) and -the point at which the 2 strands of DNA ribonucleic acid (RNA) separate is called the replication fork. Large, complex organic molecules composed 2. Another enzyme (DNA polymerase) binds to of nucleotides separated strands and starts moving along Control the cell’s life processes original Deoxyribonucleic acid (DNA) DNA. - Transmits information from one generation to the next 3. DNA polymerase assembles a complementary Ribonucleic acid (RNA) strand from free nucleotides that are found in the nucleoplasm - Involved in protein synthesis Adenosine Triphosphate (ATP) Nucleotides An organic compound of prime importance for Repeating units that form nucleic acids energy Order of nucleotides in a nucleic transfers in biological systems. acid chain determines the specific ATP is a nucleotide that performs many information encoded essential Adenosine triphosphate (ATP) roles in the cell. A modified nucleotide compound It is the major energy currency of the cell, providing important in energy transfers in the energy for most of the energy-consuming biological systems activities of the cell. It is one of the monomers used in the synthesis of RNA and, after conversion to deoxyATP (dATP), DNA. It regulates many biochemical pathways. Biomolecules Building Blocks Biological Role DNA Replication Carbohydrates Monosaccharide Structural, energy 1. Helicase enzymes separate two strands of reservoirs nucleotides (break the H-bonds that hold bases Proteins Amino Acids Framework material together).  Lipids Fatty acids + Mechanical The first law of thermodynamics states energy glycerol protection, can be harnessed and thermal insulation transformed but not created or destroyed. Nucleic Acids Nucleotide Storage and The second law of thermodynamics states that transmission every transfer of energy of genetic material increases the entropy (disorder) of matter in the universe. Thermodynamics Enzymes - An organic catalyst, produced within FIRST LAW OF THERMODYNAMICS an organism, that accelerates specific chemical Energy cannot be created or destroyed, Reactions although it can be Speed up a chemical reaction by lowering transformed from one form to another its activation energy (energy needed to SECOND LAW OF THERMODYNAMICS initiate the reaction) When energy is converted from one form to another, some of it is Most enzymes are highly specific and degraded into a lower-quality, less useful form catalyze only a single chemical reaction Energy Without enzymes, chemical reactions in The ability to do work cells would occur too slowly to support life Plants and other organisms cannot Activation Energy - The energy required to initiate a chemical reaction create the energy they require to live, but must capture energy from the environment and use it to do biological work Potential and Kinetic Energy Entropy Continuously increases in the Energy & Chemical Reactions universe as usable energy is Energy can be stored and can move or change matter: Potential energy is converted to lower-quality, less stored energy, while kinetic energy is energy usable form (heat) having to do with motion. As each energy transformation occurs in organisms, some energy changes to heat Given off into the surroundings Can never be used again for biological work Alkaloids ○ a group of naturally occurring chemical compounds that contain mostly basic nitrogen Secondary Metabolites atoms. Primary metabolites are compounds that are o produced by a large variety of organisms, directly involved in the growth and including bacteria, fungi, plants, and animals, development of a plant whereas secondary and are part of the group of natural products. metabolites are organic compounds produced o They often have pharmacological effects and are in other metabolic pathways. used as medications, as recreational drugs, or They are not directly involved in the in entheogenic rituals. normal growth, development or reproduction Phenolics of an organism. ○ Organisms that synthesize phenolic often play an important role in plant defense. compounds Humans use secondary metabolites as do so in response to ecological pressures such medicines, flavorings, and recreational drugs. as Biosynthesis is the term for the in vivo pathogen and insect attack, UV radiation and synthesis of metabolites. wounding. ○ Alkaloids ○ they are present in plants used in traditional ○ Terpenoids medicine of several cultures ○ Phenolics ○ their role in human health and disease is a subject of research because some phenols are found to have germicidal property and are used Characteristics of Living Things-PLANTS in formulating disinfectants. Interaction with environment Plants respond to stimuli in their environment Plants undergo growth and development Reproduction Botany Plants form new individuals by asexual or sexual science of plant life. reproduction Also called as plant science(s) or plant biology The term "botany" comes from the Ancient Greek Root Growth and Gravity word βοτάνη (botane) meaning "pasture“ Botanist is a scientist who specializes in this field of study Plant scientist Characteristics of Living Things-PLANTS Organization Plants and other organisms are highly organized with cells as their basic building blocks Energy Plants and other organisms take in and use energy  Asexual Reproduction Response to Stimuli Characteristics of Living Things-PLANTS Heredity DNA molecules transmit genetic information from one generation to the next in plants and other organisms Evolution Plants and other organisms evolve Populations change or adapt to survive in changing environments Germination Adaptation Plant Cells Photosynthesis KEY TERMS SPECIES A group of organisms with similar structural and functional characteristics In nature, they breed only with one another and have a close common ancestry KEY TERMS KINGDOM A broad taxonomic category made up of related phyla; many biologists currently recognize six kingdoms of living organisms DOMAIN A taxonomic category that includes one or more kingdoms  Organisms are classified into a hierarchy Six-Kingdom Classification 1 The main categories of classification are: 1. Archaea Domain 2. Bacteria Kingdom 3. Protista Phylum protozoa, algae, water molds, slime molds Class 4. Fungi Order molds, yeasts Family 5. Animalia Genus 6. Plantae Species Three Domains: King Phillip Came Over Fearing Green Snakes Bacteria, Archaea, Eukarya Three-Domain Classification Six Kingdoms: Archaea Bacteria Archaea Protista Plantae Animalia Fungi Kingdom archaea Bacteria Prokaryotes (lack membrane-bound Kingdom bacteria organelles); unicellular; most are heterotrophic Eukarya (obtain food by eating other organisms), All other kingdoms but some are photosynthetic or Kingdoms and Domains chemosynthetic Three Domains: 1. Bacteria 2. Archaea Prokaryotes; 3. Eukarya unicellular; Six-Kingdom microscopic; 1. Bacteria most live in 2. Archaea 3. Protista extreme 4. Plantae 5. Animalia environments 6. Fungi ; differ in biochemistry and in cell cellulose wall structure Eukaryotes; from multicellular; bacteria heterotrophic; most move Eukaryotes; about by mainly muscular unicellular or contraction; simple nervous system multicellular; coordinates maybe responses to heterotrophic stimuli or photosynthetic; Eukaryotes; most include multicellular; protozoa, heterotrophic; algae, and absorb slime molds nutrients; Eukaryotes; do not photo- multicellular; synthesize; photosynthetic ; cell walls of life cycle chitin with alternation of Fig. 1-11, p. 14 generations; cell walls of Classification (Binomial System) mainly under the aspects of utility and medicinal use. TABLE 1-1 Over 400,000 species of plants have been The Classification of Corn documented Domain Eukarya: several million species on Earth. Organisms with a eukaryotic cell structure This multitude of species plays a critical role in Kingdom Plantae: about 330,000 species the food web, biogeochemical cycles and maintaining ecological balance. Terrestrial, multicellular, photosynthetic eukaryotes Development of Botanical Study Phylum Anthophyta: about 300,000 species Plant species are generally good examples of Vascular plants with flowers, fruits, and seeds complex relations of interdependence—both Class Monocotyledones: more than 90,000 among various plant species and between plant species Monocots: flowering plants with one and animal species. seed leat (cotyledon) As with animals, plants also rely heavily on Order Commelinales: about 17,300 species sexual reproduction between male and female Monocots with reduced flower parts, elongated parts—often, in plants, however, the male and leaves, and dry, one-seeded fruits female parts coexist within a single flower. Family Poacee: about 9000 species Among the first cultivated plants were a number of graminaceous plants, the cereals, Grasses with hollow sterns, fruit that is a grain. that continue to be the most important and abundant endosperm in seed cultivated plants until today. Genus Zea: 2 species Early Botanists Tall annual grass with separate male and female Theophrastus flowers Student of Aristotle Species Zea mays: 1 species “father of botany” because of his Corn: one of two species in genus two surviving works on plant studies. Classification (Binomial System) Pedanius Dioscorides Historically, botany covered all organisms not provided important evidence on considered to be animals, including some Greek and Roman knowledge of "plant-like" medicinal plants. organisms. He categorized plants based on The very first ancient documents about plants was their medicinal, culinary, or aromatic value. Leonardo Co (1953-2010) Robert Hooke he was one of the classically discovered cells in cork and a trained botanists in plant short time later in living plant taxonomy and systematics in tissue. the Philippines. Carl Linnaeus Bachelor of Science published Species degree in Botany in 2009 Plantarum, which included Branches of Botany 6,000 plant species. Plant Morphology He established the binomial study of the evolution and development of leaves, nomenclature, which has been roots, and stems with a focus on the tissues at used in the naming of the living things ever since. tips of stems where the cells have the ability to Leon Maria Guerrero divide. His scientific curiosity led him to Plant Systematics study the therapeutic uses of the study of plant characteristics, especially Philippine plants, from which he for the purpose of discerning their evolutionary relationships and establishing extracted pharmacological differences. It concerns itself with scientific ingredients. classification of species and other taxa. He was appointed head of the Plant molecular biology military pharmacy. Structures and functions of important Filipino Botanists biological molecules (proteins, nucleic acids) Eduardo Quisimbing Plant cell biology author of taxonomic and Structures, functions, and life processes of morphological papers, many of plant cells which deal with orchids, Plant Genetics including ‘Medicinal plants in investigate the structure and behavior of the Philippines’ (Manila 1951). genes Filipino Botanists in plants and plant heredity in order to develop greenhouse gases crops that are resistant to diseases and pests. Utilize medicine and materials Plant Physiology Understand environmental changes the study of the vital processes of plants, such Maintain ecological, biodiversity, as photosynthesis, respiration, and plant and ecosystem function nutrition Plant ecology bacterial cells and fungal cells are very different Interrelationships among plants, and cell types. between plants ands their environment In fact, fungal cells have more in common with your cells- which are animal cells- than they Plant Pathology have in common with bacterial cells. studies the causes and control of plant And that has a lot to do with the comparison of diseases. prokaryotic cells with eukaryotic cells which is what we will focus on. Paleobotany Modern Cell Theory - that all living things are deals with the biology and evolution of plants made of one or more cells. All living things. by studying the fossil record in order to reconstruct the 600 million year history of plant In the three domains of life, prokaryotes are life on this planet organisms that can be bacteria and archaea. Economic botany 3 Domains (with examples of Prokaryotes and Eukaryotes) study the economic impact of plants as they They are unicellular which means they are relate to human needs for food, clothing, and single-celled organisms. shelter. Eukaryotes are organisms that all fit in this last Significance of Botany domain Eukarya---eukaryotes may be protists, plants, animals, or fungi. Feed the world plants are at the base of nearly all food They can be unicellular or they can be chains multicellular, which means they can be made up of many cells. Understand fundamental life processes understanding the response of plants to the word "prokaryote" is typically used to refer climate change and the feedback to the organism itself. mechanisms that occur with increased Same for eukaryote- "eukaryote" typically refers They tend to be larger than most prokaryotic to the organism itself and when you describe its cells. cells, those are eukaryotic cells. “pro” in prokaryote rhymes with “no” and “eu” Similarities of Prokaryotic Cells and Eukaryotic in eukaryote rhymes with “do.” Cells Prokaryotic cells have no nucleus to contain Prokaryotic cells and eukaryotic cells do have a their DNA. lot in common. So you will find their DNA is not contained - Both have DNA. within a nucleus; it’s a bit messy here. Both prokaryotic cells and eukaryotic cells have They have no membrane-bound organelles. ribosomes, which are small organelles---an Membrane-bound organelles are fancy organelle being like a “tiny” organ. organelles that have their own membrane like the nucleus, mitochondria, the endoplasmic reticulum, and the golgi apparatus. The ribosomes have the important job of making protein. A big indicator of eukaryotic cells is this nucleus- eukaryotic cells DO have a nucleus to contain their DNA. Both cell types have cytoplasm, the jelly like Depending on what type of eukaryotic cell it fluid within cells. is---it could have different types of membrane-bound organelles. Both of them have a cell membrane- also known For example, a plant cell is likely to have as a plasma membrane- which is critical because chloroplasts while an animal cell would not. it controls what goes in and out of the cell and It’s important to grasp that all cells of living therefore maintaining homeostasis. things fall in one of these two categories. All cells have a cell membrane! And understanding the characteristics of these Now as for cell walls---most prokaryotic cells two cell types can help us better understand have cell walls. the diversity of living things whether they are Many eukaryotic cells--- plant cells and fungus archaea, bacteria, protists, fungi, plants, or cells for example—can have cell walls. animals. But there are plenty of eukaryotic cells that And in the case of my example- realizing don’t have cell walls such as animal cells. whether an infection you’re dealing with involves prokaryotic cells (such as bacteria) or Differences of Prokaryotic Cells and Eukaryotic eukaryotic cells (such as the fungus). Cells What makes prokaryotic cells and eukaryotic cells different is especially interesting. When you are talking about osmosis, you are talking about the movement of water through a Eukaryotic cells are more complex than semi-permeable membrane, like a cell prokaryotic cells. membrane. Water molecules are so small that they can That doesn’t mean that the water molecules travel through the cell membrane unassisted, or aren’t moving---water molecules like to they can travel in larger quantities through move---but the net movement across the two protein channels like aquaporins. sides is zero. That means, the overall change in the direction of movement is zero. The movement of water molecules traveling across a cell membrane is passive transport, Now let’s imagine on side B, you dump a huge which means it does not require energy. amount of salt there. In osmosis, water molecules travel from areas of So which direction will the water initially move a high concentration (of water molecules) to a towards---A or B? low concentration (of water molecules). Think about what we mentioned with osmosis. But there’s another way to think about water has a higher solute concentration than side A. movement in osmosis. Water moves to areas of higher solute A low water concentration likely means there is concentration, which is also the area of lower a greater solute concentration. water concentration. Solutes are substances--- like salt or sugar---that The water level on side B will be higher in the can be dissolved within a solvent----like water. U-tube. Water has the tendency to move to areas where You can almost think of the water as trying to there is a higher solute concentration, which equalize the concentrations---diluting side B. would mean less water concentration. Once equilibrium is reached, the net movement of water across the two sides will be zero but So if you want to easily figure out where the remember that water still likes to move and water will travel----look to the side where there movement still occurs. is a greater solute concentration. Here’s some vocabulary to add in here---we call Unless we bring in another variable, like side B hypertonic. pressure, water will generally have a net movement to the area of higher solute This means higher solute concentration! concentration. But we can’t just say something is hypertonic So let’s bring out a U-tube! without comparing it to something else. There’s a semi-permeable membrane in the We say Side B is hypertonic to side A because it middle of it. has a higher solute concentration than side A. In osmosis, water moves to the hypertonic side. Let’s assume that it is similar to a cell membrane in that water molecules can squeeze We say side A is hypotonic (hypo rhymes with through it—the molecules are quite small—but low which helps me remember low solute salt can’t. concentration) Right now, there is just water in this U-tube. when compared to side B. Let’s get a little more real life now instead of just the U-tube. The water levels on side A and side B are equal. As you know, water is important for your body If a person needs fluids, they typically will and many processes that occur in the body. receive a solution that is isotonic to their blood plasma. When someone gets an IV in a hospital---it may look like the fluid in the IV is just Isotonic means equal concentration so you won’t have any swelling or shrinking red blood Osmosis in Animal Cells Example cells. pure water. Or let’s talk about the aquarium. But it is certainly not pure water. I have always wanted a saltwater fish tank, ever That would be a disaster because of since I was a little kid. osmosis---let’s explain. But I’ve only had freshwater tanks. Let’s say hypothetically pure water was in an IV. I did often question when I was a kid, why is it Now an IV tube typically runs through a vein, so that a saltwater fish can’t be in that you have access to your blood stream. one reason why this would be dangerous to a Really useful for running medication through. saltwater fish and how it relates to osmosis. Blood actually consists of many different types In the saltwater fish cells? of components and red blood cells are a great Or in the freshwater that the fish would be example. placed in? So what do you think has a higher solute Definitely in the saltwater fish cells. concentration? So where would the water go? The hypothetical pure water in this IV tube? It goes to the area where there is a higher Or the red blood cells? solute concentration----the hypertonic side----so Well cells are not empty vessels---they contain it goes into the cells of that poor saltwater fish. solutes. If not rescued, it could die. The pure water that hypothetically is running through this IV tube has no solutes. Now one thing to clarify: saltwater fish and freshwater fish are not necessarily isotonic their So where does the water go? surroundings. It goes to the areas of higher solute But they have special adaptations that allow concentration—inside the cells. them to live in their environment and usually The cells are hypertonic compared to the pure cannot make a major switch from a saltwater water in the IV tube because the cells have environment to freshwater. a greater solute concentration. The cells would Now---not all fish have this problem. swell and possibly burst! There are some fish that have amazing Exploding red blood cells are not good. adaptations to switch between fresh and salt water, and they have to deal with this osmosis problem. Salmon for example. Water will travel to areas of lower water potential. I think if I could pick to be a fish, I’d be a salmon. But exerting pressure can raise the pressure Osmosis explains how many kinds of plants get potential, a positive value, therefore raising the their water. total water potential. Sure, many plants have roots. Let’s give a quick example. But how does the water get in the roots? In the popular water potential in potato cores When it rains, the soil becomes saturated with lab---all kinds of neat variations of this lab water. procedure exist online---you can calculate the water potential in potato cores using the water Osmosis in Plant Cells Example potential formula. The root hair cells generally have a higher When a potato core is first put into distilled concentration of solutes within them than the water—that’s pure water---the potato corecells solute concentration in the saturated soil. starts to gain water. The water travels into the root cells as the root The water is moving towards the higher solute hair cells are hypertonic compared to the concentration. hypotonic soil. Thanks to their higher solute concentration, By the way, you may wonder---well, why don’t they have a lower solute potential. those root hair cells burst with all that water? That mean a lower total water potential than That brings us to our next osmosis topic and the surroundings and water travels to areas of why plant cells walls are amazing! lower water potential. So let’s bring in another variable that can But over time as the potato core cells gain influence osmosis: pressure potential. water, the water that has entered exerts Water Potential pressureagainst the plant cell walls from inside the plant cells. This is when it’s very useful to understand how one can calculate water potential. Therefore raising the overall water potential in the potato core cells. Water potential considers both solute potential AND pressure potential. We want to point out that this turgor pressure that results in plant cells, thanks to osmosis and In osmosis, water travels to areas of lower water plant cell walls, is critical for overall plant potential. structure and the ability of plants to grow So the formula is water potential = pressure upright and not wilt. potential + solute potential. Turgor pressure is definitely something to Adding solute actually causes the solute explore. potential to have a negative value and the In summary, where would living organisms be overall water potential to lower. without osmosis? After all, it involves movement of one of our They would flow from areas of higher to lower very valuable resources: water. concentration. Picky Cells Eventually, they will reach equilibrium, where there will be equal concentrations on both sides Cells have a very finite range of conditions in of the membrane. which they can survive. However, in the case of a liquid like salt water, If the conditions are too hot, too cold, too the salt molecules are much, much too big to fit watery, too salt, too acidic or too basic, they through the cell membrane. can’t function properly. So the only particle that can move is water. Types of Solutions Let’s look a little more closely. So, we’re going to explore what happens when you place a cell in a solution that is much more Ion Dipole Interactions salty (hypertonic), much more watery Water molecules are highly attracted to salt (hypotonic), or has an equal salt concentration molecules. (isotonic). They cluster around salt and really, really don’t The Cell Membrane want to move. Remember that cell membranes are selectively The positive parts of the water molecule stick to permeable; they allow certain particles to pass the negative parts of the sodium chloride, and through, but not others. vice versa. Usually, larger molecules can’t fit through the The interactions between oxygen and sodium, membrane without special channels. and between hydrogen and chlorine are called ion-dipole interactions, which you might The cell membrane is fitted with special protein remember from chemistry. channels called Aquaporins, which allow water Water molecules that are not stuck to a molecules to pass through without expending molecule of salt are far more likely to relocate. energy. Hypertonic Liquid & Plasmolysis However, the ease with which the water molecules can cross is going to depend on Today, we’re going to immerse a cell in three something called the concentration. kinds of liquids; a very solute-rich liquid, a very watery liquid, and a liquid that’s in between. Concentration, Diffusion and Dynamic Equilibrium Then we’ll see what happens to the water molecules. Concentration is a measure of how much solute there is per volume of solvent. In this first scenario, the liquid surrounding the cell has many molecules of solute in it. This In other words, whether the liquid is more salty, liquid is hyper-tonic compared to the cell. or more watery. It has a much higher concentration of solute We’d usually expect that the molecules would particles, and a much lower concentration of follow a process called diffusion. water. Unfortunately, the solute molecules can’t pass Should You Drink Sea Water? through the membrane to reach equilibrium, Now let’s return to our sea water question. but water molecules can. Sea water is incredibly salty, much more salty The molecules of water on the outside of the than our body’s cells. cell are going to be obstructed from passing through by the many molecules of solvent. Since it’s such a hypertonic solution, if you immersed your cells in it, they would shrivel up However, the molecules on the inside have and die. much less solvent getting in the way. The real danger, however, lies in how your Water will begin rushing out of the cell. kidneys would react to sea water. Some water will come in, but the net The kidneys would attempt to remove the toxic movement, the overall movement, of water levels of salt by using water pulled from your molecules will be outwards, and the cell will cells. shrink. Your body would actually use more water in We call this cell contraction plasmolysis. removing the salt than was originally contained This is also how pickles are made. in the seawater itself. Hypotonic Liquid & Cytolysis In summary, drinking sea water is a lousy idea, even in extreme circumstances. Now let’s immerse a cell in a much less concentrated solution; a hypotonic solution. Hypertonic, hypotonic and isotonic solutions, as well as a couple of practical examples! Compared to the cell, it’s much less salty. Some water molecules will exit the cell, but even more will rush in because they aren’t Have you ever wondered what it must be like to obstructed by solute particles. be inside a cell? Imagine the genetic material, the cytoplasm, the ribosomes---you will find The cell grows in size, and it may even undergo that in almost ALL cells----prokaryotes and cytolysis and burst! eukaryotes. Eukaryote cells in addition have Isotonic Liquid membrane bound organelles. All of those organelles have different functions. But cells are Placing a cell in an isotonic solution, where the not isolated little worlds. They have a lot going concentrations inside and outside the cell are equal, is much more pleasant. on inside them, but they also interact with their environment. Equal amounts of water molecules continue to pass in and out of the cell. Importance of Cell Membrane for Homeostasis The system is in dynamic equilibrium; particles It makes sense that to keep a stable are continuing to move, but the net movement environment inside them---otherwise known as is zero. homeostasis---they must have some control on what goes in and out of them. A very important The cell neither grows, nor shrinks, and is much structure for this that ALL cells contain is the cell more likely to survive. membrane. By controlling what goes in and out, the cell membrane helps regulate homeostasis. And these are good things, because it’s helping Let’s take a look at the cell membrane. You with molecules that may be too big to cross the could have a course on the cell membrane membrane on their own or molecules that are polar---and therefore need the help of a Cell Membrane Structure itself---it has amazing transport protein. This is known as facilitated structure and signaling abilities. But to stick to diffusion. It’s still diffusion, and it still moves very basics, it is made of a phospholipid bilayer. with the concentration gradient of high to low. Bilayer means two layers, so you have these two It does not require energy so it is a type of layers of lipids. Part of them---the head is polar. passive tran sport. It’s just that the proteins are The tail part is nonpolar. facilitating, or helping, things pass. Charged ions Some molecules have no problem going through often require a protein channel in order to pass the cell membrane and directly go through the through. phospholipid bilayer. Very small non-polar Glucose needs the help of a transport protein to molecules fit in this category and are a great pass through. In osmosis, for water to travel at a Simple Diffusion fast rate across the membrane, it passes through protein channels called aquaporins. example. Like some gases. Oxygen and carbon These are all examples of facilitated diffusion, dioxide gas are great examples. This is known as which is a type of passive transport and moves simple diffusion. Also, it doesn’t take any energy with the concentration gradient of high to low to force these molecules in or out so this is concentration. known as passive transport. Simple diffusion moves with the flow. Meaning, it moves with Now all the transport we’ve mentioned has the concentration gradient. Molecules move been passive in nature, that means it’s going from a high concentration to a low from high concentration to low concentration. concentration. That’s the natural way molecules But what if you want to go the other way? like to move---from high to For example, the cells lining your gut need to What does it mean to "go with the take in glucose. But what if the concentration of concentration gradient?" low---so when you glucose in the cell is higher than the hear someone saying it’s going with the environment? We need to get the glucose in gradient then that’s what they mean. and it’s going to have to be forced against the regular gradient flow. Movement of molecules Remember how we said the cell membrane is from low to high concentration takes energy actually a pretty complex structure? Well, one because that’s against the flow. Typically ATP thing we haven’t mentioned yet are proteins in energy. A reminder that ATP ---adenosine the membrane, and some of them are transport triphosphate---it has 3 phosphates. When the Facilitated Diffusion bond for the last phosphate is broken, it releases a great amount of energy. It’s a pretty proteins. Some transport proteins act as awesome little molecule. ATP can power Active channels. Some of these proteins actually Transport to force those molecules Active change their shape to get items across. Some of Transport.(including endocytosis exocytosis )to them open and close based on a stimulus of go against their concentration gradient, and one some kind. way it can do that is actually energizing the transport protein itself. One of our favorite back to those polysaccharides---did you know examples of active transport is the that large carbohydrates are also really sodium-potassium important for making plant cell walls? Cell walls are different from cell membranes----all cells pump so that’s definitely something worth have membranes but not all cells have a wall. checking out! But if you are going to make a cell wall, you’re - There’s other times the cell needs to exert going to need to get those carbohydrates that are produced in the plant cell out of the cell to energy for transport – we’re still in active make the wall. So there’s a great example of transport for now. But let’s say a cell needs a when you’d need exocytosis right there. very large molecule---let’s say a big polysaccharide (if you check out Plant Cells our biomolecule video, that’s a large carbohydrate)---well you may need the cell membrane to fuse with the molecules it’s taking in to bring it inside. This is called Endocytosis--- think endo for “in.” Often, this fusing of substances with the cell membrane will form vesicles that can be taken inside the cell. Endocytosis is a general term, but there are Cell Theory actual different types of endocytosis depending Theory that the cell is the basic unit of life, of on how the cell is bringing substances inside. which all living things are composed, and that Amoebas for example rely on a form of all cells are derived from preexisting cells endocytosis. Pseudopods stretch out around METHODS TO STUDY CELLS what they want to engulf and then it gets pulled into a vacuole. There are other forms too such Light and Electron Microscopes as the fancy receptor-mediated endocytosis---where cells can be very, very, very picky about what’s coming in because the incoming substances actually have to bind to receptors to even get in. Or pinocytosis---which allows the cell to take in fluids. So to the Google to find out more details of the different types of endocytosis. Exocytosis is the reverse direction of Two fundamentally different types of cells: endocytosis, so this is when molecules prokaryotic and eukaryotic​ exit---think exo and exit. Exocytosis can also be EUKARYOTIC CELL​ used to get rid of cell waste but it’s also really important A cell that posses a nucleus and other membrane-bound organelles​ for getting important materials out that the cell has made. Want a cool example? Thinking PROKARYOTIC CELL​ ​NUCLEUS​ A cellular organelle that contains DNA and serves as control center of the cell A cell that lacks nuclei and other membrane-bound organelles (archaea and bacteria)​ PLASTID​ - A group of membrane-bound organelles occurring in photosynthetic eukaryotic cells​ Chloroplasts, leucoplasts, and chromoplasts “Typical” Plant Cells Chloroplasts ​ - Sites of photosynthesis PLASMA MEMBRANE​ MITOCHONDRION​ Living surface membrane of a cell ​ - An intracellular organelle associated Acts as a selective barrier to passage of with cellular respiration (in which materials into and out of the cell chemical energy in fuel molecules is transferred to ATP)​ RIBOSOME​ A cellular organelle; site of protein ​ENDOPLASMIC RETICULUM (ER)​ synthesis An organelle composed of an interconnected network of internal membranes within eukaryotic cells ​ Site of enzymatic activity​ Synthesizes membranes such as nuclear envelope​ Rough ER is associated with ribosomes; smooth ER lacks ribosomes THE EVOLUTION OF EUKARYOTIC CELL GOLGI BODY​ CYTOSKELETON​ An organelle composed of a stack of Composed of microtubules and flattened membranous sacs​ microfilaments​ Modifies, packages, and sorts proteins Maintains the cell’s shape​ that will be secreted or sent to the Involved in cellular movement plasma membrane or other organelles CELL WALL​ VACUOLE​ Comparatively rigid supporting wall A large, fluid-filled, membrane-bound exterior to the plasma membrane in sac within the cytoplasm that contains a plants, fungi, prokaryotes, certain solution of salts, ions, pigments, and protists waste materials  FLUID MOSAIC MODEL​ Current model for the structure of the plasma membrane and other cell membranes in which protein molecules “float” in a fluid phospholipid bilayer​ Explains membrane structure​ Each membrane is composed of a phospholipid bilayer in which varying proteins are embedded Communication between plant cells—despite the presence of rigid cell walls between the plasma membranes of adjacent cells—is accomplished by specialized channels called plasmodesmata. Phospholipid Bilayer Nonpolar, hydrophobic fatty acid chains of phospholipids project into interior of the double-layered membrane​ Polar, hydrophilic heads located on two surfaces of the double-layered membrane  Turgor Pressure DIFFUSION ​ Net movement of particles (atoms, molecules, or ions) along a concentration gradient from an area of higher concentration to an area of lower concentration. FACILITATED DIFFUSION​ A carrier protein helps move a material OSMOSIS ​ across a membrane in the direction of the concentration gradient, from high to Net movement of water (principle low concentration solvent in biological systems) by diffusion through a selectively ACTIVE TRANSPORT​ permeable membrane. Energy is expended to move a material against the concentration gradient, from low to high concentration DIFFUSION, FACILITATED DIFFUSION, and ACTIVE TRANSPORT​ Shoot system ​ generally aerial ​ obtains sunlight and carbon dioxide for plant ​ Shoot system consists of ​ a vertical stem bearing leaves (main organs of photosynthesis) ​ flowers and fruits (reproductive structures) Buds (undeveloped embryonic shoots) develop on stems ​ Although separate organs (roots, stems, and leaves) exist in the plant, many tissues are integrated throughout the plant Plant Tissues and the multicellular body, providing continuity from Plant Body organ to organ The Plant Body 3 Tissue Systems in Plant Body Root system ​ GROUND TISSUE SYSTEM ​ generally underground ​ All tissues of the plant body other than obtains water and dissolved minerals vascular tissues and dermal tissues ​ for plant ​ VASCULAR TISSUE SYSTEM ​ usually anchors the plant firmly in place Tissue system that conducts materials throughout the plant body​ DERMAL TISSUE SYSTEM ​ Tissue system that provides an outer covering for the plant body Ground Tissue System Ground Tissue System PARENCHYMA CELL ​ PARENCHYMA TISSUE ​ Relatively unspecialized plant cell; thin walled, Composed of living parenchyma cells may contain chlorophyll, loosely packed​ with thin primary cell walls. Usually holds the chlorophylls.​ Functions include photosynthesis, storage, and secretion COLLENCHYMA CELL ​ Living plant cell with moderately but unevenly thickened primary walls SCLERENCHYMA CELL ​ Plant cell with extremely thick walls; provides strength and support to plant body COLLENCHYMA TISSUE ​ Composed of collenchyma cells with unevenly thickened primary cell walls ​ Provides flexible structural support SCLERENCHYMA TISSUE ​ XYLEM ​ Composed of sclerenchyma cells with A complex vascular tissue that conducts both primary and secondary cell walls ​ water and dissolved minerals Sclerenchyma cells are often dead at throughout the plant body ​ maturity, but provide structural support Actual conducting cells of xylem are tracheids and vessel elements Vascular Tissue System Conducts materials throughout the plant body and provides strength and Pit Pairs support ​ - Xylem ​ - Phloem PHLOEM ​ A complex vascular tissue that conducts Epidermis covering aerial parts secretes food (carbohydrate) throughout the a wax layer (cuticle) that reduces water plant body ​ loss ​ Conducting cells of phloem are Gas is exchanged between interior of sieve-tube elements assisted by shoot system and surrounding companion cells. atmosphere through stomata ​ Some even have trichomes (plant hairs), either for self/UV protection, thermal insulator. Dermis Tissue System Outer protective covering of the plant body ​ PERIDERM ​ - Epidermis - Periderm Outermost layer of cells covering a woody stem or root (the outer bark that replaces epidermis when it is destroyed during secondary growth) EPIDERMIS ​ Outermost tissue layer, usually one cell thick​ Covers the primary plant body (leaves, young stems and roots) ​  APICAL MERISTEM ​ An area of cell division at the tip of a stem or Growth in Plants root tip in a plant; produces primary tissues Involves cell division, cell elongation, and cell differentiation​ Plants grow only in specific areas (meristems) composed of cells that do not differentiate Location of growth differs between plants and animals​ When a young animal grows, all parts of its body grow, although not necessarily at the same rate Primary Growth An increase in stem and root length due to the activity of apical meristems at the tips of roots and at the buds of stems BUD ​ A dormant embryonic shoot that eventually develops into an apical meristem  1. Secondary growth Cross-sectional cut – horizontal to the part (e.g. stem, leaf midrib).​ Increase in a plant’s stem and 2. Lateral cut – Perpendicular to the organ. root girth due to the activity of Usually the middle portion of the plant lateral meristems (the vascular organ. cambium and cork cambium) ​ Woody plants have secondary Plants Organs: Roots growth ​ - In addition to primary Functions of Roots growth​ Anchorage ​ Secondary growth is localized, Absorption​ typically as long cylinders of Conduction​ active growth throughout the Storage ​ lengths of older stems and roots Roots System TAPROOT SYSTEM ​ A root system consisting of one prominent main root with smaller lateral roots branching from it ​ FIBROUS ROOT SYSTEM How to see those under a microscope A root system consisting of several adventitious Two ways to cut a plant organ roots of approximately equal size that arise from the base of the stem  Increase surface area of root in contact with moist soil, increasing root’s absorptive capacity Unique structures ROOT CAP ​ A covering of cells over the root tip that Primary Eudicot Roots protects delicate meristematic tissue directly behind it ​ Outer protective covering​ - Epidermis​ ROOT HAIR ​ Ground tissues ​ - Cortex ​ An extension of an epidermal cell of a root that - Pith (in certain roots) ​ increases absorptive capacity of the root ​ Vascular tissues​ - Xylem​ - Phloem ROOT CAP ​ Each root tip has a root cap​ A protective thimble-like layer ​ Many cells thick​ Covers delicate root apical meristem ​ Epidermis ​ May orient root so it grows downward - Protects the root​ - Root hairs help absorb water and dissolved minerals ​ Cortex ​ - Consists of parenchyma cells​ - Usually stores starch ROOT HAIRS ​ Short-lived, unicellular extensions of epidermal cells near the growing root tip ​  XYLEM ​ conducts water and dissolved minerals​ ENDODERMIS ​ PHLOEM ​ Innermost layer of the cortex of the conducts dissolved sugar root that prevents water and dissolved materials from entering the xylem by passing between cells ​ CASPARIAN STRIP ​ A band of waterproof material around the radial and transverse cells of the endodermis​ Ensures that water and minerals enter the xylem only by passing through the endodermal cells Comparing Monocot and Eudicot ​ PERICYCLE ​ A layer of cells just inside the endodermis of the root ​ Monocot roots often have a pith in the Gives rise to lateral roots center of the root​ In herbaceous eudicot roots, xylem and phloem form a solid mass in center of root​ ​  Monocot roots lack a vascular SYMPLAST ​ cambium​ A continuum consisting of the cytoplasm of Do not have secondary growth many plant cells, connected from one cell to the Monocot Root next by plasmodesmata ​ APOPLAST ​ A continuum consisting of the interconnected, porous plant cell walls, along which water moves freely Water Movement In a primary eudicot root, water moves from soil into center of root:​ Modified Roots Root hair → epidermis → cortex (symplast or PROP ROOT ​ apoplast pathway) → endodermis → pericycle → xylem of root ​ An adventitious root that arises from the stem and provides additional Water is transported upward through root xylem into stem xylem and rest of plant CONTRACTILE ROOT ​ A specialized root, often found on bulbs or corms, that contracts and pulls the plant to a desirable depth in the soil Other Modified Roots Suckers ​ Aboveground stems that develop from PNEUMATOPHORE ​ adventitious buds on the roots​ Asexual reproduction method of some A specialized aerial root produced by roots​ certain trees living in swampy habitats​ Certain epiphytes have roots that are May facilitate gas exchange between modified to photosynthesize the atmosphere and submerged roots Buttress roots ​ Swollen bases or braces that hold trees upright ​ Aid in extensive distribution of shallow Important Foods roots​ Found in some tropical rainforest trees ​ oots which store the products of R photosynthesis are important sources of food for human consumption ​  Some roots are used as flavorings​ Example: root beer flavoring (dried greenbrier roots) Plants Organs: Stems Root Crops Support ​ - leaves and reproductive structures ​ ​ redominantly taproots ​ P Conduct ​ carrots, beets, sugar beets, parsnips, - water, dissolved minerals, turnips, rutabagas, radishes ​ carbohydrates ​ Some fibrous roots ​ Produce new living tissues ​ sweet potatoes, cassava - at apical meristems ​ - at lateral meristems (secondary growth) Tissues in Herbaceous Stems Epidermis ​ - protective outer layer ​ - covered by water-conserving cuticle ​ Vascular tissues​ - Xylem conducts water and dissolved minerals ​ - phloem conducts dissolved MYCORRHIZA ​ carbohydrates (sucrose)​ A mutually beneficial association between a Storage tissues​ fungus and a root that helps the plant absorb essential minerals from the soil​ - Cortex and pith​ - ground tissue NODULE ​ A small swelling on the root of a leguminous plant in which beneficial nitrogen-fixing bacteria (Rhizobium) live.  Difference Between Stems and Roots Unlike roots, stems have nodes and internodes, leaves and buds ​ Unlike stems, roots have root caps and root hairs Herbaceous Eudicot Stems Have vascular bundles arranged in a circle (in cross section)​ Have a distinct cortex and pith NODE ​ Area on a stem where one or more leaves is attached; stems have nodes, but roots do not ​ INTERNODE ​ Stem area between two successive nodes ​ BUD ​ Monocot Stems An undeveloped shoot that contains an Have scattered vascular bundles ​ embryonic meristem ​ Have ground tissue instead of distinct May be terminal (at tip of stem) or cortex and pith axillary (on side of stem)  Primary Growth: Eudicot VASCULAR CAMBIUM ​ A lateral meristem that produces secondary xylem (wood) to the inside and secondary phloem (inner bark) to the outside Differences Between Stems and Roots Internally ​ herbaceous roots possess an endodermis and pericycle ​ stems lack a pericycle and rarely have an endodermis ​ Occurs in woody eudicots and conifers ​ Produced by vascular cambium​ Between primary xylem and primary phloem​ Is not initially a solid cylinder of cells becomes continuous when production of secondary tissues begins  Arises near the stem’s surface ​ Is either a continuous cylinder of dividing cells or a series of overlapping arcs of meristematic cells that form from parenchyma cells in successively deeper layers of the cortex and, eventually, secondary phloem Certain parenchyma cells between vascular bundles​ retain ability to divide ​ connect to vascular cambium cells in each vascular bundle​ form a complete ring of vascular cambium Development: Woody Eudicot CORK CAMBIUM ​ A lateral meristem that produces cork parenchyma to the inside and cork cells to the outside​ Cork cambium and the tissues it produces make up the outer bark of a woody plant ​ 3-Year-old stem Stomata are replaced by lenticels, areas of the cork in which the cork cells are loosely arranged, permitting gas exchange through the periderm. Onset of Secondary Growth Woody Stem Trees – contains conspicuous trunks​ Shrubs – produce branches from or near the ground Stem Life Cycle Variation of Bark Annuals – completes their life cycle in one growing season.​ Biennial – the lower part of the stem, often modified for food storage, persist after the first growing season and bears buds from which an erect stem arises during the second growing season.​ Lenticles Perennial – short stem may produce new shoots for many years. ​ As a stem thickens from secondary growth, the epidermis, including the stomata that allowed gas exchange for the herbaceous stem, dies. ​ Heartwood and Sapwood SAPWOOD​ The functional secondary xylem​ the younger, lighter- colored wood closest to the bark. ​ ​HEARTWOOD​ Annual Rings The older wood in the center of the trunk​ Typically a brownish red.​ No longer functions in conduction.​ Heartwood is denser than sapwood​ Provides structural support for trees. ​ More resistant to decay (some evidence).​ Figure 7.13: A block of wood showing (a) cross, (b) tangential, and (c) radial sections. ​ Both tangential and radial sections are longitudinal sections. A tangential section is cut in a plane that does not pass through the center of the stem but instead passes at a right angle to a radius. A radial section is cut in a plane that passes through the center along a radius of the stem. Rays and annual rings are distinctive for each section. Tree-ring dating ​ Tree-ring dating. Scientists develop a master chronology by using progressively older pieces of wood from the same geographic area. They can then accurately determine the age of a wood sample by using a computer to match its rings to the master chronology.​ VINE ​ Example: white potato weak-stemmed plants that depend on other plants for support​ A plant with a long, thin, often climbing stem Modified Stem RHIZOME ​ - A horizontal underground stem that often serves as a storage organ and a means of sexual reproduction ​ BULB ​ Example: iris A rounded, fleshy underground bud that consists of a short stem with fleshy leaves​ Example: onion TUBER ​ The thickened end of a rhizome that is fleshy and enlarged for food storage ​ CORM ​ Construction Material (Timber & Lumber) ​ A short, thickened underground stem Condiments (Herbs & Spices)​ specialized for food storage and asexual Furnitures, Toys, Aesthetics​ reproduction​ Scents and Perfumes​ Example: crocus Hair Dyes​ Paper​ Clothings​ Art Materials STOLON ​ An aerial horizontal stem with long internodes; often forms buds that develop into separate plants​ Rain Forest Distribution Example: strawberry DEFORESTATION ​ The temporary or permanent clearance of large expanses of forests for agriculture or other uses Significance of Stem Food and Cooking materials​ Medicine​  LEAF MORPHOLOGY​ PHOTOSYNTHESIS ​ Plant Organs: Leaves The biological process that includes the capture “Typical” Leaf of light energy and its transformation into chemical energy of organic molecules (such as BLADE ​ glucose), which are manufactured from carbon Broad, flat part of a leaf​ dioxide and water PETIOLE ​ Part of a leaf that attaches blade to stem Tissue in a leaf blade EPIDERMIS​ The transparent epidermis allows light to penetrate into the mesophyll, where photosynthesis occurs ​ CUTICLE ​ Waxy covering over epidermis of aerial parts (leaves and stems) of a plant​ Enables the plant to survive in the dry conditions of a terrestrial environment STOMA ​ Small pores in epidermis of stem or leaf ​ Permit gas exchange for photosynthesis and transpiration ​ Flanked by guard cells​ Stomata typically open during the day, when photosynthesis takes place, and close at night​ GUARD CELL ​ Trichomes Two guard cells form a pore (stoma) Are specialized epidermal cells located on aerial parts of plants and are associated with a wide array of biological processes.​ Protect plants from adverse conditions including UV light and herbivore attack and are also an important source of a number of phytochemicals. MESOPHYLL ​ Photosynthetic ground tissue in the interior of a leaf​ Contains air spaces for rapid diffusion of carbon dioxide and water into, and oxygen out of, mesophyll cells Dicot: Leaf Cross Sections monocot: Leaf Cross Sections Vascular Bundle Leaf veins have:​ Dicot: Leaf Cross Sections xylem to conduct water and essential minerals to the leaf ​ phloem to conduct sugar produced by photosynthesis to rest of plant BUNDLE SHEATH ​ One or more layers of nonvascular cells (parenchyma or sclerenchyma) surrounding the vascular bundle in a leaf Monocot and Eudicot Leaves Monocot leaf​ Usually narrow ​ Wrap around the stem in a sheath ​ Have parallel venation​ Eudicot leaf​ Usually have a broad, flattened blade ​ Have netted venation Variation in guard cells Bulliform Cells Large, thin-walled cells on upper epidermises of leaves of certain monocots (grasses):​ - Located on both sides of the midvein ​ Figure 8.8: Variation in guard cells. ​ - May help leaf roll or fold inward during drought Guard cells are associated with special epidermal cells called subsidiary cells. Stomatal Opening 4. Chloride ions also enter guard cells through ion channels​ 1. Blue light activates proton pumps​ - Ions accumulate in vacuoles of guard in guard-cell plasma membrane cells​ - Solute concentration becomes greater than that of surrounding cells FACILITATED DIF