Biology Chapter on Cell Efficiency

Unit Goals

• The unit will explore microscopy and the emergence of cell theory.
• It will also identify cellular structures and functions.
• The role of cell membranes in active and passive matter transport will be explored.
• Cell specialization in multicellular organisms, specifically in plants, will be discussed.

Topic 1: Cell Theory

• Intro Brainstorm: What does it mean to be a living thing?
• Recall: What is a cell?
• Scientists identify five characteristics of living things: they need energy, produce waste, reproduce, grow, and respond/adapt to their environment.
• The theory of spontaneous generation (abiogenesis) was widely accepted for over 2,000 years. Aristotle based this on observation only and didn't conduct experiments to validate it.

Topic 2: History of Cell Theory

• Aristotle (~350 BCE): Observed nature, classified organisms into plant or animal kingdoms, and observed spontaneous generation.
• Francesco Redi (1668): Conducted controlled meat experiments to test spontaneous generation, suggesting that maggots did not arise spontaneously.
• Louis Pasteur (~1850): Proved microorganisms cause fermentation and disproved spontaneous generation. His swan-neck flask experiment showed that microbes in the air were trapped, preventing contamination.

Topic 3: Discovering Cells

• Scientists could only learn so much by observing things with unaided eyes.
• Microscopy allowed them to study the structures of organisms in much more detail.
• Scientists eventually concluded that all living things are composed of cells.

Topic 4: Developing Cell Theory

• Robert Hooke (1665): Observed and named cells in once-living matter. His observations were detailed in a book.
• Antonie van Leeuwenhoek (1674): Observed single-celled organisms in pond water, blood, and other substances.
• Schleiden and Schwann (1839): After examination, concluded that all organisms are composed of cells. Observed nuclei in young cells, concluding that new cells developed from the original.
• Rudolf Virchow (1855): Found that new cells develop from pre-existing cells, stating that all cells come from other cells, completing the cell theory.

Topic 5: The Cell Theory

• The cell is the smallest functional unit of life.
• All organisms are composed of one or more cells.
• All cells are produced from pre-existing cells.
• Not all cells are the same (many types with diverse functions).

Topic 6: Levels of Cellular Organization

• Cells are the fundamental units of life, but composed of smaller components - organelles.
• Each organelle performs a specialized function that contributes to the overall cell function. Example: the nucleus contains DNA.
• Cells specialize to form tissues
• Tissues with similar functions unite to form organs
• Organs work together with similar functions to become an organ system e.g. heart, etc.
• A diagram shows levels of organization from atoms to organ systems in the human body.

Topic 7: Exceptions to Cell Theory

• Viruses, though resembling cells and having genetic material, cannot survive or reproduce outside a host due to their lack of metabolic and reproductive capabilities.
• Striated muscle cells: long and narrow cells bundled together by a single membrane, containing multiple nuclei.
• Fungal hyphae are large, elongated cells that have multiple nuclei. They form a continuous cytoplasm.

Topic 8: How do we study very tiny things?

• Microscopy is used to study nearly all types of cells.
• Scientists use special tools to make the nearly invisible structures appear bigger to see them in detail.

Topic 9: Microscopy

• Janssen (1595): Invented the first microscope with an objective and eyepiece.
• Hooke (1665): Improved the microscope with a three-lens system to better illuminate and study the specimens.

Topic 10: Simple and Compound Light Microscopes

• Simple Microscopes: Use only one lens—similar to a magnifying glass.
• Compound Light Microscopes: Use two or more lenses placed one on top of the other to allow for greater magnification up to 2000 times actual size.

Topic 11: Improving Microscope Technology

• Electron Microscopes: Illuminate specimens with beams of electrons to achieve much higher resolution. Advanced examples have recently been used to image atoms.
• Staining helps define details of specimens like cell membranes and genetic material so they can be seen more easily under a microscope, and aids in viewing cell division (e.g. of cell components).

Topic 12: Cell Membranes

• Materials entering or exiting a cell must pass through the cell membrane (which changes according to a cell's needs).
• The cell membrane regulates the movement of substances in and out of the cell and is called a semi-permeable membrane; meaning only certain materials can move through a cell.
• The flow of matter between a cell and its environment makes it an open system.
• Phospholipid bilayer: The cell membrane is often referred to as a phospholipid bilayer because it is composed of a double layer of phospholipids and has proteins and other molecules embedded within .
• Membrane structure: The lipid bilayer is made of components, including a head with a hydrophilic (water-loving) charge and a tail with a hydrophobic (water-fearing charge). The heads face outwards and the tails inwards.
• Movement of a substance accross a membrane: The fluidity of the membrane allows mobility of proteins and lipids. This fluidity helps the cell change shape and proteins to react to changes in the environment.
• Proteins in membranes: Integral proteins are permanent part of the bilayer , while peripheral proteins are temporarily attached.
• Cholesterol maintain the fluidity of the membrane, and thus allowing to maintain integrity
• Function of membranes: Membranes act as filters, regulating the movement of certain substances across them. This is important because this is how cells interact with their environment.

Topic 13: Transport Across Cell Membranes

• Selective transport: Movement across cell membranes is called selective transport because only certain substances are allowed to cross.
• Concentration gradient: Without selectivity, ions and other particles outside the cell would reach equilibrium with the inside, disrupting cellular activities.
• Equilibrium: A state of balance and stability.

Topic 14: Passive Transport

• Diffusion: A passive movement of solute particles from high to low concentration. This is how gas exchange occurs.
• Osmosis: Movement of water molecules through a semipermeable membrane from high to low concentration.
• Facilitated diffusion: Transport of substances across a membrane with protein assistance.

Topic 15 : Passive Transport-Hypotonic, Hypertonic and Isotonic solutions

• Hypotonic solution : the concentration of solute is lower outside the cell compared to inside, this causes water to move into the cell.
• Hypertonic solution : the concentration of solute is higher outside the cell compared to inside, this causes water to move out of the cell.
• Isotonic solution : the concentration of solute is equal inside and outside the cell, this causes no water movement.

Topic 16: Active Transport

• Materials move from an area of low concentration to high concentration during active transport. Energy is required for this process.
• Example: Plant root cells use active transport to take in minerals from the surrounding soil

Topic 17: Endocytosis and Exocytosis

• Endocytosis: The cell membrane forms a pocket around the material to be transported and encloses the material into a sphere, forming a vesicle. The contents are transported within the cell.
• Exocytosis: A vesicle inside the cell approaches the cell membrane, joins with it and expels the contents from the cell.
• Pinocytosis : (cell drinking) Molecules dissolved in fluids are taken into the cell via endocytosis.
• Phagocytosis : (cell eating) Solids are taken into the cell via endocytosis.

Topic 18: Cell Surface Area to Volume Ratio

• Cells in general have best function when the distance over which substances must diffuse is minimized.
• The surface area of a cell does not increase proportionally to its volume, making larger cells less efficient in transporting materials.
• Larger cells may starve or be poisoned by their own waste products if transport is inefficient, making cell size limited.
• Certain cell shapes can increase the ratio of surface area to volume, increasing transport efficiency.

Topic 19: Plant Cell Specialization

• Cells need a large surface area for exchanging nutrients with their surroundings, but the ratio of surface area to volume decreases as cells grow in size.
• Multicellular organisms are better at supporting larger size.
• Plant cells are adapted to perform photosynthesis.
• Plants have evolved a number of specialized organ systems, cells, and tissues to overcome the challenges of multicellularity.
• Cuticle: A waxy substance that prevent water evaporation,
• Epidermis: The outer covering of leaves and has an important role in letting light pass through.
• Palisade cells: Tightly packed cells packed under epidermis, where most photosynthesis occurs.
• Spongy tissue cells: Layer below palisade tissue cells, contains chloroplasts and perform photosynthesis while maintaining gas/water exchange.
• Stomata: Small openings on the underside of leaves that allow gases and water in/out of the leaf. The two guard cells surrounding the stomata control the stoma’s size.
• Vascular tissue (vessels) deliver fluids throughout the plant. Xylem transports water and minerals from the roots to the leaves. Phloem transports sugars produced in the leaves to various parts of the plant.
• Plant cells have special adaptations.

Topic 20: Plant Water Transport

• Water transport is different in a unicellular vs. multicellular organism. In unicellular organisms, water transport is via osmosis. In multicellular organisms, water transport is over a larger distance using a vascular system.
• Xylem cells transport water and dissolved minerals from roots to leaves.
• Water moves into the root cells by osmosis and diffuses throughout the tissue until it reaches xylem.
• Roots and shoots use cohesion/adhesion to pull water upwards through a vascular system.
• Adhesion: Water molecules stick to the xylem walls,
• Cohesion:Water molecules stick together.

Topic 21: Plant Control System

• Tropisms: Plant responses (growths) in a specific direction toward or away from a stimulus. • Phototropism: Growth toward or away from light. • Gravitropism: Growth toward or away from gravity.
• Auxin is a plant hormone controlling phototropism.
• Other examples of plant responses, like how a mimosa leaf or Venus flytrap respond to touch, are termed “nastic response.”

Topic 22: Chemical Reactions

• A chemical reaction occurs when one or more substances react to form new substances with different chemical properties.
• Evidence of chemical reactions includes: • Change in energy (temperature) • Formation of a precipitate or gas (bubbles) • Change in color or odor • Change in pH.

Topic 23: Predicting Solubility

• Solubility: The ability of a solute to dissolve in a solvent.
• Saturated solution: A solution with the maximum amount of solute dissolved.
• Unsaturated solution: A solution in which more solute can be dissolved.
• Solubility Tables : used to predict whether a substance will dissolve or form a precipitate in a solution.

Topic 24: Types of Chemical Reactions

• Formation reactions: Two or more elements combine to form a new compound.
• Decomposition reactions: A compound breaks down into its elements.
• Single replacement reactions: Element A replaces element B in compound AB, becoming a new compound AC + B.
• Double replacement reactions: Elements in two compounds are swapped to create two new compounds.
• Hydrocarbon combustion reactions: Hydrocarbons are burned with oxygen to form carbon dioxide and water vapor and release thermal energy

Topic 25: Balancing Chemical Equations

• Chemical equations must balance the number of atoms of each element on both sides of the equation.
• Coefficients are used to balance an equation. The subscripts within the formulas are not changed.

Topic 26: The Nature of Matter

• Matter is made up of atoms (which are made up of subatomic particles including electrons, protons, and neutrons).
• Elements are substances made up of only one type of atoms.
• Compounds are substances formed from the bonding of two or more different elements.
• Mixtures are a combination of two or more pure substances/elements or compounds.

Topic 27: Organizing Matter

• The ways matter can be classified into different categories, and the relationships between these categories.

Topic 28: The Periodic Table

• Organization of elements by atomic number, showing periodic trends in chemical properties.
• Elements in the same periodic groups/families also have similar properties, particularly in their valence electrons (the outermost electrons of an atom).

Topic 29: Forming lons

• Ions: Charged atoms that have lost or gained electrons. • Anions: Negatively charged ions (gained electrons • Cations: Positively charged ions (lost electrons)
• The Stable Octet Rule: Atoms tend to gain or lose electrons to achieve 8 valence electrons to gain stability (identical to the noble gas configuration.)

Topic 30: Drawing Bohr Diagrams

• Bohr diagrams represent how electrons are arranged in energy levels around an atomic nucleus.
• The number of protons and neutrons are present in the nucleus.
• The number of electrons in the Bohr model is equal to the atomic number.

Topic 31: Naming lons

• Naming lons includes identifying the charge and using prefixes for clarity.

Topic 32: Naming Compounds

• Naming compounds includes using the correct prefixes and identifying all types of compounds.

Topic 33: Naming Acids and Bases

• Acids release hydrogen ions (H⁺) when combined with water.
• Bases release hydroxide ions (OH⁻) when combined with water.
• The rules used to named both acids and bases are based on the periodic table and knowledge of chemical terminology.

Topic 34: States of Matter

• Solids, liquids, and gases are three states of matter.
• An illustration describing the arrangement of particles in each of the three states.