Untitled Quiz

Particle Theory of Matter

• All matter is composed of small particles that are constantly moving randomly (Brownian motion).
• The speed of particles increases with temperature.
• Example: Smelling garbage more strongly in the summer than winter.

Transport across the Cell Membrane

• A concentration gradient is a difference in concentration across a membrane.
• Dynamic equilibrium occurs when substances move back and forth across the membrane at equal rates, resulting in no net movement, but a gradient still exists,
• Equilibrium is when there is no gradient and the system is balanced.

Transport across Cell Membranes - Dependent on Size and Polarity

• Proteins, carbohydrates, nucleic acids, and lipids can not pass through the cell membrane easily unless assistance.
• Small, non-polar molecules pass through the cell membrane easily.
• CO₂ and O₂ are examples of substances that pass through easily.
• Charged ions are repelled by the hydrophobic tails of the membrane.

Passive Transport

• Always moves down the concentration gradient, from high concentration to low concentration.
• Does not require energy (no ATP needed).
• There are three types: diffusion, osmosis, and facilitated diffusion.

1. Diffusion

• Net movement of particles from high concentration to low concentration.
• Driven by the kinetic energy (E_k) of molecules.
• Non-polar, small molecules (O₂, CO₂) move by diffusion.

2. Osmosis

• The net movement of water across a selectively permeable membrane from high water concentration to low water concentration.
• Water moves when a solute cannot pass through the membrane.

3. Facilitated Diffusion

• Many polar molecules and ions diffuse across the membrane with the help of transport proteins.
• Still passive as it moves down the concentration gradient.

a. Channel Proteins

• Contain hydrophilic channels that allow molecules/ions to pass through the membrane.
• Example: Aquaporins allow the entry of billions of water molecules per second in the kidneys.

b. Carrier Proteins

• Undergo a shape change to transport molecules across the membrane.
• Example: Glucose transporter.

Tonicity

• What happens when cells are placed in solutions
• Isotonic = equal water & solute concentration; there's equal flow in both directions.
• Hypertonic = relatively higher solute concentration & lower water concentration; water moves out of the cell.
• Hypotonic = relatively lower solute concentration & higher water concentration; water moves into the cell.

Dialysis

• Process of material passage across semi-permeable membranes.
• Used to correct imbalances caused by damaged kidneys.
• Blood is pumped outside the body and bathed in solutions that help remove waste products.
• Blood is then returned to the body.

Diffusion & Osmosis Examples #1

• The dialysis tubing is permeable to water but not to solutes.
• Determine the missing percentages.
• Determine whether the tube is hypotonic, hypertonic, or isotonic to the surrounding solution.
• Identify the flow of water.

Diffusion & Osmosis Examples #2

• U-tube with sides A & B separated by a semi-permeable membrane.
• Determine the percentage concentrations at equilibrium.
• Assume the membrane is impermeable to starch.

Diffusion & Osmosis Experiments

• Includes iodine diffusion via dialysis tubing, egg mass change via osmosis, potato length change via osmosis.

Active transport

• Requires energy (ATP).
• Solutes are "pumped" against their concentration gradient (from low to high).
• Done by carrier proteins.
• Allows cells to maintain a different internal environment than the external environment.

1. Protein Pumps

• Each solute has its own pump.
• Sodium-Potassium Pump (Na⁺/K⁺-ATPase)
• Animal cells need high K⁺ and low Na⁺ concentrations.
• The pump pumps 3 Na⁺ out for every 2 K⁺ in.

2. Exocytosis

• Cells excrete molecules using vesicles.
• Vesicles fuse with the cell membrane, releasing contents outside the cell.
• Cell membrane, Golgi, and ER can all be involved in forming vesicles.

3. Endocytosis

• Cells take in molecules by forming vesicles from the cell membrane.

a. Phagocytosis

• "Cell eating"
• Cells bring in large materials that will be digested.
• Cells fuse with lysosomes to digest molecules.

b. Pinocytosis

• "Cell drinking"
• Cells absorb fluid and small solutes/nutrients in droplets absorbed within the cell.

c. Receptor-Mediated Endocytosis

• Uses protein receptors in the membrane to identify, bind, and bring in specific materials that will be used by the cell.

Plant Adaptations

• Features, structures, and behaviors that enable survival in their environment.
• Examples: darker leaves absorb more light, larger leaves increase surface area, waxy cuticles reduce water loss.

Tropisms

• Directional growth responses to environmental factors.
• Positive tropism = grow towards the stimulus; negative tropism = grow away from stimulus.

Types of Tropism

• Phototropism = response to light; gravitropism = response to gravity; thigmotropism = response to contact; hydrotropism = response to water.

Investigations of Phototropism

• Darwin & Darwin experiments, controlled the tip of emerging cereal plants and confirmed that the growing tip was responsible for phototropism.

Boysen-Jensen

• Proposed a chemical moving from the tip as the mechanism for communication with the elongation area.

Went

• Confirmed auxin as the chemical in the tip responsible for phototropism.
• Auxin is a hormone, a chemical compound made in one area and transported to stimulate the growth of new plant cells.
• Auxin spreads faster on the darker side of the plant, causing cells to elongate on that side and the plant to bend towards the light.

Transport in Plants

• Plants move nutrients from a source (e.g., leaves, storage bulbs) to a sink (e.g., meristems, roots).

Transport in the Xylem

• Begins with root pressure; minerals enter via active transport, and water follows via osmosis.
• Increases pressure in the xylem.
• Water moves up the plant via a combination of pushing (root pressure) and pulling (transpiration).
• Cohesion & adhesion of water molecules help in the pulling process.
• Transpiration creates a pull of water, causing water to move upward through the xylem.

Transport in the Phloem

• Sugar is transported from leaves to other parts of the plant via phloem.
• Transports sugars from a source to a sink.
• Pressure-flow theory explains the transport mechanism, involving osmosis and turgor pressure.

Surface Area to Volume Ratio

• High surface area:volume ratio means better absorption and diffusion.
• Important for cells to maintain efficient nutrient/waste exchange and to sustain essential functions.
• Large cells require more energy to transport nutrients due to the reduced surface area:volume ratio.
• Smaller cells have higher ratios (larger SA), allowing faster exchange.

Cell Size and Function

• Diffusion over long distances is slow and inefficient.
• Cell size is limited as larger cells risk not being able to efficiently meet their metabolic needs.
• Smaller/flatter cells provide larger surface areas relative to their volumes.

Relationship between Surface Area and Volume

• High surface area: large amount of exchange across the membrane
• Small volume: efficient delivery of nutrients.

Levels of Organization of an Organism

• Cells→Tissues→Organs→Organ Systems→Organisms
• Cells= Basic building blocks
• Tissues= Groups of cells specialized for similar functions
• Organ = Groups of tissues in a coordinated way
• Organ System = Groups of organs that share a common function
• Organisms = Individuals, complex systems of interacting parts

Plant Organ Systems

• Shoot systems (everything above the ground, photosynthesis)
• Root systems (everything below the ground, obtain water and nutrients)

Plant Organs

• Flowers: reproduction
• Stem/shoot: support, transport, energy capture
• Leaves: gas exchange, photosynthesis
• Roots: water and nutrient absorption

Specialized Cells in the Plant

• Xylem: non-living cells that conduct water & minerals; one-way flow
• Phloem: sieve tube cells that transport sugars through the plant; two-way flow.

Other Specialized Structures

• Lenticels: pores in bark for gas exchange.
• Root hairs: extensions that increase the surface area for water & mineral absorption.
• Pollen: male gametes of plants.
• Seeds: embryonic plant, protective coating.
• Needles: retain water in coniferous trees.

The Cell Membrane (Plasma Membrane)

• Composed of a phospholipid bilayer with proteins, carbohydrates, and cholesterol.
• Semi-permeable, regulating material passage.
• Phospholipids are the main structure
• Proteins help transport materials.
• Carbohydrates recognize and bind substances.
• Cholesterol keeps the membrane fluid.

Phospholipid Bilayer

• Phospholipids have hydrophilic heads and hydrophobic tails.
• Arrange in a bilayer with heads facing outward (towards the water). Hydrophobic tails inward.

Fluid-Mosaic Model of the Cell Membrane

• Flexible and made of small, movable components.
• Cells are open systems; they gain materials and energy from the environment to maintain homeostasis.
• They control the movement of matter and energy through the membrane.
• They maintain equilibrium.

Meristem

• Unspecialized cells located throughout the plant.
• Site of cell division where cells begin to become specialized.
• Found in buds, leaves, flowers, and shoot tips.

Cells (Specialized Cells in the Leaf)

• Plants photosynthesize, taking CO₂ + H₂O + energy to produce sugars and O₂
• They also undergo cellular respiration like animals.

Stomata

• Holes on the underside of leaves where gas exchange and water loss occurs.