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Questions and Answers

What is the definition of a concentration gradient?

A difference in concentration of a substance across a membrane.

What does dynamic equilibrium mean in the content of cell transport?

Equal concentrations of substances on either side of the membrane, with substances still moving back and forth across the membrane at an equal rate.

Water can easily pass through the cell membrane using simple diffusion.

True

Which of the following molecules would require a transport protein to move across a membrane?

Glucose ($C_6H_{12}O_6$) Signup and view all the answers

Define passive transport.

Movement of substances across a membrane that doesn't require the cell to expend energy. Signup and view all the answers

What are the three types of passive transport?

Osmosis Signup and view all the answers

What is diffusion?

The net movement of particles from an area of high concentration to an area of low concentration. Signup and view all the answers

What is osmosis?

The net movement of water across a semi-permeable membrane from an area of high water concentration to an area of low water concentration. Signup and view all the answers

What is facilitated diffusion?

The passive transport of molecules across a membrane with the help of transport proteins. Signup and view all the answers

Which of these is NOT a type of transport protein?

Sodium-potassium pump Signup and view all the answers

What is active transport?

The movement of substances across a membrane that requires the cell to expend energy. Signup and view all the answers

How does the Sodium-Potassium pump work?

It actively transports sodium ions ($Na^+$) out of the cell and potassium ions ($K^+$) into the cell. Signup and view all the answers

What is the function of the proton pump?

Actively transports hydrogen ions ($H^+$) out of the cell, creating a concentration gradient that can be used for other processes. Signup and view all the answers

Explain endocytosis.

The process by which cells take in large molecules or substances by forming new vesicles from the cell membrane. Signup and view all the answers

What are the two types of endocytosis, and how do they differ?

Phagocytosis, the process where cells engulf large particles like food or bacteria, and pinocytosis, the process where cells engulf droplets of liquid including small solutes or nutrients. Signup and view all the answers

Define tonicity.

A comparison of the solute concentration of a solution to the solute concentration of a cell or other solution. Signup and view all the answers

What is receptor-mediated endocytosis?

The process of cells taking in specific substances by using protein receptors on their cell membrane. Signup and view all the answers

What happens to a red blood cell placed in a hypotonic solution?

The cell swells and may burst Signup and view all the answers

Which of the following describes the mechanism of transport in the xylem?

A combination of active and passive transport Signup and view all the answers

Which of the following is NOT a factor that influences the transport of water in the xylem?

Adhesion Signup and view all the answers

What is the pressure flow theory?

A theory that explains how sugars are transported in the phloem from the source to the sink. Signup and view all the answers

What is the significance of the surface area to volume ratio (SA:VOL) for cells?

It determines the efficiency of a cell in exchanging materials with its surroundings. Signup and view all the answers

Smaller cells have a higher surface area to volume ratio than larger cells.

True Signup and view all the answers

Which of the following is NOT a way that large, multicellular organisms solve the limitations of size and SA:VOL?

Having cells that are independent of each other Signup and view all the answers

What is the hierarchy of organization found in multicellular organisms?

The organization from cells, to tissues, to organs, organ systems, and finally the whole organism. Signup and view all the answers

What are the two primary organ systems in plants?

The shoot system, which includes everything above ground, and the root system, which includes everything below ground. Signup and view all the answers

Which type of cell is responsible for transporting water and minerals in plants?

Xylem cell Signup and view all the answers

What are some examples of specialized structures in plants, and what are their functions?

Lenticels: lens-shaped pores in the bark of trees that allow gas exchange. Root hairs: small growths that increase the surface area of roots for water and nutrient absorption. Pollen: male gametes for reproduction. Seeds: embryonic plants enclosed in a protective coating. Needles: modified leaves that help retain water in coniferous trees. Signup and view all the answers

What is the function of meristem tissue in plants?

Meristematic tissue is responsible for cell division and growth in plants. Signup and view all the answers

Which of these is NOT one of the functions of a leaf?

Water absorption Signup and view all the answers

Which type of cell is responsible for transporting sugars produced during photosynthesis?

Phloem cell Signup and view all the answers

What are stomata, and what is their function?

Stomata are small pores or openings found on the underside of leaves that control the exchange of gases and water vapor. Signup and view all the answers

What is the role of guard cells in stomata?

Guard cells regulate the opening and closing of stomata, controlling gas exchange and water loss in plants. Signup and view all the answers

Why is the cell membrane described as a fluid mosaic model?

It is flexible and made up of different components, including phospholipids, proteins, and carbohydrates, that move within the membrane structure. Signup and view all the answers

How do phospholipids contribute to the structure of the cell membrane?

They form a bilayer, with their hydrophilic heads facing towards the watery environments (extracellular fluid and cytoplasm) and their hydrophobic tails facing inward, creating a barrier. Signup and view all the answers

What are the main functions of the proteins embedded within the cell membrane?

Proteins can act as transport channels, carriers for the passage of molecules across the membrane, and they can also act as receptors for cell signaling and recognition. Signup and view all the answers

What is the function of cholesterol in the cell membrane?

Cholesterol helps to maintain membrane fluidity and stability by preventing the fatty acid tails from packing too tightly together. Signup and view all the answers

Study Notes

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.

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