Study guide: Cell Transport and Surface Area

📋 Course Outline

1. Cells and Life Processes
2. Organelles and Protein Pathway
3. Elements and Biological Molecules
4. Membrane Structure and Permeability
5. Apoptosis and Particle Theory
6. Transport Across Cell Membranes
7. Tonicity and Water Movement
8. Active Transport Mechanisms
9. Surface Area and Volume

📖 1. Cells and Life Processes

🔑 Key Concepts & Definitions

• Cell: The smallest structural and functional unit of life and the smallest structure able to carry out all processes necessary for life.
• Organelle: A specialized structure inside a cell that performs a specific job.

★ Must-know

📌 An open system exchanges both matter and energy with its surroundings, a closed system exchanges energy but not matter, and an isolated system exchanges neither matter nor energy.

• Living cells are open systems because they exchange matter and energy with their surroundings.

Further detail

📌 Cells are structural units because all living things are made of cells, and functional units because they perform the processes needed to stay alive.

• Cell life processes include:
  • intake
  • nutrition
  • growth
  • gas exchange
  • reproduction
  • movement
  • response to stimuli
  • waste removal or excretion

📖 2. Organelles and Protein Pathway

★ Must-know

• The nucleus contains DNA and regulates many cell activities, while the nuclear envelope surrounds it and controls movement through nuclear pores.

📌 Ribosomes build proteins, rough ER processes proteins for transport or membranes, and smooth ER makes lipids and helps detoxify some substances.

• The Golgi apparatus modifies, sorts, and packages proteins and lipids.

• 🔄 A secreted protein follows this pathway:

  1. DNA in the nucleus provides instructions
  2. A ribosome builds the protein
  3. Rough ER helps it fold and undergo initial processing
  4. A transport vesicle carries it to the Golgi apparatus
  5. The Golgi modifies, sorts, and packages it
  6. A secretory vesicle carries it to the cell membrane
  7. The vesicle fuses with the membrane and releases the protein by exocytosis

Further detail

• Mitochondria carry out cellular respiration, which produces most of the cell’s ATP.

• The cell membrane controls entry and exit; the cell wall supports, protects, and shapes plant cells; and chloroplasts carry out photosynthesis.

• Other organelle functions include cytoplasm hosting many chemical reactions, lysosomes digesting waste and old cell parts, vesicles transporting or storing materials, vacuoles storing substances, the cytoskeleton helping maintain shape and organize movement or transport, and centrioles helping organize microtubules during cell division in many animal cells.

• Not every cell has every structure: mature human red blood cells lack a nucleus, and not all plant cells contain chloroplasts.

💡 Memory Hook

Follow a protein from DNA instructions to ribosome, rough ER, Golgi, and cell membrane.

📖 3. Elements and Biological Molecules

📝 Essential Points

• The four major biological elements are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), remembered as CHON; phosphorus and sulfur are also important in living things.

📌 Carbohydrates are built from simple sugars and provide energy, energy storage, and some structural support; examples include glucose, starch, glycogen, and cellulose.

• Lipids often include glycerol and fatty acids, vary in structure, and function in long-term energy storage, insulation, membranes, and some hormones; examples include fats, oils, phospholipids, and steroids.

• Proteins are built from amino acids and function in structure, enzymes, transport, signaling, and defense; examples include enzymes, antibodies, and hemoglobin.

• Nucleic acids are built from nucleotides and store, transmit, and use genetic information; DNA and RNA are examples.

💡 Memory Hook

CHON names carbon, hydrogen, oxygen, and nitrogen.

📖 4. Membrane Structure and Permeability

🔑 Key Concepts & Definitions

• Selective permeability: The property of allowing some substances to pass more easily than others, helping maintain relatively stable internal conditions called homeostasis.
• Phospholipid bilayer: The membrane’s main structure, consisting of two layers of phospholipids, each with a phosphate-containing hydrophilic head and two hydrophobic fatty acid tails.
• Fluid mosaic model: The membrane as a flexible phospholipid bilayer containing proteins and other molecules that can move within it.
• Aquaporin: Aquaporins are channel proteins that allow water to cross the membrane quickly without using ATP to pump it; water moves according to its gradient and the conditions on each side.

★ Must-know

📌 Hydrophilic heads interact favourably with water and face the watery fluids inside and outside the cell, whereas hydrophobic tails interact poorly with water and point inward.

📌 Small nonpolar molecules such as oxygen and carbon dioxide usually cross directly through the bilayer, while charged ions such as Na+, K+, Ca2+, and Cl− and large polar molecules such as glucose generally need transport proteins.

Further detail

• Membrane proteins can transport substances or receive signals; channel proteins form passages, carrier proteins bind substances and change shape to move them, and receptor proteins receive specific chemical signals.

• Cholesterol helps regulate fluidity and stability in animal-cell membranes, while glycoproteins and glycolipids have attached carbohydrate chains often involved in recognition or signaling.

💡 Memory Hook

Picture phospholipid heads facing water on both sides while their tails meet inward.

📖 5. Apoptosis and Particle Theory

🔑 Key Concepts & Definitions

• Apoptosis: Controlled programmed cell death in which a cell breaks itself down, helping normal growth and development, removing damaged or unnecessary cells, and maintaining healthy tissues.

★ Must-know

• The particle theory states that: all matter consists of tiny particles, particles of a pure substance share identical basic properties, spaces between particles depend on the state of matter, particles are always moving and usually move faster when heated, particles attract one another with strength depending on particle type and distance

Further detail

• Random particle movement helps explain diffusion, while water movement across a selectively permeable membrane is osmosis.

💡 Memory Hook

Apoptosis is controlled cell death; necrosis follows damage or injury.

📖 6. Transport Across Cell Membranes

🔑 Key Concepts & Definitions

• Diffusion: The net movement of particles from higher to lower concentration because of random particle motion; no direct ATP or membrane protein is required when particles pass directly through the bilayer.
• Osmosis: The net movement of water across a selectively permeable membrane from higher to lower water concentration; water tends toward the side with a higher concentration of dissolved, nonpenetrating solutes.
• Facilitated diffusion: Passive movement of a substance down its gradient through a membrane protein, without direct ATP expenditure.
• Cell transport: The movement of substances into or out of a cell across its membrane to take in nutrients and oxygen, remove waste, balance water and ions, and release substances.
• Concentration gradient: A difference in the concentration of a substance between two areas.
• Electrochemical gradient: A combination of concentration forces and electrical forces acting on charged particles.
• Equilibrium: A state in which concentrations are balanced and there is no net movement overall, although particles continue moving randomly in both directions.

★ Must-know

📌 Passive transport moves substances down a concentration or electrochemical gradient without direct ATP expenditure, whereas active transport requires energy directly or indirectly and often moves substances against a gradient or in vesicles.

• Movement down a concentration gradient is from higher to lower concentration, whereas movement against it is from lower to higher concentration and generally requires energy.

Further detail

• Oxygen and carbon dioxide can cross the cell membrane by simple diffusion.

• Osmosis requires no direct ATP, and water can cross the bilayer or move more quickly through aquaporins.

📌 Channel proteins form pathways for particular substances, whereas carrier proteins bind a specific substance and change shape to move it across the membrane.

📖 7. Tonicity and Water Movement

🔑 Key Concepts & Definitions

• Plasmolysis: A process in which a plant cell loses water and its membrane and cytoplasm shrink away from the cell wall, often in a hypertonic solution.
• Turgor pressure: The pressure of a plant cell’s contents against the cell wall when water enters by osmosis; the filled central vacuole pushes outward while the rigid wall resists expansion.

★ Must-know

• An isotonic solution has the same effective solute concentration outside and inside the cell, so there is no net water movement; an animal cell stays about the same size and a plant cell is often less firm.

• A hypertonic solution has a higher effective solute concentration outside the cell, so water moves out; an animal cell shrinks and a plant cell may undergo plasmolysis.

• A hypotonic solution has a lower effective solute concentration outside the cell, so water moves in; an animal cell swells and may burst, while a plant cell becomes turgid and firm.

Further detail

• Turgor pressure helps plant stems and leaves remain upright, and a turgid cell is firm and swollen with water.

• 🔄 Plasmolysis proceeds as follows:

  1. Water leaves by osmosis
  2. The vacuole becomes smaller
  3. The cell contents shrink
  4. The membrane pulls away from the cell wall

• A plant cell wall helps prevent a healthy plant cell from bursting when water enters, whereas an animal cell lacks a cell wall and can swell more in a hypotonic solution.

💡 Memory Hook

Hypertonic outside draws water out; hypotonic outside draws water in.

📖 8. Active Transport Mechanisms

🔑 Key Concepts & Definitions

• Protein pump: A membrane protein that uses energy to move specific substances across a membrane, often against their concentration or electrochemical gradient.
• Endocytosis: A process that brings material into a cell when the cell membrane surrounds it, folds inward, and forms an energy-requiring vesicle.
• Exocytosis: A process that releases material outside a cell when an energy-requiring vesicle moves to and fuses with the cell membrane, releasing its contents.

★ Must-know

• The sodium-potassium pump uses ATP to move sodium ions out of many animal cells and potassium ions into them, helping maintain gradients needed for normal cell function.

Further detail

• 🔄 A protein pump operates in this sequence:

  1. A substance binds to the pump
  2. Energy is supplied, often from ATP
  3. The pump changes shape and moves the substance across the membrane
  4. The pump returns to its original shape

• Materials released by exocytosis include:

  • Proteins
  • Hormones
  • Neurotransmitters

💡 Memory Hook

For a pump: bind, energize, change shape, transport, reset.

📖 9. Surface Area and Volume

🔑 Key Concepts & Definitions

• Surface area: The total area of an object’s outside surfaces.
• Volume: The amount of space an object occupies.

★ Must-know

📐 Formula - The surface area of a rectangular prism is $SA = 2(LW) + 2(LH) + 2(WH)$, where $L$ is length, $W$ is width, and $H$ is height; surface area is measured in square units such as $\mathrm{cm}^2$ or $\mathrm{mm}^2$.

📐 Formula - The volume of a rectangular prism is $V = LWH$, and volume is measured in cubic units such as $\mathrm{cm}^3$ or $\mathrm{mm}^3$.

📐 Formula - The surface-area-to-volume ratio is calculated as $SA:V = \frac{SA}{V}$.

Further detail

📌 Smaller cells generally have a higher surface-area-to-volume ratio, whereas larger cells generally have a lower ratio.

• The cell membrane is the surface through which many substances enter and leave, while cell volume represents the material needing nutrients and producing waste.

• Cells can remain small, divide, or develop folds or extensions to support exchange.

• For a rectangular cell measuring 2 cm by 1 cm by 1 cm, the surface area is 10 cm², the volume is 2 cm³, and the surface-area-to-volume ratio is 5:1.

📊 Synthesis Tables

Passive Transport Comparison