Cells & Transport

Unit 1 - Human Biology ATAR: Cells & Transport

Organisation of Systems

• Hierarchy of Organisation:

  • Cells → Tissues → Organs → Systems

  • Specialisation: Each level of structure contributes to the overall function of the human body.

    • Example: Muscle cells (specialised) combine to form muscle tissue, which makes up the heart (organ), which is part of the circulatory system (system).

Levels of Classifying Body Systems

• Understanding Functionality:

  • Importance lies in knowing how organs, tissues, and cells cooperate to support daily functions of the body.

Structure of the Cell

• Key Organelles:

  • Nucleus

  • Cell Membrane

  • Cytoplasm

  • Mitochondria

  • Endoplasmic Reticulum

  • Golgi Apparatus

  • Ribosomes

  • Vacuole

  • Lysosome

  • Cytoskeleton

Structure of the Cell Organelles

• Definition of Organelles:

  • Organelles are specific cellular structures that carry out distinct functions.

  • Example: The nucleus contains genetic material essential for cell regulation and control.

Cell Membrane

• A double layer composed of lipid molecules (phospholipids and cholesterol) and various proteins.

• Properties:

  • Semi-permeable: Only allows certain materials to pass through it.

  • Selective Permeability: Depends on material type and transport method.

• Transport Mechanisms:

  • Passive Transport: Includes diffusion and osmosis.

  • Active Transport: Includes phagocytosis and pinocytosis.

Cytoplasm

• Description:

  • Material in which cell contents are suspended.

  • Composition: 75–90% water.

  • Types of Substances in Cytoplasm:

  • Dissolved: Sugars and inorganic materials.

  • Suspended: Proteins and lipids.

• Protoplasm: The sum of the cytoplasm and nucleus.

Nucleus

• Structure:

  • Surrounded by a nuclear membrane (double-layer with nuclear pores).

• Functionality:

  • Contains DNA that dictates protein synthesis and regulates cell activities.

  • Chromatin: DNA in non-dividing cells; forms chromosomes during cell division.

Nucleolus

• Description:

  • Substructure within the nucleus.

• Composition: Primarily made of RNA, crucial for protein synthesis.

• Suspension: Both nucleolus and chromatin are suspended within the nucleoplasm.

Ribosomes

• Characteristics:

  • Small, spherical organelles; can be free in cytoplasm or bound to endoplasmic reticulum.

• Function:

  • Synthesize proteins by linking amino acids in accordance with DNA sequences.

Mitochondria

• Shape: Can be spherical or elongated.

• Membranes: Double membrane structure (outer is smooth, inner is folded).

• Functionality:

  • Known as the ‘powerhouse of the cell’; site of ATP production via cellular respiration.

Endoplasmic Reticulum (ER)

• Structure: Parallel membranes forming a network of channels.

• Types:

  • Rough ER: Ribosomes attached (granular).

  • Smooth ER: No ribosomes (agranular).

• Functions:

  • Offers a surface for chemical reactions; inner channels store and transport molecules.

Golgi Apparatus

• Structure: Layered, flattened membranous bags.

• Functions:

  • Modifies, packages, and secretes proteins.

  • Can add various molecules (sugars, phosphates, etc.) to proteins.

  • Forms vesicles for transporting modified proteins out of the cell.

Centrioles

• Description: Pair of cylindrical structures near the nucleus.

• Structure: Made up of triplet microtubules arranged perpendicularly to one another.

• Function: Essential role in cell division (mitosis).

Lysosome

• Description: Contains digestive enzymes.

• Functionality:

  • Breaks down lipids, proteins, nucleic acids, and some carbohydrates.

  • Digests worn-out organelles and contents from vesicles.

Cytoskeleton

• Description: Network of protein fibers that provide structural support to the cell.

• Components:

  • Microtubules: Hollow rods that stabilize and fix organelles.

  • Microfilaments: Involved in movement within the cytoplasm and can move the entire cell.

Cilia and Flagella

• Function: Projecting structures aiding in movement of materials or entire cells.

• Types of Projections:

  • Cilia: Shorter, fine projections (e.g., respiratory tract).

  • Flagella: Longer, fewer projections (e.g., sperm).

Inclusions / Extras

• Description: Non-cellular components (e.g., melanin in skin, hemoglobin in RBC).

• Vacuoles: Liquid inclusions surrounded by a membrane, primarily used for storage; more common in plant cells.

Cell Membrane Structure, Passive vs. Active Transport & Cell Size

The Cell Membrane

• Composition: Phospholipid bilayer with embedded proteins.

• Properties: Semi-permeable;

  • Hydrophilic Heads: Attracted to water.

  • Hydrophobic Tails: Repel water.

Membrane Proteins

• Variety of Functions: Include transport, receptor sites for hormones.

Movement through the Membrane

• Diffusion Limitations: Water-soluble substances cannot easily diffuse through the lipid bilayer; exceptions include oxygen and carbon dioxide.

Membrane Transport Proteins

• Channel Proteins: Facilitate simple diffusion (e.g., ion channels for Na+, K+).

• Carrier Proteins: Enable facilitated diffusion and active transport processes.

Membrane Transport

• Passive Processes:

  • Characteristics: No cellular energy required; substances move from high to low concentration.

  • Examples: Diffusion, osmosis, facilitated diffusion.

• Active Processes:

  • Characteristics: Requires ATP; substances move from low to high concentration (against gradient).

  • Examples: Specific membrane pumps, phagocytosis, pinocytosis.

Surface Area to Volume Ratio

• Importance of Size: Smaller cells maintain a favorable surface area to volume ratio for efficient material exchange.

• Consequences of Cell Growth: As a cell grows, its volume increases faster than surface area, limiting its capacity to exchange necessary materials.

• Example: A cell doubled in diameter has volume increase by 8 times and surface area increase by 4 times.

Types of Transport

Passive Transport

• Processes Included:

  • Diffusion

  • Osmosis

  • Facilitated Diffusion

Active Transport

• Processes Included:

  • Active Transport

  • Vesicular Transport (Endocytosis: Phagocytosis, Pinocytosis; Exocytosis)

Diffusion

• Definition: Movement of particles from high concentration to low concentration due to kinetic energy.

Simple Diffusion

• Description: Simple diffusion involves direct movement from high to low concentration.

Facilitated Diffusion

• Definition: Process whereby molecules move across cell membranes with the assistance of transport proteins.

  • Passive: No ATP required; occurs along the concentration gradient.

  • Examples: Glucose, amino acids.

Concentration Gradient

• Definition: Difference in concentration of a substance across two regions, driving diffusion until equilibrium is reached.

Osmosis

• Definition: Specific diffusion of water across a selectively permeable membrane.

  • Water moves from high concentration to low concentration; passive process, no ATP required.

Active Transport

• Requirements: Energy (ATP); substances move from low concentration to high concentration, against the concentration gradient.

  • Example: Sodium (Na+) pump.

Endocytosis

• Description: Process where cells engulf large particles to form vesicles in the cytosol.

  • Types:

  • Phagocytosis: “Cell eating” for large particles.

  • Pinocytosis: “Cell drinking” for small particles.

Endocytosis & Exocytosis

• Definitions:

  • Endocytosis: Intake of substances into the cell.

  • Exocytosis: Release of substances from the cell.

Overview of Learning

• Key Definitions:

  • Simple Diffusion

  • Passive Transport

  • Facilitated Diffusion

  • Active Transport

  • Vesicles

  • Pumps

  • Osmosis

  • Channel Proteins

  • Carrier Proteins

  • Exocytosis

  • Endocytosis

  • Isotonic, Hypertonic, Hypotonic conditions

  • Types of Endocytosis: Phagocytosis, Pinocytosis.

Tissue Types

Overview of Tissues

• Tissues are the 2nd structural level in biological organization, groups of similar cells that work together for a specific function.

• Four Main Types of Tissues:

  • Epithelial

  • Connective

  • Muscular

  • Nervous

1. Epithelial Tissue

• Function: Covers or lines organs; forms the outer layer of skin.

  • Characteristics: Cells closely packed; varied shapes (squamous, cuboidal, columnar).

2. Connective Tissue

• Function: Provides support and holds various parts of the body together.

  • Characteristics: Cells are spread out, separated by matrix (non-cellular material).

  • Examples: Bone, cartilage, tendons, ligaments, fat storage tissue, blood.

3. Muscular Tissue

• Function: Responds to stimuli by contracting.

  • Characteristics: Long, thin muscle fibers.

  • Types:

  • Skeletal Muscle: Voluntary control, striated, attached to bones.

  • Cardiac Muscle: Involuntary control, heart muscle that pumps blood, striated.

  • Smooth Muscle: Involuntary, found in walls of hollow organs (e.g., stomach, blood vessels).

4. Nervous Tissue

• Description: Comprised of neurons that transmit signals.

• Location: Found in brain, spinal cord, and nerves.

Microscopes & Field of View (FOV)

• Tasks:

  • Understanding Field of View (FOV) in microscopy.

Mini Grids for Magnification: