Biology: Basic Functions and Cell Structures

Seven Basic Functions of Living Things

• Metabolism: Chemical reactions are essential for survival.
• Reproduction: Living things produce offspring through sexual or asexual processes.
• Sensitivity: Living things respond to internal and external stimuli.
• Homeostasis: Maintaining a stable internal environment is crucial.
• Excretion: Removal of waste products is necessary.
• Nutrition: Exchange of materials and gases with the environment.
• Growth/Movement: Living things can move and change shape or size.

Four Common Structures in All Cells

• Plasma Membrane: An outer border that maintains an internal chemistry distinct from the exterior.
• Genetic Material: Coded instructions control internal cell activities.
• Ribosomes: Ribosomes translate coded cell instructions into functional elements.
• Cytoplasm: Internal fluid that serves as a medium for metabolic processes.

Prokaryotic Cells

• Genetic material resides in the nucleoid region of the cytoplasm.
• Ribosomes are small (70S) and responsible for protein synthesis.
• All prokaryotes possess a cell wall; some have an outer coating.
• Pili are hair-like extensions that aid in adhesion.
• Flagella are whip-like projections that enable movement.

Drawings of Prokaryotic Cells

• Genetic material should be represented as a loop.
• Pili and flagella extend from the cell wall.
• Ribosomes are depicted as filled dots labeled 70S.
• Flagella are thicker and longer than pili.
• Shape should reflect the specific type of bacteria.

Eukaryotic Organisms

• Cells contain a nucleus and numerous membrane-bound organelles.
• Exhibit a higher level of structural complexity.
• Four types: Animal, Plant, Fungi, and Protist.

Eukaryotic Cells

• Genetic material is housed within the nucleus, a double-membrane structure.
• Ribosomes are larger (80S).
• Share membrane-bound organelles: mitochondria, endoplasmic reticulum, Golgi apparatus, vesicles.
• Plant cells also possess chloroplasts and a large central vacuole.

Drawings of Eukaryotic Animal Cells

• Nucleus should be a double membrane structure with pores.
• ER network is connected membranes, while Golgi membranes are unconnected.
• Ribosomes are filled dots labeled 80S.
• Mitochondria are sausage-shaped with highly folded inner membranes.
• Peroxisomes, lysosomes, and secretory vesicles have similar appearances.

Drawings of Plant Cells

• A large central vacuole occupies significant space.
• Cell wall made of cellulose is a thicker external line.
• Chloroplasts are double-membrane structures with internal stacks of flattened discs.

Microscopes

• Scientific instruments used to visualize objects too small for the naked eye.
• Two main types: Light and Electron.

Light Microscopes

• Use glass lenses to bend light and magnify images.
• Employ visible light and lenses to magnify mounted specimens.
• Include ocular and objective lenses.

Electron Microscopes

• Provide much higher magnification and resolution than light microscopes.
• Cannot view living specimens in natural color.

Calculating Magnification

• Formula: Magnification = Image size ÷ Actual size
• Image size and actual size must be in the same units.

Stem Cells

• Undifferentiated cells capable of dividing and differentiating into various cell types.
• Found in plants and animals.
• Plant stem cells are located in meristems (root and shoot tips).
• Animal stem cells are found in embryos, adult tissues (bone marrow, blood cells), and cord blood.
• Used in treating diseases like leukemia, lymphoma, and diabetes.

Stem Cell Characteristics

• Self-renewal: Continuous division and replication.
• Potency: Capacity to differentiate into specific cell types.

Stem Cell Niches

• Locations where stem cells reside, including bone marrow, hair follicles, heart, intestines, and brain.
• Bone marrow: Haemopoietic stem cells give rise to different blood cell types.
• Hair follicles: Contain epidermal stem cells involved in hair growth and wound repair.

Cell Membrane

• Encloses the cell, separating internal components from the external environment.
• Controls internal conditions and maintains homeostasis.
• Semi-permeable: Allows only certain materials to cross.
• Selective: Regulates the passage of materials that cannot freely cross.

Cell Membrane Components

• Phospholipid bilayer: Forms a barrier to certain materials.
  • Hydrophobic core limits permeability to large and charged substances.
• Membrane proteins: Embedded within the phospholipid bilayer, acting as transport points for large and charged substances.
  • Enable the transport of hydrophilic materials according to need.

Phospholipids

• Composed of a polar head (glycerol and phosphate) and two non-polar tails (fatty acid chains).
• Hydrophilic (water-loving) head region faces outwards.
• Hydrophobic (water-repelling) tail region faces inwards.
• Spontaneously arrange into a bilayer.

Phospholipid Bilayer Properties

• Held together by weak hydrophobic interactions between tails.
• Restricts the passage of many substances.
• Individual phospholipids move within the bilayer, contributing to fluidity and flexibility.
• Allows for spontaneous breaking and reforming of membranes.

Movement Across Biological Membranes

• Passive transport: Movement along a concentration gradient (high to low).
  • Simple diffusion: Movement of small or lipophilic molecules across the bilayer.
  • Osmosis: Movement of water molecules through the bilayer.
  • Facilitated diffusion: Movement of large or charged molecules via transmembrane proteins.
• Active transport: Movement against a concentration gradient (low to high).
  • Primary active transport: Uses ATP hydrolysis to move a molecule against its gradient.
  • Secondary active transport: Couples movement of one molecule against its gradient to another molecule moving down an electrochemical gradient.

Osmosis

• Special form of simple diffusion involving the movement of free water molecules.
• Water acts as a solvent, dissolving polar or charged molecules to create a solution.
• Water, being small enough to move between phospholipids, facilitates this movement.
• The net movement of water goes from a region of low solute concentration to a region of high solute concentration.
• Solutions can be categorized as hypertonic, hypotonic, or isotonic based on their relative solute concentrations.
• Hypertonic: Higher solute concentration.
• Hypotonic: Lower solute concentration.
• Isotonic: Equivalent solute concentrations.