Chapter 11

• Organelles 


  Formed by molecules built together, are specialised structures or compartments within cells that have specific functions

  • an organelle's structure directly relates to its function
• Unicellular organisms are simpler than multicellular 


  Simple unicellular prokaryotes, such as species in Domains Archaea and Bacteria are though to be the earliest organisms to inhibit the earth.

  • prokaryotes are most widespread organisms but size and simplicity limits functions e.g. limited number of metabolic activities can be performed in a cell at once
• Paramecium: an example of a unicellular eukaryote 


  • within Kingdom Protista
  • found in ponds, slow-moving streams or enclosed areas containing water
  • obtains requirements for survival through surroundings
  • shaped like a football and covered in hair-like cilia that help it move
• Multicellular organisms are more complex

  • cells in multicellular organisms have different structures and functions
  • in unicellular organisms, one cell performs all functions while multicellular organisms cannot survive independently; they rely on other cells
• Cell specialisation 


  This specialisation can increase the efficiency with which an organism functions and can be essential for survival

  • The process a cell goes through to become specialised is called cellular differentiation
• 3 organising principles required for evolution of unicellular organisms to multicellular organisms 


  1. divide
  2. specialise
  3. communicate
• Differentiation 


  The process of a cell to become specialised is differentiation

  • Differentiation is the process by which cells in a multicellular organism become different from each other in structure and function -> this allows them to perform specific tasks effectively
• How differentiation occurs

  1. Differentiation begins with stem cells
  2. Gene expression
  3. Influencing factors
  4. Transcription and translation
  5. Development and specialisation
  6. Formation of tissues and organs
• Step One: Stem cells

  Stem cells are unique cells with potential to become various specialised cell types

  Characteristics that make them unique

  • Unspecialised: Can transform into various types of specialised cells depending on organism's needs
  • Potential for division and replication: Can divide and replicate for a long time, providing supply throughout organism life
  • Differentiation: Have potential to differentiate into different types of specialised cells, can become muscle cells, nerve cells, blood cells
• Step Two: Gene Expression


  Each cell type "switches on" different genes to produce the proteins it need for its specific function

  • Gene activation: environment and position of the cell in the organism influence which genes are activates -> results in the cell's specialisation
• Step Three: Influencing factors

  The surrounding environment of the cell can influence its differentiation -> includes signals from other cells, physical contact with other cells
• Step Four: Transcription and Translation

  • Transcription: The DNA in the cell's nucleus is transcribed into messenger mRNA
  • Translation: the mRNA is translated into proteins that will determine the cell's structure and function
• Step Five: Development and Specialisation

  • Developmental Pathways: During development, stem cells are guided by a combination of genetic instructions and environmental signals
  • Cell Shape and Function: as cells differentiate, they acquire unique shapes and functions
• Step Six: Formation of tissues and organs

  • Cell organisation: specialised cells organise into tissues and organs
  • Coordination: specialised cells work together within tissues and organs to perform complex functions
• Cellular differentiation occurs when stem cells transform, as a result of the activation of particular sets of genes

  • Mostly occurs during embryonic development
• Costs and Benefits of Specialisation

  Benefits: Specialised cells make the organism more efficient because each cell type performs its unique tasks well

  Costs: - Specialised requires coordination and communication between cells

  - Specialised cells depend on other cells to provide nutrients, oxygen and to remove wastes, if it is isolated from the rest of organisms it cannot function on its own and will die.
• Hierarchy of structures: from cells to multicellular organism

  cells -> tissues -> organs -> systems -> multicellular organisms
• Two systems of nutrients delivery in vascular plant

  Root system --comprised of parts below ground and is responsible for absorbing water and nutrients from the soil (roots and root hair)

  Shoot system -- comprised of all parts found above ground: plant, stem, leaves, and reproductive organs. It is responsible for supporting the plant physically, resource transport, absorption of oxygen and carbon dioxide, and carrying out photosynthesis in leaves
• Vascular Plants have four main types of plant tissues 


  • Meristematic -- meristems: found at tips of roots and shoots, are the only places where cells divide -> they enable growth in length and width
  • Dermal -- composed of the outermost cell layers of the plant (epidermis) -> it has a waxy cuticle to prevent water loss from leaves. Also contains root hairs which aid in absorption of nutrients
  • Ground -- composed of all internal cells -> specialised for storagem support and photosynthesis
  • Vascular -- involved in the transport of substances in the plant
• Animal bodies consist of 4 basic tissues

  Connective

  Epithelial

  Nervous

  Muscle
• Connective tissue 


  Provides support and holds body parts together, crucial in binding and supporting other tissues, protects against damage, infection, and heat loss

  • Examples: bone, adipose tissue, cartilage, ligaments
• Epithelial

  Covers the surface of the body and linings of body cavities such as airways, acts as a protective layer and barrier against infectious agents and water loss

  • Examples: stratified squamous -- found in outermost layers of skin, vagina, and mouth
• Types of epithelial:

  • Simple squamous -- found in lining of blood vessels and alveoli of lungs
  • Stratified Squamous -- found in outermost layer of skin, mouth, vagina
  • Simple Columnar -- found in digestive organ lining
  • Stratified Columnar -- found in mammary glands, lining of larynx
  • Simple Cuboidal -- lines kidney tubules and glands
  • Stratified Cuboidal -- found in lining of sweat gland ducts
• Nervous

  Provides the means of communication between all body structures, transmits nerve impulses

  • Examples: neurons
• Muscle 


  Comprises thin and thread-like cells called muscle fibres which use ATP energy to perform movements, these fibres can contract when stimulated by nerve impulses

  • Examples: skeletal muscle (voluntary, controlled with conscious thought), cardiac muscle (involuntary, moves without conscious thought), smooth muscle (involuntary muscle)