Cells and Tissues

• Cells

  The smallest structure that can perform life's functions - they are the basic structural and functional unit of all living things
• Organisms (living things) can be made of one or many cells
• Humans contain approx. 37.2 trillion cells
• The structure and function of the human body is a result of all of its cells
• Cells


  • They vary in shape and size, but they all have the same basic structure
• Parts of a cell

  • Cell membrane
  • Cytoplasm
  • Organelles
  • Cytosol
  • Cytoskeleton
  • Inclusions
• Cell membrane

  Outer boundary of the cell, separating it from neighbouring cells and external environment
• Cytoplasm


  Jelly-like fluid inside cells and the organelles suspended in it (excluding nucleus)
• Cytosol


  Liquid part of the cytoplasm - 75-90% water, mixture of dissolved substances and non-soluble substances suspended in fluid
• Cytoskeleton


  Framework of protein fibres giving cell shape and assisting in movement
• Inclusions


  Chemical substances (granules or liquid droplets) in cytoplasm
• Organelles


  • Nucleus
  • Mitochondria
  • Golgi body
  • Endoplasmic Reticulum
  • Ribosomes
  • Lysosomes
  • Cilia and Flagella
• Nucleus


  Almost all cells have a single nucleus, which is the largest organelle and has an oval/spherical shape. It contains the inherited information (DNA) that determines the structure and function of the cell.
• Mitochondria


  Sausage-shaped organelles spread throughout the cytoplasm, with a double membrane. They are the site of some cellular respiration reactions, thus making energy available for the cell's activity.
• Golgi body


  Series of flattened membranes stacked on top of each other, usually near the nucleus. Proteins produced at ribosomes pass through ER channels to the Golgi body where they are modified and packaged into small sacs of liquids surrounded by a membrane (vesicles) for secretion from the cell.
• Endoplasmic Reticulum


  Pairs of parallel membranes extending through the cell from the nucleus to the cell membrane, creating channels. It provides a surface for chemical reactions and channels for storing/transporting molecules. Rough ER has ribosomes attached while Smooth ER does not.
• Ribosomes


  Very small, spherical organelles that are the site at which amino acids are joined to make proteins. They can be free in the cytoplasm or attached to membranes (e.g. endoplasmic reticulum).
• Lysosomes


  Small spheres bound by a membrane and formed from the Golgi body. They contain digestive enzymes that can break down large molecules and worn-out organelles.
• Cilia and Flagella


  Fine projections that can beat back and forth. Cilia are short and numerous, while flagella are longer and fewer in number.
• Fluid compartments in the body


  • Intracellular fluid
  • Extracellular fluid (Intercellular fluid/Tissue fluid and Intravascular fluid/Blood plasma)
• Cell membrane


  The outer boundary of the cell that separates it from the external environment and neighbouring cells. It is made of a double layer of lipids and associated proteins, and is differentially permeable - allowing some substances in/out but not others.
• Passive transport


  A process where substances move across the cell membrane without the expenditure of cellular energy
• Active transport


  A process where substances are moved across the cell membrane using cellular energy, usually in the form of ATP supplied by mitochondria
• Diffusion


  The movement of substances from an area of high concentration to an area of low concentration, driven by a concentration gradient
• Osmosis


  The movement of water molecules across a semi-permeable membrane from an area of high water concentration to an area of low water concentration
• Facilitated diffusion


  The movement of substances across the cell membrane with the help of carrier proteins, driven by a concentration gradient but requiring no cellular energy
• Vesicular transport


  The movement of substances across the cell membrane enclosed within membrane-bound vesicles, requiring cellular energy
• Endocytosis


  The process of a cell engulfing material from the extracellular environment by forming a vesicle around it
• Exocytosis


  The process of a cell secreting material to the extracellular environment by fusing a vesicle with the cell membrane
• Phagocytosis


  A type of endocytosis where the cell engulfs large particles or even whole cells
• Pinocytosis


  A type of endocytosis where the cell engulfs small droplets of extracellular fluid
• The mitochondria supply the energy for active transport processes in the form of ATP
• As the size of a cell increases


  The surface area-to-volume ratio decreases, which can affect the rate of processes like diffusion
• As the concentration gradient of a substance increases


  The rate of diffusion of that substance increases
• The chemical nature of materials being exchanged


  Affects their movement across a cell membrane
• Active transport process


  Process that requires energy to move substances across a cell membrane against a concentration gradient
• Active transport


  1. Role of carrier proteins

  2. Energy requirements (ATP from mitochondria)
• Substances transported by active transport


  • Certain ions
  • Glucose
  • Amino acids
• Vesicular transport


  Movement of substances across a cell membrane in membranous sacs called vesicles
• Endocytosis


  Taking in liquids (pinocytosis) or solids (phagocytosis) into the cell