SEM 2

• Characteristics of species living on Earth

  • Use a source of energy
  • Gain nutrients, grow, reproduce
  • Respond to stimuli
  • Excrete wastes
  • Are made of cells
• Autotrophs and Heterotrophs


  • Acquire energy and nutrients differently
• Photosynthesis


  A series of reactions that occur in the stroma and thylakoid membrane system of the chloroplast
• Chlorophyll


  Absorbs light energy and makes it available for use in photosynthesis
• Chloroplasts are oval-shaped organelles found in some eukaryotic cells that contain chlorophyll
• Photosynthesis reactions


  Carbon dioxide and water combined to produce glucose, oxygen and water
• Cellular respiration


  1. First stage in cytoplasm

  2. Final stage in mitochondria
• Mitochondria


  • Small, oval-shaped structures found scattered throughout the cytosol
  • Outer smooth membrane
  • Highly folded inner membrane
• Crista


  Folds in the inner membrane of mitochondria that provide features for cellular respiration
• Crista features


  • Enzymes for cellular respiration located mainly on cristae
  • Numerous folds provide large surface area for chemical reactions
• Variety of cells


  • Vary in size
  • Shape
  • Composition
  • Function
  • Mobility
• Unicellular organisms carry out all processes needed to support life
• Cells in multicellular organisms may carry out a specialised role and rely on other cells
• Requirements of cells


  • Gases for photosynthesis and respiration
  • Excretion of wastes
  • Ions for muscle and nerve cell function
  • Water for biochemical reactions
  • Nutrients for growth and development
• Common features of all cells


  • Contents enclosed in a cell membrane
  • Semi-fluid substance called cytosol
  • Contain chromosomes with genes
  • Have ribosomes to make proteins
• Prokaryotic cells


  • No membrane-bound organelles
  • One single circular chromosome
  • Unicellular
  • Relatively small (1 – 10 micrometers)
• Eukaryotic cells


  • Size 10–100mm in length and 0.2–2.0mm in diameter
  • Membrane-bound organelles
  • Cytoplasm made up of cytosol and organelles
  • Ribosomes synthesize proteins
  • Membrane-bound nucleus contains DNA
• Prokaryotes


  • Have ribosomes but lack membrane-bound organelles
  • Do not have a nucleus
  • Significantly smaller than eukaryotes
  • Usually have a single, circular chromosome made of DNA
• Eukaryotes


  • May be unicellular or multicellular
  • Cells are larger and more complex than prokaryotes
  • Contain many different membrane-organelles
  • Nucleus contains linear chromosomes
• Photosynthesis

  • Main organelle: chloroplast
  • Converts the Sun’s light energy into stored chemical energy in the form of carbohydrates
  • Reactants: carbon dioxide and water
  • Other essential inputs: light energy and chlorophyll
  • Products: glucose and water
• Respiration

  • Main organelle: mitochondria

  The chemical bonds in glucose are broken, providing energy in the form of ATP

  Reactants: glucose and oxygen

  Products: carbon dioxide and water

  Other significant output: Energy in the form of ATP
• Metabolism describes the sum of total of the physical and chemical processes by which cell components transform matter and energy to sustain life
• Heterotrophs consume autotrophs or other heterotrophs to gain energy and nutrients for assimilation
• Autotrophs use photosynthesis to produce glucose, a form of stored chemical energy
• Organisms made of one cell are called unicellular
• Organisms made of more than one cell are called multicellular. They consist of cells organised into functional groups of tissues, organs and systems.
• Prokaryotic cell

  • E.g. Cyanobacteria, methanogens, nitrogen-fixing bacteria, archaea, eubacteria
  • Nucleus = Absent
  • Size = Most in range 1-10 µm
  • Genetic material is found clumped in a region of the cytoplasm called the nucleoid; DNA occurs as a single circular chromosome or smaller circular plasmids
  • Ribosomes are small but may be numerous (up to 350 000 per cell)
  • Cell wall is usually present, complex composition including peptidoglycan
  • Membrane enclosed organelles Absent
  • Cell division is usually binary fission
• Eukaryotic cell


  A type of cell with a nucleus and membrane-bound organelles
• Nucleus


  • Present and containing nucleoli
• Size of eukaryotic cells
• Genetic material


  • DNA wrapped around proteins, called histones in nucleus
  • Located on linear chromosomes when cells divide
• Ribosomes


  • Large (small ones may be inside some organelles)
• Cell wall


  • Present in plant and fungi cells
  • Simple composition (cellulose)
• Membrane enclosed organelles


  • Present, including mitochondria
  • Lysosomes
  • Endoplasmic reticulum
  • Golgi bodies
  • Chloroplasts (in plant cells)
• Cell division


  Mitosis
• Organelles: Any specialised structure within a living cell, allow cells to carry out their function
• Organelle word bank


  • Nucleus
  • Cell Membrane
  • Nucleolus
  • Cytoplasm
  • Cytosol
  • Endoplasmic Reticulum
  • Mitochondria
  • Golgi Body
  • Ribosomes
  • Lysosomes
  • Centrioles
  • Chloroplasts
  • Cell Wall
  • Large Vacuole
• Nucleus


  A large organelle containing DNA and is the control centre of the cell
• Cell Membrane


  Semi-permeable membrane made of a phospholipid bi-layer that surrounds a cell and determines what enters/exits the cell
• Nucleolus


  Involved in production of ribosomes