Human and Social Biology Syllabus

• Characteristics of living things

  • Excretion
  • Movement
  • Growth
  • Irritability
  • Reproduction
  • Nutrition
  • Respiration
  • Made up of cells
• Cell


  The structural unit of most organisms
• Cell organelles in plant and animal cells

  • Nucleus
  • Cytoplasm
  • Vacuole
  • Mitochondrion
  • Endoplasmic reticulum
  • Ribosome
  • Cell membrane
  • Cell wall
  • Chloroplast
• Bacteria


  • Have a simple cell structure
  • Surrounded by cell walls not made of cellulose
  • Some have a slime capsule
  • Have a nucleoid region with a loop of DNA within the cytoplasm - no nucleus
  • Some have flagella for movement

  
• Fungi


  • Most are multi-cellular
  • Each cell has a nucleus and a cell wall made of chitin
  • Reproduce by making spores
  • Most feed on dead or decaying matter
  • Require water, oxygen and suitable warm temperature
• Viruses


  • Not cells, but particles made up of genetic material (DNA or RNA) surrounded by a protein coat
  • Parasites that enter the cells of other organisms (host) to multiply
  • Do not respire, cannot make their own protein or genetic material
  • Take over host cells to produce new viruses
  • Can reproduce very quickly and do not respond to antibiotics
• Unspecialised cells


  Cells which divide and have no specific function, e.g. stem cells
• Differentiated cells


  Cells which develop to perform one specific function, forming tissues
• Types of differentiated cells and their functions

  • Muscle cell - contracts to bring about movement
  • Neurone (nerve cell) - transmits electrical impulses
  • Epithelial cell - covers surfaces, some have cilia
  • Ovum (egg cell) - female gamete
  • Sperm - male gamete
  • Red blood cell - transports oxygen
• Tissue


  A collection of similar cells working together to carry out the same function
• Main types of tissues

  • Epithelial
  • Connective
  • Nervous
  • Muscle
• Organ


  A collection of different tissues working together to carry out one function
• Organ system


  A collection of different organs and tissues working together to carry out one major function
• Diffusion


  Movement of molecules or ions from a region of high concentration to a region of low concentration until evenly distributed
• Osmosis


  Movement of water from a dilute solution to a more concentrated solution through a semi-permeable membrane
• Turgid cells


  Cells full of water so contents push against cell wall
• Flaccid cells


  Cells that have lost water and become limp
• Plasmolysis


  Movement of cell surface membrane away from cell wall when cell loses water
• Active transport


  Energy demanding transfer of a substance across a cell membrane, against its concentration gradient
• Photosynthesis


  Chemical process by which green plants make their own food in the presence of light energy
• Raw materials for photosynthesis

  • Water
  • Carbon dioxide
• Products of photosynthesis


  • Glucose (sugar)
  • Oxygen
• Producers


  Organisms that make their own food by photosynthesis
• Consumers


  Organisms that feed on producers
• Types of consumers


  • Herbivore
  • Carnivore
  • Omnivore
• Food chain


  Simple diagram showing feeding relationships between organisms

  
• Food web


  Shows interconnections of many food chains
• Trophic level


  The position an organism occupies in a food chain
• Decomposers


  Bacteria and fungi that feed on dead and decaying matter
• Plants capture only a small percentage of the sun's light energy that reaches them
• Energy is lost as food passes up the trophic levels, limiting the number of animals at each consumer trophic level</b>
• Reasons for energy loss up the trophic levels include undigested and unabsorbed food passing out in faeces, much energy used for respiration, and energy lost as heat to the environment
• Carbon cycle


  How carbon atoms are continuously taken up, converted into compounds and then recycled
• Nitrogen cycle


  The circulation of nitrogen in the atmosphere and nitrogen-containing substances in soil and living organisms

  
• The element nitrogen (N) is found in many organic molecules
• CO2 cycle


  1. Taken from atmosphere and water by photosynthesis in plants, algae and some photosynthetic bacteria

  2. Released to atmosphere and water by respiration in all organisms

  3. Released to atmosphere by combustion of wood and fossil fuels

  
• Fossil fuels


  Formed from the dead and fossilised remains of organisms, e.g. coal, oil, gas, peat
• Carbon cycle


  1. Carbon compounds pass along food chains from plants to herbivores and then to carnivores

  2. Decomposers feed on dead and decaying plant and animal matter and release CO2 by their respiration

  3. Some carbon compounds accumulate in carbon sinks and eventually form fossil fuels

  
• Importance of nitrogen cycle

  • Convert nitrogen from its un-reactive form (nitrogen gas) to its reactive forms (nitrates, nitrites and nitrogen oxides)
  • Makes nitrogen available for biological molecules, e.g. proteins, DNA, RNA
  • Allows nitrogen to be reused by living organisms

  
• Nitrogen fixation


  Bacteria convert nitrogen gas from the air into ammonium ions and nitrates