CIE IGCSE bio

• • Sensitivity: the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses
• • Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both
• • Reproduction: the processes that make more of the same kind of organism
• Xylem functions:

  • To transport water/mineral salts / named salts/ions from roots to leaves.
  • To provide structural support
  • Transpiration
• Phloem functions :

  Transport amino acids / sugars / sucrose / organic materials from leaves to storage area or place of use

  Translocation
• root hair cell:

  Increases the surface area of the root for absorption of water and mineral ions. Provides anchorage for the plant
• Each root hair is a long epidermal cell; this increases the surface area for absorption
• Root hairs are long & thin and so can penetrate between the smallest soil particles for absorption
• pathway taken by water

  Root hair cells --> Root cortex cells--> xylem of root --> xylem of stem -->xylem of leaf -->mesophyll cells
• Transpiration is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
• why wilting occurs?

  To prevent huge water loses through transpiration
• transpiration factor: increase in temperature

  
  

  explanation: increases the kinetic energy of the water molecules so they diffuse faster
• transpiration factor: increase in light intenisty

  explanation: stomata open to allow gas exchange for photosynthesis so water vapor can diffuse out the leaf
• Translocation ‐ movement of sucrose and amino acids in phloem, from regions of production or of storage to regions of use for respiration or growth
• 'Source' is the part of a plant where substances are produced (e.g. leaves for sucrose, amino acids) or enter the plant.
• in summer, the leaves are sources and the growing stem tubers are sinks.
• In spring, the stem tubers are sources and the growing leaves are sinks.
• Pathogen is a disease‐causing organism
• Transmissible disease is a disease in which the pathogen can be passed from one host to another
• Active immunity is defence against a pathogen by antibody production in the body
• Antibodies lock on to antigens leading to direct destruction of pathogens, or marking of pathogens for destruction by phagocytes
• mechanical barriers, limited to skin and hairs in the nose
• chemical barriers, limited to mucus and stomach acid
• cells, limited to phagocytosis and antibody production by white blood cells
• Memory cells are not produced in passive immunity
• Pathogens have markers on their surface membranes called antigens
• Antibodies stick to these antigens and destroy the pathogen. or marking them for phagocytes to act on them.
• A person has active immunity to a disease if they have made their own antibodies and memory cells that protect against it. These memory cells can last for many years.
• passive immunity lasts for a short time because the antibodies eventually break down. No lymphocytes have been stimulated to make clones and the body hasn’t made memory cells.
• Antibodies are passed from mother to baby through breast feeding or across the placenta during pregnancy.
• The immune system is the body’s defence against disease and foreign bodies. There are two main types of white blood cells – lymphocytes & phagocytes:
• phagocytosis:

  •  Phagocytes have the ability to move out of capillaries to the site of infection;
  • They then engulf (ingest) the infecting pathogen and kill them by digesting them. A process called phagocytosis.
• Wall of the alveolus is thin (a single layer of cells) to allow gases to diffuse across them quickly
• alveolus walls have a large surface area so that a lot of gas can diffuse at the same time
• alveolus walls are moist to prevent cells from dying and allow gases to dissolve
• alveolus walls have a high concentration gradient ‐ maintained by the movement of air & blood.
• circulatory system


  system of blood vessels with a pump and valves to ensure one-way flow of blood

  
• Single circulatory system


  Blood only passes once through the heart

  
• Double circulatory system


  Blood completes two cycles around the heart before leaving to the rest of the body

  
• Advantages of double circulation


  Deliver greater blood flow rate to tissues around body