human and plant organs

• diffusion in the liver

  
• diffusion in leaves is a passive process, so it requires no energy from the sun

  
• diffusion in the aveolus

  
• diffusion

  particles (molecules and ions) in a liquid and gas move continuously, so particles will spread out evenly

  diffusion is the process of particles moving from a high concentration gradient to a low concentration gradient

  the particles:

  • will move in any direction but will have a net (overall) movement from a high to low concentration
  • will end up spread out evenly and will continue to move
• factors affecting diffusion

  • concentration- the greater the difference the quicker the rate of diffusion
  • temperature- higher temperature the more kinetic energy ---> particles move faster meaning they move and spread out quicker
  • surface area of cell membrane seperating regions (for diffusion in/out of cells)- the larger the surface area the quicker the rate of diffusion
• osmosis: the diffusion of water molecules from a region of high water concentration to a region of low water concentration

  cells contain dilute solutions of ions, sugars and amino acids

  the cell membrane is partially permeable

  water moves in and out of cells by osmosis
• osmosis- in plant cells

  plant cells placed in dilute solutions or water will take in water by osmosis

  eg: root hair cells: if soil is wet/moist it will also take up water by osmosis
• plant cells (unless it is raining or high humidity) will have a tendancy to loose water as there's more water in the leaf and less in the air

  cell wall: supports cell and stops it from bursting when it gains water

  in a more concentrated solution cells loose water by osmosis
• osmosis in animal cells

  animal cells also take in and loose water by osmosis. however they don't have a cell wall, so they do change size and shape

  eg: red blood cells could:

  • lose water and shrink
  • gain water, swell and burst, making a more dilute solution
• osmosis in animal cells

  in animals the concentration of body fluids (blood, plasma, tissue fluid)must be kept in strict limits

  if animal cells gain or loose too much water they do not function properly
• active transport

  substances are transported passively in osmosis and diffusion

  passive transport: transport of molecules that occurs as random movements. it does not require energy

  active transport: process required to move molecules against a concentration gradient. it requires energy

  low concentration gradient ---> high concentration gradient (other way round to osmosis and diffusion)
• Diffusion


  Particles (molecules and ions) in a liquid and a gas move continuously and spread themselves evenly throughout the liquid or gas
• If there is a situation where particles of a substance are in a higher concentration, they will move from this region to where they are in a lower concentration. This is called diffusion.
• Particles will move in both directions, but there will be a net movement from high to low concentration
• Particles will end up evenly spread throughout the liquid or gas, but will continue to move
• Concentration gradient


  Particles will move down a concentration gradient, from a high concentration to a low concentration
• Diffusion occurs across membranes, between the outside and inside of cells
• Factors affecting the rate of diffusion

  • The concentration gradient
  • The temperature
  • The surface area of the cell membrane separating the different regions
• Reason for factors affecting rate of diffusion

  • The greater the difference in concentration, the quicker the rate of diffusion
  • The higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly
  • The greater the surface area, the faster the rate of diffusion
• For simple multicellular organisms, substances diffuse into the leaves and roots over their surface. Once inside the plant, they don't need to move far.
• As organisms increase in size, their surface area does not increase at the same rate as their volume. For example, the surface area to volume ratio of a puppy is several times greater than that of an adult dog.
• Osmosis


  The diffusion of water molecules, from a region where the water molecules are in higher concentration, to a region where they are in lower concentration, through a partially permeable membrane
• Osmosis refers to the movement of water molecules only
• The cell membrane is partially permeable. Water will move into and out of cells by osmosis.
• What happens to plant cells in different solutions

  1. In pure water, the cell contents push against the cell wall and the cell becomes turgid

  2. In a more concentrated solution, the cell contents lose water by osmosis, shrink and pull away from the cell wall, becoming flaccid and plasmolysed

  3. In a very concentrated solution, the cell undergoes full plasmolysis as the cells lose more water
• Plants would be exposed to higher concentrations of solutes if there was less water in the soil - for instance, if plants were not watered, or plants in drought conditions. Plant cells would then lose water by osmosis.
• Aquatic, freshwater plants placed in the sea, or a seaweed in a rock pool where the water evaporated in the Sun, would also lose water by osmosis.
• Animal cells also take in and lose water by osmosis. They do not have a cell wall, so will change size and shape when put into solutions that are at a different concentration to the cell contents.
• Active transport


  A process that is required to move molecules against a concentration gradient. The process requires energy.
• Active transport in plants

  For plants to take up mineral ions, ions are moved into root hairs, where they are in a higher concentration than in the dilute solutions in the soil. Active transport then occurs across the root so that the plant takes in the ions it needs from the soil around it.
• Active transport in animals

  Glucose molecules have to be moved across the gut wall into the blood. The glucose molecules in the intestine might be in a higher concentration than in the intestinal cells and blood - for instance, after a sugary meal - but there will be times when glucose concentration in the intestine might be lower. All the glucose in the gut needs to be absorbed. When the glucose concentration in the intestine is lower than in the intestinal cells, movement of glucose involves active transport. The process requires energy produced by respiration.
• Processes for substances to move into and out of cells

  • Diffusion
  • Osmosis
  • Active transport
• Diffusion


  Substances move from a high to a low concentration down a concentration gradient. No energy required.
• Osmosis


  Water moves from a high to a low concentration across a partially permeable membrane and down a concentration gradient. No energy required.
• Active transport


  Substances move against a concentration gradient. Energy required.
• Levels of organisation in multicellular organisms

  • Cells
  • Tissues
  • Organs
  • Organ systems
• Cell


  The basic building block of all living organisms
• Tissue


  A group of cells working together to perform a shared function, and often with similar structure
• Organ


  A structure made up of groups of different tissues, working together to perform specific functions
• Organ system


  A group of organs with related functions, working together to perform certain functions within the body