3 - Movement into and out of the cell

• energy for diffusion comes from the kinetic energy of random movement of molecules and ions
• factors that influence diffusion:

  • surface area = increased surface area increases the rate of diffusion
  • temperature = the higher the temperature, the higher the kinetic energy, therefore, the higher the rate of diffusion
  • concentration gradients = the greater the difference in concentration, the higher the rate of diffusion
  • diffusion distance = the closer the distance, the higher the rate of diffusion
• passive transport -

  • from higher to lower concentration
  • doesn’t require energy
  • requires a partially permeable membrane
• active transport - 

  • from lower to higher concentration
  • requires energy (ATP) - one of the products from cellular respiration
  • requires a partially permeable membrane
  • requires a protein carrier
• water is essential for:

  • digestion = water helps to break down and dissolve food molecules in the process of digestion
  • transport = blood is made up of cells and a water based liquid called plasma, the plasma is a way of transporting many dissolved cells
  • excretion = water is important in the process of excretion in animals because some of the excretory materials, for example urea, are toxic. Water dilutes these to make them less poisonous
• Osmosis:

  • a special form of diffusion
  • plants rely on osmosis to obtain water through their roots
  • use water as a transport medium to carry dissolved substances around the plant through the xylem and phloem vessels
  • maintain the firmness of cells (turgor pressure)
  • when young plants lose more water than they gain, cells become limp and the plants wilt
  • can affect the tissues of organisms by causing them to lose or gain water
  • gain water → gain mass
  • lose water → lose mass
• Isotonic solution - 

  • when two solutions have the same water potential
  • no net flow of water
  • animal cell:
  • normal size cell
  • plant cell:
  • normal size cell
• Hypotonic solution - 

  • when a solution has a higher water potential than another solution (more dilute)
  • water flows in
  • animal cells:
  • cells swell then burst (animal cell has no cell wall to maintain structure)
  • plant cells:
  • becomes a normal turgid cell
  • doesn’ t burst because of cell wall
  • cytoplasm expands
  • vacuole increases in size
• Hypertonic solution - 

  • when a solution has a lower water potential than another solution (more concentrated)
  • water flows out 
  • animal cells:
  • cells become shrivelled
  • plant cells:
  • cytoplasm shrinks from cell wall
  • vacuole decreases in size
  • cell wall stays the same
  • is plasmolysed
• Comparison

  A) down

  B) down

  C) against

  D) no

  E) no

  F) yes

  G) yes

  H) no

  I) no

  
• • water diffuses through partially permeable membranes by osmosis
  • water moves into and out of cells by osmosis through the cell membrane
• • energy for diffusion comes from the kinetic energy of random movement of molecules and ions
  • some substances move into and out of cells by diffusion through the cell membrane
• Effect of osmosis on plants - 

  • plants are supported by the pressure of water inside the cells pressing outwards on the cell wall (turgor pressure)
  • maintain the firmness of cells (turgor pressure)
  • when young plants lose more water than they gain, cells become limp and the plants wilt
• Active transport:

  • the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
  • protein carriers move molecules or ions across a membrane during active transport
  • important for the movement of molecules/ions across membranes, including ion uptake by root hair