Movement of Molecules In and Out of Cells

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  • Movement of Molecules In and Out of Cells
    • Dissolved substances
      • Move by: Diffusion & active transport
      • Osmosis: Diffusion of water from dilute to more concentrated solution through a partially permeable membrane
      • Partially permeable membrane: allows water molecules through & stops solute molecules getting through (too large)
    • Osmosis and Cells
      • When concentrations in & out of a cell water moves by osmosis to balance
      • Osmosis gradually dilutes more concentrated solution
      • e.g. from soil - plant's root hair cells along a concentration gradient
    • Active Transport
      • Sometimes substances are absorbed against concentration gradient.
        • Requires energy from respiration
      • Allows cells to absorb ions & sugar, which pass through cell membranes from very dilute solutions
      • In humans sugar's absorbed from intestine & kidney tubules
      • Soft drinks & sports drinks contain water, sugar & ions to replace:
        • 1) sugar used to release energy during exercise
          • 2) Water & ions lost during sweating
      • |f they aren't replaced, the ion & water balance of body is disturbed & cells don't work as efficiently
    • Exchanging Materials
      • Many organ system are specialised for exchanging materials
      • Large surface area, thin (short diffusion path), efficient blood supply (animals), being ventilated (animals) for gas exchange
      • The larger & more complex an organism is, the more difficult exchanging materials is
      • Exchange surfaces are adapted to maximise effectiveness
      • In humans: Villi increase surface area of small intestine
      • In humans: Alveoli increase surface area of lungs
    • Villi in the Small Intestine
      • Villi line the walls
      • Massive surface area for exchanging materials across
      • Extensive network of blood capillaries to absorb products of digestion by diffusion & active transport
    • The breathing system
      • Located in upper thorax (upper part of body)
      • Involves lungs
      • protected by rib cage
      • Thorax is divided from abdomen by muscular sheet called diaphragm
      • take air in & out of body so: oxygen can diffuse into your body & CO2 can diffuse from blood into air
    • Alveoli in the Lungs
      • air goes through trachea to lungs
      • Trachea has rings of cartilage to prevent it from collapsing
      • trachea divides into 2 tubes (bronchi)
      • Bronchi divides into bronchioles
      • bronchioles divide until they end in air sacs
      • Air sacs are called alveoli (millions of them)
      • Alveoli are close to blood capillaries.
        • They're effeicient at exchanging O2 & CO2 because they have: large, moist surface area & excellent blood supply
    • Ventilation
      • Movement of air into & out of lungs is known as ventilation
      • As you inhale your rib cage moves up & diaphragm flattens (contracts)
      • As you exhale, your rib cage moves in & down & diaphragm moves up (relaxes)
      • Artificial aids for breathing, such as ventilators, have been developed for medical use. They improve gas exchange in body.
    • Exchanging Systems in Plants
      • CO2 enters & leaves by diffusion
      • Water & mineral ions are absorbed by roots
      • Roots & leaves are adapted to carry out the exchange of materials
        • Root hairs = large surface area
        • Leaves = broad, thin & flat with lots of internal air spaces = largest surface area possible
      • Tiny holes called stomata on leaves. 
        • During photosynthesis the stomata: let CO2 in (needed for photosynthesis)
        • During photosynthesis the stomata: let oxygen out (a product of photosynthesis)
      • Plants mainly lose water vapour from leaves mostly through the stomata
      • Movement of water through plant = transpiration
      • Evaporation is more rapid in hot, dry & windy conditions
      • If plants lose water through leaves than its replaced by roots, stomata close =prevents wilting
        • This means photosynthesis can't take place
      • Size of stomata controlled by guard cells, which surround them

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