Plant Structures (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Transport Systems

Plant organs

• Multicellular organisms usually have transport systems, as diffusion, osmosis and active transport are too slow to meet all of a larger organism’s needs

• In plants, transport systems are required to move substances between plant organs, including:

  • roots

  • stems

  • leaves

• Transport systems in plants allow:

  • movement of water and mineral ions from the roots to the stems and the leaves

  • movement of sugars and amino acids from where they are produced or stored, to where they are needed

Exchange of Materials in Plants

Exchange in the leaf

• Plants take in carbon dioxide from the air for photosynthesis

• Plants take in oxygen for respiration

Gas exchange during respiration

• Respiration occurs all the time in plant cells, day and night

• Aerobic respiration requires oxygen and produces carbon dioxide

• At night, when no photosynthesis occurs:

  • Oxygen diffuses into the leaf down a concentration gradient

  • Oxygen is used in respiration so its concentration stays low inside cells

  • Carbon dioxide diffuses out of the leaf down a concentration gradient

Gas exchange during photosynthesis

• Photosynthesis occurs in daylight in cells with chloroplasts

  Photosynthesis requires carbon dioxide and releases oxygen

  When photosynthesis is occurring:

  • Carbon dioxide diffuses into the leaf down a concentration gradient

  • Oxygen diffuses out of the leaf down a concentration gradient

  Some oxygen produced in photosynthesis is used in respiration

Exchange in the roots

• Plant roots have root hairs to increase the surface area for absorption of water and mineral ions from the soil

  • Root hair cells take in mineral ions from the soil either by active transport when dissolved in water

  • Important mineral ions for plants include:

    • Nitrate ions are needed to make proteins

    • Magnesium ions are needed to make chlorophyll

• The uptake of minerals lowers the water potential of the root hair cells

• Water is then absorbed from the soil by the roots by osmosis

  • Water is used in the process of photosynthesis