B2 topic 2-life processes

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The process in which leaves absorb light and carbon dioxide to produce carbohydrates for the plants growth.

xylem and phleom = transport tissues

Transpiration: When water evaporates from the leaves, resulting in more water being drawn up from the roots, it is called transpiration.

Leaves are adapted for efficient photosynthesis:

  • Leaves are broad, so theres a large amount of the surface area exposed to the light
  • leaves contain chlorophyll which absorb light.
  • Leaves are full of little holes called stomata. They open and close to allow gases like carbon dioxide and oxygen in and out.The also allow water vapour ro escape (transpiration)
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Photosynthesis: limiting factors

Rate of photosynthesis effected by (limiting factors):

  • the light intensity
  • concentration of carbon dioxide
  • the temperature

Environmental factors effect the limiting factors:

  • At night, the light is the limiting factor
  • The temperature in Winter
  • If its warm and bright enough then carbon dioxide is often limited.
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The rate of photosynthesis: light intensity


  • Light provides the energy needed for photosynthesis
  • Beyond a certain point, the intensity wont make a difference; the temperature or CO2 the become the limiting factor
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The rate of photosynthesis: Carbon dioxide


  • CO2 is one of the raw materials needed for photosynthesis
  • The carbon dioxide concentration effects the rate of photosynthesis only up to a certain point; if carbon dioxide and light are in plentiful supply then temperature must be the limiting factor.
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The rate of photosynthesis: temperature


  • usually if temperauture is the limiting factor then its to low- the enzymes needed work slowly at lower temperature.
  • If the temperatures to hot the enzymes denature (around 45 degrees)
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The movement of water molecules across a partially permeable membrane from a region of high water concentration to that of a low water concentration

  • partially permeable membrane= membrane with VERY small holes (only substances with tiny molecules like water can pass through; bigger molecules like sucrose can't)
  • water molecules go through both sides of the membrane.
  • Because there are more water molecules on one side than on another, theres a steady net flow of water into the region with less water molecules, meaning the sugar solution becomes more dilute.
  • water concentration tries to 'even out' on either side of the membrane
  • osmosis is a special type of diffusion.
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Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump.

  • Its caused by the evaporation and diffusion of water from the inside of the leaves.
  • This creates a shortage of water in the leaf and so water is drawn up from the rest of the plant through the xylem vessels to replace it.
  • This means more water is taken up from the roots, so theres a constant transpiration stream in the plant.
  • transpiration happens because of the way the leaves are adapted to photosynthesis; because of the stomata, water is lost. However, transpiration keeps the water levels high.
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xylem- transport water and minerals from the root to the rest of the plant
phleom- transport sugars from the leaves to growing and storage tissues 

Root Hairs-

The roots are covered in microscopic hairs which stick out in the soil, giving the plant a large surface area which absorbs water. Because there is a higher concentration of water in the soil, the water enters the root hairs by osmosis.

Active transport

Root hairs take in minerals using active transport. The concentration of mineral is usually higher in the root hair cell than in the soil, so normal diffusion doesnt explain how minerals are taken up. This proces is called active transport.

active transport uses energy from respiration to help the plant pull minerals into the root hair against the concentration gradient. this is essential for growth.

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