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Plant Nutrition and Transport
Photosynthesis:
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Photosynthesis is the process that produces ‘food’ in plants
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It happens in the leaves of all green plants – this is largely what these are for
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Chloroplasts contain a pigment called chlorophyll, which absorbs sunlight
and uses its energy to convert carbon dioxide and water into glucose
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6CO2 + 6H2O  C6H12O6 + 6O2
It converts light energy to chemical energy, which is stored as glucose
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Leaves are broad, so there’s is a large surface area exposed to light
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It is near the top of the leaf
where they can get lots of light
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Leaves have a network of vascular bundles – transport vessels like phloem and
xylem
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Also support the structure
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The adaptions of leaves for efficient gas exchanges also make photosynthesis
efficient
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Light intensity, carbon dioxide, concentration and temperature can all be limiting
factors
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Photosynthesis Experiments:
Testing for Starch:
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Leaf needs to be killed by dunking it in boiling water
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Put the leaf inside a boiling tube with some ethanol and heat the tube in a water
bath
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The leaf should now be a pale colour
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If starch is
present, it will turn blue-black
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Cut a leaf from the plant and test it for starch
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A source of white light is placed at a
specific
distance
from
the
pondweed
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As it photosynthesises, the
oxygen released will collect in the
capillary tube
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Temperature and time need to be controlled
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They get these from mineral ions in the soil
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Nitrates:
o Contain nitrogen for making amino acids and proteins
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o If a plant can’t get enough it will be stunted and have yellow older leaves
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o Without them, plant will have poor root growth and purple older leaves
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o Without enough, poor flower and fruit growth and discoloured leaves
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o Without, they have yellow leaves
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In unicellular organisms, these substances can diffuse directly into and out of the cell
across the cell membrane
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In multicellular organisms direct diffusion from the outer surface would be too slow
– there are much larger distances to travel
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Plants:
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Xylem – Carry water and mineral salts from the roots up the shoot to the leaves in
the transpiration stream
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This movement of food substances around
the plant is known as translocation
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This gives the plant a large surface area for absorbing water from the soil
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There’s usually a higher concentration of water in the soil that there is inside the
plant, so the water is drawn into the root hair cell by osmosis
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Most of it happens at the leaves
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This in turn means more water is drawn up from the roots, and so there’s a constant
transpiration stream of water through a plant
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They
have to have stomata in them to that gases can be exchanged easily
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Transpiration Rate:
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Light Intensity – The brighter the light, the greater the transpiration rate
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Photosynthesis can’t happen in the dark, so
they don’t need to be open to let carbon dioxide in
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Temperature – The warmer it is, the faster transpiration happens
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Wind Speed – The higher the wind speed around a leaf, the greater the transpiration
rate
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This means that there’s a high concentration of water outside the leaf,
so transpiration doesn’t happen as quickly
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If the air
is humid there’s a lot of water in it already, so there’s not much difference between
the inside and the outside of the leaf
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It measures water uptake by a plant, but it’s assumed that water uptake by the plant
is directly related to water loss from the leaves
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Cut it at a
slant to increase the surface area
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3) Remove the apparatus
from the water but keep the end of the capillary tube submerged in water
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5) Dry the leaves, allow time for
the shoot to acclimatise and then shut the tap
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7) Record the starting position of the
bubble
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9) Keep the conditions constant throughout the experiment
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To
decrease, put in a cupboard
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Humidity – Spray water into a clear plastic bag, before sealing it around the plant
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