IGCSE Biology Plant Nutrition and Transport

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Photosynthesis

Carbon dioxide + Water -----> Glucose + Oxygen

6CO2 + 6H2O ------> C6H12O6 + 6O2

Photosynthesis happens inside the chloropasts, and releases energy from converting sunlight into chemical energy.

A limiting factor means something which stops a process from happening any faster. The limiting factor is dependent on the environment.

  • LIGHT INTENSITY- If this is increased, the rate of photosynthesis will increase up to a certain point, until temperature or carbon dioxide levels are now the limiting factor.
  • CARBON DIOXIDE- A similar pattern to light intensity: If it is increased, the rate will correspond, until light and temperature are limiting factors.
  • TEMPERATURE- As it increases, so does the rate of photosynthesis up to a certain point, unless it is too hot, and the enzymes involved become de-natured.
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Graphs

(http://t0.gstatic.com/images?q=tbn:ANd9GcSaL5hb8wAk8tw0sF63Mm3xp92sc4VlyRGmHFRpsqG6jdEatcAa6w)  (http://t3.gstatic.com/images?q=tbn:ANd9GcTcjnHk-AhDj1wse9BOU5ylioQXLtoMWnssK0IJEfMFw-MBJ3QpSw)(http://t3.gstatic.com/images?q=tbn:ANd9GcRfcgFMNFPWIZFqv9e6qVuhzWOjIPDxjSTSN4gcljRNCT25yoFo)

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Testing a leaf for starch

  •  First place the leaf into boiling water which essentially kills the leaf and no chemical reactions can continue.
  • Next place the leaf into a tube with ethanol, and position it into a water bath. This should remove the cholorphyll so that the leaf appears a pale colour.
  •  Rinse the leaf in cold water and add a few drops of iodine solution . If starch is present, it will turn blue-black.

You can prove that chlorophyll is needed for photosynthesis by taking a variegated leaf which has been exposed to sunlight, and recording which parts are green or not. Then complete the starch test and record which parts contain starch. The parts of the leaf (green) which photosynthesise should produce starch.

You can prove that carbon dioxide is needed for photosynthesis by leaving a plant inside a sealed bell jar with soda lime which aborbs CO2. Shine a light through the jar and leave it. When you test the leaves, they should show no starch.

You can prove light is needed by placing it in a cupboard, and starch is not produced.

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Minerals needed for healthy growth

Nitrates- Contain nitrogen, so therefore nitrates are used to make proteins in plants. Therefore there is cell growth. Without nitrates, the plant will become stunted with yellow leaves.

Phosphates- contain phosphorus which is needed to make DNA and cell membranes. They are also needed for respiration and growth. Without this mineral, plants have purple leaves and bad root growth.

Potassium- helps the enzymes which are needed for respiration. Without it, the plant has discoloured leaves and poor fruit growth.

Magnesium- is only needed in small amounts, but is required to make chlorophyll. Without it, the plant has yellow leaves.

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The rate of photosynthesis

You can measure the vol of oxygen given from Candian pondweed, to show the rate of photosynthesis. The plant is left for a set time, and after, the vol of oxygen is recorded. Then the lamp is moved away/closer to the plant each time, by an equal distance. 

(http://www.sciencequiz.net/jcscience/jcbiology/pphotosynthesis/images/pondweed01.jpg)

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Transport in plants

Multicellular organisms need transport systems , to receive a variety of required nutrients such as water, but also to get rid of waste substances. 

In unicellular organisms, this is not needed, as they are only one cell, and the products can directly diffuse in/out of the membrane. However, in multicellular organisms, the diffusion this way would be too slow, therefore they need a quicker way.

1) The XYLEM carries water and mineral salts from the roots, and up the shoot to leaves. (transpiration stream.)

2) PAPER TWO- The Phloem transports nutrients such as sucrose and amino acids from the leaves where they are made, to the other parts of the plant. This movement is called translocation. 

Both of these systems go to every part of the plant.

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Transport in plants

Also root hairs take in minerals by active transport, and water by osmosis. The cells on the plant root grow into long hairs, and each branch is covered in millions of these microscopic hairs. Due to these hairs, the plant has a larger surface area for absorbing water. 

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Transpiration

Transpiration is the loss of water from a plant, and is caused by evaporation and diffusion from a plant's surface, (mostly at the leaves.)

This process results in a water shortage in the plant, and as a response, more water is drawn up through the xylem tissueThis direction of flow is the transpiration stream. 

Plants need stomata so that gases can be exchanged easily, but because of the concentration gradient of water, the water diffuses from inside the plant, to outside via the stomata.

FACTORS AFFECTING THE TRANSPIRATION RATE.

  • Light intensity- A brighter light results in a higher rate. The stomata close when it is dark, as they cannot photosynthesise. When they are closed, little water escapes.
  • Temperature- when warmer, the rate is faster. The atoms evaporate faster.
  • Wind speed- higher wind speed results in a higher rate. The wind removes the water vapour from outside, meaning there is a steeper concentration gradient, and faster diffusion.
  • Humidity- The drier the air, the faster the rate. When there is a greater difference between humidity inside and outside the plant, diffusion is faster. 
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Transpiration Rates

Potometers measure the water uptake of a plant to estimate the loss of water through transpiration. 

(http://revisionworld.co.uk/sites/default/files/imce/potometer.jpg)

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Transpiration Rates

Cut the shoot underwater, and at an angle to prevent air from entering the xylem, and to maximise surface area for water uptake. Assemble the apparatus in water, so that no air can enter. Dry the leaves, and then shut the tap to the water reservoir. Remove the capillary tube from the beaker until ONE  bubble has formed. 

Record the starting position of the bubble, start a stopwatch , and record the distance moved by the bubble. 

To show the effects of:

light intensity, you could do one control experiment, and then 2 more, one in a cupboard, and one next to a bright light.

temperature, you could put it in a hotter/colder environment than the control.

Windspeed, you could use a fan.

Humidity, you could spray water vapour into a closed system with the plant, e.g plastic bag.

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