Plants and Photosynthesis

• Photosynthesis is a very complicated set of chemical reactions that converts carbon dioxide and water molecules into sugar (glucose).
  

• The raw materials needed are carbon dioxide and water
  

• Sunlight provides the energy for the reaction.
  

• Chlorophyll is the chemical that absorbs the sunlight. It is the green pigment in chloroplasts, and why most plants are green).
  

• Glucose is the product of the reaction (but there is also some oxygen left over).
  

Leaves contain many different types of cells, but there is one type that is essential for photosynthesis.....Palisade Cells.

If you were plant doctor, what would be your diagnosis for this plant below?

• Plants need Mg (Magnesium) to make chlorophyll.
  

• If plants don't get enough Mg then they can't make chlorophyll.
  

• This is bad news because if plants can't make chlorophyll then they can't photosynthesise
  

• No photosynthesis = no sugar (so no carbohydrates for energy).
  

Nitrates are made of one nitrogen atom and three oxygen atoms.

Plants need the nitrogen atom so that they can create proteins.

Protein is needed for plant growth, therefore if a plant does not get enough nitrate then it will be unable to make proteins.

• During photosynthesis plants make glucose (a simple carbohydrate).
  

• Plants convert some of the glucose into starch and store it their leaves
  

• Starch is a complex carbohydrate (this basically means it a very large carbohydrate molecule).
  

• Basically, starch is a long molecule made up of many glucose molecules joined together (have a look at the picture below)
  

1. Place a leaf in boiling water (this breaks down the cell membranes)

2. Turn off the flame, then place the leaf inside a test tube that contains ethanol (this gets the chlorophyll out of the leaf).

3. Place the test tube (with the leaf/ethanol mixture inside) in the hot water (keep the flame OFF!!)

4. Place a few drops of iodine on the leaf.....if it turns a blue/black colour then you have found starch!

• Iodine is a chemical that will turn dark blue or black if there is starch present.
  
• After we have prepared the leaf by boiling and using ethanol we can add iodine to see if it contains starch (see the picture below).
  

Plant need water for photosynthesis and they absorb all the water they need through their roots.

The roots have specially adapted cells called root hair cells (see the picture below).

What structure (found in palisade cells) is missing from root hair cells?

• As you can see there are no chloroplasts found in root hair cells because they are underground and do not need to absorb sunlight!
  

• The job of the root hair cells is to absorb water and mineral nutrients (magnesium and nitrates) from the soil.

• They are very good at doing this because they have an adaptation (the long projection) that increases the amount of surface area for water to pass through.

• Below is what root hair cells look like under a microscope...
  

1. Photosynthesis! Look at the equation, water is a raw material for photosynthesis.

2. Water also helps to keep the plant cool (so it does not overheat). Water can evaporate from the leaves through tiny pores called stomata, when it evaporates it takes some heat energy with it (see the pictures below)....

3. Support! Plant cells contain a lot of water which helps to keep the plant firm. If there is not enough water then the plant becomes droopy, it has wilted.

4. Transporting nutrients from the soil such as magnesium and nitrates.

Water enters a plant through the root system (root hair cells) but it is needed in the leaves for photosynthesis so how does it get there?

• Xylem (pronounced 'zy-lem') is a tissue that transports water and nutrients from the roots to the leaves.
  

• Xylem works in one direction only - it does not carry water downwards
  

• See our experiment below....
  

Some plants cannot get all the nitrates they need from the soil they are in, and some have evolved unique adaptations to get what they need....

1. Plants need minerals from the soil, name two minerals that plants need and explain how they get into the plant.

2. How are leaves adapted for photosynthesis?

3. Imagine you are a drop of rain, describe your journey from the soil to the leaf.

4. Mr Pless bought some plants, he watered them everyday and made sure they received plenty of sunlight. Despite this he noticed some of the leaves were starting to turn yellow, why do you think this is? What would be your solution to this problem?

5. Describe all the stages of how to test a leaf for starch

6. Name the raw materials needed for photosynthesis and explain how they enter the plant and get to the leaves.

7. Plants make glucose (a carbohydrate), what do you think this is needed for?

8. Why do carnivorous plants need to eat meat?