UNIT 1 - Photosynthesis and Plants (2) Flashcards
Describe the word and symbol equation for photosynthesis in plants. (1 mark)
Water + Carbon Dioxide –> Glucose (Starch) + Oxygen
6 H20 + 6 CO2 –> C6H12O6 + 6 O2
Describe how a leaf can be tested for starch. (5 marks [2 for written communication] ).
- Place a leaf in boiling water, to kill the leaf and stop all chemical processes.
- Place the leaf in ethanol to fully extract all the chlorophyll, the ethanol should be heated in boiling water.
- Rinse the leaf in water, the heated ethanol would make it brittle.
- Drop iodine solution on the leaf, it should turn blue/black if starch is present.
What substance removes carbon dioxide? (1 mark)
Soda lime (Sodium Hydroxide)
Give one other raw material a plant requires apart from CO2 for photosynthesis. (1 mark)
H2O, Water
Suggest one way you can vary the light intensity in a photosynthesis test using a lamp. (1 mark)
Moving the lamp closer or further away.
Name the gas given off in photosynthesis. (1 mark)
Oxygen gas
Apart from light intensity, what other factor will affect the rate of photosynthesis in a plant. (1 mark)
Temperature.
Explain how starch, produced by photosynthesis, is used by a plant. (2 marks)
The starch produced by the plant can be used to carry out respiration, be stored as glucose or used to grow or develop the organism.
Describe the features of a gas exchange cell. (2 marks)
Thin cell membrane, spaced apart for gas, few chloroplasts are needed.
Describe a test to prove chlorophyll is needed for photosynthesis to occur. (3 marks)
- Take a variegated leaf.
- Place a leaf in boiling water, to kill the leaf and stop all chemical processes.
- Place the leaf in ethanol to fully extract all the chlorophyll, the ethanol should be heated in boiling water.
- Rinse the leaf in water, the heated ethanol would make it brittle.
- Drop iodine solution on the leaf, the green parts of the leaf containing chlorophyll will turn blue/black (The white parts will not).
Describe a test to show oxygen is a product of photosynthesis. (3 marks).
- Put pondweed in a beaker full of water.
- Place an inverted tube in to collect the oxygen bubbles.
- The plant will photosynthesise, creating oxygen into the tube.
- Take the tube and place a glowing splint inside of it after the experiment.
- The glowing splint should relight.
Describe a plants leaf structure. (3 marks)
The top layer of cells, the epidermis, is transparent. It has a waxy waterproof layer over it that stops the leaf from drying out. Light passes through the epidermis to the next layer of cells, the palisade layer. Inside the leaf, most cells are green. They contain green chloroplasts where food is made. Palisade cells are specialised for photosynthesis. They are provided with water by the veins in a leaf. Below the palisade layer is a layer called the Spongy Mesophyll. In this layer the air spaces act as reservoirs for the gases that palisade cells need. There is another layer of epidermis on the lower surface of the leaf. This is waterproof too. Gases such as Carbon Dioxide enter and leave through tiny pores called Stomata. Guard Cells by each Stoma shut the Stomata at night. Water is also needed for photosynthesis.
Why will a graph showing the rate of photosynthesis and CO2 concentration, level off at a certain point. (1 mark)
Due to another limiting factor.
Explain why the rate of photosynthesis in plants is higher at 20°C than at 10°C. (2 marks)
As temperature is a contributing factor, it will effect the efficiency of the plants enzymes, which will limit the rate at lower temperatures.
Light absorption is maximised by: (3 marks)
- The short distance from top to bottom allowing all cells to receive light.
- Large surface area.
- Thin transparent cuticle to prevent water loss but will not stop light.
- Presence of chloroplasts rich in chlorophyll.
- Regular structure of Palisade Mesophyll, ensures many cells rich in chloroplasts are packed together near the upper side of leaf.
