FLOWERING PLANTS (2.17 – 2.22)
2.17 – Describe the process of photosynthesis and understand its importance in the
conversion of light energy to chemical energy.
– Photosynthesis uses sunlight to convert carbon dioxide and water into glucose and
oxygen.
– Light energy is absorbed by chlorophyll in plant leaves.
– Light energy is converted into chemical energy in the form of glucose.
2.18 – Write the word equation and the balanced chemical symbol equation for
photosynthesis.
CARBON DIOXIDE + WATER → GLUCOSE + OXYGEN
6CO2 + 6H2O → C6H12O6 + 6O2
2.19 – Understand how varying carbon dioxide concentration, light intensity and
temperature affect the rate of photosynthesis.
– CARBON DIOXIDE
• The rate of photosynthesis is directly proportional to the concentration of carbon
dioxide.
– LIGHT INTENSITY
• The rate of photosynthesis is directly proportional to the intensity of light.
– TEMPERATURE
• The rate of photosynthesis is maximised at the optimum temperature.
• The rate of photosynthesis is slower below the optimum temperature as enzymes
are inactive.
• The rate of photosynthesis is minimal above optimum temperature as enzymes
denature.
– Carbon dioxide and light are limiting factors.
– The rate of photosynthesis will not be able to increase further if one of the factors
exceed a certain amount.
– The rate of photosynthesis can be increased by adding more of another limiting factor.
2.20 – Describe the structure of the leaf and explain how it is adapted for photosynthesis.
– The leaf has a large surface area to maximise light absorption.
– The leaf is thin for a short diffusion distance of gases.
– The upper epidermis and waxy cuticle are transparent and lets light through.
– Chloroplasts and chlorophyll absorb light.
– Palisade cells are closely compacted, full of chloroplasts and are close to the surface
to maximise light absorption.
– Diffusion occurs in the spongy mesophyll layer to allow carbon dioxide and oxygen to
diffuse in and out.
– Guard cells open and close the stomata to control the entry and exit of substances.
– The xylem absorbs water so that it can be used for photosynthesis.
2.21 – Understand that plants require mineral ions for growth and that magnesium ions
are needed for chlorophyll and nitrate ions are needed for amino acids.
– Plants require minerals for growth.
2.22 – Describe experiments to investigate photosynthesis, showing the evolution of
oxygen from a water plant, the production of starch and the requirements of light, carbon
dioxide and chlorophyll.
– EVOLUTION OF OXYGEN FROM A WATER PLANT
• Submerge pond weed in several beakers filled with water.
• For each beaker, investigate a factor that affects photosynthesis.
– Carbon dioxide: Add sodium bicarbonate (baking soda) that produces carbon
dioxide when reacting with water.
– Light: Move a lamp closer for far away from the plant.
– Chlorophyll: A green plant is tested with a variegated plant (containing both
green and white bits; green has more chlorophyll).
• The rate of bubble production is measured (e.g. counted or downwards
displacement), which is proportionate with the rate of photosynthesis.
– PRODUCTION OF STARCH
• Remove leaf from plant.
• Kill the leaf in boiling water to stop chemical reactions (i.e. photosynthesis) that may
affect the experiment.
• Remove chloroplasts/chlorophyll in boiling ethanol. This also removes the waxy
cuticle layer which prevents iodine solution from being absorbed.
• Wash the leaf in cold water and make it soft.
• Place the leaf on a tile and add drops of iodine solution.
– The solution turns blue-black if starch is present.
– The solution stays yellow-brown if starch is not present.