Photosynthesis

Chlorophyll is a green pigment found in chloroplasts within plant cells. Its primary function is to absorb light energy, which is then transferred into chemical energy for the synthesis of carbohydrates during photosynthesis.

1) Starch as an energy store (

Nitrate ions are essential for making amino acids, which are the building blocks of proteins. Proteins are vital for plant growth, enzyme production, and various metabolic processes; deficiency leads to stunted growth and yellowing of leaves.

Magnesium ions are essential for making chlorophyll, the green pigment responsible for absorbing light energy during photosynthesis. Magnesium deficiency leads to chlorosis, causing leaves to turn yellow due to reduced chlorophyll production.

Use two plants. Place one in light and one in darkness. After a few days, test a leaf from each for starch using iodine solution. The leaf from the plant in the light should test positive for starch (blue-black colour change), indicating photosynthesis occurred, while the other does not.

The three main limiting factors of photosynthesis are light intensity, carbon dioxide concentration, and temperature. The rate of photosynthesis is limited by the factor that is in shortest supply.

Generally, increasing light intensity increases the rate of photosynthesis, up to a certain point. Beyond that point, other factors like carbon dioxide or temperature become limiting.

Increasing the carbon dioxide concentration generally increases the rate of photosynthesis, up to a saturation point. Beyond this point, the rate plateaus as other factors like light intensity or temperature become limiting.

Increasing temperature generally increases the rate of photosynthesis, as it increases the rate of enzyme-catalyzed reactions. However, beyond an optimal temperature, the rate decreases because the enzymes involved in photosynthesis become denatured (

The three main limiting factors are:

1. Light intensity — as light increases, photosynthesis rate increases until another factor becomes limiting
2. Carbon dioxide concentration — increasing CO₂ increases the rate up to a point
3. Temperature — affects the rate of enzyme-controlled reactions in photosynthesis

The factor in shortest supply at any time is the limiting factor. Increasing it will increase the rate, but increasing the others will not.

1. Boil the leaf in water for 30 seconds (kills cells, makes cell membrane permeable)
2. Place the leaf in hot ethanol in a water bath (removes green chlorophyll)
3. Dip the leaf briefly in hot water (softens it)
4. Spread the leaf on a white tile and add iodine solution
5. If starch is present, the leaf turns blue-black
6. If no starch, the leaf stays brown/yellow

Safety: ethanol is flammable — always use a water bath, never a direct flame.

Nitrate ions (NO₃⁻):
• Needed to make amino acids (and therefore proteins)
• Without nitrate: stunted growth, yellow older leaves
• Absorbed from the soil by roots (often by active transport)

Magnesium ions (Mg²⁺):
• Needed to make chlorophyll (the green pigment)
• Without magnesium: yellow leaves (chlorosis) — cannot photosynthesise effectively
• Only needed in small amounts

1. Destarch a plant by placing it in darkness for 48 hours (uses up stored starch)
2. Cover part of a leaf with aluminium foil (blocks light from that area)
3. Leave the plant in bright light for several hours
4. Remove the leaf and test for starch using the iodine test

Expected result:
• Uncovered area: turns blue-black (starch present — photosynthesis occurred)
• Covered area: stays brown (no starch — no photosynthesis without light)

The covered part is the control.

Glucose from photosynthesis can be:

1. Used in respiration — to release energy for cell processes
2. Converted to starch — for storage (starch is insoluble, so doesn't affect osmosis)
3. Converted to cellulose — for making cell walls
4. Converted to sucrose — for transport in phloem to other parts of the plant
5. Used to make amino acids — combined with nitrate ions to build proteins
6. Converted to lipids (fats/oils) — for energy storage in seeds

1. Place an aquatic plant (