Photosynthesis Flashcards
What is photosynthesis?
Endothermic reaction using light energy from sun to convert reactants carbon dioxide and water into products glucose and oxygen.
What absorbs energy from sunlight?
Green pigment chlorophyll in chloroplasts in palisade cells in the leaf.
What is the word equation for photosynthesis?
Light energy trapped
Carbon dioxide + water > glucose + oxygen
By chlorophyll
What is the symbol equation for photosynthesis?
6CO2 + 6H2O > C6H12O6 + 6O2
What are the reactant of photosynthesis?
Carbon dioxide, diffuses into stomata in leaf.
Water, diffuses by osmosus into root hair cells.
What are the products of photosynthesis?
Glucose, used in many ways by plant.
Oxygen, diffuses out of cells by diffusion.
What are the uses of glucose?
Respiration, provide energy.
Converted into starch and oils for storage.
Cellulose (for cell walls), chlorophyll and protein for growth.
What is the test for starch?
- Plant destarched.
- Leaf removed from plant in bright light, placed in boiling water for 30 seconds. Kills leaf, stopped chemical reactions.
- Leaf placed in boiling ethanol. Use water bath as ethanol highly flammable, not be exposed to direct flame. Removes chlorophyll from leaf making it whitish-green colour and brittle.
- Leaf dipped into water to soften.
- Leaf spread out on white tile and iodine solution added.
Starch present - yellow-brown to blue-black.
Starch absent - stay yellow-brown.
How and why is a plant destarched?
Placed in dark room or cupboard for 48 hours.
Ensure any starch already in pant used up or removed.
How is light absorption in leaf maximised?
Short distance between upper and lower epidermis, allows cell receive light.
Large surface area.
Thin transparent cuticle reduces water loss by evaporation, allows light enter leaf.
Epidermis lacks chloroplast, allows light into leaf.
Presence chloroplasts rich in chlorophyll absorbs light.
Regular structure palisade mesophyll ensures many cells rich in chloroplasts placed together near upper surface of leaf.
How is gas exchange in leaf by diffusion maximised?
Intercellular air spaces spongy mesophyll allow carbon dioxide enter and oxygen exit photosynthesising cells, mainly concentrated in palisade layer.
Stomata allows carbon dioxide and oxygen leave and enter leaf. Small pores occur between cells in epidermis lower surface of leaf. Surrounded by two guard cells, regulate opening and closing of stomata. Stoma open day, closed night.
Some plants, stomata occur both sides of leaf. Some all one upper surface.
Thin allows gases move in and out of cells quicker.
How to you investigate the need for carbon dioxide in photosynthesis?
Control leaf only have water (or chemical increases carbon dioxide levels) in flask and therefore carbon dioxide present.
Other flask contains sodium hydroxide solution to remove carbon dioxide and so leaf cannot photosynthesis.
What is a control?
Group or condition remains unchanged.
Reference point to compare with experimental group or condition.
Helps scientists determine effect of independent variable (factor being tested) by providing baseline for comparison.
Wha this the method for showing that CO2 is necessary for photosynthesis?
- Destarch plant.
- Put clear plastic bag over plant, seal with elastic band to trap air, sodium hydroxide in cup absorbs CO2 form air.
- Leave plant in bright light at least 6 hours.
- Tea leaf for starch.
Negative - carbon dioxide necessary.
Control set up same but sodium hydroxide replaced by water.
Clear polythene bag used ensure plant receive light and photosynthesis.
What are limiting factors?
Environmental factor that limits rate of photosynthesis due to factor being present in too small amount.
