Photosynthesis and Gas Exchange Flashcards
In photosynthesis, light energy is converted into ……………?
Chemical energy (in the form of glucose; then stored as starch or sucrose)
Write a word equation for photosynthesis
Carbon dioxide + water –> glucose + oxygen
Write a balanced chemical equation for photosynthesis
6CO2 + 6H2O —> C6H12O6 + 6O2
State three factors that affect the rate of photosynthesis
Light intensity, carbon dioxide concentration and temperature
Oxygen gas is produced in photosynthesis and can be collected. How would you test that this gas was oxygen?
A glowing splint would be re-lit
Describe how the upper epidermis is adapted for photosynthesis
Clear/transparent to allow light through to reach the palisade cells
Describe the purpose of a waxy cuticle on the surface of a leaf
Waterproofing, reduced water loss by transpiration; reflects excess sunlight preventing damage
Describe how the palisade mesophyll cells are adapted for photosynthesis
Contain many chloroplasts; cells packed tightly together to absorb maximum light for photosynthesis
Describe the purpose of the air spaces between cells of the spongy mesophyll layer
Act as reservoirs of gases to maintain diffusion gradients for carbon dioxide to enter the photosynthesising cells and oxygen to leave
Plant cell walls are made out of which carbohydrate?
Cellulose
What is the function of the xylem vessels?
Transport water from the roots to the leaves
What is the function of the phloem vessels?
Transport sucrose/amino acids away from the leaves
Describe how stomata change size with light levels during the day
When light, guard cells open stomata (become turgid) so carbon dioxide can enter the leaf; at night, guard cells close stomata (become flaccid) to conserve water and oxygen (respiration)
Describe how you would safely test a leaf for the presence of starch
Boil leaf in water to kill it (denatures enzymes); boil in ethanol (no naked flames as ethanol highly flammable; use water bath) to extract chlorophyll; dip in hot water to soften; add iodine solution; if starch present, blue-black colour
Explain the purpose of destarching a leaf
To test whether starch is produced as a result of photosynthesis (many glucose molecules produced from photosynthesis are packaged into large, insoluble starch molecules). TO destarch a plant, place in the dark for 24 hours so photosynthesis cannot take place; the plant will convert the starch into glucose and respire it to stay alive
Name the chemical used to test the requirement of carbon dioxide for photosynthesis (HINT: it absorbs CO2)
Soda lime (sodium/potassium hydroxide)
Name the chemical used to investigate changes in carbon dioxide levels when leaves are photosynthesising under different conditions
Hydrogen carbonate indicator
By what process does carbon dioxide enter a leaf and oxygen leave a leaf?
Diffusion
TRUE/FALSE: all the oxygen produced in photosynthesis exits a leaf via diffusion through the stomata.
FALSE: some will be used in aerobic respiration within leaf cells
What are present in the spongy mesophyll layer that maintain high concentration gradients for diffusion of carbon dioxide into the cells?
Air spaces
Through which structures in the leaf do gases enter and leave?
Stomata
Which cells control the opening and closing of the stomata? How do they do this?
Guard cells (become turgid to open the stomata; become flaccid to close the stomata)
TRUE/FALSE: The rate of respiration is greater than the rate of photosynthesis in a plant AT NIGHT
TRUE: no light available for photosynthesis so plant continues to respire
TRUE/FALSE: The rate of respiration is greater than the rate of photosynthesis in a plant during the day
FALSE: plants will use sunlight to convert light energy into chemical energy; plants will still respire but at a lower rate
By what process do plants lose water through the stomata?
Transpiration
