Plant Nutrition Lesson 1 Flashcards
Define photosynthesis
A chemical process used by plants to make glucose and oxygen from carbon dioxide and water
Balanced chemical equation for photosynthesis
6 CO2 + 6 H2O → C6H12O6 + 6 O2
Word equation for photosynthesis
Carbon dioxide + water —chlorophyll, light—> glucose + oxygen
Steps in carrying out the starch test to prove that the leaf has been producing glucose and photosynthesising and safety precautions
- Put the plant in boiling water to kill it - stops further chemical reactions
- Place the leaf in boiling ethanol - removes chlorophyll making the leaf paler in colour
- Dip the leaf in lukewarm water - softens it
- Spread the leaf evenly onto a white tile and add iodine solution to test for starch - it will turn blue-black if starch is present
SAFETY PRECAUTIONS:
Wear safety goggles throughout the experiment
Do not expose the ethanol to a naked flame as it is highly flammable
How to destarch a plant
Place it in the dark for at least 48 hours. During this time, starch will be replaced or used.
Define variegated leaf
A leaf that possesses more than one colour
Steps to prove that light is needed for photosynthesis
- Destarch the plant
- Cover part of the leaf with lightproof paper/foil
- Make a drawing of the leaf - control variable
- Place the plant in bright light for several hours
- Test the leaf for starch with the 4-step starch test
- Make another drawing of the leaf. In the drawing, show the areas that tested positive and negative for starch
Results:
Only areas that have been exposed to light will turn blue-black, meaning starch is positive in those areas and they have been photosynthesising. The rest of the leaf will not turn blue-black because it has not been photosynthesising therefore no starch is present.
Photosynthesis limiting factors
CO2 concentration - 0.04% of air is CO2
Light intensity - chlorophyll use light to perform P.S
Temperature - if above 40 degrees Celsius, enzymes will begin to denature (become destroyed)
How leaves are adapted for efficient photosynthesis
Broad - large surface area exposed to light
Most of the chloroplasts are located in the palisade layer, near the top of the leaf where they can get the most light
Upper epidermis is transparent so light can pass through to get to the palisade layer
Very thin - reduces diffusion distance of important gasses through the leaf
Waxy cuticle prevents water loss through evaporation
Use of magnesium ions in plants and symptoms of deficiency
Use - to produce chlorophyll
Symptoms of deficiency - chlorosis (discolouration of plant), yellowing between plant veins, early leaf fall
Use of nitrate ions and symptoms of deficiency
Use - to produce amino acids and proteins for plant growth
Symptoms of deficiency - stunted growth and yellowing
How does humidity affect photosynthesis?
If the temperature is high (yet below 45 degrees celcius) and the humidity is normal than more stomata will open, allowing more carbon dioxide for photosynthesis.
Limiting factor definition
A condition, that when in shortage, slows and limits the rate of a reaction.
What are 6 uses of glucose
- To produce sucrose which is transported in phloem tubes (when glucose and fructose, products of P.S. , react).
- To produce starch - a polysaccharide that is compact, insoluble and used for storage for glucose
- To produce cellulose which is used in creating cell walls.
- To produce proteins and DNA which are used in cell membranes, hormones, tissues, enzymes and so on.
- To produce lipids which are stored in the form of chemical energy in seeds.
- To produce chlorophyll which absorbs light energy for photosynthesis.
Name the different components of a leaf and their uses
Waxy cuticle - prevents water loss through evaporation.
Upper epidermis - transparent to allow light to reach the palisade mesophyll. Protective layer again bugs and bacteria.
Palisade mesophyll - cells containing the most chloroplasts, responsible for photosynthesis.
Spongy mesophyll - cells with air spaces between them to allow the diffusion of gasses through the leaf to the cells where they are needed and to allow the gasses to escape the plant.
Plant vein - contains xylem and phloem. Xylem is used for transporting water and minerals from the soil to leaves and phloem is used for transporting glucose to the rest of the plant where it is needed.
Lower epidermis - protective layer on the underside of the leaf, containing guard cells and stomata.
Stomata - tiny pores on the surface of leaves which allow most carbon dioxide to diffuse into the plant for P.S. and to allow oxygen to leave the plant. Water vapour also diffuses out of the stomata via transpiration
Guard cells - control the opening and closing of the stomata. They become turgid (firm and swollen) and flaccid (soft and shrunken) to open and close.
