Plant Nutrition and Plant Gas Exchange

Plants are autotrophs because they make their own glucose through photosynthesis
Plants store their food (glucose) as starch

Plants make their food (glucose) through photosynthesis
Photosynthesis happens in the leaf cells, which contain chloroplasts, and other green parts of the plant
Chloroplasts contain a pigment called chlorophyll, which absorbs sunlight and uses its energy to convert CO2 and water into glucose and oxygen

Light intensity (chlorophyll absorbs light energy which is converted to chemical energy)
Carbon dioxide
Temperature (affects enzymes involved)

carbon dioxide + water ---> glucose + oxygen

6CO2 + 6H2O ---> C6H12O6 + 6O2

Photosynthesis is an endothermic reaction that requires energy from sunlight
Respiration is the opposite equation and is exothermic

Nucleus (stores DNA)
Cell wall
Cell membrane
Mitochondria (where respiration takes place)
Ribosome (makes protein)
Cytoplasm (where chemical reactions take place)
Chloroplasts (Contain chlorophyll and carry out photosynthesis)
Vacuole (Keeps cell turgid)

Large surface area exposed to light
Upper epidermis is transparent so that light can pass through to the palisade mesophyll layer
Chloroplasts found in palisade mesophyll layer, near the top of the leaf, where they can get the most light for photosynthesis
Waxy cuticle helps to reduce water loss by evaporation
Spongy mesophyll cells have air spaces for gas exchange
Thin so short diffusion distance
Lower epidermis contain many holes called stomata
Guard cells can change their shape to open and close the stomata, allowing to carbon dioxide to diffuse into the leaf for photosynthesis

Nitrates
Phosphates
Potassium
Magnesium

Contain nitrogen for making amino acids and proteins which are needed for cell growth
If a plant doesn't get enough, growth will be stunted and the leaves will turn yellow

Contain phosphorous for making DNA and cell membranes as well as for respiration and growth
If a plant doesn't get enough, it will have poor root growth and the leaves will turn purple

Helps the enzymes needed for photosynthesis and respiration
If a plant doesn't get enough, it will have poor flower and fruit growth and discoloured leaves

Magnesium ions are required to make chlorophyll (that is needed to absorb sunlight for photosynthesis)
Plants without enough magnesium have yellow leaves

Plants store glucose (a product of photosynthesis) as starch so any glucose they don't use in respiration will be stored

It would have used all the glucose for respiration so none would be left to store as starch

Waxy cuticle is waterproof (so pour hot water over the leaf to melt the wax)
Chlorophyll is a pigment that will affect the colour change as the green could be too dense (so bleach leaf in ethanol as chlorophyll is soluble in ethanol)
May start photosynthesising the experiment if it has been deprived of CO2 so it will gain starch during the experiment (so place the leaf in boiling water which will kill the leaf and stop any chemical reactions)

Place leaf in boiling water
Place ethanol in water bath and put leaf in ethanol, stirring until decoloured
Rinse leaf in warm water and place on white tile
Add iodine solution which turns blue-black if starch is present

Patches of green and white on leaf

In light- positive test
In dark- negative test (no light for photosynthesis)
In sealed bell jar- negative test (no CO2 for photosynthesis)
Variegated and in light- positive in areas of green but no photosynthesis in white bits as there is no chlorophyll)

High concentration of CO2 is yellow
Atmospheric (normal) concentration of CO2 is orange
Low concentration of CO2 is purple

Use pondweed (oxygen is a colourless gas and its bubbles can only be seen under water)
Sodium hydrogencarbonate added to water to make sure there's enough CO2 (if too much is added the water will become too acidic)
The rate of photosynthesis should increase as the light intensity increases

Lamp warmed up so it was heating the water so the temperature was not controlled (use LED lamp instead)
Small bubbles and big bubbles (only reliable if bubbles are the same size)
Pondweed has to be the same mass, surface area and species

Gases move by diffusion in and out of the stomata
More CO2 moves into the leaf from an area of high concentration to an area of low concentration

Photosynthesis only happens during the day (when there is light) but plants are always respiring
When light intensity is high, plants make more oxygen than they use up in respiration so they release oxygen but take in CO2 as they use up more CO2 than they produce
When the light intensity is low, plants only respire so they take in oxygen and release CO2

large surface area for diffusion
thin so short diffusion pathway
air spaces inside spongy mesophyll layer that allow gases to move easily between cells and increase surface area for gas exchange
full of holes (lower side) called stomata allow gases to diffuse in and out
Stomata close when it is dark so CO2 isn't let in (as the plant isn't photosynthesising) and water can't escape to stop the plant drying out
Stomata close when water supplies from roots dry up so the plant doesn't dry out and die
Opening and closing of the stomata is controlled by guard cells that increase in volume to open and decrease to close