ag (1112) - Lettuce: photosynthesis & respiration

this was our last lesson on working with the plant production topic.

first we talked about what overspraying (pesticides) can do.. it was mainly impact the enfironment.. in 4 ways:

- kills worms and other decomposers in the soil
- kills beneficial insects such as ladybird beetles, bees and predatory wasps
- kills aquatic organisms such as fish and seaweed (if getting into waterways)
- harms humans (if they drink from these waterways) and grazing livestock like cows or sheep

then we talked about photosynthesis and respiration, which we know that are pretty much each other's opposite processes.

water + CO2 -> (light energy goes in) -> glucose + oxygen

the glucose is the main product and oxygen is the byproduct

cellular respiration is the opposite

glucose + oxygen -> (ATPs released) -> water + CO2

coz oxygen is needed to release ATPs from glucose

the net assimiliation rate (NAR) refers to the rate at, which the plant grows. ie. the difference between photosynthesis and respiration. if its equal to 0, the plant just survives.. it doesnt grow.

photosynthesis and respiration is most easily controlled in greenhouses.

to control PHOTOSYNTHESIS:
- CO2 sensors detect when to pump gas into greenhouse
- temperature can be regulated with irrigation (water cools things) and airconditioning in greenhouses
- irrigation (eg drip irrigation) helps control water, and ground cover (eg mulch) helps to reduce waterloss
- light wavelength. this one is confusing. greenhouses are green to reflect green wavelength light out. plants dont need green wavelength light to photosynthesize (probably why plants are green too) and so the greenhouse reflects green light away and the rest comes in.
- to control light exposure (it cant really be controlled for field crops) but indoor crops it can be controlled by using artificial lights (to extend or control day length) tricking plants into fruiting (flowering out of season)

we didnt talk about respiration yet.. i take it we will tomorrow