2.9 photosynthesis Flashcards
how do you obtain water free of carbon dioxide?
boil and cool water
how to improve paper chromatography?
use thin layer chromatography for better results
what are autotrophs?
- organisms able to convert energy and derive nutrition from non-biotic sources to produce high energy molecules for biological use or storage
- plants who photosynthesise and chemotrophs who derive energy from deep sea volcanic vents
- autotrophs vs heterotrophs: dependent on other living organisms for energy and nutrition
explain the photosynthesis process
6CO2 + 6H2O –(SUNLIGHT)–> C6H12O6 + 6O2
- C: carbon is ‘fixed’ from CO2 and used to produce glucose
- H2: water is split; hydrogen used to help in production of glucose, O2 excreted as waste gas
- sunlight: light energy transferred to chemical energy stored in glucose molecule
- C6H12O6: used in respiration, stored as starch / used to build cell walls or cellulose
- metabolic pathways controlled by enzymes
2 phases
LIGHT DEPENDENT
- light energy used by chlorophyll to carry out photolysis (splitting) of water
- electrons released from photolysis become excited; gain energy converted from light energy
- energy from excited electrons used to produce high energy compounds (atp and reduced nadph)
LIGHT INDEPENDENT
- energy from high energy compounds used to reduce CO2 to produce C612O6
- carbon fixation: conversion of inorganic CO2 to organic molecules like glucose
how is oxygen produced in photosynthesis?
2H2O –(SUNLIGHT + CHLOROPHYLL)–> O2 + 4H+ +4e
- light energy used by chlorophyll (facilitator) to split water into oxygen, hydrogen ions (protons), electrons
how are carbohydrates and other compounds produced from carbon dioxide?
- ENERGY needed
- light dependent phase: light energy needed to generate high energy compounds (atp and reduced nadph)
- energy from these compounds used in calvin-benson cycle to convert CO2 –> g3p (glyceraldehyde 3 phosphate)
- g3p –> glucose –> other monosaccharides –> link together to form disaccharides and polysaccharides (in condensation reaction; form glycosidic bonds)
why do leaves and most plants appear green in colour?
- plant pigments like chlorophyll found on thylakoid membrane of chloroplasts in plant cells
- pigments absorb some light and reflect others
- chlorophyll absorbs red and blue light and reflects light in green wavelength
what is the absorption spectrum for and how does it work?
- specialised equipment can be used to shine light of different wavelength on leaf and determine absorption / reflection of light at different wavelength
- results can be plotted on a graph: absorption spectrum
what are the different pigments in leaves?
- photosynthetic pigments:
- 2 main types of chlorophyll: chlorophyll a & chlorophyll b - accessory pigments: absorb light at slightly different wavelength –> extend range of light absorption for photosynthesis
- chlorophyll is broken down first during senescence (deteriorating of plant w age) –> other pigments become more visible
- leaves turn yellow / reddish brown before shedding
how does carbon dioxide concentration / light intensity affect rate of photosynthesis?
- when carbon dioxide concentration / light intensity increases the rate of photosynthesis increases; at low levels it is the limiting factor
- at high levels of carbon dioxide concentration / light intensity further increases have no effect on rate of photosynthesis; another factor is limiting rate of photosynthesis (chloroplasts working at maximum efficiency, temp, enzymes)
- photosynthesis is enzyme-catalysed metabolic pathway
- CO2 is substrate for metabolic pathway; relationship is similar to how enzyme reactions are limited by substrate concentration
how does temperature affect rate of photosynthesis?
- photosynthesis is a metabolic pathway catalysed by enzymes; hence relationship is similar to how enzyme reactions are affected by temperature
- increase in temp gives molecules more kinetic energy –> substrates collide w active sites more frequently –> rate of photosynthesis increases
- as temp approaches optimum temp, enzymes begin to denature (active site changes to become non-functional) –> rate of photosynthesis increases more slowly and eventually peaks
- after optimum temp enzymes rapidly denature –> fast decrease in rate of photosynthesis as temp increases
how can you record rate of photosynthesis experimentally?
SHORT TERM:
- CO2 sensor –> determine changes in CO2 concentration in sealed chamber containing plant [can also use pH sensor as CO2 is slightly acidic in water]
- O2 probe –> measures concentration fo dissolved oxygen; use aquatic plant
LONG TERM:
- measure conc. of glucose / starch in leaf by measuring biomass
how did photosynthesis affect the earth over time?
- atmosphere, ocean, rock deposition
- primordial earth: highly reducing atmosphere w v. little oxygen
- prokaryotes w chlorophyll started photosynthesising; oxygen produced as by-product
- over time oxygen conc. in atmosphere slowly started to increase
- w evolution of plants, photosynthesis took place on larger scale and atmospheric oxygen levels started to increase until stabilised at 21%
- process of photosynthesis allows inorganic CO2 to enter ecosystem in organic forms
- organisms consume others –> derive carbon
- many marine organisms use carbon to form CaCO3, as seen in hard shells of molluscs and corals
- when they die, shells are deposited at bottom of ocean and over long periods of time are compressed to form limestone
