biology C1.3

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How is light energy converted to chemical energy in photosynthesis?

Light energy is absorbed by chlorophyll and other pigments, exciting electrons that drive the synthesis of ATP and NADPH, which are then used to convert CO₂ into glucose.

flowchart for energy conversions in living organisms

Sunlight → chemical energy in glucose → ATP → energy for cell activities → heat.

why do organisms need energy?

active transport

biosynthesis of macromolecules

movement

what is the principal energy source in most ecosystems?

sunlight

chemical equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

source of atoms for glucose

carbon from CO2

hydrogen from water 

oxygen from CO2

define photolysis

Splitting of water molecules using light energy to produce electrons, protons, and oxygen.

source of oxygen in photosynthesis

Water molecules split during photolysis.

outline pigment seperation using chromatography

extract pigments from leaves

spot extract on chromatography paper

place paper in solvent; pigments move at different rates

measure pigment positions to calculate Rf values

how to identify pigments

by colour and Rf value

range of visible light

400-700 nm

function of pigments?

absorb light energy for photosynthesis

primary and accessory pigments

primary: chlorophyll a

accessory: chlorophyll b

why are most plants green?

chlorophyll reflects green light and absorbs mainly red and blue light

absorption spectrum

light wavelengths absorbed by pigments

action spectrum

rate of photosynthesis at different wavelengths

Why does action spectrum curve match absorption spectrum?

Higher absorption at certain wavelengths → more energy for photosynthesis → higher rate.

how to measure photosynthesis rate?

measure O2 production or CO2 consumption

define limiting factor

Environmental factor that restricts the rate of a process, even if other factors are optimal.

how do factors limit photosynthesis?

light intensity

CO2 concentration

temperature

techniques for varying factors

light

CO2

temperature

source of atmospheric CO2 beyond historical 300 ppm?

fossil fuel combustion and human activites

greenhouse experiments

encolsed, controlled environemtn; precise CO2 control

FACE

open-air, realistic conditions

questions addressed in CO2 enrichment experiments

effect of higher CO2 on photosyntheiss rate

effect on plant growth

possible limitations by other factors (nutrients, water, light)