Biochemical and Microscopy Lab Protocols for Plant and Food Analysis
Table of Contents
- Overview
- Starch test (iodine)
- Reducing sugars (Benedict's)
- Proteins (Biuret)
- Lipids (ethanol emulsion test)
- Vitamin C (DCPIP)
- Hydrogen carbonate indicator and CO2 sources
- Stomata counting
- Control tests
- Humidity adjustments
- Colorimetry and endpoint clarity
- Drops of liquid experiments and error handling
- Investigation questions
- Surface area calculation with grid paper
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Overview
This document lists a set of laboratory tests to detect biomolecules and assess plant leaf features and experimental reliability. It covers starch detection with iodine, reducing sugars with Benedict's solution, protein detection with Biuret, lipid detection with an ethanol emulsion method, and vitamin C quantification with DCPIP. It also discusses indicators for CO2, stomatal counting on leaves, control experiments, humidity adjustments, the use of colorimetry for accurate endpoints, and common experimental errors with improvements. It includes guidance on formulating an investigation question, variables, procedure, safety, repetition, and a method for calculating leaf surface area using grid paper. The content preserves stepwise actions, data points, and context from the source material.
Starch test (iodine)
Presence of starch - iodine solution
- turns from yellow brown to blue-black
Reducing sugars (Benedict's)
Presence of reducing sugars - Benedict's solution
- turns from blue to orange red
Proteins (Biuret)
Presence of proteins - Biuret solution
- turns from blue to purple/violet
Lipids (ethanol emulsion test)
Presence of lipids - ethanol emulsion test
- mix the food with ethanol and shake
- add ethanol to distilled water
- milky white appearance
Vitamin C (DCPIP)
Presence of vitamin c - DCPIP
- purple to colourless
Hydrogen carbonate indicator and CO2 sources
Hydrogen carbonate indicator
- red at normal co2 yellow at high, purple at low
Sodium hydrogen carbonate solution - source of CO2
Sodium hydroxide - used to absorb CO2
Buffer solution - used to fix pH at a certain point
Stomata counting
To determine no of stomata
- polish leaf with varnish
- leave to dry and remove the varnish layer
- put it on a microscopic slide and count
Control tests
- adding water instead of the substance
- use boiled solution of substance to eliminate enzyme activity
- use glass bead to assess for non biological factors
Humidity adjustments
- to decrease humidity - use a dehumidifier
- to increase humidity - place hot water bowls around it
Colorimetry and endpoint clarity
- use colorimeter or colour chart when experiment involves colour change(indicator) as it is
difficult to identify endpoint with naked eyes
Drops of liquid experiments and error handling
yany experiment involving drops of a liquid.
- error → volume of drops size is inconsistent or unknown or different
- improvement → use syringe/ burette/ graduated pipette
any experiment involving shaking or stirring a liquid.
- error → different degree of shaking/mixing or stirring
- improvement → shake at a fixed speed or use a mechanical stirrer
- error → different time of mixing or shaking
- improvement → shake or stir for a fixed time;
yany experiment involving hot or cold water.
- error → temperature of the water not controlled / temperature changes
- improvement → thermostatically controlled water-bath / insulation / bunsen burner
any experiment involving unknown volume of a liquid.
- error → volume of starch not measured
- improvement → measuring cylinder / burette / pipette
Investigation questions
- independent variable
- dependant variable
- constant/controlled variables (need at least 2 max 3)
- procedure of investigation (methods)
- safety precautions (goggles,mask,gloves)
- repeat experiment two or more times
Surface area calculation with grid paper
how to calculate surface area with grid paper :
Fig shows the lower surface of a dicotyledon leaf; to the nearest cm^2. The example area is around 30-36 cm^2. Methods include counting empty squares or partial squares and subtracting from total grid squares to estimate leaf surface area. Strategies note counting dots to avoid double counting; whole squares included in total leaf area.
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