Edexcel IAL Biology Unit 3

Describe the difference between a semi-quantitative and a quantitative test

A semi-quantitative test gives {an estimate / a range} of the concentration of a substance

A quantitative test determines the exact concentration of a substance

Describe how you could test for protein

addition of {biuret reagent / base and copper sulfate}

it turns to a purple colour

Some of the total nitrogen content of a food is not due to protein. Give one other type of organic molecule that contains nitrogen.

nucleic acids, lipids, amino acids, ATP

Describe how each of these variables could be kept constant : Temperature, light intensity, humidity and pH

temperature - use of thermostatically or controlled water bath/incubator

pH - use of buffer

light intensity - use same bulb / same distance from bulb / light bank / same windowsill

humidity - air-conditioned room

Explain how you could modify a method to decide is two variables are statistically significant on a graph.

repeat readings under the same conditions (each time) and calculate (mean and) standard deviation and then look for overlap in SDs / perform t-test to see any significance

Describe how a suitable pH could be decided on experimentally.

carry out the experiment described at constant {temperature / substrate / enzyme concentration} At a range of pHs (controlled by buffers) choose the pH which gives a time which is not {too short / too long} (for practicality)

Describe a safe method to prepare and examine the structure of human cheek cells.

bud into disinfectant/sterile/fresh bud/toothpick/wear gloves/ goggles/safe use of microscope/slides/careful use of bud/stain to prevent injury

use of cotton bud, followed by use of stain/dye, place cells (on slide) under coverslip, use of high power of microscope

State two differences you would observe between a plant cell and a human red blood cell when using a light microscope.

plant cell has nucleus, RBC does not
(allow one mark if both statements correct but not comparative)

plant has /vacuole/large(r) vacuole/chloroplasts/cell wall/regular shape unlike RBC

Explain the role of the pollen tube in plant reproduction.

it {carries / transports} the male gametes / nuclei / generative nucleus to the ovule / micropyle / ovary / ovum / female gamete to {fuse with / fertilise} {ovum / egg (cell) / female gamete / female nucleus / polar nuclei digest tissue of style

Explain why pollen tubes grow in the same direction from the stigma, after pollination.

the tubes grow towards the {micropyle / ovule / ovary / ovum / female gamete} {due to chemicals (released by the embryo sac) / it is chemotropic}

Explain why changes in temperature will affect an investigation.

it involves {enzymes / (chemical) reactions} and enzymes / (chemical) reactions are affected by temperature

Describe a safe method to observe the stages of mitosis in roots

cut root tip and then place root tips in (warm) acid (acetic / ethanoic) orcein / toluidine blue /methylene blue)

then root tip placed on a microscope slide and macerated / teased / described} / squashed,

use of high power (on a microscope)

rinsing tips in water / wearing gloves / goggles

Describe how the data in the table could have been obtained using a 1% starch solution

Carry out serial dilution using 1% of available stock solution. To 1ml of 1% solution, add 9ml of distilled water to obtain 0.1%. Then take 1ml of the 0.1% and add 9ml of distilled water to it to obtain 0.01%. Continue this dilution trend two more times to obtain 0.0001%. To each test tube of solution add the same volume and conc. of iodine . Observe the color of resultant solution in test similar in diameter. Note down the observed color of solution

Explain how increasing the quantity of plant foods that contain vitamin C in the diet may protect against heart disease

because (antioxidants / vitamin C) reduce (the quantity of) free radicals that cause damage to {cells / tissues / blood vessels / endothelium} reducing {plaque / atheroma} formation

DCPIP Experiment

use {equal / controlled} masses of the foods, use {standard / same} extraction method, measure out {equal / same} volume of DCPIP solution then add food extract dropwise until {no colour remains / blue to colourless}, record {volume / number of drops} used, calculate vitamin C content / description of calibration of DCPIP with known vitamin C concentration

State one difference and one similarity between the nuclear envelope and the cell membrane.

Difference:

nuclear envelope double membrane, cell membrane single OR {nuclear pore present in nuclear envelope, not in cell membrane / cell membrane has channels}

Similarity:

both membranes are phospholipid (bilayer) transport of different substances, both control movement of {substances / relevant named}

Name two types of cell found in plant fibres

xylem and sclerenchyma

Fibres have cell walls with secondary thickening of lignin. Describe two ways in which secondary thickening affects the properties of the cell.

increased strength / support

makes cell (wall) impermeable / reduces permeability e.g., stops / reduces water entering or leaving

Describe how fibre diameter could be measured accurately using a microscope.

cut {thin / transverse} section (of fibre) / lay (fibre on slide) on microscope and measure using (eyepiece) graticule which has been calibrated with stage micrometer

Explain two reasons why aseptic techniques are used

prevents escape / spreading of bacteria

prevents {contamination of the agar or cultures with (other types of) bacteria) / cross contamination /effect on the results

Why is a low power and then a high power microscope is used?

Using a low power microscope to locate the specimen and a high power microscope to magnify

Why does incubation of plants take place?

To allow chemicals in the extract to diffuse into agar

Reason behind placing root tips in acid

To break and soften the middle lamella

Risks and how to minimize them.

hot water / scalding risk so wear a lab coat / (heat resistant) gloves ;

(Bunsen) risk of burning so keep away from flame ;

alkaline solution risk to skin or eyes so wear goggles or gloves / lab coat / wash affected area immediately ;

skin contact allergy so wear gloves / lab coat / wash affected area immediately or use coated enzyme ;

inhalation allergy so wear mask / use coated enzyme ; spillages so clean up immediately ;

ethanol is flammable so keep it away from naked flames

To estimate the reliability of data what should be done?

more readings / repeat / need to know how many times it was repeated

(idea of replication) under same conditions ;

standard deviation / standard error / range

Assuming that the stem is circular, suggest how stem cross-sectional area could be determined accurately.

measure diameter with {calipers / vernier calipers/micrometer (screw gauge)} and then use πr2

State how three mineral ions are used by plants.

nitrates are needed for {proteins / amino acids / DNA / RNA)

magnesium is needed for chlorophyll for photosynthesis

calcium is needed for tsuport of cell wall and stength

Explain how optimum temperature can be determined.

find the rate of production of glucose / find the {concentration / eq} of glucose after set time at a (suitable) range of temperatures

idea that optimum temperature is the temperature at which the reaction is quickest

e.g add a known volume of a known concentration of enzyme to the cellulose / add a known mass of cellulose (to a known volume of water) / idea of equilibration to the appropriate temperature / idea of sugar test / use of Benedict's / keeping pH constant / plot graph of temp against glucose production / repeat at narrow range around where optimum thought to be from graph

State two factors, other than the antimicrobial effect, that could affect the area of the zone of inhibition

{solubility / concentration / volume} of extract / solvent used size of molecules in the extract

rate of diffusion of extract into agar

Describe how plants from these rainforests could be tested for their antimicrobial properties.

idea of testing {different / named} parts of each plant

idea of grinding the plant material up

idea of preparing a lawn of bacteria

description of how extract will be added to culture incubating bacteria at temperature in range 20 º to 35ºC and stated time in range 1 to 7 days

idea of measuring {diameter / area} of zones of inhibition indication of using aseptic technique

repeat experiment and calculating a mean

To calculate the tensile strength of the fibre, the cross-sectional area has to be determined. (i) Devise a method to determine the cross-sectional area of a fibre, using the following equipment:

• a sharp blade

• a microscope

• a microscope slide and coverslip

• an eyepiece graticule • a stage micrometre

a (transverse) section/layer/slice of the fibre is cut, ensure section is flat, graticule calibrated (with stage micrometer) diameter measured/found and converted to measurement with calibration data and area calculated using πr2

Describe a valid method that could be used to compare the breaking force of different fibres.

fiber is fixed between two clamps, and gradual masses are added to it, and record when the fiber breaks, replicate the experiment and calculate the mean/SD and Relative humidity / temperature / length of fibre should be kept constant

What is the independent variable

Factor changed in the investigation

State what a Dependent variable is

measured variable that changes as a result of independent variable