(U3) Practicals

Question 1

Describe the details of the Benedict’s test for reducing sugars. (2)

What are the colour changes for positive results?

Answer 1

1. • add an equal vol of Benedict’s reagent to the test solution
   • heat to ~80ºC in a water bath
2. • Blue = -ve
   • green —> yellow —> orange = partially positive
   • brick-red ppt = +ve

Question 2

Describe the details of the Benedict’s test for non-reducing sugars. (4)

What are the colour changes for positive results?

Answer 2

1. • test part of solution for reducing sugar (benedicts test 1)
   • if none is present, hydrolyse by heating with HCl in a water bath
   • once cooled, neutralise with NaHCO₃
   • test with Benedict’s reagent
2. • blue = -ve
   • green —> yellow —> orange = partially positive
   • brick-red ppt = +ve

Question 3

Name a glucose specific test and state it’s colour changes

Answer 3

• clinistix strips
• pink to purple

Question 4

How do you test for starch?

What are the colour changes?

Answer 4

• add iodine solution
• yellow-brown (-ve) to blue-black (+ve)

Question 5

Outline the Biuret test

State the colour changes

Answer 5

1. • add equal volumes of KOH to the test sample
   • then a few drops of CuSO₄ solution
   • shake
2. Blue (-ve) to lilac/mauve (+ve)

Question 6

How do you calculate Rf values during chromatography?

What number should the value always be less than?

Answer 6

• (Distance moved by solute / distance moved by solvent front) x 100
• less than 1

Question 7

Describe how to conduct a belt transect (6)

Answer 7

• lay out a measuring tape down the area from zone A to E
• place a quadrat at regular intervals of 5m along the tape
• use a key to identify species
• calculate percentage cover
• repeat the process at a different area - increase reliability
• record results in a table & represent on a histogram

Question 8

Describe how to conduct a random sample (8)

Answer 8

• lay out a 2 measuring tapes perpendicularly
• Find co-ordinates using a random number generator
• place a quadrat at random intervals along the tapes
• use a key to identify and record types of plants
• calculate percentage cover of each species
• repeat the process at 10 or more different co-ordinates - get reliable average
• repeat in another area for comparison
• record results & represent on a bar chart

Question 9

Describe how to conduct a line transect (3)

What is it used for?

Answer 9

1.

• Just count along a measuring tape e.g. every meter
• use a key to identify individual species types
• no quadrat

2. Abundance calculation

Question 10

Describe how to conduct a pitfall trap (4)

What is it used to sample?

Answer 10

• Dig a hole
• Place container into hole, flush with ground level
• Raise the lid (leaf) with rocks at each side
• Collect sample 24 hours later

2. Ground invertebrates e.g. ground beetle

Question 11

What solution is used to stain chromosomes in a root tip squash?

Answer 11

Acetic orecin

Question 12

What substance can be used to absorb carbon dioxide in a respirometer?

Answer 12

Potassium / sodium hydroxide

Question 13

State 2 precautions necessary when drawing a base line in chromatography

Answer 13

any 2 from

• use a pencil (as its insoluble)
• ensure solvent is below the base line
• wear gloves

Question 14

Describe how to set up and develop a chromatogram to identify unknown amino acids

Include a safety precaution

(8)

Answer 14

Safety precaution: conduct in a fume cupboard

Setting up:

• fill base of tank with solvent
• draw base line in pencil above the solvent
• add a spot of the solution via a capillary tube to the baseline, concentrate by applying several times
• add spots of known amino acids for comparison
• wear gloves to avoid contamination

Developing:

• allow chromatogram to dry, then spray with ninhydrin
• heat with a hairdryer to develop the spots

Question 15

Describe how to conduct a pooter (2)

What is it used to sample?

Answer 15

1.

• place tube without gauze over insect
• place tube with gauze into mouth and suck insect into pot

2. Small invertebrates e.g. aphids

Question 16

What device is used to measure wind speed?

Answer 16

Anemometer

Question 17

What device is used to measure soil water content?

Answer 17

Soil moisture meter

Question 18

What device is used to measure soil pH?

Answer 18

Soil pH meter

Question 19

What device is used to measure light?

Answer 19

Lux meter

Question 20

What device is used to measure soil temperature?

Answer 20

Soil thermometer

Question 21

How do you determine the colour filter to use during colorimetry?

Answer 21

• Blue/green solution - red filter
• Red solution - green filter
• Yellow/orange solution - blue filter

Question 22

Why might students avoid placing transect tape over rock pools when sampling seaweed?

Answer 22

isn’t representative of the shore

Question 23

Why might systematic sampling be used on a rocky shore to sample seaweed?

Answer 23

There is gradation/zonation (of conditions) up the shore

Question 24

What is the dorsal side of the heart?

Answer 24

The back of the heart

Question 25

Which is the **ventral side** of the heart?

Answer 25

The **front** of the heart

Question 26

What is an **interrupted Belt Transect**? When is it used?

Answer 26

- Same as normal belt transect but **sample at intervals** - over long distances

Question 27

How do you measure **soil moisture content**? (**4**)

Answer 27

- Collect soil sample using *soil auger*, - **weigh, dry** in desiccator until *constant mass* - + calc **% soil moisture content** - ((Initial soil mass - final soil mass)/initial soil mass) x 100

Question 28

How do you measure **soil organic content**? (**6**)

Answer 28

- Place **dry soil in crucible + reweigh**, - **burn off humus** with bunsen burner, - mix soil at intervals so *all organic content* **burnt**, - allow to *cool, burn + reweigh* to constant mass. - Calc **% organic content** - ((Dry soil mass - burnt soil mass)/initial soil mass) x 100

Question 29

Describe how to **dissect** a mammalian **heart** (**4**)

Answer 29

- use a **scalpel** on a **dissection board** - cut through the **ventral/front wall** - from the **atrium to the base of the ventricle** along the septum - *pull* the *two sides apart* to **expose** the **two heart chambers**

Question 30

Describe how to measure the **average water potential** of *potato cells* using the **weighing method** (**6**)

Answer 30

- prepare *cylinders of potato* and **weigh** - add the cylinders of potato to a **range of sucrose** solutions - leave for between **1–48 hours** - *remove* the potato, **surface dry and reweigh** - calculate **percentage change in mass** for each potato cylinder - where the *line of best fit* **crosses the x-axis**, the **solute potential** of the *immersing solution* is **equal** to the **water potential** of the *potato tissue*

Question 31

Describe how to *calibrate* an **eyepiece graticule** (**4**)

Answer 31

- at *low power*, **line up the 0 values** of the *eyepiece graticule and stage micrometer* - find a **position** further along the slide where the *marked division lines* in **both scales overlap** - this **distance can be calculated** on the *stage micrometer* - **length of each eyepiece division** can be calculated by **dividing the distance** calculated on the stage micrometer *by* the **number of eyepiece divisions**

Question 32

Describe how to **convert** colorimeter readings from **% transmission** into **starch concentrations** (**2**)

Answer 32

- Plot a calibration curve of % transmission vs starch concentration; - **using standard/known concentrations of starch** or use serial dilution to create calibration curve of known starch concentration and % transmission

Question 33

Outline how to conduct a **root tip squash** experiment (**6**)

Answer 33

- *allow* an onion to **grow roots tips**, then **cut** *approx 5mm* using a *scalpel* - place the root tips in **HCl** to *breakdown their cell walls & soften* them - **rinse with cold water** via a pipette - place the **root tip** on a clean **slide** and apply **acetic orecin** (to stain chromatids) - use a *scalpel* to **cut the tip** further, then place a **cover slip** over the tip and **press down** with your thumb - use a **microscope** to observe