BIOLOGY Practicals EOY

Question 1

Microscopy

Answer 1

use a light microscope to observe, draw and label a selection of plant and animal cells.

Question 2

MICROSCOPY: Purpose of practical / Background

Answer 2

Light microscopes are really useful for studying cells. In the past they have been used to learn about how cells work. Scientists often produce drawings of what they see down a microscope

Question 3

MICROSCOPY: Safety

Answer 3

Stains may irritate skin/eyes - wear protection
Don’t use direct sunlight as a source of light
If using a lamp be aware it may get hot.
Take care when cutting plant tissue samples.
Swabs used to collect cheek cells should be sterile and disposed of properly.

Question 4

MICROSCOPY: Sample method / Apparatus

Answer 4

Place a tissue sample on a microscope slide.
Add a few drops of a suitable stain
Lower the coverslip (at an angle) onto the tissue
Place the slide on the microscope stage and focus on the cells using the lower power objective lens (+ the coarse and fine focus knobs)
Change to higher powered objective lens and focus
Draw any types of cells that cann be seen
Add a magnification scale to the diagram.

Question 5

MICROSCOPY: Why do you need a stain?

Answer 5

To make certain structures visible

Question 6

MICROSCOPY: Why lower the coverslip and press carefully?

Answer 6

To remove any bubbles

Question 7

MICROSCOPY: Why can you see the nucleus and cell wall but not the mitochondria?

Answer 7

They’re too small

Question 8

MICROSCOPY: How could we see the smaller structures (e.g. ribosomes)?

Answer 8

You would need to use an electron microscope which has a higher magnification and higher resolution.

Question 9

MICROSCOPY: You must be able to remember, use and rearrange the magnification equation

Answer 9

You might need to use your ruler to measure the size of images and work out their real size or magnification
Measure carefully and remember it’s usually best to work in mm rather than cm
Make sure you can convert between units. The important ones are 1mm = 1000 um and 1um = 1000nm

Question 10

MICROSCOPY: Drawings (there are rules to scientific drawings)

Answer 10

no shading, no broken/sketchy/overlapping lines, labels should be added with ruled lines (NOT ARROWS) and there should be a magnification/scale bar

Question 11

OSMOSIS

Answer 11

Investigate the effect of a range of concentrations of sugar or salt solutions on the mass of plant tissue

Question 12

OSMOSIS: Calculate the change in mass as a percentage change

Answer 12

change in mass / starting mass x 100

Question 13

OSMOSIS: Purpose of practical / Background

Answer 13

Osmosis is the movement of water molecules from a more dilute solution to a more concentrated solution through a partially permeable membrane.
Sugar and salt are examples of solutes (they dissolve in water). The more solute dissolved, the more concentrated the solution is. Potatoes are often used for this investigation.

Question 14

OSMOSIS: Variables

Answer 14

IV - The concentration of sugar/salt
DV - The change in mass of the potato
CVs - The temperature, the length of time the cylinders are left for, the shape of the cylinders, drying the cylinders before re-weighing, skin should be removed from cylinders, the cylinders should be fully submerged in the solution.

Question 15

OSMOSIS: other information

Answer 15

Length could be used instead of mass
A bung might be used to prevent the water from the solutions evaporating (as this would change the concentration)

Question 16

OSMOSIS: Safety

Answer 16

Care must be taken when cutting the cylinders of potato

Question 17

OSMOSIS: Sample method / apparatus

Answer 17

Cut some cylinders of potato tissue using a cork borer and measure their mass.
Submerge the cylinders in different concentrations of salt/sugar (e.g. 0.0 molar, 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar, 1 molar)
After 30-60 minutes, remove the cylinders, dab them dry and reweigh them
Calculate the change in mass or length.

Question 18

OSMOSIS: Results

Answer 18

High concentration of salt/sugar in solution = water moves out of potato cells into solution by osmosis. Potato loses mass
Low concentration of salt/sugar in solution = water moves into potato cells from solution by osmosis. Potato gains mass
If no water goes into or out of the potato overall and it doesn’t change mass,, then the solution is exactly the same concentration as inside the potato.

Question 19

OSMOSIS: You should be able to use a table or a graph to calculate the concentration of the cytoplasm of the plant tissues

Answer 19

This will be when there is no overall movement of water into or out of the cell so there will be no change in mass (on a graph this might be where the line crosses the axis)

Question 20

OSMOSIS: Why is it better to measure the change in mass/percentage change in mass rather than just the final mass?

Answer 20

This allows a clear comparison to be made even if the starting masses are slightly different

Question 21

OSMOSIS: How to calculate the rate of water uptake?

Answer 21

The water uptake is measured by recording the time taken for a bubble in the tube to move a set distance

Question 22

FOOD TESTS:

Answer 22

Use qualitative reagents to test for a range of carbohydrates, lipids and proteins

Question 23

FOOD TESTS: purpose of practical / background

Answer 23

to find out whether starch, sugars or protein are present in samples

Question 24

FOOD TESTS: other information

Answer 24

food samples might need to be chopped up or crushed to release the substance being tested for
it’s important to refer to “iodine solution” not just iodine
Don’t forget to mention that for the test for sugars, the sample needs to be heated

Question 25

FOOD TESTS: safety

Answer 25

care should be taken when using hot water bath the chemical used can be irritants so eye protection should be worn

Question 26

FOOD TESTS: STARCH (method/apparatus/results)

Answer 26

CHEMICAL: iodine solution TESTS FOR: starch HOW TO CARRY OUT THE TEST: Add the iodine solution directly to the substance to be tested (in solid or liquid form) and look for a colour change RESULT: Turns blue black with starch

Question 27

FOOD TESTS: PROTEIN (method/appparatus/results)

Answer 27

CHEMICAL: Biuret's solution TESTS FOR: protein HOW TO CARRY OUT THE TEST: Add the Biuret's solution / suspension to the substance to be tested and look for a colour change RESULT: Turns purple with protein

Question 28

FOOD TESTS: SUGAR (method/apparatus/results)

Answer 28

CHEMICAL: Benedict's solution TESTS FOR: sugar HOW TO CARRY OUT THE TEST: Add Benedict's solution / suspension to the substance to be tested Heat for 2 mins in a water bath at boiling point and look for a colour change

Question 29

FOOD TESTS: LIPIDS (method/apparatus/results)

Answer 29

CHEMICAL: ethanol TESTS FOR: lipid HOW TO CARRY OUT THE TEST: Add ethanol to the solution / suspension to be tested and shake thoroughly Then add water and look for a colour change RESULT: Turns cloudy / milky with lipid

Question 30

FOOD TESTS: What is meant by a qualitative test?

Answer 30

A test that shows whether a particular substance is present This is different to a quantitative test which would give you numerical data (how much of something is present)

Question 31

FOOD TESTS: How could mistakes be made?

Answer 31

Think about whether contamination could have occured during the investigation, e.g. Has the same chopping board been used for two different food samples? Qualitative experiments can be subjective (based on human judgement) - different people might judge a colour differently.

Question 32

ENZYMES:

Answer 32

Investigating the effect of pH on the rate of reaction of amylase enzyme

Question 33

ENZYMES: purpose of practical / Background

Answer 33

To find out what happens to the rate of enzyme activity when the pH changes. An enzyme is a biological catalyst which speeds up reactions in the body. Amylase is an enzyme that breaks down starch into sugars. In the body it is made in the salivary glands and pancreas pH: how acidic or alkali a substance is (1 = strong acid, 7 = neutral, 14 = strong alkali)

Question 34

ENZYMES: variables

Answer 34

IV - the pH (this can be changed using different pH buffers) DV - the time taken for amylase to digest starch (measured by using iodine solution to test for the presence of starch) CVs - temperature, concentration of amylase, starting concentration of starch

Question 35

ENZYMES: Other information

Answer 35

You should be aware of how this experiment could be modified to investigate a different variable on the enzyme e.g. temperature. For those investigations, pH would be a control variable, (kept the same using a pH buffer)

Question 36

ENZYMES: Safety

Answer 36

iodine/enzyme solution could irritate skin, pH buffer solutions could be corrosive - take care, wear eye protection, wash off skin

Question 37

ENZYMES: sample method / apparatus

Answer 37

Put a test tube of amylase and a test tube of starch into a water bath until they are both the same temperature Add the amylase to the starch Every 30s remove a drop and add to a spotting tile containing iodine solution until it stops turning blue black and stays orange Record how long it takes for the starch to be completely digested Repeat this at different pH values using different buffer solutions

Question 38

ENZYMES: results

Answer 38

if the iodine solution changes to blue/black, it means the starch is present (hasn't been fully digested) The more active the enzyme is (closer to its optimum) the quicker it will be until the iodine solution stays orange/brown

Question 39

ENZYMES: equipment

Answer 39

spotting tile water bath dropper

Question 40

ENZYMES: to interpret results and explain them using knowledge of enzymes

Answer 40

at pH values that are too high/too low compared to the optimum pH, the enzyme will denature (the active site changes so the substrate can no longer fit)

Question 41

ENZYMES: sources of error

Answer 41

subjective measurement (the colour change is based on human judgement)

Question 42

ENZYMES:why do you need a water bath

Answer 42

to maintain the temperature, because temperature affects the rate of reation

Question 43

ENZYMES: why place the enzyme and starch solution in the water bath separately for 5 minutes

Answer 43

to allow the solutions to reach the same temperature as each other (and the water bath) because temperature affects the rate of reaction. A temperature of 40oC is often used for human enzymes, as this is around the optimum temperature

Question 44

If you test at pH 3, 4, 5, 6, 7, 8, 9 and 10, Why don't we know the exact optimum pH?

Answer 44

Although two answers may show quick reactions (e.g. pH 7 and pH 8), the actual optimum pH could be between those numbers (e.g. pH 7.6) so you need to test different smaller pH intervals between these values to determine the optimum more accurately