Paper 3 - 6 Main Praticals

Question 1

Use of a light microscope to investigate the structure of cells and tissues :

How do you focus your microscope?

Answer 1

1) put slide on the stage, with most promising region in middle where light comes throug
2) focus at low power first even if you need high power magnification
3) focus with larger coarse-focusing knobs then when you nearly have item in focus use fine focusing knobs
4) if you want to increase magnification, move slide so that the most promising region is exactly in the middle of the field view and then change to higher magnification lens

Question 2

Use of a light microscope to investigate the structure of cells and tissues :

How do you look after your microscope?

Answer 2

1) always focus by moving lens and the specimen further apart never close
2) make sure slide is clean and dry before putting it on the stage
3) never touch the surface of the lends with your fingers
4) carry microscope carefully with a hand under it to supper its weight securely

Question 3

Use of a light microscope to investigate the structure of cells and tissues :

Troubleshooting (5)

Answer 3

1) Problem: nothing is visible when I try to focus
Solution: make sure specimen is actually under the lens, it is easier to find it starting in Lower power
2) Problem: a circle with a thick black rim is visible
Solution: air bubble on slide- ignore it and try to improve technique
3) problem: blurred part of the image even when I focus it as well as I can
Solution: lense or slide has dirt on it - ask teacher to clean it
4) problem: image is very dark
Solution: increase the amount of light passing through specimen by adjusting the diaphragm
5) problem: image looks rather bleached
Solution: decrease the amount of light passing through the specimen by adjusting the diaphragm

Question 4

Use of a light microscope to investigate the structure of cells and tissues :

Types of slides?

Answer 4

Type of slide can be permanent or temporary
Permanent ones are usually made by experts -
- Temporary are easier and quicker and we can do this ourselves

Question 5

Use of a light microscope to investigate the structure of cells and tissues :

Examining and drawing plant and animal cells

Answer 5

1) place the cells on the slide in a layer not more than one cell thick
2) add Drop of water or stain
3) carefully lower a cover slip into the drop, try to avoid trapping bubbles
4) remove excess fluid or stain by putting the slide inside a folded piece of paper towel and pressing lightly on the cover slip

Question 6

Use of a light microscope to investigate the structure of cells and tissues :

Moss leaf

Answer 6

Use a moss leaf with very think leaves

Drop of water or methylene blue stain

Question 7

Use of a light microscope to investigate the structure of cells and tissues :

Banana fruit cell

Answer 7

Scrap small amount of soft tissue from banana

Drop of iodine

Question 8

Use of a light microscope to investigate the structure of cells and tissues :

Mammalian liver cell

Answer 8

Scrap from freshly cut liver

Smear onto slide

Add methylene blue to stain

Question 9

Use of a light microscope to investigate the structure of cells and tissues :

Leaf lower epidermis

Answer 9

Peel the lower epidermis off a leaf

Mount in water or in methylene blue

Question 10

Use of a light microscope to investigate the structure of cells and tissues :

Human cheek cell

Answer 10

Scrape from inside of your cheek with cotton bud

Methylene blue

Question 11

Use of a light microscope to investigate the structure of cells and tissues :

White blood cell

Answer 11

Thin layer of mammalian blood

Leishmans stain

Question 12

Calculation of the magnification of drawings and the actual size of structures shown in drawings or micrographs

School microscopes level:

Answer 12

X 40 low power
X 100 medium power
X 400 high power

Question 13

Calculation of the magnification of drawings and the actual size of structures shown in drawings or micrographs

What’s a micrograph?

Answer 13

A picture taken down a ncropscope

Question 14

Calculation of the magnification of drawings and the actual size of structures shown in drawings or micrographs

Equations for magnification

Answer 14

Mag= size of image/ actual size of specimen

Question 15

Calculation of the magnification of drawings and the actual size of structures shown in drawings or micrographs

How are millimetres concerned into micrometers?

Answer 15

By mutiplying by a thousand

Question 16

Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions:

What are the 4 osmotic ally active solute that are used in osmosis experiments?

Answer 16

Glucose
sodium ions
Potassium ions
Chloride ions

Question 17

Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions:

What is the osmolarity of a solution?

Answer 17

The total concentration of osmotic ally active solutes

Question 18

Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions:

Units for measuring osmolarity?

Answer 18

Osmoles or milliosmoles - normal osmolarity of human tissue is about 300 mOsm

Question 19

Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions:

What do hypertonic solutions and hypotonic solutions have?

Answer 19

Hytertonic- has a higher osmolarity
Hypotonic- lower osmolarity
Isotonic- solution has the same osmolarity as a tissue

Use hypotonic and hypertonic to find out the isotonic

Question 20

Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions:

Explain experiment for osmolarity using potato tubers

Answer 20

1) dilute a 1 mol dm-3 sodium chloride solution to obtain the conc shown on graph
2) obtain samples of a plant tissue that are similar enough to each other to give comparable results
3) ensure that the surface of the tissue samples is dry when finding their mass, at both the start and the end of the experiment
4) ensure that all variables are kept constant apart from salt concentration of the bathing solution
5) leave the tissue in the solutions for long enough to get a significant mass change but not so long that another factor affects the mass such as decomposition

Question 21

Experimental investigation of a factor affecting enzyme activity:

Catalase and this experiment

Answer 21

Catalase is more the most widespread enzymes it catalyses the conversion of hydrogen peroxide toxic - byproducts of metabolism -into water and oxygen

Question 22

Experimental investigation of a factor affecting enzyme activity:

Explain practical:

Answer 22

Use yeast as a catalase - see how it breaks down

Safety goggles must be worn if this experiments is performed- care should be taken not to get hydrogen peroxide on skin

Question 23

Separation of photosynthetic pigments by chromatography:

Outline thin layer chromatography

Answer 23

Done with a plastic strip has been posted the thin-layer of porous material - a spot contain pigment extracted from leaf tissue is placed near one end of the strip a solvent is allowed to run up the strip to separate the different types of pigment

Question 24

Separation of photosynthetic pigments by chromatography:

Explain the experiment of thin layer chromatography

Answer 24

1) tear up a leafs into small pieces and put them in a mortar
2) add a small amount of sand for grinding
3) add a small volume of propanone
4) use the pestle to grind the leave tissue and dissolve out the pigments
5) if the propanone all evaporates add a little more
6) when the propanone has turned dark green allowed to stand and other solids to settle then pour the propanone off into a watch glass
7) use a hairdryer to evaporate all the propanone and water from the Cells cytoplasm
8) when you have a smear of dry pigments in the watch glass at 3 to 4 drops of Propanone and use a paintbrush to dissolve the pigments
9) use the paintbrush to transfer a very small amount of the pigment solution to the TLC strip. Your aim is to make a very small spot of pigment in the middle of the strip 10mm from one end. Should be very dark- this achieved by repeatedly putting a small drop into the strip and then allowing it to dry before adding another amount
10) One spot is dark enough slide the other end of the strip on the slot in Cork or bung that fits into the tube that is wider than the TLC strip
11) insert the court and strip in the specimen tube. - TLC strip should extend nearly to touch the bottom of the tube
12( Mark the outside of the tube just below the level of support on the tLC strip
13) take the strip and the cork out of the tube
14)Pour running solvent into the specimen tube at the level that you marked
15) Place specimen tube on our bench carefully lower the TLC and cork into the tube so that tube is sealed and TLC strip is just dipping into the running solvent- solvent must not touch pigment spot
16) leave tube alone for 5 mins - allow solvent to run up strip
17) when solvent has nearly reached too remove it and separte from cork
18) rule two peni lines across the strips, one at the level reached by the solvent, one by the initial pigment spot
19) draw a circle around each of the separated pigments and a cross in the centre of the circle

Question 25

Separation of photosynthetic pigments by chromatography:

Explain what u so after you take out the strip

Answer 25

20) using a rule with my measure the distance moved g the running solvent - distance between both lines- and the distance moved by each pigment - distance between the lower line and the cross in centre of circle-
21) calculate the Rf for each pigment when Rf is the distance run by the pigment divide by the distance run by the solvent
22) show all the results in a table, staring with the pigment that moved lease far

Question 26

Setting up a sealed mescosms to try and establish sustainability :

What are mesocosms for? What’s another?

Answer 26

To find out the effects of varying one of more conditions

Is to test what types of ecosystems are sustainable - involves sealing up a community of organisms together with air and soil or water

Question 27

Setting up a sealed mescosms to try and establish sustainability

What should you consider before doing it?

Answer 27

1) large glass jars ideal but transparent plastic containers could also be used- should the side of the container be transparent or opaque?
2) which of these groups of organisms must be included to make up for sustainable community: autotrophs, consumers, saprotrophs and detritivores ?
3) how can we ensure that the pxygen supply sufficient for all the organisms in the mesocosm as once it is sealed, no more oxygen can go in?
4) how can we prevent any organisms suffering as a result of being placed in a mesocosm?

Question 28

Monitoring of ventilation in humans at rest and after mild and vigorous exercise:

What is the independent variable and what is the dependent variable?

Answer 28

Independent- intensify of excercise

Dependent- ventilation parameter

Question 29

Monitoring of ventilation in humans at rest and after mild and vigorous exercise:

What is the tidal volume?

Answer 29

The volume of air drawn in and expelled out

Number if times that the air is drawn in or expelled per minute is the ventilation rate

Question 30

Monitoring of ventilation in humans at rest and after mild and vigorous exercise:

Explain measuring ventilation rate

Answer 30

1) measure ventilation rate is by simple observation- clunt the number of times the air is inhaled or exhales
2) can be measured by data logging- an inflatable chest belt is placed around the thorax and air is pumped in with a bladder- differential pressure sensor is then used to measure pressure variations inside the belt due to chest expansion- rate of ventilation can be deduced and the relative size of ventilation can be recorders

Question 31

Monitoring of ventilation in humans at rest and after mild and vigorous exercise:

Explain measuring tidal volume:

Answer 31

1) can use delivery tube which you blow into, pneumatic trough with water in it, and a bell jar with graduations to measure the amount of co2
- not safe to use for too long as co2 conc will raise to high
2) designed spirometers are available for use with data logging - measure flow rate into and out of the lungs from these measurements lung volumes can be deduced
- – all variables apart from independent and dependent should be kept constant
- — ventilation parameters should be measured several times at all levels of wxcersise with each person on trial

Question 32

Use of a light microscope to investigate the structure of cells and tissues :

Name the parts of the microscope

Answer 32

Eyepiece lens
Coarse focusing knob
Fine focusing knob
Turret
Objective lens
Specimen stage
Light from mirror or light bulb