[Part 1]- Required practicals🔬

Question 1

This is a required practical to investigate the effect of pH on the rate of reaction, of amylase enzyme. 🥠

Describe a method you would use to investigate this.

• Hint: drop of iodine solution, add 2cm^3, water bath, combine, stirring, every

Answer 1

1) place one drop of iodine solution into each well of a spotting tile

2) take three test tubes in the first add 2cm3 of starch solution, in the second add 2cm3 of amaylse solution; in the third add 2cm3 of pH 5 buffer solution- [this is used to control the pH].

3) place all three test tubs in a water bath, at 30c. Then leave for 10 minutes so the solution can reach the correct temperature

4) now combine three solutions into one test tube and mix with a stirring rod, then return to the water bath and start a stopwatch.

5) after 30 secs, use stirring rod to transfer one drop of solution to a well in the spotting tile (which contains iodine). Iodine should turn blue-black

6) take a sample every 30 secs, and continue until iodine remains orange.

7) [when reaction is completed, record results time for this in results and repeat experiment using different pH’s such as 6,7,8].

Question 2

When investigating the effect of pH on the rate of reaction, of amylase enzyme, why is a pH buffer used? 🥠

Answer 2

• to control the pH.

Question 3

When investigating the effect of pH on the rate of reaction, [of amylase enzyme].

What is a problem about this practical ? 🥠

Hint: every 30 seconds

Answer 3

• only taking samples every 30 secs, means that we only have an approximate time for the reaction to complete.
• so to address this, take samples every 10 secs.

Question 4

When investigating the effect of pH on the rate of reaction, [of amylase enzyme]

What is another problem about this practical? 🥠

Hint: dosen’t, gradual, ask people

Answer 4

• Because we’re looking for the time when the solution doesn’t go blue-black this isn’t always obvious.
• this is because, the colour change tends to be gradual as some wells might have a small amount of blue-black mixed with orange.
• So it’s difficult to see when the reaction has finished.
• To address this, we can ask several people to look at the spotting tile and decide when the reaction is complete.

Question 5

When investigating the effect of pH on the rate of reaction, [of amylase enzyme]

What is the independent variable ? 🥠

Answer 5

Independent variable- the pH

Question 6

When investigating the effect of pH on the rate of reaction, [of amylase enzyme]

What are the dependent variables involved? 🥠

Answer 6

• dependent variable- the time taken for the starch to be digested

Question 7

When investigating the effect of pH on the rate of reaction, [of amylase enzyme]

What are the control variables involved ? 🥠

Answer 7

• control variable: temperature, concentration and the volume of starch or amylase

Question 8

What does the centre of the optical microscope have ? 🔬

Answer 8

• the centre of the optical microscope, has a stage- this is where the microscope slide is placed. [it also has clips to hold the slides in place]

Question 9

What is the role of the light, in a optical microscope ? 🔬

Answer 9

• below the stage there is a lamp, and light from the lamp passes up through the microscope slides.

Question 10

How are some optical microscopes different to each other ? 🔬

Hint: mirror

Answer 10

• some optical microscopes, might have a mirror beneath the stage, rather than having a lamp.
• the mirror reflects light up through the microscope slide.

Question 11

What are objective lenses ? 🔬

Hint: above

Answer 11

• objective lenses, are above the stage and most microscopes will normally have three different objective lenses.
• these objective lenses, tend to have a magnification of x4, x10 or x40.

Question 12

What is the eyepiece ? 🔬

Hint: contains

Answer 12

• found at the top of the microscope, the eyepiece is where we look through.
• ; the eyepiece contains the eyepiece lens- which has a magnification of x10.

Question 13

Describe the required practical, of how to use an optical microscope, to look at cells on a prepared microscope slide. 🔬

Hint: place the prepared slide, select the lowest, position objective lens,

Answer 13

1) place the prepared slide onto a stage, using the clips to hold the slide in place.

2) then select the lowest power objective lens- normally x4.

3) position the objective lens, so it almost touches the microscope slide- slowly turn the coarse focusing dial, to do that.

4) whilst adjusting the position of the objective lens, look at the microscope from the slide

5) ; when the objective lens almost touches the slide, stop turning the dial.

6) now look down through the eyepiece, slowly turning the coarse focusing dial [until the cells come into focus]- this increases the distance between the objective lens and the slide.

7) then use the fine focusing dial, to bring the cells into a clear focus.

[after multiplying the total magnification, select a higher power objective lens and adjust the fine focusing dial, to bring the cells back into focus.]

Question 14

What can happen if we look through the eyepiece, whilst positioning the objective lens ? 🔬

Answer 14

• if we look through the eyepiece, whilst positioning the objective lens, there’s a risk we could damage the slide.

Question 15

What does turning the coarse focusing dial do ? 🔬

Hint: increases the distance

Answer 15

• slowly turning the coarse focusing dial [until the cells come into focus], increases the distance between the objective lens and the slide.

Question 17

How can the total magnification be calculated ? 🔬

Answer 17

• multiply the magnification of the eyepiece lens by the magnification, of the objective lens.

Question 17

How can we make a clear labelled drawing, [of some of the cells viewed in the optical microscope] ? ✏️

Answer 17

• use a pencil to make a clear labelled of some of the cells viewed in the optical microscope; with an optical microscope, you can only see limited detail.
• in animal cells we can see the: cell membrane, nucleus and cytoplasm [perhaps the mitochondria]
• ; in plants cells we can see the: nucleus, cytoplasm, cell wall [and perhaps chloroplasts and the vacuole]

Question 18

What is a magnification scale ? 🔬

Answer 18

• a magnification scale, should be drawn on the drawing of a cell.
• a clear, plastic ruler should be drawn over the stage and the diameter of the field of view, should be measured in millimetres.
• then show this on a scale bar, also showing the magnification.

Question 19

How can a magnification scale be drawn? 🔬

Answer 19

• a clear, plastic ruler should be drawn over the stage and the diameter of the field of view, should be measured in millimetres.
• then show this on a scale bar, also showing the magnification.

Question 20

[Referring to a slide to view onion cells,] How can a microscope slide be prepared? 🔬

Answer 20

• add a drop of water to the middle of a clean slate and then cut up an onion, separating it into layers.
• then use tweezers to peel off some epidermal tissue, from the bottom of the layers.
• place the epidermal tissue into the water on the slide, using the tweezers.
• adding a drop of iodine, place a cover slip [a square of thin, transparent plastic/glass] on top.
• to do this, stand the cover slip upright on the slide [next to the water droplet] and carefully tilt, or lower the cover slip so it covers the specimen.

Question 21

When preparing a slide, why might a stain added ? 🔬

Answer 21

• When preparing a slide, a stain- [e.g- drop of iodine] might be added to highlight objects in a cell, by adding colour to them.