OCR Gateway GCSE Biology: Practical Activity Groups: Food Tests, Cheek Cell Staining, Enzyme Controlled Reactions, Photosynthesis, Physiology, Responses and Respiration and Osmosis

What is the purpose of staining?

To make certain cell structures visible.

Which structures should be labelled in an animal cell?

Cell membrane, cytoplasm, nucleus.

How should a cover slip be placed on a microscope slide, and why?

By using a mounted needle to lower the cover slip slowly onto the slide to prevent the formation of air bubbles.

Outline the procedure to preparing a cheek cell slide.

Rub the inside of your cheek with a cotton bud and wipe on a glass slide with a drop of methylene blue on it. Place a cover slip on the slide.

How should a cell diagram be labelled?

With ruled lines that do not cross.

State a hazard and safety precaution involved in this practical (cheek cells).

Methylene blue is an irritant, wear eye protection when handling. Cheek cells are a biohazard, dispose of cotton bud in disinfectant after use.

How do you prepare a sample of food for testing?

Grind up food samples using pestle and mortar, mix with water, and filter with funnel and filter paper.

How do you test for the presence of starch in a sample?

Add iodine solution to the sample. If starch is present, the solution turns from brown to blue-black.

How do you test for the presence of a reducing sugar in a sample?

Add Benedict's reagent to the sample, boil the test tube in a hot water bath. If reducing sugar is present, a brick red precipitate forms; if not, the solution remains blue.

How do you test for the presence of protein in a sample?

Add Biuret reagent (potassium hydroxide and copper (II) sulphate), shake the mixture. If protein is present, the solution turns from blue to purple.

How do you test for the presence of lipids in a sample?

Add ethanol to the sample, then add water and shake the test tube. A white emulsion forms if lipid is present.

What is the word equation for the action of catalase?

Hydrogen peroxide → Water + Oxygen

How is the rate of catalase activity indicated?

By measuring the volume of oxygen gas released in a fixed time.

What is the function of potato in this practical?

It provides the source of catalase.

What is the independent variable of this practical and how is it varied (photosynthesis???) ?

Concentration of hydrogen peroxide, varied by making a simple dilution with distilled water.

What are the controlled variables of this practical?

Temperature, pH, volume of hydrogen peroxide solution, time allowed to measure gas volume, length and width of potato discs.

How is the apparatus set up to measure the volume of gas produced?

Fill a trough with water, invert a measuring cylinder in the trough, and connect it to a conical flask with a delivery tube.

Why must the bung connecting the conical flask and measuring cylinder be airtight?

To ensure all gas produced displaces the water in the measuring cylinder.

How is the rate of reaction calculated?

Rate of reaction = volume of gas produced / time.

What are the hazards and safety precautions involved in this practical?

Hydrogen peroxide is an irritant; wear safety goggles and avoid skin contact. Handle sharp cork borer and scalpel with care.

What factors affect the rate of photosynthesis?

Light intensity, carbon dioxide concentration, temperature.

How is the rate of photosynthesis measured?

By counting the number of bubbles produced by cut pondweed in sodium hydrogen carbonate solution over time.

How is light intensity controlled in experiments?

By placing the lamp/light source at different distances from the plant.

Why is the number of bubbles formed per minute counted?

It indicates the production of oxygen during photosynthesis, and the rate of bubble formation is proportional to the rate of photosynthesis.

What is a source of error in measuring photosynthesis with bubbles?

Bubbles may appear too quickly to be accurately counted.

What is the purpose of adding sodium hydrogen carbonate to the beaker with pondweed?

To provide carbon dioxide for photosynthesis.

What is the inverse square law?

Light intensity is inversely proportional to the square of distance: Light intensity ∝ 1/distance².

How is the effect of carbon dioxide concentration on the rate of photosynthesis investigated?

By keeping light intensity and temperature constant while changing the concentration of sodium hydrogen carbonate solution.

How is the effect of temperature on the rate of photosynthesis investigated?

By immersing the setup in a thermostatically-controlled water bath while keeping light intensity and carbon dioxide concentration constant.

How can the reliability of the practical be improved?

By repeating the practical at each light intensity at least twice and taking a mean number of bubbles.

What is the procedure to investigate the effect of exercise on pulse rate?

Measure the pulse rate by counting the number of pulses in one minute, perform an exercise for a set duration, and measure the pulse rate again.

What is the procedure to investigate the effect of exercise on ventilation rate?

Measure the ventilation rate using a calibrated spirometer by counting the number of breaths in one minute, perform an exercise for a set duration, and measure the ventilation rate again.

How can the reliability of the results be improved?

By repeating the practical with more participants.

What is a risk associated with this practical?

Make sure the participant is healthy and able to partake in the exercise to prevent any health issues from arising.

What is osmosis?

The movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane.

How would you carry out an investigation into osmosis using potato tissue?

Cut identical potato cylinders using a cork borer, measure and record their length and mass, add each cylinder to one of three solutions (1M sugar, 0.5M sugar, distilled water), leave overnight, remove and blot them, then record length and mass again and draw a graph of change in mass against concentration.

Why is it necessary to use a cork borer to cut the cylinders?

It results in equal sized samples so changes in length and mass can be compared easily.

Why is it necessary to blot the cylinders with paper after removing them?

Each cylinder may have a different amount of water on its surface, so blotting allows for comparable masses.

What safety precautions should be taken with this experiment?

Handle cork borer and scalpel with care.

How can the water potential of the plant cells be found?

Plot a graph of change in mass against concentration and find the x-intercept, which is the concentration of solution that is isotonic to the plant cells.

What is a source of error in this practical (photosynthesis)?

Plant tissue taken from different parts of the plant may have different water potentials.