How can the rate of a reaction controlled by an enzyme be measured?

By timing how quickly the substrate disappears or how quickly a product appears.

How is a steady temperature maintained during an enzyme investigation?

The tubes are stood in a water bath set to the chosen temperature.

Why is a buffer solution added in an enzyme investigation?

It holds the pH steady at the chosen value while the reaction runs.

How can the activity of catalase be measured using hydrogen peroxide?

By collecting the oxygen given off and measuring the volume of gas produced in a fixed time.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition, mutualism and parasitism

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination and characteristics controlled by many genes Variation within a population, and classification Natural selection and evolution Evidence for evolution from fossils and antibiotic resistance

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples White blood cells, antibodies and platelets Non-specific defences and the immune system Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Homeostasis and control systems in the body Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Cell Level Systems

Enzyme action, and investigating enzymes

3 things to know
Paper 7 (Biology)

Overview

Measuring the rate of an enzyme reaction with amylase and catalase, controlling pH and temperature, the active site and lock and key model, and how temperature, pH and concentration change the rate.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain how enzyme activity changes as pH leaves the optimum, why extra substrate eventually stops raising the rate, and why extra enzyme raises it.

Key term

In an investigation of amylase, how can you tell when all the starch has been broken down?

Key term

Which variables must be kept the same when investigating the effect of pH on amylase activity?

Questions from this subtopic

Each one with the model answer underneath.

1
How can the rate of a reaction controlled by an enzyme be measured?
Model answer
By timing how quickly the substrate disappears or how quickly a product appears.
2
In an investigation of amylase, how can you tell when all the starch has been broken down?
Model answer
A sample no longer turns iodine solution blue-black but stays orange-brown.
3
Which variables must be kept the same when investigating the effect of pH on amylase activity?
Model answer
The temperature, the concentration of enzyme and starch, and the volumes used.
4
How is a steady temperature maintained during an enzyme investigation?
Model answer
The tubes are stood in a water bath set to the chosen temperature.
5
Why is a buffer solution added in an enzyme investigation?
Model answer
It holds the pH steady at the chosen value while the reaction runs.
6
How can the activity of catalase be measured using hydrogen peroxide?
Model answer
By collecting the oxygen given off and measuring the volume of gas produced in a fixed time.

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Cell Level Systems

Community Level Systems

Genes, Inheritance and Selection

Global Challenges

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AA diet high in sugar and fat leads to obesity.

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