Cell Level Systems | OCR GCSE Biology A, Higher tier (J247)

Cell Level Systems

220 questions
10 subtopics
Paper 3
Paper 3

Cell Level Systems is examined in Biology A Paper 3.

It covers microscopy, and sub-cellular structures, dNA structure: polymer, double helix and nucleotides, protein synthesis and the triplet code, 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 and limiting factors in photosynthesis.

Sample questions from Cell Level Systems

Answer each one closed book first, then open the answer.

Microscopy, and sub-cellular structures

Why does a very active cell such as a muscle cell contain large numbers of mitochondria?

Show the answer
Mitochondria contain the enzymes for cellular respiration, so more of them supply more energy for the cell's work.
DNA structure: polymer, double helix and nucleotides

How many strands make up a molecule of DNA?

Show the answer
Two.
Protein synthesis and the triplet code

What happens during translation?

Show the answer
The nucleotide sequence of the mRNA is read and amino acids are joined together in the order it specifies.
Enzyme action, and investigating enzymes

What does the lock and key hypothesis describe?

Show the answer
The substrate fits into the active site as a key fits a lock, so only a matching substrate can bind.
Cellular respiration as an exothermic process

Name three processes in an organism that depend on the ATP supplied by respiration.

Show the answer
Muscle contraction, active transport and the building of large molecules such as proteins.
Aerobic and anaerobic respiration compared

Which substrate is broken down in both aerobic and anaerobic respiration?

Show the answer
Glucose.
Synthesis and breakdown of carbohydrates, proteins and lipids

What happens when a protein is broken down?

Show the answer
The chain is split back into its individual amino acids.
Photosynthesis: producers and the process

Why would almost all life on Earth end if photosynthesis stopped?

Show the answer
No new food or biomass would be made and the oxygen used up in respiration would not be replaced.

The 10 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Microscopy, and sub-cellular structures	The parts of a light microscope and preparing and staining slides, calculating magnification, where genetic material and plasmids sit in plant, animal and bacterial cells, the jobs of mitochondria, chloroplasts, the membrane and its receptors, and ribosomes, resolution and what electron microscopes revealed, converting between millimetres, micrometres and nanometres, real sizes and magnifications in standard form, estimating cell sizes, and significant figures.	33
DNA structure: polymer, double helix and nucleotides	What a polymer is and why DNA is one built from nucleotides, how monomers and polymers differ, how a long chain stores information, the two strands twisted into a double helix like a ladder and why that shape is stable, the sugar, phosphate and base in each of the four nucleotides, and complementary base pairing of A with T and C with G.	21
Protein synthesis and the triplet code	How DNA unzips and a gene is transcribed into mRNA in the nucleus, why mRNA leaves instead of DNA, translation at the ribosomes with tRNA carrying amino acids, the order of events, the triplet code and how base order sets amino acid order, how a single base change can alter a protein, calculating numbers of bases and amino acids, and how amino acid order decides a protein's shape and function.	16
Enzyme action, and investigating enzymes	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.	31
Cellular respiration as an exothermic process	What cellular respiration and ATP are, why respiration is universal and continuous, the processes that depend on its ATP, the mitochondrion, how respiration differs from breathing, why it is exothermic, the germinating seeds experiment and its control, and how respiration keeps mammals and birds warm, heats the body in exercise and warms a compost heap.	16
Aerobic and anaerobic respiration compared	The word equations for aerobic and anaerobic respiration, their difference in oxygen and ATP yield, the products in yeast and muscle, lactic acid and fatigue, and yeast in bread and brewing.	14
Synthesis and breakdown of carbohydrates, proteins and lipids	How glucose builds starch and glycogen and why they are stored and broken down, amino acids as the monomers of proteins and why about twenty of them give so many proteins, the roles of proteins, lipids built from fatty acids and glycerol and broken down by lipase, why lipids store energy and their other uses, and the Benedict's, biuret and emulsion food tests.	30
Photosynthesis: producers and the process	Why photosynthetic organisms are the main producers of biomass, algae and phytoplankton as producers, where the carbon and energy in consumers come from, why life depends on photosynthesis and food chains start with producers, the word equation, chloroplasts and chlorophyll, where the reactants come from, the two stages, and what happens to the glucose made.	16
Photosynthesis as endothermic, and investigating it	Endothermic reactions and where the energy in photosynthesis ends up, how it compares with respiration, measuring the rate in pondweed with a lamp, and testing a leaf for starch to show light is needed.	27
Limiting factors in photosynthesis	How light intensity, carbon dioxide concentration and temperature each change the rate of photosynthesis, what a limiting factor is, reading graphs of rate against light, and heating and lighting a greenhouse.	16

Cell Level Systems is 220 of the 1,137 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.