Pearson Edexcel GCSE Combined Science · B1

Key concepts in biology

Revision questions with answers for B1 Key concepts in biology in Pearson Edexcel GCSE Combined Science (spec 1SC0). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

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Question 1 · Spec B1.1
What distinguishes eukaryotic cells from prokaryotic cells?
Answer:
Eukaryotic cells have a nucleus enclosing DNA; prokaryotic cells lack a nucleus and have DNA in the cytoplasm.
Question 2 · Spec B1.1
What do the nucleus and cell membrane do?
Answer:
The nucleus contains genetic information and controls cell activities. The membrane controls movement of substances into and out of the cell.
Question 3 · Spec B1.1
What are the roles of mitochondria and ribosomes?
Answer:
Mitochondria are the main site of aerobic respiration; ribosomes make proteins.
Question 4 · Spec B1.1
Which plant-cell structures are absent from animal cells?
Answer:
A cellulose cell wall, chloroplasts and a large permanent vacuole.
Question 5 · Spec B1.1
How do a plant cell wall and vacuole support the cell?
Answer:
The wall strengthens the cell; water in the vacuole helps maintain turgor pressure against the wall.
Question 6 · Spec B1.1
What do chloroplasts contain, and what do they do?
Answer:
They contain chlorophyll, which absorbs light for photosynthesis.
Question 7 · Spec B1.1
How do bacterial chromosomal DNA and plasmid DNA differ?
Answer:
Chromosomal DNA is the main genetic material; plasmids are smaller additional DNA rings.
Question 8 · Spec B1.1
What are bacterial flagella and ribosomes used for?
Answer:
Flagella enable movement; ribosomes synthesise proteins.
Question 9 · Spec B1.2
How does a sperm cell's acrosome aid fertilisation?
Answer:
It contains enzymes that help the sperm penetrate the egg's outer layers.
Question 10 · Spec B1.2
Why does a sperm cell have many mitochondria and a tail?
Answer:
Respiration transfers energy for the tail's movement, enabling the sperm to swim towards an egg.
Question 11 · Spec B1.2
Why are sperm and egg nuclei haploid?
Answer:
They contain half the normal chromosome number, allowing fertilisation to restore the diploid number.
Question 12 · Spec B1.2
Why does an egg cell contain nutrient-rich cytoplasm?
Answer:
The nutrients support the early embryo before it obtains a separate nutrient supply.
Question 13 · Spec B1.2
Why does the egg membrane change after fertilisation?
Answer:
It helps prevent additional sperm entering, maintaining the correct chromosome number.
Question 14 · Spec B1.2
How are ciliated epithelial cells adapted to their function?
Answer:
Their beating cilia move material along a surface, such as mucus and trapped particles in airways.
Question 15 · Spec B1.3
Why do electron microscopes reveal more cell detail than light microscopes?
Answer:
They have greater resolving power and magnification, allowing smaller structures to be distinguished.
Question 16 · Spec B1.3
Distinguish magnification from resolution.
Answer:
Magnification is image enlargement; resolution is the ability to distinguish two nearby points as separate.
Question 17 · Spec B1.4
Why is estimating a cell's size sometimes useful?
Answer:
It checks whether a calculated value is plausible when exact measurements are unavailable or limited.
Question 18 · Spec B1.5
What do milli, micro, nano and pico mean?
Answer:
One-thousandth, one-millionth, one-billionth and one-trillionth of the base unit, respectively.
Question 19 · Spec B1.5
Convert 0.025 mm to µm.
Answer:
0.025 × 1,000 = 25 µm.
Question 20 · Spec B1.5 · Higher only
Write 0.0000042 m in standard form.
Answer:
4.2 × 10⁻⁶ m.
Question 21 · Spec B1.6 · Core practical
State the magnification equation.
Answer:
Magnification = image size / actual size, using the same units for both sizes.
Question 22 · Spec B1.6 · Core practical
A 40 µm cell has a 16 mm image. Calculate magnification.
Answer:
16 mm = 16,000 µm; magnification = 16,000 / 40 = x400.
Question 23 · Spec B1.6 · Core practical
How should a light microscope initially be focused?
Answer:
Start with the lowest-power objective; use coarse then fine focus before increasing magnification.
Question 24 · Spec B1.6 · Core practical
What should a scientific drawing of observed cells include?
Answer:
Clear single outlines, labels for observed structures and an appropriate scale or stated magnification.
Question 25 · Spec B1.7
What is an enzyme?
Answer:
A biological catalyst that increases reaction rate without being used up overall.
Question 26 · Spec B1.7
Why are enzymes specific to particular substrates?
Answer:
Their active sites have shapes complementary to particular substrate molecules.
Question 27 · Spec B1.8
What happens when an enzyme is denatured?
Answer:
Its active site changes shape, so the substrate no longer fits effectively.
Question 28 · Spec B1.9
Why does enzyme activity initially rise as temperature increases?
Answer:
Particles move faster, increasing successful collisions between enzyme and substrate.
Question 29 · Spec B1.9
Why does enzyme activity fall above its optimum temperature?
Answer:
The enzyme denatures, reducing the number of functional active sites.
Question 30 · Spec B1.9
Why can unsuitable pH reduce enzyme activity?
Answer:
Changes in pH alter the active site's shape and may denature the enzyme.
Question 31 · Spec B1.9
Why does increasing substrate concentration eventually stop increasing enzyme rate?
Answer:
All active sites become occupied, so enzyme availability limits the rate.
Question 32 · Spec B1.10 · Core practical
How can amylase be used to investigate pH and enzyme activity?
Answer:
Mix starch, amylase and a buffer; test timed samples with iodine until starch disappears, repeating at different pH values.
Question 33 · Spec B1.10 · Core practical
Why use a buffer in the enzyme practical?
Answer:
It maintains the chosen pH during the reaction.
Question 34 · Spec B1.10 · Core practical
Which variables should be controlled in the pH investigation?
Answer:
Temperature, enzyme and substrate concentrations, volumes and sampling intervals.
Question 35 · Spec B1.10 · Core practical
What iodine result indicates that starch has disappeared?
Answer:
The iodine remains orange-brown rather than turning blue-black.
Question 36 · Spec B1.11
An enzyme reaction reaches a fixed endpoint in 40 s. Calculate 1/time as a comparative rate.
Answer:
Rate = 1 / 40 = 0.025 s⁻¹.
Question 37 · Spec B1.12
What molecules result from carbohydrate and protein digestion?
Answer:
Carbohydrates form sugars; proteins form amino acids.
Question 38 · Spec B1.12
What molecules result from lipid digestion?
Answer:
Fatty acids and glycerol.
Question 39 · Spec B1.12
How do enzymes contribute to synthesis as well as digestion?
Answer:
They catalyse reactions that build carbohydrates, proteins and lipids from smaller molecules, as well as reactions that break them down.
Question 40 · Spec B1.15
Define diffusion.
Answer:
Net movement of particles from a higher to a lower concentration, down a concentration gradient.
Question 41 · Spec B1.15
Which factors increase diffusion rate?
Answer:
A steeper concentration gradient, higher temperature, larger surface area and shorter diffusion distance.
Question 42 · Spec B1.15
Define osmosis.
Answer:
Net movement of water through a partially permeable membrane from a more dilute to a more concentrated solution.
Question 43 · Spec B1.15
Define active transport.
Answer:
Movement against a concentration gradient using energy transferred by respiration.
Question 44 · Spec B1.15
Why can a root hair need active transport to absorb mineral ions?
Answer:
Their concentration may be lower outside than inside the cell, so uptake occurs against the gradient.
Question 45 · Spec B1.16 · Core practical
What is changed and measured in the potato osmosis practical?
Answer:
Change the surrounding solution concentration and measure the potato pieces' mass change.
Question 46 · Spec B1.16 · Core practical
Why use equal-sized potato pieces and equal immersion times?
Answer:
These control surface area and exposure time, isolating the effect of solution concentration.
Question 47 · Spec B1.16 · Core practical
Why blot potato pieces before their final weighing?
Answer:
To remove surface solution that would otherwise affect the measured mass.
Question 48 · Spec B1.17
A potato piece rises from 2.0 g to 2.3 g. Calculate percentage mass change.
Answer:
(2.3 − 2.0) / 2.0 × 100 = +15%.
Question 49 · Spec B1.17
A potato piece falls from 2.5 g to 2.0 g. Calculate percentage mass change.
Answer:
(2.0 − 2.5) / 2.5 × 100 = -20%.
Question 50 · Spec B1.16 · Core practical
What does zero mass change suggest about the potato and solution?
Answer:
Their effective concentrations are equal, so there is no net water movement by osmosis.

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Key concepts in biology

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