AQA GCSE Combined Science: Trilogy · 4.1

Cell biology

Revision questions with answers for 4.1 Cell biology in AQA GCSE Combined Science: Trilogy (spec 8464). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All questions and answers

Question 1 · Spec 4.1.1.1
What distinguishes eukaryotic from prokaryotic cells?
Answer:
Eukaryotic cells enclose genetic material in a nucleus. Prokaryotic cells have no nucleus; their DNA lies in the cytoplasm.
Question 2 · Spec 4.1.1.1
Where is the main bacterial DNA, and what are plasmids?
Answer:
The main DNA is a single loop in the cytoplasm. Plasmids are small additional rings of DNA.
Question 3 · Spec 4.1.1.2
What is the function of the nucleus?
Answer:
It contains genetic material and controls the cell's activities.
Question 4 · Spec 4.1.1.2
What happens in the cytoplasm?
Answer:
Most of the cell's chemical reactions occur there, controlled by enzymes.
Question 5 · Spec 4.1.1.2
What does the cell membrane do?
Answer:
It controls the movement of substances into and out of the cell.
Question 6 · Spec 4.1.1.2
What are mitochondria and ribosomes used for?
Answer:
Mitochondria are the main site of aerobic respiration. Ribosomes are the site of protein synthesis.
Question 7 · Spec 4.1.1.2
Name three structures often present in plant cells but absent from animal cells.
Answer:
A cellulose cell wall, chloroplasts and a permanent vacuole containing cell sap.
Question 8 · Spec 4.1.1.2
How do chloroplasts and the cellulose cell wall help a plant cell?
Answer:
Chloroplasts absorb light for photosynthesis. The cellulose cell wall strengthens the cell.
Question 9 · Spec 4.1.1.3
How is a sperm cell adapted to fertilisation?
Answer:
Its tail enables swimming, many mitochondria supply energy through respiration, and enzymes in its head help it enter the egg.
Question 10 · Spec 4.1.1.3
How are nerve and muscle cells specialised?
Answer:
Nerve cells have long extensions to carry impulses. Muscle cells contain contractile structures and many mitochondria for energy transfer.
Question 11 · Spec 4.1.1.3
How does a root hair cell's shape help absorption?
Answer:
Its long projection gives a large surface area for absorbing water and mineral ions.
Question 12 · Spec 4.1.1.4
What is cell differentiation?
Answer:
The process by which a cell develops specialised structures so it can carry out a particular function.
Question 13 · Spec 4.1.1.4
How does differentiation differ in animals and plants?
Answer:
Most animal cells differentiate early. Many plant cells retain the ability to differentiate throughout life.
Question 14 · Spec 4.1.1.5
What is the difference between magnification and resolution?
Answer:
Magnification is how much larger an image appears. Resolution is the ability to distinguish two close points as separate.
Question 15 · Spec 4.1.1.5
Why do electron microscopes reveal more cell detail?
Answer:
They have greater magnification and higher resolving power than light microscopes, so smaller structures can be distinguished.
Question 16 · Spec 4.1.1.5
State the magnification equation.
Answer:
Magnification = image size / real size. Use the same units for both sizes.
Question 17 · Spec 4.1.1.5
A 40 µm cell has an image 20 mm wide. Calculate magnification.
Answer:
20 mm = 20,000 µm. Magnification = 20,000 / 40 = x500.
Question 18 · Spec 4.1.1.5
A cell image is 12 mm wide at x400. Find the real width.
Answer:
Real width = 12 / 400 = 0.030 mm = 30 µm.
Question 19 · Spec 4.1.1.5
Convert 0.006 mm into µm and metres.
Answer:
0.006 mm = 6 µm = 6 × 10⁻⁶ m.
Question 20 · Spec 4.1.1.5 · Required practical
How should you first focus a light microscope on a slide?
Answer:
Start with the lowest-power objective. Use coarse then fine focus; move to higher power and use fine focus.
Question 21 · Spec 4.1.1.5 · Required practical
How can you prepare a plant-cell slide and record observations?
Answer:
Place a thin sample in water, add a suitable stain and lower a coverslip carefully. Draw and label observed cells and include a magnification scale.
Question 22 · Spec 4.1.2.1
What are chromosomes made from, and what do they carry?
Answer:
Chromosomes are made of DNA and carry many genes. In body cells they are normally present in pairs.
Question 23 · Spec 4.1.2.2
What happens before mitosis in the cell cycle?
Answer:
The cell grows, increases sub-cellular structures and replicates its DNA to make two copies of each chromosome.
Question 24 · Spec 4.1.2.2
What happens during mitosis and the final stage of cell division?
Answer:
Chromosome sets separate and the nucleus divides. The cytoplasm and cell membrane then divide, forming two genetically identical cells.
Question 25 · Spec 4.1.2.2
Why is mitosis important in a multicellular organism?
Answer:
It produces genetically identical cells for growth, development, repair and replacement.
Question 26 · Spec 4.1.2.3
What is a stem cell?
Answer:
An undifferentiated cell that can divide to produce more cells and can differentiate into specialised cell types.
Question 27 · Spec 4.1.2.3
Compare embryonic and adult bone-marrow stem cells.
Answer:
Embryonic stem cells can form most human cell types. Adult bone-marrow stem cells can form a more limited range, including blood cells.
Question 28 · Spec 4.1.2.3
What can meristem stem cells be used for?
Answer:
Producing plant clones quickly, conserving rare species and multiplying crop plants with useful features such as disease resistance.
Question 29 · Spec 4.1.2.3
Why may therapeutic cloning reduce rejection?
Answer:
An embryo is produced with the patient's genes, so its stem cells are genetically matched to the patient.
Question 30 · Spec 4.1.2.3
Give a potential benefit, risk and ethical concern of embryonic stem cells.
Answer:
They may replace damaged cells; viral infection could be transferred; some people object to the use or destruction of embryos.
Question 31 · Spec 4.1.3.1
Define diffusion.
Answer:
The net movement of particles from a region of higher concentration to a region of lower concentration.
Question 32 · Spec 4.1.3.1
How does concentration gradient affect diffusion rate?
Answer:
A steeper concentration gradient increases the rate of net diffusion.
Question 33 · Spec 4.1.3.1
Why does higher temperature usually increase diffusion rate?
Answer:
Particles have more kinetic energy and move faster, so they spread out more quickly.
Question 34 · Spec 4.1.3.1
How do surface area and diffusion distance affect exchange?
Answer:
A larger surface area and a shorter diffusion distance increase the rate of exchange.
Question 35 · Spec 4.1.3.1
Give three examples of substances transported by diffusion in humans.
Answer:
Oxygen and carbon dioxide during gas exchange, and urea moving from cells into blood plasma.
Question 36 · Spec 4.1.3.1
Find the surface area to volume ratio of a cube with 2 cm sides.
Answer:
Surface area = 6 × 2² = 24 cm²; volume = 2³ = 8 cm³; ratio = 3:1.
Question 37 · Spec 4.1.3.1
Why do large multicellular organisms need exchange surfaces and transport systems?
Answer:
Their small surface area to volume ratio and long diffusion distances make diffusion alone too slow to meet all cells' needs.
Question 38 · Spec 4.1.3.1
How do alveoli support rapid gas exchange?
Answer:
Many alveoli provide a large surface area. Thin walls, ventilation and a good blood supply maintain rapid diffusion.
Question 39 · Spec 4.1.3.1
How are fish gills and intestinal villi adapted for exchange?
Answer:
They provide a large surface area, a short diffusion distance and a good blood supply.
Question 40 · Spec 4.1.3.2
Define osmosis.
Answer:
The net movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
Question 41 · Spec 4.1.3.2
What happens to a plant cell placed in a very dilute solution?
Answer:
Water enters by osmosis. The vacuole expands and the cell becomes turgid; the wall helps prevent bursting.
Question 42 · Spec 4.1.3.2 · Required practical
What are the independent and dependent variables in the potato osmosis practical?
Answer:
Independent: salt or sugar concentration. Dependent: change in mass, usually expressed as a percentage.
Question 43 · Spec 4.1.3.2 · Required practical
Name three controls in the potato osmosis practical.
Answer:
Use equal-sized pieces from comparable tissue, equal solution volumes and the same immersion time and temperature.
Question 44 · Spec 4.1.3.2 · Required practical
Why blot potato pieces before weighing after immersion?
Answer:
To remove surface solution, so the measured change mainly reflects water entering or leaving the tissue.
Question 45 · Spec 4.1.3.2 · Required practical
A potato piece changes from 2.00 g to 2.30 g. Find percentage mass change.
Answer:
Percentage change = (2.30 − 2.00) / 2.00 × 100 = +15%.
Question 46 · Spec 4.1.3.2 · Required practical
What does zero percentage mass change indicate on an osmosis graph?
Answer:
The external solution and tissue have equal effective concentrations, so there is no net movement of water.
Question 47 · Spec 4.1.3.3
Define active transport.
Answer:
Movement of substances from a lower to a higher concentration, against the concentration gradient, using energy from respiration.
Question 48 · Spec 4.1.3.3
Why do root hair cells use active transport for mineral ions?
Answer:
The ion concentration may be lower in the soil than inside the cells, so uptake must occur against the concentration gradient.
Question 49 · Spec 4.1.3.3
Why can intestinal cells use active transport to absorb sugars?
Answer:
It allows sugars to enter the blood even when their concentration in the gut is lower than in the blood.
Question 50 · Spec 4.1.3.3
Compare diffusion, osmosis and active transport.
Answer:
Diffusion moves particles down a gradient; osmosis does this for water across a partially permeable membrane; active transport moves substances against a gradient using energy.

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