AQA GCSE Biology · 4.1

Cell biology

50 exam-style questions with answers for 4.1 Cell biology in AQA GCSE Biology (spec 8461). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 4.1.1.1 · Eukaryotes and prokaryotes
State two differences between prokaryotic and eukaryotic cells. [2 marks]
Answer:
Any two from: prokaryotic cells have no nucleus; their DNA is a single loop in the cytoplasm (1); prokaryotes may have plasmids (1); prokaryotic cells are much smaller (1); prokaryotes have no mitochondria or chloroplasts (1).
Question 2 · Spec 4.1.1.1 · Eukaryotes and prokaryotes
What are plasmids? [1 mark]
Answer:
Small rings of DNA found in the cytoplasm of some bacteria, in addition to the main DNA loop.
Question 3 · Spec 4.1.1.1 · Orders of magnitude
A bacterium is 2 µm long and an animal cell is 20 µm long. How many orders of magnitude bigger is the animal cell? [1 mark]
Answer:
One order of magnitude (10 times bigger).
Question 4 · Spec 4.1.1.2 · Animal and plant cells
State the function of the mitochondria. [1 mark]
Answer:
They are the site of aerobic respiration, releasing energy for the cell.
Question 5 · Spec 4.1.1.2 · Animal and plant cells
State the function of ribosomes. [1 mark]
Answer:
They are the site of protein synthesis.
Question 6 · Spec 4.1.1.2 · Animal and plant cells
Name three structures found in plant cells but not animal cells. [3 marks]
Answer:
Cell wall made of cellulose (1); chloroplasts (1); permanent vacuole filled with cell sap (1).
Question 7 · Spec 4.1.1.2 · Animal and plant cells
State the function of the cell membrane. [1 mark]
Answer:
It controls the movement of substances into and out of the cell.
Question 8 · Spec 4.1.1.2 · Animal and plant cells
State the function of the cell wall. [1 mark]
Answer:
It strengthens the cell and supports it.
Question 9 · Spec 4.1.1.3 · Cell specialisation
Explain how a sperm cell is adapted to its function. [2 marks]
Answer:
Any two from: a tail to swim to the egg (1); many mitochondria to release energy for swimming (1); an acrosome containing enzymes to digest through the egg membrane (1); a haploid nucleus (1).
Question 10 · Spec 4.1.1.3 · Cell specialisation
Explain how a root hair cell is adapted to absorb water. [2 marks]
Answer:
It has a long hair-like projection (1); which gives a large surface area for absorbing water by osmosis and mineral ions by active transport (1).
Question 11 · Spec 4.1.1.3 · Cell specialisation
Explain how xylem cells are adapted to their function. [2 marks]
Answer:
They are dead cells with no end walls, forming hollow tubes (1); strengthened by lignin to withstand the pressure of water moving up the plant (1).
Question 12 · Spec 4.1.1.3 · Cell specialisation
Explain how a nerve cell is adapted to its function. [2 marks]
Answer:
It is long, to carry impulses over long distances (1); it has many branched endings (dendrites) to connect with other cells (1).
Question 13 · Spec 4.1.1.4 · Cell differentiation
What is cell differentiation? [1 mark]
Answer:
The process by which a cell changes to become specialised for a particular function.
Question 14 · Spec 4.1.1.4 · Cell differentiation
How does differentiation differ in animals and plants? [2 marks]
Answer:
Most animal cells differentiate at an early stage and lose this ability (1); many plant cells keep the ability to differentiate throughout life (1).
Question 15 · Spec 4.1.1.5 · Microscopy
State two advantages of an electron microscope over a light microscope. [2 marks]
Answer:
Higher magnification (1); higher resolution, so smaller structures such as ribosomes can be seen in detail (1).
Question 16 · Spec 4.1.1.5 · Microscopy
Define the term 'resolution'. [1 mark]
Answer:
The ability to distinguish between two points that are close together.
Question 17 · Spec 4.1.1.5 · Microscopy
An image of a cell is 30 mm wide. The magnification is ×1500. Calculate the real width in µm. [2 marks]
Answer:
Real size = image size ÷ magnification = 30 ÷ 1500 = 0.02 mm (1); = 20 µm (1).
Question 18 · Spec 4.1.1.5 · Microscopy
Write 0.000 004 m in standard form. [1 mark]
Answer:
4 × 10⁻⁶ m.
Question 19 · Spec 4.1.1.5 · Required practical 1
Describe how to prepare an onion cell slide for a light microscope. [3 marks]
Answer:
Peel a thin layer of epidermis and place it on a glass slide (1); add a drop of iodine solution to stain it (1); lower a coverslip at an angle to avoid air bubbles (1).
Question 20 · Spec 4.1.1.5 · Required practical 1
Why should you start with the lowest power objective lens? [1 mark]
Answer:
It has the widest field of view, so it is easier to find the cells before increasing magnification.
Question 21 · Spec 4.1.1.6 · Culturing microorganisms
State two aseptic techniques used when culturing bacteria. [2 marks]
Answer:
Any two from: sterilise the inoculating loop by passing it through a flame (1); sterilise Petri dishes and agar before use (1); secure the lid with tape but do not seal it fully (1); work near a Bunsen flame (1).
Question 22 · Spec 4.1.1.6 · Culturing microorganisms
Why are cultures incubated at 25 °C in school laboratories? [1 mark]
Answer:
To reduce the chance of growing pathogens that grow best at body temperature (37 °C).
Question 23 · Spec 4.1.1.6 · Culturing microorganisms
A bacterium divides every 20 minutes. How many bacteria will one become after 2 hours? [2 marks]
Answer:
2 hours = 6 divisions (1); 2⁶ = 64 bacteria (1).
Question 24 · Spec 4.1.1.6 · Culturing microorganisms · Higher only
A population starts with 1 bacterium and divides every 30 minutes. Give the number after 10 hours in standard form. [2 marks]
Answer:
10 hours = 20 divisions, so 2²⁰ = 1 048 576 (1); ≈ 1.05 × 10⁶ bacteria (1).
Question 25 · Spec 4.1.1.6 · Required practical 2
How do you calculate the area of a clear zone with a diameter of 12 mm? [2 marks]
Answer:
Area = πr², with r = 6 mm (1); π × 6² = 113 mm² (1).
Question 26 · Spec 4.1.1.6 · Required practical 2
What does a larger clear zone around an antibiotic disc show? [1 mark]
Answer:
The antibiotic is more effective at killing or stopping the growth of those bacteria.
Question 27 · Spec 4.1.2.1 · Chromosomes
Describe the structure of a chromosome. [2 marks]
Answer:
A chromosome is made of a long DNA molecule (1); carrying a large number of genes (1).
Question 28 · Spec 4.1.2.1 · Chromosomes
How many chromosomes are in a human body cell? [1 mark]
Answer:
46 (23 pairs).
Question 29 · Spec 4.1.2.2 · Mitosis
Describe what happens in the cell cycle before mitosis. [2 marks]
Answer:
The cell grows and the number of sub-cellular structures such as ribosomes and mitochondria increases (1); the DNA replicates to form two copies of each chromosome (1).
Question 30 · Spec 4.1.2.2 · Mitosis
Describe what happens during mitosis. [2 marks]
Answer:
One set of chromosomes is pulled to each end of the cell (1); the nucleus divides (1).
Question 31 · Spec 4.1.2.2 · Mitosis
What happens in the final stage of the cell cycle? [1 mark]
Answer:
The cytoplasm and cell membrane divide to form two identical cells.
Question 32 · Spec 4.1.2.2 · Mitosis
State two reasons why mitosis is important. [2 marks]
Answer:
Any two from: growth (1); repair of damaged tissue (1); replacing worn-out cells (1); asexual reproduction (1).
Question 33 · Spec 4.1.2.3 · Stem cells
What is a stem cell? [1 mark]
Answer:
An undifferentiated cell that can divide to make more stem cells and can differentiate into other types of cell.
Question 34 · Spec 4.1.2.3 · Stem cells
Compare embryonic stem cells and adult bone marrow stem cells. [2 marks]
Answer:
Embryonic stem cells can differentiate into most types of human cell (1); adult bone marrow stem cells can form many types of cell, including blood cells, but not all (1).
Question 35 · Spec 4.1.2.3 · Stem cells
Where are stem cells found in plants? [1 mark]
Answer:
In meristem tissue, for example at the tips of roots and shoots.
Question 36 · Spec 4.1.2.3 · Stem cells
What is therapeutic cloning? [2 marks]
Answer:
An embryo is produced with the same genes as the patient (1); its stem cells will not be rejected by the patient's body (1).
Question 37 · Spec 4.1.2.3 · Stem cells
Give two ethical objections to using embryonic stem cells. [2 marks]
Answer:
Any two from: embryos are destroyed (1); some people believe an embryo has a right to life (1); religious objections (1).
Question 38 · Spec 4.1.2.3 · Stem cells
Give two uses of plant meristem cloning. [2 marks]
Answer:
Any two from: producing clones of rare plants to prevent extinction (1); producing large numbers of identical crop plants with useful features, such as disease resistance (1); quickly and cheaply (1).
Question 39 · Spec 4.1.3.1 · Diffusion
Define diffusion. [1 mark]
Answer:
The spreading out of particles from an area of higher concentration to an area of lower concentration.
Question 40 · Spec 4.1.3.1 · Diffusion
State three factors that affect the rate of diffusion. [3 marks]
Answer:
The difference in concentration (concentration gradient) (1); temperature (1); the surface area of the membrane (1).
Question 41 · Spec 4.1.3.1 · Diffusion
Name two substances that diffuse in and out of cells. [2 marks]
Answer:
Any two from: oxygen and carbon dioxide in gas exchange (1); urea from cells into the blood plasma (1); glucose (1).
Question 42 · Spec 4.1.3.1 · Surface area to volume
Calculate the surface area to volume ratio of a cube with sides of 2 cm. [2 marks]
Answer:
Surface area = 6 × 2 × 2 = 24 cm² and volume = 2 × 2 × 2 = 8 cm³ (1); ratio = 24 : 8 = 3 : 1 (1).
Question 43 · Spec 4.1.3.1 · Exchange surfaces
Explain why multicellular organisms need exchange surfaces. [2 marks]
Answer:
They have a small surface area to volume ratio (1); so diffusion through the body surface alone is too slow to supply all their cells (1).
Question 44 · Spec 4.1.3.1 · Exchange surfaces
State three ways exchange surfaces are adapted for efficient exchange. [3 marks]
Answer:
Any three from: large surface area (1); thin membrane for a short diffusion path (1); efficient blood supply (in animals) (1); ventilation (for gas exchange in animals) (1).
Question 45 · Spec 4.1.3.2 · Osmosis
Define osmosis. [2 marks]
Answer:
The diffusion of water from a dilute solution to a concentrated solution (1); through a partially permeable membrane (1).
Question 46 · Spec 4.1.3.2 · Required practical 3
Why do you calculate percentage change in mass in the osmosis practical? [1 mark]
Answer:
The potato pieces may start with different masses, so percentage change allows a fair comparison.
Question 47 · Spec 4.1.3.2 · Required practical 3
A potato piece goes from 2.50 g to 2.20 g. Calculate the percentage change in mass. [2 marks]
Answer:
Change = −0.30 g (1); −0.30 ÷ 2.50 × 100 = −12% (1).
Question 48 · Spec 4.1.3.2 · Required practical 3
What does it mean if a potato piece neither gains nor loses mass? [1 mark]
Answer:
The concentration of the solution is the same as the concentration inside the potato cells.
Question 49 · Spec 4.1.3.3 · Active transport
Define active transport. [2 marks]
Answer:
The movement of substances from a more dilute solution to a more concentrated solution, against a concentration gradient (1); using energy from respiration (1).
Question 50 · Spec 4.1.3.3 · Active transport
Give two examples of active transport. [2 marks]
Answer:
Absorption of mineral ions from dilute soil water into root hair cells (1); absorption of sugar molecules from the gut into the blood when the concentration in the gut is lower (1).

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