Animal, plant and bacterial cells, what each part does, and how cells are adapted for their jobs.
Objectives
Describe the structures in animal, plant and bacterial cells and state the job of each.
Explain the difference between eukaryotic and prokaryotic cells.
Link the structure of a specialised cell to its function.
Specification references this topic covers: AQA 4.1.1; Edexcel B1.1, B1.2.
Cell structure and specialised cells explained
Start here
Every living thing is made of cells. A cell is the basic building block of life. Your body is made of a huge number of them.
Cells are not all the same. Animal cells, plant cells and bacterial cells each have their own parts, and every part has a job. Many cells in your body are also specialised, which means they are built for one particular job.
By the end you will name the parts of each type of cell and say what they do. You will explain how cells with a nucleus differ from cells without one. You will also link the structure of a specialised cell to its job.
Parts of an animal cell
Animal cells are eukaryotic cells, which means they have a nucleus. The nucleus holds the genes and controls the cell. The cytoplasm is the jelly around it, and most chemical reactions happen there.
The cell membrane is a thin skin that controls what moves in and out. Mitochondria are where aerobic respiration happens. That is the process that uses oxygen to release energy from food. Ribosomes are where proteins are made.
Think of a school. The nucleus is the head teacher's office, giving the instructions. The membrane is the school gate, letting some people through. The mitochondria are the power supply.
An animal cell with the cell membrane, cytoplasm, nucleus, mitochondrion and ribosomes labelled.
Extra parts in plant cells
A plant cell has all the parts of an animal cell, plus three extras. The first is a cell wall made of cellulose. It is a tough outer layer that strengthens the cell and supports the plant.
The second is a permanent vacuole, a large bag filled with cell sap, which is a watery liquid. It keeps the cell firm. The third is chloroplasts. These contain chlorophyll, a green substance. They are where photosynthesis happens, which is how a plant makes its food.
Not every plant cell has chloroplasts. Root cells are underground, where there is no light, so they have none.
A plant cell with the cell wall, membrane, permanent vacuole, nucleus, chloroplast and mitochondrion labelled.
Bacterial cells
Bacteria are prokaryotic cells. This means they have no nucleus. Their DNA is a single loop that floats in the cytoplasm. Bacterial cells are also much smaller than animal and plant cells.
Many bacteria also carry plasmids, which are small extra rings of DNA. Think of a plasmid as a spare memory stick holding a few extra files. A bacterium has a cell membrane, cytoplasm and a cell wall that is not made of cellulose. Some have a flagellum, a tail that spins to move the cell.
A bacterium has no nucleus and no mitochondria.
A bacterial cell with the cell wall, membrane, cytoplasm, circular DNA, plasmid and flagellum labelled.
Comparing the three cell types
Let us put the three cell types side by side. Animal cells and plant cells are eukaryotic. Both have a nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes.
Plant cells also have a cell wall, a permanent vacuole and chloroplasts. Bacterial cells are prokaryotic. They have no nucleus, and their DNA is a loop in the cytoplasm.
Two quick rules help. A cell with a nucleus and chloroplasts is a plant cell. A cell with no nucleus is a bacterium.
Specialised cells
Most cells in a many-celled organism are specialised. This means their structure is adapted to their job. Differentiation is the process where a cell becomes specialised.
A sperm cell has a tail to swim and many mitochondria for energy. Its head holds enzymes that help it break into the egg. A nerve cell is long, with branched ends, so it can carry electrical impulses and connect to other cells.
A muscle cell has protein fibres that shorten to make it contract, and many mitochondria for energy. Think of a football team. A goalkeeper and a striker have different skills, but they are on the same team.
An egg cell has nutrients in its cytoplasm to feed the embryo, and a haploid nucleus with half the normal number of chromosomes. Straight after one sperm enters, the cell membrane changes so that no other sperm can get in. The head of a sperm cell has an acrosome, which holds enzymes that digest the outer layer of the egg, and a haploid nucleus.
Ciliated epithelial cells line the airways. Their cilia are tiny hair-like projections that move together to sweep mucus, with its trapped dust and microbes, away from the lungs.
Specialised plant cells
A root hair cell has a long, thin hair. The hair gives a large surface area for taking in water and minerals from the soil. Think of a towel. A spread-out towel soaks up more than a screwed-up one.
A xylem cell is hollow and strengthened with lignin, a tough substance, so it can carry water. A phloem cell has holes in its end walls, so dissolved food can pass through.
Most animal cells differentiate early in life. Many plant cells can differentiate throughout life.
Recap
Eukaryotic cells have a nucleus. Prokaryotic cells, such as bacteria, do not.
Plant cells also have a cell wall, a permanent vacuole and chloroplasts.
Specialised cells have a structure that suits their function.
Worked examples
Example 1
Name the part of a plant cell that contains chlorophyll and state what the cell uses it for.
Chlorophyll is found in the chloroplasts.
Chloroplasts are where photosynthesis happens.
So the chloroplast is the part, and the cell uses it for photosynthesis.
Answer: chloroplast, used for photosynthesis
Common slips
Slip: It is found in the nucleus. The nucleus holds the genes. Chlorophyll is in the chloroplasts.
Slip: Chloroplasts release energy. Mitochondria release energy. Chloroplasts make glucose.
Slip: The cell uses it for respiration. Respiration happens in the mitochondria, not with chlorophyll.
Example 2
Give two differences between an animal cell and a bacterial cell.
An animal cell has a nucleus. A bacterial cell does not.
The DNA in a bacterial cell is a single loop in the cytoplasm.
Bacterial cells also have a cell wall and are much smaller.
Answer: The animal cell has a nucleus but the bacterial cell does not, and the bacterial cell has a cell wall
Common slips
Slip: Both cells have a nucleus. Only the animal cell has a nucleus.
Slip: The bacterial cell has mitochondria. Bacteria have no mitochondria.
Slip: The animal cell is smaller. Bacterial cells are much smaller than animal cells.
Example 3
A sperm cell has many mitochondria and a tail. Explain how each feature helps the sperm cell.
Mitochondria carry out aerobic respiration, which releases energy.
The tail moves the cell, so the energy is needed for swimming.
So the mitochondria supply the energy that the tail uses to swim to the egg.
Answer: The mitochondria release energy by respiration and the tail uses it to swim
Common slips
Slip: Mitochondria make proteins. Ribosomes make proteins. Mitochondria release energy.
Slip: The tail lets the cell make its own food. The tail is for movement, not for making food.
Slip: Mitochondria help the cell divide. Their job is to release energy by respiration.
Questions and answers
Cell structure and specialised cells practice questions for GCSE Combined Science Biology. Try each one, then open the answer. Easy questions come first.
Question 1 Easy
Name the part of a cell where aerobic respiration takes place.
Show answer
Answer: mitochondria
Aerobic respiration releases energy.
It happens in the mitochondria.
Question 2 Easy
Name the part of a cell where proteins are made.
Show answer
Answer: ribosomes
Amino acids are joined into proteins.
This happens on the ribosomes.
Question 3 Easy
What is the cell wall of a plant cell made of?
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Answer: cellulose
The wall is strong and supports the cell.
It is made of cellulose.
Question 4 Easy
Name the part of a plant cell that contains cell sap.
Show answer
Answer: permanent vacuole
Cell sap is stored in a vacuole.
It is the permanent vacuole.
Question 5 Easy
Name the part of a cell that contains the genes.
Show answer
Answer: nucleus
The genes are stored in one part.
This is the nucleus.
Question 6 Easy
In which part of a cell do most chemical reactions happen?
Show answer
Answer: cytoplasm
The jelly inside the membrane holds the reactions.
This is the cytoplasm.
Question 7 Medium
Name the type of cell that has no nucleus.
Show answer
Answer: prokaryotic
Cells without a nucleus are prokaryotes.
Bacteria are the example.
Question 8 Medium
Name the small extra ring of DNA found in a bacterial cell.
Show answer
Answer: plasmid
Bacteria have a main DNA loop.
The small extra rings are plasmids.
Exam-style questions
Longer questions in the style of a written paper, with the marking points. These are Yumio practice questions.
Exam-style question 14 marks
(a) Name two structures found in a plant cell but not in an animal cell. [2 marks] (b) Explain why a root hair cell does not contain chloroplasts. [2 marks]
Show answer and marking points
Answer: (a) cell wall and chloroplasts (b) it is underground, so no light reaches it and it cannot photosynthesise
(a) first correct structure from cell wall, permanent vacuole, chloroplasts (1)
A sperm cell is specialised for its function. (a) Give two features of a sperm cell. [2 marks] (b) Explain how one of these features helps the sperm to fertilise an egg. [2 marks]
Show answer and marking points
Answer: (a) a tail, many mitochondria, or enzymes in the head (b) the mitochondria release energy for the tail to swim to the egg
(a) first feature (1)
(a) second feature (1)
(b) links the feature to the job, for example the tail moves the sperm (1)
(b) gives the reason, for example mitochondria release energy for swimming (1)
Common mistakes
Saying a bacterial cell has a nucleus
Bacteria have no nucleus. Their DNA is a loop in the cytoplasm.
Saying the cell wall controls what enters and leaves the cell
The cell membrane controls this. The cell wall is a strong outer layer that supports the cell.
Saying mitochondria make energy
Mitochondria release energy from glucose by respiration. Energy is not made.
Saying the cell wall is made of cellulose in bacteria
Plant cell walls are cellulose. Bacterial cell walls are a different material.
Questions students ask
Is Cell structure and specialised cells on the Foundation or Higher tier?
Cell structure and specialised cells is on both Foundation and Higher papers for GCSE Combined Science Biology, aimed at around grade 3.
What is a common mistake on Cell structure and specialised cells?
Saying a bacterial cell has a nucleus. Bacteria have no nucleus. Their DNA is a loop in the cytoplasm.
Where are the answers to the Cell structure and specialised cells questions?
Open Show answer under each question on this page. The questions are Yumio practice questions, not past exam questions.